JP3887366B2 - Flow measuring device and flow measuring method - Google Patents

Description

  The present invention is a flow rate measuring device used in the field of gas meters, flow meters, and the like, and in particular, a thermal type flow rate measuring device that measures a flow velocity using a temperature change of a resistance value of a heating resistor due to a fluid flow. And a flow rate measuring method.

  In recent years, a flow meter using a fluidic fluid element has been actively studied as a next-generation gas meter that replaces a conventional integral membrane meter. However, since the fluidic fluid element cannot measure a low flow rate of 150 [L / H] ("L" indicates liter; the same applies hereinafter) or less, it is exposed to the fluid on the microbridge as a flow measurement device in a low flow range. A flow rate measuring device which is a heat-sensitive flow sensor provided with a heating resistor is used.

  Conventionally, various methods have been proposed as such a flow rate measuring device (flow sensor).

  As a first method, a flow rate measuring device using a balanced bridge circuit to drive a heating resistor at a constant temperature is disclosed in Japanese Utility Model Publication Nos. 7-51618, 7-117436, and Japanese Patent Laid-Open No. 5-31616. It is described in gazettes. A conventional example of such a flow rate measuring apparatus will be described with reference to FIG. The flow rate measuring apparatus 1 exemplified here has a balanced bridge circuit 2, and the balanced bridge circuit 2 has a resistance temperature detector 3 and a heating resistor 4. These resistors 3 and 4 have the same resistance temperature coefficient, and the resistance temperature coefficient is large. A temperature setting resistor 5 having a small resistance temperature coefficient is connected to the resistance temperature detector 3, and a resistance temperature detector portion 6 is formed by these resistors 3 and 5. A third resistor 7 is connected to the temperature measuring resistor portion 6, and a fourth resistor 8 is connected to the heating resistor 4. These resistors 7 and 8 have the same resistance temperature coefficient, and the resistance temperature coefficient is small. The balanced bridge circuit 2 is formed by connecting these resistors 7 and 8.

  A connection point 9 between the resistors 3 and 4 is grounded, and a DC power source 12 is connected to a connection point 10 between the resistors 7 and 8 via a control transistor 11. A differential amplifier 15 is connected to the connection point 13 of the resistors 6 and 7 and the connection point 14 of the resistors 4 and 8, and the differential amplifier 15 is fed back to the control transistor 11. It is connected.

  In the flow rate measuring apparatus 1 having such a configuration, the resistance temperature detector 3 and the heating resistor 4 are arranged in the fluid flow path, and feedback control is executed so that the balance of the balanced bridge circuit 2 is maintained. In the state where the balanced bridge circuit 2 is balanced, the electric power consumed by the heating resistor 4 corresponds to the flow rate of the fluid. In this state, if the output of the differential amplifier 15 or the voltage at the connection point 14 is measured. The flow rate of the fluid can be measured. According to such a flow rate measuring device 1, the flow rate of the fluid can be measured by feedback control of the balance of the balanced bridge circuit 2 that fluctuates corresponding to the flow of the fluid. However, in such a flow rate measuring apparatus 1, since an error occurs in the flow rate measurement result when the fluid temperature changes, it is necessary to correct the flow rate measurement result in accordance with the fluid temperature.

  For this reason, for example, in the flow rate measuring device described in JP-A-4-204119, the resistance temperature detector is made detachable from the balanced bridge circuit, and the resistance temperature detector removed from the balanced bridge circuit is a constant current. The voltage drop is measured by driving, and the temperature of the fluid is calculated from the measurement result. In addition, in the flow rate measuring apparatus described in Japanese Patent Laid-Open No. 5-164583, a temperature measuring resistor driven by a constant current is provided separately from a heating resistor driven by a constant voltage, and the temperature of the fluid obtained from the temperature measuring resistor is provided. By multiplying the data by the flow rate data obtained from the heating resistor, the measurement error of the flow rate due to the temperature of the fluid is corrected. Further, in the flow rate measuring device described in Japanese Patent Application Laid-Open No. 2-120621, a pair of temperature measuring resistors is arranged upstream and downstream of one heating resistor, and these temperature measuring resistors are arranged. A balanced bridge circuit is formed. Data corresponding to the temperature difference between the pair of temperature measuring resistors is detected from the balance fluctuation of the balanced bridge circuit, and data corresponding to the heating temperature of the heating resistor is detected from the resistance value of the pair of temperature measuring resistors. Data corresponding to the flow rate of the fluid is obtained by dividing the temperature difference data by the heat generation temperature data.

  As a second method, a constant current is provided in which heating resistors are arranged upstream and downstream of the flow path, each generates heat by constant current driving, and the flow rate of the fluid is measured based on a change in the resistance value of these heating resistors. There is a drive type.

  As a conventional example of such a flow rate measuring apparatus, an example shown in Japanese Patent Publication No. 3-52028 will be described with reference to FIG. The flow rate measuring device 21 exemplified here includes a first heat generating resistor 22 and a second heat generating resistor 23 each having a large resistance temperature coefficient, and these first and second heat generating resistors 22, For example, 23 is formed on the surface of a wiring board (not shown) by printed wiring. The first and second heating resistors 22 and 23 are respectively connected with first and second operational amplifiers 24 and 25 as first and second measuring means, and feedback loops 26 and 27 are provided here. Is formed.

  A potentiometer 29 is connected to the pair of input terminals 28, and the feedback loops 26 and 27 are connected to the potentiometer 29 via resistors 30 and 31. For this reason, the feedback loops 26 and 27 from the input terminal 28 function as first and second power feeding means for supplying variable current and constant power to the first and second heating resistors 22 and 23. To do. Resistors 32 to 35 and a third operational amplifier 36 are connected to the feedback loops 26 and 27, and the third operational amplifier 36 and the ground terminal 37 are individually connected to a pair of output terminals 38. ing.

  The flow rate measuring device 21 having such a configuration can measure the flow rate of a fluid such as a gas. In this case, the first and second heating resistors 22 and 23 are sequentially positioned according to the fluid flow direction by appropriately arranging the wiring board in the fluid flow path. In this state, when power is supplied from the input terminal 28 to the feedback loops 26 and 27, the first heat generating resistor 22 and the second heat generating resistor 23 are supplied with variable voltage and constant current power. Fever.

  When the fluid flows in this state, the amount of heat moves from the upstream first heating resistor 22 to the downstream second heating resistor 23, so that the first heating resistor 22 having a large resistance temperature coefficient has a resistance value. The resistance value of the second heating resistor 23 which is lowered and has a large resistance temperature coefficient increases. However, since the current amounts of the feedback loops 26 and 27 are kept constant, the output voltage of the feedback loop 26 increases, the output voltage of the feedback loop 27 decreases, and this potential difference is detected by the third operational amplifier 36. The Since the detected potential difference corresponds to the fluid flow rate, the fluid flow rate can be detected from the output voltage of the output terminal 38.

Moreover, as a configuration example of a signal processing system related to such a constant current drive type flow rate measuring apparatus, there is one as disclosed in Japanese Patent Publication No. 6-64080, for example. FIG. 36 shows the electrical configuration rewritten. In the flow rate measuring device 41, first, two temperature sensitive resistors (heating resistors) 42, 43 arranged in a fluid flow path are connected in series. A temperature sensitive resistor 44 used for measuring the temperature around the sensor is also provided, and a current source 45 is connected to the temperature sensitive resistor 44. An operational amplifier 46 having a positive input terminal connected to a connection point P ₁₁ between the temperature sensitive resistor 44 and the current source 45 is provided, and an output terminal of the operational amplifier 46 is connected to one end of the resistor array (the temperature sensitive resistor 42). One end). Further, an output terminal is drawn from the connection point P ₁₂ of the temperature sensitive resistors 42 and 43.

In such a configuration, by supplying the output voltage of the operational amplifier 46 to the resistor string, and measures the flow rate by the voltage change of the connection point P _12. Here, the temperature-sensitive resistor 44 is used to measure the ambient temperature, and the voltage at the connection point P ₁₁ changes corresponding to the ambient temperature. Therefore, the output voltage of the operational amplifier 46 also changes corresponding to the ambient temperature. Thus, the influence of the ambient temperature of the output voltage obtained at the connection point P ₁₂ is removed.

  Further, as another example, for example, there is the one shown in JP-T-8-509066. FIG. 37 shows the electrical configuration rewritten. In the example of the flow rate measuring device 51, four resistors 53, 54, 55, and 56 that form a balanced bridge circuit 52 are used. Of these, ordinary resistors having substantially the same characteristics are used for the resistors 55 and 56. On the other hand, the resistors 53 and 54 are disposed in the fluid flow path 57, and heat generating resistors having substantially the same characteristics that generate heat upon receiving power supply are used. Here, the resistor 53 side is set on the upstream side. A current source 58 is connected to a connection point between the resistors 54 and 56 of the balanced bridge circuit 52, and a transistor 62 is connected to a connection point between the resistors 53 and 55. The connection point A of the resistors 53 and 54 is connected to the negative input terminal of the operational amplifier 59. The positive input terminal of the operational amplifier 59 is grounded, and a feedback resistor 60 is connected between the negative input terminal and the output terminal. Thereby, the connection point A is virtually grounded by the operational amplifier 59. On the other hand, the connection point B of the resistors 55 and 56 is connected to the negative input terminal of the operational amplifier 61. The operational amplifier 61 has a positive input terminal grounded and a resistor 55 and a transistor 62 connected between the negative input terminal and the output terminal.

  In such a configuration, the balanced state of the balanced bridge circuit 52 is destroyed by the flow of fluid in the flow path 57, but the amount of current flowing to the connection point A changes in order to keep the connection point A at virtual ground. This change in current at the connection point A is obtained as the output of the operational amplifier 59. Therefore, the flow rate of the fluid can be measured by monitoring the output of the operational amplifier 59.

  In this type of thermal flow measuring device, as described above, if the fluid temperature (environmental temperature) changes, an error occurs in the flow measurement result, so the flow measurement result is corrected according to the fluid temperature. There is a need. At the same time, the heat-sensitive flow rate measuring device is responsible for measuring the flow rate in the low flow rate range, and it is important that the flow rate “0” state in which no fluid is flowing can be accurately measured. Since the output state of the output fluctuates depending on the environmental temperature, it is necessary to achieve temperature stability considering the flow rate “0” state in order to improve the measurement accuracy.

  However, the flow rate measuring device of Japanese Patent Laid-Open No. 4-204119 measures the flow rate and temperature of the fluid, but does not have a function of correcting the measurement result of the flow rate based on the temperature. Further, in the flow rate measuring apparatus of Japanese Patent Laid-Open No. 5-164583, when the heating resistor deteriorates with time and the flow rate data changes, it is not possible to correct this and measure the accurate flow rate. In this regard, according to the flow rate measuring apparatus of Japanese Patent Laid-Open No. 2-120621, although the flow rate of the fluid can be measured regardless of the deterioration of the heating resistor over time, the resistance temperature detector is the heater. In the case of long-term use, measurement errors will occur due to deterioration, and the resistance thermometer also generates heat due to power supply to the balanced bridge circuit, and the heat generation temperature depends on the environmental temperature and flow rate. Since it fluctuates, an error occurs in the flow rate measurement result based on the resistance value of the resistance temperature detector.

  Eventually, all of these flow rate measuring devices use a balanced bridge circuit to measure fluid flow, which requires that the balanced bridge circuit be balanced. However, multiple resistors that form a balanced bridge circuit will deteriorate over time, and in particular, the resistance of heating resistors will vary depending on the heat generation temperature and usage environment. It is difficult. Also, when using a balanced bridge circuit, the voltage applied to the heating resistor must be lower than the voltage applied to the balanced bridge circuit itself. For example, when a battery-driven flow meter is to be configured, The usable voltage range is narrowed, and the voltage applied to the heating resistor is significantly reduced. As a result, the selection range of the resistance value of the heating resistor is narrowed, or a resistance value that is difficult to realize depending on the manufacturing method must be selected.

  On the other hand, in the flow rate measuring device 21 as shown in FIG. 35 as shown in Japanese Patent Publication No. 3-52028, the first and second heating resistors 22 and 23 arranged according to the fluid flow direction are driven with a constant current, Although the flow rate of the fluid is measured from the difference between the voltages at both ends, this measurement result does not reflect only the flow rate of the fluid, and the temperature of the fluid affects it. I can't.

  This point will be described in detail below. First, the resistance value “R” of the heating resistor is the heating resistance value “R0” in the reference state of the flow rate “0” at a predetermined temperature, the difference “dT” between the reference temperature and the temperature of the heating resistor, the heating resistor Is approximated as “R = R0 (1 + α · dT)”. That is, the resistance value R of the heating resistor varies depending on the temperature. The temperature of the heating resistor in the fluid is a temperature obtained by adding the heating temperature due to Joule heat of the current passed through the heating resistor and the temperature of the fluid, and subtracting the amount of heat transferred to the fluid from the amount of heat. .

  In the case of the flow rate measuring device 21 as described above, the resistance value of the upstream first heating resistor 22 and the downstream second heating resistor 23 changes in accordance with the temperature of the fluid, so that it is constant. When current is applied, the Joule heat changes and the heat generation temperature also changes. Since the fluid takes part of the Joule heat, the amount of heat transferred from the first and second heating resistors 22 and 23 to the fluid changes when the Joule heat changes.

  The first and second operational amplifiers 24 and 25 output a voltage corresponding to the heat generation temperature of the first and second heat generating resistors 22 and 23 related to the factors as described above, and the difference between these voltages is output to the third. The operational amplifier 36 outputs the flow rate measurement result of the fluid, and this output result reflects the difference in the amount of heat transferred from the first and second heating resistors 22 and 23 to the fluid. It will change with temperature. In addition, when the resistance temperature coefficient of the first and second heating resistors 22 and 23 and the resistance value at the reference temperature are different, an output result is generated when the temperature changes even if the fluid does not flow. It is difficult to even determine the presence or absence of flow (flow rate “0”).

  Further, in the case of the example of the flow rate measuring device 41 of FIG. 36 as shown in Japanese Patent Publication No. 6-64080, in order to remove the influence of the ambient temperature on the temperature sensitive resistors 42, 43, 44, these resistance values are used. Must be adjusted so that specific conditions are satisfied, which is difficult in production. Further, in the case of the example of the flow rate measuring device 51 of FIG. 37 as shown in JP-T-8-509066, the resistors 53 and 54 in the resistor constituting the balanced bridge circuit 52 are accompanied by heat generation. It is easy to deteriorate, it is difficult to maintain the balanced state of the balanced bridge circuit 52 for a long period of time, and it is not suitable for application to a gas meter or the like.

The invention according to claim 1 is a first heating resistor having a large resistance temperature coefficient disposed in the fluid flow path,
A second heating resistor having a large resistance temperature coefficient disposed downstream of the first heating resistor;
First power supply means for supplying electric power with constant voltage and constant current to the first heating resistor;
A second power supply means for supplying a constant current with a variable voltage to the second heating resistor;
First measuring means for measuring a voltage across the first heating resistor;
Second measuring means for measuring a voltage across the second heating resistor;
Coefficient multiplication means for multiplying the measurement voltage of the first measurement means by a predetermined correction coefficient;
Subtraction processing means for subtracting the multiplication result from the measurement voltage of the second measurement means;
Division processing means for dividing the subtraction result by the measurement voltage of the first measurement means;
Is provided.

According to a second aspect of the present invention, in the flow rate measuring device according to the second aspect, the coefficient multiplying means calculates the resistance value of the second heating resistor in the reference state of the flow rate “0” at a predetermined temperature as the first heating resistance. A numerical value obtained by dividing by the resistance value of the body is set as a correction coefficient.

According to a third aspect of the present invention, in the flow rate measuring device according to the second aspect, the coefficient multiplying unit determines the measurement voltage of the second measuring unit in the reference state of the flow rate “0” at the predetermined temperature. A numerical value obtained as a result of division by the measured voltage is set as a correction coefficient.

According to the first aspect of the present invention, the first heating resistor having a large resistance temperature coefficient disposed in the fluid flow path and the first resistance temperature coefficient disposed downstream of the first heating resistor. The second heating resistor, a first power supply means for supplying a variable voltage and constant current power to the first heating resistor, and a second voltage supplying a variable voltage and constant current power to the second heating resistor. Power supply means, first measurement means for measuring the voltage across the first heating resistor, second measurement means for measuring the voltage across the second heating resistor, and measurement by the first measurement means Coefficient multiplication means for multiplying the voltage by a predetermined correction coefficient, subtraction processing means for subtracting the multiplication result from the measurement voltage of the second measurement means, and division for dividing the subtraction result by the measurement voltage of the first measurement means And a processing means, so that a predetermined correction coefficient is added to the measurement voltage of the first measuring means. Since the multiplication result is subtracted from the measurement voltage of the second measurement means, and the subtraction result is divided by the measurement voltage of the first measurement means, the first heating resistor and the second heating resistor If the flow rate is “0” even if the conditions such as the resistance value and the amount of current are different from each other, the above calculation result can be set to “0”. Since it can be determined accurately and the above calculation result corresponds linearly to the flow rate of the fluid, the flow rate of the fluid can also be measured based on this.

According to the invention described in claim 2 , the coefficient multiplying unit divides the resistance value of the second heating resistor in the reference state of the flow rate “0” at the predetermined temperature by the resistance value of the first heating resistor. Is set as a correction coefficient, and the correction coefficient is multiplied by the voltage across the first heating resistor, so that the resistance value between the first heating resistor and the second heating resistor is Even if they are different, the calculation result can be set to “0” when the fluid flow rate is “0”, and the presence or absence of fluid flow can be accurately determined.

According to the third aspect of the present invention, the numerical value obtained as a result of dividing the measurement voltage of the second measurement means in the reference state of the flow rate “0” at the predetermined temperature by the measurement voltage of the first measurement means is set as the correction coefficient. Therefore, since this correction coefficient is multiplied by the voltage across the first heating resistor, even if the resistance value and current amount of the first heating resistor and the second heating resistor are different, When the flow rate of the fluid is “0”, the calculation result can be set to “0”, and the presence or absence of the fluid flow can be accurately determined.
Further, in Reference Example 1, the first heating resistor having a large resistance temperature coefficient arranged in the fluid flow path, the first heating resistor, the resistance temperature coefficient, and the resistance value in the reference state are the same. A second heating resistor disposed downstream of the first heating resistor, a first power feeding means for supplying a variable voltage and constant current power to the first heating resistor, and the first power feeding means, Second power supply means for supplying the same power to the second heating resistor, first measuring means for measuring the voltage across the first heating resistor, and voltage across the second heating resistor Second measuring means, subtracting means for subtracting the measurement voltage of the first measuring means from the measured voltage of the second measuring means, and division processing for dividing the subtraction result by the measured voltage of the first measuring means The measurement voltage of the first measurement means is subtracted from the measurement voltage of the second measurement means. Since this subtraction result is divided by the measurement voltage of the first measuring means, this calculation result is “0” when the flow rate is “0”. Based on this, the presence or absence of fluid flow is determined. Since it can be determined accurately and the above calculation result corresponds linearly to the flow rate of the fluid, the flow rate of the fluid can also be measured based on this.

In Reference Example 2, m-th power processing means for raising the measurement voltage of the first measurement means to the mth power, n-th power processing means for raising the measurement voltage of the second measurement means to the power of n, and the division result of the division processing means to the mth power Since the result correction means for multiplying the m-th power result of the processing means and the n-th power result of the n-th power processing means is provided, the calculation result that is the measurement result of the fluid flow rate is the voltage across the first heating resistor. Is corrected by multiplying the mth power result by the nth power result of the voltage across the second heating resistor, the temperature correction ratio between the first heating resistor and the second heating resistor is the multiplier “m”. , N ″, the influence of the temperature on the measurement result of the fluid flow rate can be reduced, and the fluid flow rate can be accurately measured regardless of the temperature.

In Reference Example 3, since “m = 1, n = 1”, the calculation result, which is the measurement result of the fluid flow rate, includes the m-th power result of the voltage across the first heating resistor and the second heating resistor. The arithmetic processing for multiplying the n-th power result of the voltage between both ends can be executed as a simple multiplication that does not require a power, and the arithmetic processing can be simplified and the structure of hardware and software can be simplified.

In Reference Example 4, since the relationship of “m + n = 1.5” is satisfied, the rate of temperature correction between the first heating resistor and the second heating resistor can be adjusted optimally, so that the fluid flow rate is the temperature. It is possible to measure accurately regardless of.

In Reference Example 5, the first heating resistor having a large resistance temperature coefficient arranged in the fluid flow path, the first heating resistor, the resistance temperature coefficient, and the resistance value in the reference state are the same, and the first heating resistor is the first heating resistor. A second heating resistor disposed downstream of the heating resistor, a first power supply means for supplying a variable voltage and a constant current to the first heat generating resistor, and the same as the first power supply means A second feeding means for supplying power to the second heating resistor; a first measuring means for measuring a voltage across the first heating resistor; and a second measuring means for measuring the voltage across the second heating resistor. 2 measurement means, subtraction processing means for subtracting the measurement voltage of the first measurement means from the measurement voltage of the second measurement means, and multiplication processing means for multiplying the subtraction result by the measurement voltage of the second measurement means Therefore, the measurement voltage of the first measurement means is subtracted from the measurement voltage of the second measurement means. Since the subtraction result is multiplied by the measurement voltage of the second measuring means, the calculation result is “0” when the flow rate is “0”. Based on this, the presence or absence of fluid flow is accurately determined. Since the above calculation result corresponds linearly to the flow rate of the fluid, the flow rate of the fluid can also be measured based on this.

In Reference Example 6, the first heating resistor having a large resistance temperature coefficient disposed in the fluid flow path and the second heating resistor having a large resistance temperature coefficient disposed downstream of the first heating resistor. And a first power supply means for supplying a constant current with variable voltage to the first heating resistor, a second power supply means for supplying constant power with a variable voltage to the second heat generation resistor, The first measuring means for measuring the voltage across the first heating resistor, the second measuring means for measuring the voltage across the second heating resistor, and the first measured voltage from the second measuring means. Subtraction processing means for subtracting the measurement voltage of the measurement means, coefficient multiplication means for multiplying the measurement voltage of the first measurement means by a predetermined correction coefficient, and addition processing for adding the multiplication result to the subtraction result of the subtraction processing means And a multiplication process for multiplying the addition result by the measurement voltage of the second measurement means. The measurement voltage of the first measurement unit is subtracted from the measurement voltage of the second measurement unit, the measurement voltage of the first measurement unit is multiplied by a predetermined correction coefficient, and the result of the multiplication is described above. Since the addition result is multiplied by the measurement voltage of the second measuring means, the first heating resistor and the second heating resistor have different conditions such as resistance value and current amount. Even if the flow rate is “0”, the above calculation result can be set to “0”, and based on this, the presence or absence of fluid flow can be accurately determined. Since it corresponds linearly to the flow rate of the fluid, the flow rate of the fluid can also be measured based on this.

In Reference Example 7, the coefficient multiplication means divides the resistance value of the second heating resistor in the reference state of the flow rate “0” at a predetermined temperature by the resistance value of the first heating resistor from “1”. Since the numerical value resulting from the subtraction is set as a correction coefficient, the correction coefficient is multiplied by the voltage across the first heating resistor, and therefore the resistance between the first heating resistor and the second heating resistor. Even if the values are different, the calculation result can be set to “0” when the fluid flow rate is “0”, and the presence or absence of fluid flow can be accurately determined.

In Reference Example 8, the coefficient multiplication unit subtracts the result obtained by dividing the measurement voltage of the second measurement unit by the measurement voltage of the first measurement unit in the reference state of the flow rate “0” at the predetermined temperature from “1”. Since the numerical value of the result is set as a correction coefficient, the correction coefficient is multiplied by the voltage across the first heating resistor, so that the resistance value between the first heating resistor and the second heating resistor, etc. If the flow rate of the fluid is “0”, the calculation result can be “0”, and the presence or absence of fluid flow can be accurately determined.

In the reference example 9, the coefficient multiplication means divides the subtraction result of the subtraction processing means in the reference state of the flow rate “0” at the predetermined temperature by the measurement voltage of the first measurement means and inverts the positive / negative sign. Since the numerical value is set as the correction coefficient, the correction coefficient is multiplied by the voltage across the first heating resistor, so that the resistance values of the first heating resistor and the second heating resistor are different. Even when the flow rate of the fluid is “0”, the calculation result can be “0”. In particular, the difference between the first heating resistor and the second heating resistor is used for calculating the correction coefficient. Since the voltage can be used, the presence or absence of fluid flow can be determined more accurately.

The reference example 10 includes m-th power processing means for raising the measurement voltage of the first measurement means to the (m−1) th power and n-th power processing means for raising the measurement voltage of the second measurement means to the nth power. Since the addition result of the addition processing means is multiplied by the (m−1) th power result of the m-th power processing means and the n-th power result of the n-th power processing means, the calculation result which is the measurement result of the fluid flow rate is obtained. Since the correction is made by multiplying the (m−1) th power result of the voltage across the first heating resistor by the nth power result of the voltage across the second heating resistor, the first heating resistor and the second The ratio of the temperature correction with the heating resistor is adjusted by the multiplier “m, n”, and the influence of temperature on the fluid flow rate measurement result can be reduced, so the fluid flow rate can be accurately measured regardless of the temperature. can do.

In Reference Example 11, an A / D converter that converts an analog value into a digital value from at least one measurement voltage of the first measurement means and the second measurement means and a subtraction result of the subtraction processing means, and its digital conversion Digital addition means for adding the subtraction result and the measured voltage, and replacement processing means for replacing the addition result as the other measurement voltage of the first measurement means and the second measurement means. Since the voltage between both ends of the first heat generating resistor and the second heat generating resistor is not used at the same time for calculating the measurement result, and one of them is used as a differential voltage, the two voltages at both ends and the differential voltage are used. Can be prevented from occurring simultaneously, and the consistency of the arithmetic processing can be ensured and the fluid flow rate can be accurately measured.

In Reference Example 12, the coefficient multiplying unit subtracts a numerical value corresponding to the subtraction result of the subtracting processing unit from a numerical value corresponding to the measurement voltage of the second measuring unit in the reference state of the flow rate “0” at the predetermined temperature. Since the numerical value obtained by dividing the numerical value obtained by inverting the sign of the numerical value corresponding to the subtraction result of the subtraction processing means is set as the correction coefficient, the correction coefficient is also calculated by the second heating resistor. Since only the voltage between both ends is used and the voltage between both ends of the first heating resistor is not used, it is possible to prevent inconsistency in calculation processing by using the two end voltages and the differential voltage at the same time. It is possible to accurately measure the flow rate of the fluid while ensuring the property.

In Reference Example 13, the voltages at both ends of the first heating resistor and the second heating resistor are respectively measured, the voltages at both ends of the first heating resistor are multiplied by a predetermined correction coefficient, and this multiplication result is obtained as the first result. 2 is subtracted from the voltage across the two heating resistors, and the subtraction result is divided by the voltage across the first heating resistor, so that the voltage across the first heating resistor is multiplied by a predetermined correction coefficient. The multiplication result is subtracted from the voltage across the second heating resistor, and the subtraction result is divided by the voltage across the first heating resistor, so that the first heating resistor and the second heating resistor If the flow rate is “0”, the above calculation result can be set to “0” even if the resistance value, current amount, and other conditions are different from each other. And the above calculation results correspond linearly to the fluid flow rate, It is also possible to measure the flow rate of the body.

In Reference Example 14, the voltages at both ends of the first heating resistor and the second heating resistor are respectively measured, and the voltages at both ends of the first heating resistor are subtracted from the voltages at both ends of the second heating resistor. The voltage at both ends of the first heating resistor is multiplied by a predetermined correction coefficient, the multiplication result is added to the subtraction result of the voltages at both ends, and the addition result is multiplied by the voltage at both ends of the second heating resistor. Therefore, the voltage across the first heating resistor is subtracted from the voltage across the second heating resistor, and the voltage across the first heating resistor is multiplied by a predetermined correction coefficient. Since the result is added to the subtraction result, and the addition result is multiplied by the voltage across the second heating resistor, the conditions such as the resistance value and current amount of the first heating resistor and the second heating resistor are different. Even if the flow rate is “0”, the above calculation result can be set to “0”. Zui presence or absence of flow of fluid can be accurately determined, the calculation results of the above it corresponds to a linear flow rate of the fluid, it is also possible to measure the flow rate of the fluid based on this.

In Reference Example 15, a first heating resistor disposed in the fluid flow path, and a first heating resistor disposed downstream of the first heating resistor and connected in series with the first heating resistor. Two heating resistors, a constant current source for supplying a constant current to the resistor rows of the first and second heating resistors, and a first voltage measurement for measuring a terminal voltage of the first heating resistor. And a second voltage measuring means for measuring the terminal voltage of the second heating resistor, the same current is always supplied to the first and second heating resistors by one constant current source. Therefore, the influence of the current value on the flow rate measurement can be reduced.

Since the reference example 16 includes subtracting means for calculating the difference between the output voltage of the first voltage measuring means and the output voltage of the second voltage measuring means, the difference between the resistance values of the first and second heating resistors is provided. Measurement accuracy can be improved.

In Reference Example 17, the first heat generating resistor disposed in the fluid flow path and the first heat generating resistor disposed downstream of the first heat generating resistor and having a zero potential point in the connection path. Since the second heating resistor connected in series with the resistor in series and the constant current source for supplying a constant current to the resistor rows of the first and second heating resistors are provided. An equal current can always be supplied to one or two heating resistors by one constant current source, so that the influence of the current value on the flow rate measurement can be reduced. By setting the voltage at one end positive and the voltage at the other end of the other heating resistor negative, it is possible to have a zero potential point in the connection path connecting these heating resistors. The voltage required to measure the body terminal voltage can be kept low, so It can be set lower operating voltage of the circuit, for example, which is advantageous in battery-powered.

In Reference Example 18, the terminal voltage having the larger absolute value among the terminal voltages at both ends of the first heating resistor and the terminal voltage having the larger absolute value among the terminal voltages at both ends of the second heating resistor. Therefore, the measurement accuracy of the difference between the resistance values of the first and second heating resistors can be improved.

In Reference Example 19, the first heating resistor having a large resistance temperature coefficient arranged in the fluid flow path, the first heating resistor, the resistance temperature coefficient, and the resistance value in the reference state are the same, and the first heating resistor is the first heating resistor. A constant current is supplied to the second heating resistor disposed downstream of the heating resistor and connected in series in current, and to the resistor rows of the first and second heating resistors connected in series. Since it has a current source and an operational amplifier that keeps the connection point between the first heating resistor and the second heating resistor at a constant voltage by virtual grounding, it has a zero potential point as in the invention of claim 27 The circuit can be operated at a lower voltage without requiring a resistor or the like.

Since the reference example 20 is provided with the adding means for adding the voltages across the resistor rows connected in series, the measurement accuracy of the difference between the resistance values of the first and second heating resistors can be improved. .

In Reference Example 21, since the impedance conversion means is provided in the previous stage of the addition means, the influence of the addition means on the current flowing through the first and second heating resistors can be reduced by the impedance conversion means having a large input impedance. .

In Reference Example 22, operational amplifiers are used for the adding means and the impedance converting means, and these three operational amplifiers including the operational amplifier for keeping the connection point at a constant voltage by virtual grounding are formed on the same silicon wafer and are identical. Since the operational amplifier enclosed in the package is used, the offset voltage of all the operational amplifiers can be made the same level, and the measurement accuracy of the resistance value difference between the first and second heating resistors can be improved.

In the reference example 23, the switch means for zeroing the current value flowing through the resistor array at any time is provided, so that when the flow rate measurement is not necessary, the power value is wasted by making the current value zero. Therefore, particularly in the case of battery driving, the period during which the measurement operation can be performed without battery replacement can be extended.

  A first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the flow rate measuring device 121 of the present embodiment has first and second heating resistors 122 and 123, and these heating resistors 122 and 123 serve as power feeding means. First and second constant current sources 124 and 125 are individually connected.

  The first and second heating resistors 122 and 123 are arranged in parallel on the surface of one substrate (not shown) as a platinum thin film having a resistance temperature coefficient of about 3000 ppm / ° C., for example. , Arranged in order according to the flow direction of the fluid. Since the constant current sources 124 and 125 supply constant current power to the heating resistors 122 and 123, the heating resistors 122 and 123 have a certain amount of heat corresponding to the Joule heat of the supplied power. Fever.

  One ends of the first and second heating resistors 122 and 123 are grounded, and temperature measuring devices 126 and 127 as temperature measuring means are individually connected to the other ends. A single thermometer 128 is also connected to these temperature measuring devices 126 and 127 to measure the heat generation temperatures of the heat generating resistors 122 and 123, respectively.

  That is, these temperature measuring devices 126 and 127 have voltage measuring devices 129 and 130 and temperature calculators 131 and 132, respectively, and the voltage measuring devices 129 and 130 are the first and second heating resistors. The terminal voltages of the bodies 122 and 123 are measured respectively. The thermometer 128 is disposed in the fluid flow path and measures the temperature of the fluid regardless of flow. In the temperature calculators 131 and 132, the temperature coefficients of the heating resistors 122 and 123 are set in advance, and the heating temperatures ΔTU and ΔTL of the heating resistors 122 and 123 are determined based on the terminal voltage and the fluid temperature. Calculate each.

A flow rate calculation device 133 is connected to the temperature measuring devices 126 and 127 as division processing means. This flow rate calculation device 133 divides the difference “ΔTU−ΔTL” between the two heat generation temperatures ΔTU and ΔTL by the heat generation temperature ΔTU of the first heating resistor 122 on the upstream side. This calculation result f (u) = (ΔTU−ΔTL) / ΔTU
Is output from the output terminal 134 as a measurement result of the flow rate of the fluid.

  In such a configuration, when the flow rate of the fluid is measured by the flow rate measuring device 121 of the present embodiment, the first and second heating resistors 122 and 123 are sequentially arranged in the fluid flow path according to the flow direction. At the same time, the thermometer 128 is disposed at a position not affected by the flow inside the flow path.

  Therefore, when a constant current is supplied from the constant current sources 124 and 125 to the first and second heating resistors 122 and 123 arranged in order in the flow path as described above, the heating resistors 122 and 123 It generates heat with a certain amount of heat corresponding to. Due to this heat generation, the resistance values of the first and second heating resistors 122 and 123 change corresponding to the temperature coefficient, and the terminal voltages corresponding to the resistance values are measured by the voltage measuring devices 129 and 130, respectively. Corresponding to the voltage value and the temperature of the fluid measured by the thermometer 128, the heat generation temperatures ΔTU and ΔTL of the heat generating resistors 122 and 123 are calculated by the temperature calculators 131 and 132, respectively.

  That is, here, since the first and second heating resistors 122 and 123 are driven by the constant current I, if the terminal voltage V is measured, the resistance value R is calculated as “R = V / I”. . When the resistance value of the heating resistors 122 and 123 at the reference temperature T0 is R0 and the temperature coefficient is α, the resistance when the heating resistors 122 and 123 generate heat higher than the reference temperature T0 by the heating temperature ΔT. Since the value R is “R = R0 (1 + αΔT)”, if the reference resistance value R0 and the temperature coefficient α of the heating resistors 122 and 123 are set, the heating value is generated from the resistance value R during heating. A temperature ΔT is calculated.

  The first and second heat generating resistors 122 and 123 that generate heat are cooled corresponding to the flow rate of the fluid, but are arranged in order corresponding to the flow direction of the fluid, so the first heat generation on the upstream side. The amount of heat from the resistor 122 is transmitted to the second heat generating resistor 123 on the downstream side by the fluid. Therefore, as shown in FIG. 2, there is a temperature difference between the heat generation temperatures ΔTU and ΔTL of the first and second heat generating resistors 122 and 123 corresponding to the flow rate of the fluid.

  Thus, the amount of heat transferred from the upstream first heating resistor 122 to the downstream second heating resistor 123 depends on the flow rate of the fluid and the heating temperatures ΔTU and ΔTL of these heating resistors 122 and 123. It corresponds to. Therefore, if the difference “ΔTU−ΔTL” between the two heat generation temperatures ΔTU and ΔTL is divided by the heat generation temperature ΔTU of the upstream first heat generation resistor 122 by the flow rate calculation device 133, as shown in FIG. The calculation result f (u) accurately corresponds to the fluid flow rate.

  When the flow direction of the fluid is reversed, the flow rate f (u) measured as described above is also reversed, so that the flow rate measuring device 121 of the present embodiment measures the flow rate of the fluid and also the flow direction. Can be determined, and the flow rate of the inverted fluid can also be accurately measured.

  Since the flow rate measuring device 121 of the present embodiment can accurately measure the flow rate of the fluid as described above and calculates this measurement based on the amount of heat transmitted by the flow of the fluid, the heating resistor Even if the resistance values of 122 and 123 change with time or the temperature of the fluid changes, the flow rate of the fluid can be accurately measured. In addition, since the power is directly supplied to the heating resistors 122 and 123 without forming a balanced bridge circuit, the power consumption is low and long-term operation is possible even if the power source is a battery. Furthermore, since it is easy to heat the heating resistors 122 and 123 to a desired temperature, the degree of freedom in forming the heating resistors 122 and 123 is also good.

  The present invention is not limited to this embodiment, and various modifications are allowed. For example, in the present embodiment, it is assumed that the temperature measuring devices 126 and 127 and the flow rate calculating device 133 are formed by a dedicated analog circuit, but this is an A / D converter (Analog / Digital Converter) as an input terminal. It can also be formed by a microcomputer provided. In this embodiment, the calculation result f (u) obtained by dividing the difference between the heat generation temperatures ΔTU and ΔTL of the heat generating resistors 122 and 123 by one heat generation temperature ΔTU is actually “(ΔTU−ΔTL) / ΔTU”. However, it is also possible to modify this to calculate “1-ΔTL / ΔTU”.

  Furthermore, as shown in FIG. 4, the flow rate calculation device 142, which is an arithmetic processing means (division processing means), can multiply a constant A by at least one of the two exothermic temperatures ΔTU and ΔTL for calculating the difference. . Even if the heat generation temperatures of the first and second heating resistors 122 and 123 in a state where the fluid is stopped are different due to a manufacturing error or the like, the flow rate measuring device 141 configured as described above is multiplied by a constant A. Since it can correct | amend so that it may become the same on calculation, the flow volume of a fluid can be measured correctly.

  For example, when the flow rate measuring device 141 is a microcomputer, the constant A may be set as a parameter in the memory, and a delicate manufacturing error of the heating resistors 122 and 123 can be easily corrected. The mathematical expression “(ΔTU−A · ΔTL) / ΔTU” of this calculation can be naturally calculated as “1−A · ΔTL / ΔTU”.

  Next, a second embodiment of the present invention will be described with reference to FIG. In addition, regarding the flow measurement device 151 of the present embodiment, the same parts as those of the flow measurement device 121 described above are denoted by the same reference numerals, and description thereof will be omitted (the same applies to the following embodiments in order).

  First, the flow rate measuring device 151 of the present embodiment has the first and second heating resistors 122 and 123 as in the flow rate measuring device 121 described above. They are connected in series, and one constant current source 152 is also connected in series as a driving power source as a power supply means. For this reason, the temperature measuring device 126 is connected to both ends of the first heating resistor 122, and the temperature measuring device 127 is connected to both ends of the second heating resistor 123.

  In such a configuration, the flow measurement device 151 of the present embodiment measures the flow rate of the fluid in the same manner as the flow measurement device 121 described above. In that case, in the flow rate measuring device 151 of the present embodiment, since one constant current source 152 supplies a constant current to both the first and second heating resistors 122 and 123, the first and second heating resistors. The same current can be passed through the bodies 122 and 123, and the flow rate of the fluid can be measured more accurately. Further, the structure of the apparatus is simple, and power saving, size reduction and weight reduction, productivity improvement, and the like can be achieved.

  Furthermore, a third embodiment of the present invention will be described with reference to FIG. In the flow measuring device 161 of the present embodiment, the first and second heating resistors 122 and 123 and one constant current source 152 are connected in series. An auxiliary resistor 162 is also connected in series with the resistor 122. Both ends of the auxiliary resistor 162 are also connected to a current measuring device 163 that is a current detecting means. The current measuring device 163 calculates the temperature of the first and second temperature measuring devices 164 and 165 that are temperature measuring means. Connected to the devices 166 and 167.

  Unlike the first and second heating resistors 122 and 123, the auxiliary resistor 162 has an extremely low temperature coefficient and does not generate heat due to the power supplied from the constant current source 152. The current measuring device 163 measures the voltage across the auxiliary resistor 162 and calculates the amount of current from this voltage and the resistance value of the auxiliary resistor 162. The temperature calculators 166 and 167 of the temperature measuring devices 164 and 165 calculate the first and second current values based on the measurement result of the current amount of the auxiliary resistor 162 and the terminal voltages of the first and second heating resistors 122 and 123, respectively. The resistance values of the heating resistors 122 and 123 are calculated, and the heating temperatures of the heating resistors 122 and 123 are calculated based on these resistance values.

  In such a configuration, when the flow rate of the fluid is measured by the flow rate measuring device 161 of the present embodiment, the first and second heating resistors 122 and 123 arranged in order in the flow path are fixed from the constant current source 152. Although the current is supplied, the constant current is also supplied to the auxiliary resistor 162 in the same manner. Therefore, the amount of current is measured by the current measuring device 163 and is supplied to the temperature calculators 166 and 167 of the temperature measuring devices 164 and 165. Is output. The temperature calculators 166 and 167 calculate the resistance values of the heating resistors 122 and 123 from the input current amount of the auxiliary resistor 162 and the terminal voltages of the first and second heating resistors 122 and 123, respectively. And the heating temperatures ΔTU and ΔTL of the heating resistors 122 and 123 are calculated from the resistance value, the temperature coefficient of the heating resistors 122 and 123, and the fluid temperature measured by the thermometer 128, respectively. The flow rate calculation device 142 divides the difference “ΔTU−A · ΔTL” between the two heat generation temperatures ΔTU and ΔTL by the heat generation temperature ΔTU of the first heating resistor 122 on the upstream side, and calculates the calculation result f (u). Is output as a signal that accurately corresponds to the flow rate of.

  As described above, the flow measuring device 161 of the present embodiment calculates the resistance values of the first and second heating resistors 122 and 123 based on the current amount of the auxiliary resistor 162 connected in series thereto. Therefore, the fluid flow rate can be measured more accurately. Since the current amounts of the first and second heating resistors 122 and 123 are actually measured in this way, the driving power source does not have to be the constant current source 152 and may be a voltage source.

  A fourth embodiment of the present invention will be described with reference to FIG. In the flow measurement device 171 of the present embodiment, a third resistor 172 is provided separately from the first and second heating resistors 122 and 123 and the auxiliary resistor 162, and the third resistor 172. Is connected with a dedicated constant current source 173 as a third power supply means. A voltage measuring device 175 of a dedicated temperature measuring device 174 is connected to the third resistor 172 as a third measuring means, and the temperature calculator 176 of the temperature measuring device 174 is connected to the heating resistor 122, Since the temperature calculators 166 and 167 of the 123 temperature measuring devices 164 and 165 are connected, the thermometer 128 is not connected to these temperature calculators 166 and 167.

  The third resistor 172 is formed in the same structure as the heat generating resistors 122 and 123, but the constant current source 173 supplies a constant current with an output that does not cause the third resistor 172 to generate heat. . For example, the third resistor 172 is disposed upstream of the heating resistors 122 and 123 in the fluid flow direction, so that the third resistor 172 is thermally insulated from the heating resistors 122 and 123. Be placed.

  The temperature measuring device 174 measures the heat generation temperature of the third resistor 172, and the temperature calculators 166 and 167 of the temperature measuring devices 164 and 165 generate heat based on the heat generation temperature of the third resistor 172. The heat generation temperature of the resistors 122 and 123 is calculated. That is, since the third resistor 172 does not generate heat due to the supply of electric power, its temperature is the same as the temperature of the fluid, and based on this, the heat generation temperature of the heating resistors 122 and 123 is calculated.

  In such a configuration, when the flow rate of the fluid is measured by the flow rate measuring device 171 of the present embodiment, the third resistor 172 is also arranged in the fluid flow path together with the first and second heating resistors 122 and 123. However, the third resistor 172 is disposed at a position that is thermally insulated from the heating resistors 122 and 123. In such a state, the heating resistors 122 and 123 generate heat due to the constant current supplied from the constant current source 152, but the third resistor 172 generates heat due to the constant current supplied from the constant current source 173. Absent.

  Since the temperature measuring device 174 calculates the temperature of the third resistor 172 from the terminal voltage and temperature coefficient of the third resistor 172 and the current amount of the constant current source 173, the temperature measurement is performed based on this temperature. The devices 164 and 165 calculate the heating temperatures ΔTU and ΔTL of the heating resistors 122 and 123, respectively. Since the temperature of the third resistor 172 that does not generate heat is the same as the temperature of the fluid as described above, the heat generation temperatures ΔTU and ΔTL of the heat generation resistors 122 and 123 are accurately calculated based on this, and the flow rate is determined from these heat generation temperatures. The fluid flow rate is accurately calculated by the calculation device 142.

  Since the flow rate measuring device 171 of the present embodiment measures the temperature of the fluid by the third resistor 172 as described above, the flow rate of the fluid can be accurately measured based on this, and a dedicated thermometer 128 need not be provided.

  Next, a fifth embodiment of the present invention will be described with reference to FIG. In the flow measuring device 181 of the present embodiment, the constant current source 182 connected to the first and second heating resistors 122 and 123 as a driving power source as a power feeding means is the first and second heating resistors 122 and 123. A large current that generates heat and a small current that does not generate heat can be switched. Here, the temperature measuring devices 164 and 165 function as resistance measuring means for measuring the resistance values of the first and second heating resistors 122 and 123, and a storage device 183 as resistance storage means is connected thereto. The storage device 183 is connected to the constant current source 182, and at the timing when the constant current source 182 outputs a small current, the storage device 183 sets the resistance value in the reference state based on the temperature output of the temperature calculator 176. The converted resistance values R0 of the first and second heating resistors 122 and 123 are stored. The resistance value R0 stored in this way is output from the storage device 183 to the temperature measuring devices 164 and 165 at the timing when the constant current source 182 outputs a large current, so that these temperature measuring devices 164 and 165 The heat generation temperatures ΔTU and ΔTL of the first and second heat generating resistors 122 and 123 are calculated on the basis of the input reference state resistance value R0.

  In such a configuration, in the flow measurement device 181 of the present embodiment, for example, the constant current source 182 supplies a small current to the first and second heating resistors 122 and 123 at the time of initial setting before the start of the flow measurement. , And the resistance value R0 in the reference state in which the first and second heating resistors 122 and 123 do not generate heat is stored in the storage device 183, respectively.

  Since the constant current source 182 outputs a large current to the first and second heating resistors 122 and 123 when the initial setting is completed and the flow rate measurement is started, the first and second heating resistors are provided. The heat generation temperatures ΔTU and ΔTL of the bodies 122 and 123 are measured by the temperature measuring devices 164 and 165. At this time, the resistance value R0 of the reference state in which the first and second heating resistors 122 and 123 do not generate heat is output from the storage device 183 to the temperature measuring devices 164 and 165. The heat generation temperatures ΔTU and ΔTL of the heat generation resistors 122 and 123 are accurately calculated, and the flow rate of the fluid is accurately calculated by the flow rate calculation device 142 from these heat generation temperatures.

  Since the flow rate measuring device 181 of the present embodiment actually measures the resistance value R0 in the reference state of the first and second heating resistors 122 and 123 as described above, the flow rate of the fluid is accurately measured based on this. For example, even if the first and second heating resistors 122 and 123 deteriorate with time, the flow rate measurement accuracy does not decrease.

  Here, the calculation of the heat generation temperatures ΔTU and ΔTL based on the resistance value R0 of the reference state of the first and second heat generating resistors 122 and 123 is exemplified, but the first and second heat generating resistors 122 and 123 are illustrated. It is also possible to correct the flow rate calculation formula based on the resistance value in the reference state. For example, when the degree of change with time of the resistance value R0 is different between the first and second heating resistors 122 and 123, it is preferable to set the constant A in the flow rate calculation formula so that this is the same in the calculation. .

  Further, in the flow rate measuring device 181 described above, it is assumed that the same power is supplied from one constant current source 182 to the first and second heating resistors 122 and 123. However, the flow rate measuring device illustrated in FIG. Like 191, the first and second constant current sources 192 and 193, which are power supply means, are individually connected to the first and second heating resistors 122 and 123, and the power supplied to the second heating resistor 123 is supplied. It is also possible to set it lower than the first heating resistor 122. In the flow measuring device 191 having such a structure, a pair of auxiliary resistors 194 and 195 are individually provided between the constant current sources 192 and 193 and the first and second heating resistors 122 and 123, and these auxiliary resistors 194 are provided. , 195 are connected to first and second current measuring devices 196, 197, respectively.

  That is, since the amount of heat is transmitted from the upstream side first heating resistor 123 to the downstream side second heating resistor 123, the flow rate measurement accuracy is not hindered even if the heating temperature is lowered. For this reason, in the flow measuring device 191 described above, by reducing the power supplied to the second heating resistor 123, the overall power consumption is reduced and the deterioration of the heating resistor 123 with time is also reduced.

  Further, in the flow rate measuring device 191 described above, the five measuring devices 164, 165, 174, 196, and 197 are individually connected to the five resistors 122, 123, 172, 194, and 195. Like the flow measuring device 201 illustrated in FIG. 10, one voltage measuring device 203 is connected to the resistors 122, 123, 172, 194, 195 via the input switching device 202, and output to this voltage measuring device 203. It is also possible to connect the temperature measuring devices 205 to 207 and the current measuring devices 208 and 209 via the switching device 204.

  In this case, although it is necessary to make each part function in a time-sharing manner by the switching devices 202 and 204, since the voltage measuring device 203 is one, the terminal voltages of the five resistors 122,... Can be measured with the same characteristics. Therefore, the flow rate of the fluid can be measured more accurately.

  A sixth embodiment of the present invention will be described with reference to FIGS. In the flow rate measuring device 221 of the present embodiment, the first heat generating resistor 22 and the second heat generating resistor 23 have the same resistance temperature coefficient and resistance value in the reference state, and the first and second measuring means. The first and second operational amplifiers 24, 25 are individually connected to form feedback loops 26, 27. The negative input terminals of the first and second operational amplifiers 24 and 25 which are also the input terminals of the feedback loops 26 and 27 are connected to the input terminal 224 of the reference voltage “Vref” via the resistors 222 and 223, respectively. Are connected to the ground terminal 227 via the resistors 225 and 226 to the positive input terminals of the first and second operational amplifiers 24 and 25. 2 functions as a power supply means.

In the flow rate measuring device 221 of this embodiment, the A / D converter 228 is connected to the output terminals of the feedback loops 26 and 27, and the communication I / F of the microprocessor 229 is connected to the A / D converter 228. (Interface: not shown) is connected. The microprocessor 229 has a CPU (Central Processing Unit) (not shown) as its main body.
The PU is connected to hardware (none of which is shown) such as a ROM (Lead Only Memory), a RAM (Random Access Memory), and the communication I / F.

  For example, when various data is input to the communication I / F, the CPU executes various data processing using the data corresponding to various programs, and outputs the processing result from the communication I / F. To do. A program for causing the CPU to execute such data processing is recorded in the ROM, and various work areas used by the CPU for data processing are secured in the RAM.

  As described above, the CPU reads the program and executes various processing operations, thereby realizing various functions as various means. As such various means, the flow rate measuring device 221 according to the present embodiment includes a coefficient multiplication unit 230, a subtraction processing unit 231, a division processing unit 232, a result output unit 233, and the like. That is, a program for causing the CPU to function as these means 230 to 233 is recorded as software in the ROM.

  The A / D converter 228 converts the measured voltages “Vu, Vd” of the first and second operational amplifiers 24, 25 from analog values to digital values, respectively, and the coefficient multiplier 230 is digitized. The measured voltage “Vu” of the first operational amplifier 24 is multiplied by a predetermined correction coefficient. Here, the correction coefficient is obtained by dividing the resistance value “Rd” of the second heating resistor 23 in the reference state of the flow rate “0” at a predetermined temperature by the resistance value “Ru” of the first heating resistor 22. For example, it is recorded in the ROM as a parameter that can be read by the CPU. However, here, the temperature coefficient of resistance of the first and second heating resistors 22 and 23 and the resistance value in the reference state are the same, and the amount of current supplied to the first and second heating resistors 22 and 23 is the same. Are the same, the correction coefficient is set to “1”.

  The subtraction processing unit 231 subtracts the multiplication result of the coefficient multiplication unit 230 from the measured voltage “Vd” of the second operational amplifier 25, and the division processing unit 232 uses the subtraction result of the subtraction processing unit 231 as a first result. The result output unit 233 outputs the division result of the division processing unit 232 to the outside as digital data corresponding to the flow rate of the fluid through the communication I / F. That is, a program for causing the CPU to function as the means 230 to 33 is recorded in the ROM of the microprocessor 229.

  In such a configuration, the flow rate measuring device 221 of the present embodiment also measures the flow rate of a fluid such as gas and outputs the measurement result as digital data to the outside. In that case, the first and second heating resistors 22 and 23 are sequentially positioned according to the fluid flow direction by the arrangement of the wiring board, and in this state, the first heating resistor 22 and the second heating resistor 23 Is heated by supplying electric power with variable voltage and constant current. When the fluid flows in this state, the amount of heat moves from the first heating resistor 22 on the upstream side to the second heating resistor 23 on the downstream side, so that the respective resistance values change. The amount of current is kept constant, and the output voltage changes.

  For example, in the case of the feedback loop 26, the output terminal of the first operational amplifier 24 is feedback-connected to the negative input terminal via the first heating resistor 22. The voltage at the input terminal is the same. Here, since the positive input terminal of the first operational amplifier 24 is connected to the ground terminal 227 via the resistor 225, the voltage at the positive and negative input terminals is “0”.

  Since the resistor 222 having the resistance value “R1” is interposed between the input terminal 224 of the voltage “0” and the input terminal 224 of the reference voltage “Vref” of the first operational amplifier 24, this resistor A constant current of “I1 = Vref / R1” is supplied to 222, and this constant current is also supplied to the first heating resistor 22. Similarly, a constant current of “I2 = Vref / R2” is supplied to the resistor 223, and this constant current is also supplied to the second heating resistor 23.

  In other words, the first and second heating resistors 22 and 23 are energized with a constant current “I1, I2” even if the resistance values “Ru, Rd” change. When the resistance values “Ru, Rd” of the second heating resistors 22, 23 change, the measured voltages “Vu = I1 · Ru, Vd = I2 · Rd” of the first and second operational amplifiers 24, 25, which are the voltages at both ends thereof. "Changes. Since these measured voltages “Vu, Vd” are A / D converted by the A / D converter 228 and then input to the microprocessor 229, the microprocessor 229 performs predetermined data processing on the input data. Execute.

  That is, the measurement voltage “Vu” of the first operational amplifier 24 is multiplied by the correction coefficient “A”, and the multiplication result “A · Vu” is subtracted from the measurement voltage “Vd” of the second operational amplifier 25. This subtraction result “Vd−A · Vu” is divided by the measurement voltage “Vu” of the first operational amplifier 24, and this division result “(Vd−A · Vu) / Vu” is digital data corresponding to the flow rate of the fluid. As external output.

  For example, if this digital data is converted into an actual flow rate and displayed on a display (not shown), the flow rate of the fluid can be notified to the user, and a flow rate adjusting valve (see FIG. If the feedback control is performed, the fluid flow rate can be maintained constant.

  The flow rate measuring device 221 of the present embodiment does not use the difference between the measured voltages “Vu, Vd” of the first and second operational amplifiers 24, 25 as the flow rate measurement result, but based on these measured voltages “Vu, Vd”. By executing the predetermined arithmetic processing, the flow rate of the fluid can be measured satisfactorily, and the presence or absence of the flow can be accurately determined. This will be described in detail below.

First, since the first and second heat generating resistors 22 and 23 that generate heat as described above are arranged in order according to the flow direction of the fluid, the fluid whose calorific value has moved from the first heat generating resistor 22 is the second. The surface of the heat generating resistor 23 flows, and the first heat generating resistor 22 is cooled better than the second heat generating resistor 23 by the fluid flow. Therefore, the voltage “Vu, Vd” across the first and second heating resistors 22, 23 is
Vd = A.Vu + f (u) .Vu
This relationship is established. In this case, “f (u)” is a function that varies depending on the flow rate “u” of the fluid, and “A” is a predetermined coefficient. Since the coefficient “A” is used to correct a difference in the conditions of the first and second heating resistors 22 and 23, the resistance values “Ru and Rd” of the first and second heating resistors 22 and 23 are If the same amount of current “I1, I2” is the same, it is “1”.

  When the flow rate of the fluid is “0”, the relationship “Vd = A · Vu” is established between the voltages “Vu, Vd” across the first and second heating resistors 22, 23. It changes corresponding to the flow rate of. The change due to the flow rate is assumed to be caused by the fluid moving the amount of heat of the first heating resistor 22 on the upstream side to the second heating resistor 23 on the downstream side, which is “f (u) · Vu”. ".

In other words, the function “f (u)” becomes a signal indicating the flow rate of the fluid, and this is obtained from the above formula. F (u) = (Vd−A · Vu) / Vu
It becomes. That is, like the flow rate measuring device 221 of the present embodiment, the voltage “Vu” across the first heating resistor 22 is multiplied by the correction coefficient “A”, and this multiplication result is multiplied by the second heating resistor 23. By subtracting the voltage across both ends “Vd” and dividing the subtraction result by the voltage across both ends “Vu” of the first heating resistor 22, the division result “f (u)” becomes digital data corresponding to the fluid flow rate. Become.

  That is, as shown in FIG. 12, when the flow rate of the fluid changes, the voltages “Vu, Vd” across the first and second heating resistors 22 and 23 change nonlinearly, but as shown in FIG. Since the result “f (u)” changes substantially linearly, the flow rate of the fluid can be measured from this digital data. If the flow rate of the fluid is measured in this way, when the flow rate is “0”, the measurement result is also “0”, so it is possible to accurately determine whether the fluid is flowing.

  In particular, in the flow rate measuring device 221 of the present embodiment, the voltage “Vu” across the first heating resistor 22 is multiplied by the correction coefficient “A”. Even when the resistance value and the energization amount are different, the presence or absence of flow can be accurately determined. However, when the resistance values and the energization amounts of the first and second heating resistors 22 and 23 are the same as described above, the correction coefficient “A” is “1”, and therefore the coefficient multiplying unit 230 is omitted. Can do. In this case, the program structure of the microprocessor 229 can be simplified, the processing load can be reduced, and the processing speed can be improved.

  However, when the resistance values and energization amounts of the first and second heating resistors 22 and 23 are different, it is necessary to appropriately set the correction coefficient “A”. This is because the flow rate of the fluid is “0”. In this case, it is preferable to set “f (u)” to be “0”. For example, when high accuracy is required for the flow rate measuring device 221, the first and second heating resistors 22 and 23 must be precisely and identically formed in order to omit the multiplication of the correction coefficient “A”. However, this is difficult for manufacturing reasons.

  In this case, the flow rate of the fluid is set to “0”, the same current “I” is applied to the first and second heating resistors 22 and 23, the respective resistance values “Ru and Rd” are measured, and the ratio “Rd” is measured. / Ru "is set in the coefficient multiplication means 230 as the correction coefficient" A ", the flow rate measuring device 221 has a flow rate of" 0 "even if the resistance values of the first and second heating resistors 22 and 23 are different. In this case, the measurement result “f (u)” is “0”.

  As an operation for actually setting the correction coefficient “A” as described above, after the first and second heating resistors 22 and 23 are formed on the wiring board, the reference of the flow rate “0” at a predetermined temperature is used. Each resistance value “Ru, Rd” in the state is measured, and the numerical value of the ratio “Rd / Ru” is recorded in the ROM of the microprocessor 229 as a parameter of the correction coefficient “A” of the program of the coefficient multiplier 230. The correction coefficient “A” can be appropriately set by a simple operation.

  However, as described above, when the correction coefficient “A” is set based on the resistance values “Ru, Rd” of the first and second heating resistors 22, 23, there is no problem when the current amount is the same. It cannot cope with the difference in current amount. In such a case, the power supply and the circuit of the energized portion are actually formed, and then the voltages “Vu and Vd” across the first and second heating resistors 22 and 23 in the reference state are set to the first and second voltages. It is preferable to set the correction coefficient as “Vd / Vu = A”.

  In this case, even if the resistance values and current amounts of the first and second heating resistors 22 and 23 are different, the flow rate measuring device 221 shows that the measurement result “f (u)” is “0” when the flow rate is “0”. 0 "and the presence or absence of flow can be satisfactorily determined. Such a correction coefficient may be recorded in the ROM of the microprocessor 229 as software after the necessary hardware is manufactured, and the correction coefficient “A” can be appropriately set by a simple operation.

  The present invention is not limited to this embodiment, and various modifications are allowed. For example, in the present embodiment, the various means of the flow measurement device 221 are realized by the CPU executing data processing according to a program recorded as software in a ROM or the like. However, each of these various means can be manufactured as unique hardware, and a part of the various means can be recorded as a software in a RAM or the like and a part can be manufactured as hardware. In addition, a RAM or the like in which predetermined software is recorded and hardware of each unit can be manufactured as firmware, for example.

  Further, in the present embodiment, the measurement result “f (u)” that is “0” when the flow rate is “0” corresponding to the fluid flow rate is calculated. (u) ”includes information on the temperature of the fluid, and as shown in FIG. 14, when the temperature of the fluid changes, the slope of the measurement result“ f (u) ”also changes, so the flow rate is accurately measured. It is difficult.

  If this becomes a problem, the m-th power processing means for raising the voltage “Vu” across the first heating resistor 22 to the m-th power and the n-th power processing for raising the voltage “Vd” across the second heating resistor 23 to the n th power. Preferably, a result correction means for multiplying the division result “f (u)” of the division processing means 232 by the m-th power result of the m-th power processing means and the n-th power result of the n-th power processing means is newly added. That is, a program for causing the CPU to function as these means is recorded as software in the ROM.

  In this case, the digital data corresponding to the fluid flow rate is obtained by calculating the m-th power of the voltage “Vu” at both ends of the first heating resistor 22 and the n-th power of the voltage “Vd” at both ends of the second heating resistor 23. Since “f (u)” is multiplied, the multiplication result “f2 (u)” corresponds to the flow rate of the fluid well and is less influenced by temperature. This will be described in detail below. In the following formula, for example, the mth power of “Vu” is expressed as “Vu [mth power]”.

First, the resistance value “Ru” of the first heating resistor 22 is “Ru = Ru0 (1 + αu) by the resistance value“ Ru0 ”at the reference temperature, the temperature difference“ dT ”from the reference temperature, and the resistance temperature coefficient“ αu ”. DT) ". If the current amount I of the resistor is constant even if the temperature changes, “I · Ru = I · Ru0 (1 + αu · dT)” is obtained. If the voltage at both ends at the reference temperature is “Vu0”, the voltage at both ends is Vu = Vu0 (1 + αu · dT)
It becomes. In this case, since “Vu0” is a constant, the voltage “Vu” across the first heating resistor 22 changes depending on the temperature of the fluid, and this is the voltage across the second heating resistor 23 “Vd”. But it is the same.

Therefore, here, the flow rate measuring device is obtained by multiplying the digital data “f (u)” corresponding to the flow rate of the fluid by the voltages “Vu, Vd” across the first and second heating resistors 22, 23 a predetermined number of times. In the temperature range necessary for 221, the influence of temperature on the flow rate measurement result is minimized. The above calculation is f2 (u) = f (u) · Vu [mth power] · Vd [nth power]
Therefore, this is f2 (u) = {(Vd-A.Vu) / Vu} f (u) .Vu [mth power] .Vd [nth power]
It becomes.

  For example, when “m = n = 0”, the measurement result of the flow rate is naturally not corrected, and is influenced by the temperature of the fluid as shown in FIG. When “m = n = 0.5”, as shown in FIG. 15, it is confirmed that the influence of temperature on the flow rate measurement result is reduced, and when “m = n = 0.75”, FIG. As shown in FIG. 17, it was confirmed that the influence of temperature on the flow rate measurement result is minimized, and when “m = n = 1”, the influence of temperature increases as shown in FIG.

  Therefore, the multiplier “m, n” described above is actually optimally set according to various conditions, and an optimal example is “m = n = 0.75”. The voltage “Vu, Vd” across the first and second heating resistors 22, 23 is multiplied to the multiplier “m, n” set in this way, and this is multiplied by the flow rate measurement result “f (u)”. If the corrected measurement result “f2 (u)” is calculated, the flow rate of the fluid can be accurately measured regardless of the temperature.

  Here, in order to simplify the arithmetic processing, it is exemplified that “m = n”. However, if the both-end voltages “Vu, Vd” of the first and second heating resistors 22, 23 are substantially the same, As long as “m + n = 1.5”, as shown in FIG. 18, even if “m = 0, n = 1.5”, the influence of temperature can be minimized and the flow rate can be measured satisfactorily.

  Further, as described above, if the multiplier “m, n” is not an integer, the calculation process is complicated. Therefore, it is also practical to reduce the processing load and improve the speed by setting “m = n = 1”. Further, here, the division result “(2) of the m-th power value of the both-end voltage“ Vu ”of the first heating resistor 22 and the n-th power value of the both-end voltage“ Vd ”of the second heating resistor 23 is“ ( Vd−A · Vu) / Vu ”is multiplied, and“ Vu ”exists in the denominator of the result of the division. That is, the subtraction result “Vd−A · Vu” of the subtraction processing means 231 is the (m−1) th power of the voltage “Vu” across the first heating resistor 22 and the voltage across the second heating resistor 23 “ You may multiply by the n-th power value of Vd ", In that case, the division | segmentation process means 232 can be abbreviate | omitted.

  Further, although it is assumed here that the m-th power processing means and the n-th power processing means are individually provided, this is provided as one power processing means, and a multiplier that appropriately provides a multiplier “m, n” as a parameter thereto. Providing means may be combined.

  Next, a seventh embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 241 of the present embodiment, the first and second operational amplifiers 24 and 25 are connected to the third operational amplifier 36 as subtraction processing means together with the resistors 32 to 35, and the resistors 32 and 33. Since the resistance values of the resistors 34 and 35 are the same, the third operational amplifier 36 functions as a differential amplifier together with the resistors 32 to 35. The third operational amplifier 36 is also connected to the microprocessor 229 via the A / D converter 228. The microprocessor 229 is provided with a coefficient multiplication unit 242, an addition processing unit 243, a multiplication processing unit 244, and the like. It has been.

  The third operational amplifier 36 subtracts the voltage “Vu” across the first heating resistor 22 from the voltage “Vd” across the second heating resistor 23, and the coefficient multiplying means 242 The voltage “Vu” at both ends of the heating resistor 22 is multiplied by a predetermined correction coefficient “e”. The correction coefficient “e” is appropriately set according to various conditions. Here, the resistance value “Rd” of the second heating resistor 23 in the reference state of the flow rate “0” at a predetermined temperature is used as the first heating value. A value “e = 1−A” is set as a result of subtracting “A” as a result of dividing by the resistance value “Ru” of the resistor 22 from “1”.

  The addition processing means 243 divides the output voltage “Vdu” differentially amplified by the third operational amplifier 36 by the amplification factor to convert it into a differential voltage “V′du”, which is converted into the coefficient multiplication means 242. The result is added to the multiplication result “e · Vu”. The multiplication processing unit 244 multiplies the addition result “V′du + e · Vu” of the addition processing unit 243 by the voltage “Vd” across the second heating resistor 23, and the multiplication result “(V′du + e · The result output means 233 outputs the data “Vu) · Vd” as the flow rate measurement result “f2 (u)”.

  In such a configuration, the flow rate measuring device 241 according to the present embodiment also measures the flow rate of a fluid such as a gas and outputs the measurement result as digital data to the outside in the same manner as the flow rate measuring device 21 described above. In that case, the voltage “Vu, Vd” across the first and second heating resistors 22, 23 measured by the first and second operational amplifiers 24, 25 is converted into the resistors 32, 34 by the third operational amplifier 36. The differential voltage “Vdu” is also input to the microprocessor 229.

In the microprocessor 229, the differential voltage “Vdu” differentially amplified by the third operational amplifier 36 is divided by the amplification factor and converted into the differential voltage “V′du”. Further, the voltage “Vu” at both ends of the first heating resistor 22 is multiplied by a predetermined correction coefficient “e”, and the multiplication result “e · Vu” and the differential voltage “V′du” are added. The result “V′du + e · Vu” is multiplied by the voltage “Vd” across the second heating resistor 23. Then, the multiplication result f2 (u) = (V′du + e · Vu) Vd
Is linearly approximated to the flow rate of the fluid as compared to the voltage “Vu, Vd” across the first and second heating resistors 22, 23.

The above formula f2 (u) = (V'du + e.Vu) Vd
Transforming
f2 (u) = (Vd-Vu + e.Vu) Vd
= {(Vd-A.Vu) / Vu} .Vu.Vd
This is the same as “f2 (u)” in the case of “m = n = 1” described above. That is, the flow rate measuring device 241 of the present embodiment can accurately measure the flow rate while minimizing the influence of the fluid temperature.

  In addition, the detection of the differential voltage between the voltages “Vu and Vd” across the first and second heating resistors 22 and 23 is not performed by digital computation by the software of the microprocessor 229, but the third operational amplifier 36 which is hardware is used. Since it is executed by analog computation and amplified before being input to the microprocessor 229, the flow rate can be precisely measured even if the resolution of the A / D converter 228 is low.

  In particular, in the flow rate measuring device 241 of the present embodiment, the voltage “Vu” across the first heating resistor 22 is multiplied by the correction coefficient “e”. Even when the resistance value and the energization amount are different, the presence or absence of flow can be accurately determined. However, when the resistance values and the energization amounts of the first and second heating resistors 22 and 23 are the same as described above, the correction coefficient “e” is “0”, so that the coefficient multiplication means 242 and the addition processing means. 243 can be omitted. In this case, the program structure of the microprocessor 229 can be simplified, the processing load can be reduced, and the processing speed can be improved.

  However, when the resistance values and the energization amounts of the first and second heating resistors 22 and 23 are different, it is necessary to appropriately set the correction coefficient “e”, which means that the fluid flow rate is “0”. In this case, it is preferable to set “f (u)” to be “0”. In that case, the same current “I” is applied to the first and second heating resistors 22 and 23 in the reference state to measure the respective resistance values “Ru, Rd”, and the ratio “Rd / Ru” is set to “ The correction coefficient “e = 1− (Rd / Ru)” is calculated by subtracting from “1”, and this is set in the coefficient multiplication means 242.

  However, if the correction coefficient “e” is set based on the resistance values “Ru, Rd” of the first and second heating resistors 22 and 23 as described above, it is not preferable to deal with the difference in the current amount. After actually forming the circuit of the power source and the energized part, the voltages “Vu, Vd” of the first and second heating resistors 22, 23 in the reference state are used as the first, second operational amplifiers 24, It is preferable to set “1- (Vd / Vu)” as the correction coefficient “e”.

  More preferably, the difference voltage “V′du” in the reference state is divided by the voltage “Vu” across the first heating resistor 22 and the sign “−V′du / It is also possible to set Vu "as the correction coefficient" e ". That is, the differential voltage “Vdu” output from the third operational amplifier 36 is greatly affected by differential amplification and offset voltage. The microprocessor 229 multiplies this by the amplification factor to obtain the differential voltage “V′du”. Even if calculated, the consistency of these differential voltages “V′du” and “Vdu” is low.

  Even if the correction coefficient “e” is set based on the voltages “Vu and Vd” across the first and second heating resistors 22 and 23 as described above in this state, this and the difference voltage “V′du” are set. The accuracy of the flow rate measurement result is also low. However, the correction coefficient “e” is a parameter indicating a subtle difference between the voltages “Vu, Vd” across the first and second heating resistors 22, 23. The subtle difference is detected by analog calculation. Since the numerical value that has been amplified and then input to the microprocessor 229 and restored is the differential voltage “V′du”, the accuracy of the correction coefficient “e” can be improved by using this.

  If the correction coefficient “e” is calculated based on the differential voltage “V′du” in this way, there is a concern that an error such as an offset voltage of the third operational amplifier 36 may be included therein. Since the amplified differential voltage “Vdu” is compressed by dividing by the amplification factor by the microprocessor 229 and converted to the differential voltage “V′du”, the correction coefficient “e” can be set with high accuracy.

  Next, an eighth embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 251 of the present embodiment, the circuit structure is equivalently simplified compared to the above-described flow rate measuring device 241 and the like, and the first and second heating resistors 22 and 23 have first and second heating resistors 22 and 23, respectively. The first and second constant current sources 252 and 253, which are the second power supply means, are directly connected to each other. First and second measurement circuits 254 and 255, which are first and second measuring means, are individually connected to the first and second heating resistors 22 and 23, respectively. Circuits 254 and 255 are connected to the microprocessor 229 via the A / D converter 228, respectively. The first and second measurement circuits 254 and 255 are also connected to a differential amplifier circuit 256 as subtraction processing means, and this differential amplifier circuit 256 is also connected to the microprocessor 229 via the A / D converter 228. Has been.

The microprocessor 229 is newly provided with m-th power processing means 257 and n-th power processing means 258, and the setting contents of the multiplication processing means 259 are changed correspondingly. The m-th power processing means 257 raises the voltage “Vu” across the first heating resistor 22 to the (m−1) th power, and the n-th power processing means 258 includes the voltage across the second heating resistor 23 “Vd”. "Is raised to the nth power. The multiplication processing unit 259 adds “V′du + e · Vu” which is the addition result of the addition processing unit 243 to “Vu [(
m-1)]] is multiplied by the nth power result "Vd [nth power]", and the multiplication result (V'du + e.Vu) .Vu [(m-1) th power] .Vd [nth power] ]
The result output means 233 outputs the data as the flow rate measurement result “f3 (u)”.

  Since the m-th power processing means 257 raises the voltage “Vu” across the first heating resistor 22 to the (m−1) th power as described above, it is accurately referred to as the (m−1) th power processing means. However, since it is essentially not different here, it is referred to as “m-th power processing means” in order to simplify the expression.

  In such a configuration, in the flow rate measuring device 251 of the present embodiment, the both-end voltages “Vu, Vd” and the differential voltage “Vdu” of the first and second heating resistors 22, 23 are input to the microprocessor 229. In this microprocessor 229, the differential voltage “Vdu” is divided by the amplification factor of the differential amplifier circuit 256 to be converted into the differential voltage “V′du”, and the voltage across the first heating resistor 22 is “Vu”. A predetermined correction coefficient “e” is multiplied. Further, the multiplication result “e · Vu” and the differential voltage “V′du” are added, and the voltage “Vu” across the first heating resistor 22 is raised to the (m−1) th power, and the second The voltage “Vd” across the heating resistor 23 is raised to the nth power. The (m−1) th power result “Vu [(m−1) th power]” and the nth power result “Vd [nth power]” are multiplied by the addition result “V′du + e · Vu”. The result “(V′du + e · Vu) · Vu [(m−1) th power] · Vd [nth power]” is output as the flow rate measurement result “f3 (u)”.

  When the measurement result “f3 (u)” is calculated in this manner, this is because the rate of temperature correction between the first heating resistor 22 and the second heating resistor 23 is adjusted by “m, n”. The fluid flow rate can be accurately measured regardless of the temperature. Further, in the measurement result “f3 (u)” calculated in this way, the flow direction of the fluid can be determined based on the positive / negative.

  Furthermore, a ninth embodiment of the present invention will be described with reference to FIG. In the flow rate measuring apparatus 261 of the present embodiment, a digital addition unit 262 is newly added to the microprocessor 229, and the setting content of the n-th power processing unit 263 is changed corresponding to the digital addition unit 262. The second measurement circuit 255 is connected to the differential amplifier circuit 256 but not to the microprocessor 229, and the n-th power processing means 263 is connected to the first power addition means 262 via the digital addition means 262. One measurement circuit 254 and a differential amplifier circuit 256 are connected. In addition, the connection here does not necessarily mean only a physical connection, but includes a logical link by software.

  The digital adder 262 adds the digitally converted difference voltage “Vdu” and the voltage “Vu” across the first heating resistor 22, and the n-th power processor 263 adds the addition result “Vdu + Vu”. Instead of the voltage “Vd” across the second heating resistor 23, it is raised to the nth power. That is, the linkage of the operations of these means 262 and 263 functions here as a replacement processing means for replacing the measured voltage.

  In such a configuration, the flow rate measuring device 261 of the present embodiment does not use the voltage “Vd” across the second heating resistor 23 for the processing operation for measuring the flow rate, and uses this as the differential voltage “Vdu”. The addition result “Vdu + Vu” with the voltage “Vu” across the first heating resistor 22 is used instead.

  That is, as described above, since the differential voltage “Vdu” is a weak signal, the influence of the disturbance is large, and the calculated consistency between this voltage and the both-end voltages “Vu, Vd” of the first and second heating resistors 22, 23. May not be removed. However, if one of the two end voltages “Vu, Vd” is replaced with the addition result of the other and the differential voltage “Vdu”, the calculation consistency can be obtained, so the fluid flow rate can be measured accurately. can do.

  In the present embodiment, the both-ends voltage “Vd” of the second heating resistor 23 is substituted by the addition result of the both-ends voltage “Vu” of the first heating resistor 22 and the differential voltage “Vdu”. However, of course, it is possible to substitute the voltage “Vu” across the first heating resistor 22 by the addition result of the voltage “Vd” across the second heating resistor 23 and the differential voltage “Vdu”. is there.

  Further, when only the voltage “Vd” across the second heating resistor 23 is used for the flow rate measurement and the voltage “Vu” across the first heating resistor 22 is not used for the flow rate measurement, correspondingly, It is preferable to change the correction coefficient “e” of the coefficient multiplication means 242. That is, the differential amplifier circuit 256 is subtracted from the numerical value corresponding to the differential voltage “Vdu” of the differential amplifier circuit 256 from the numerical value corresponding to the voltage “Vd” across the second heating resistor 23 in the reference state. The sign of the numerical value corresponding to the differential voltage “Vdu” is inverted, the numerical value “−Vdu” is divided by the above-mentioned subtraction result “Vd−Vdu”, and the numerical result “−Vdu / (Vd−Vdu)” is obtained. "Is set as the correction coefficient" e "in the coefficient multiplication means 242.

  In this case, only the voltage “Vd” across the second heating resistor 23 is used to calculate the correction coefficient “e = −Vdu / (Vd−Vdu)” of the coefficient multiplying means 242, and the first heating resistor 22 is used. The voltage “Vu” at both ends of the first heating resistor 22 is also used for the flow rate measurement by using only the voltage “Vd” at both ends of the second heating resistor 23 as described above. If not used, the overall consistency of the arithmetic processing is improved.

  A tenth embodiment of the present invention will be described with reference to FIG. Prior to the description of the present embodiment, the configuration of the presumed flow rate measuring device 241 will be reviewed with reference to FIG. This rewrites and shows the configuration corresponding to the seventh embodiment described above. In the illustrated flow measuring device 241, an output corresponding to the resistance value of the first heating resistor 22 is obtained as the output voltage Vu of the operational amplifier 24, and a second heating resistor is provided as the output voltage Vd of the operational amplifier 25. An output corresponding to the resistance value of the body 23 is obtained. Therefore, a voltage value corresponding to the difference between the resistance values of the first and second heating resistors 22 and 23 is obtained as the differential voltage Vdu of the operational amplifier 36. Here, the first and second heating resistors 22 and 23 generate heat due to an electric current, but the heat is thermally coupled to the fluid, so that it is cooled by the fluid. This amount of heat taken away corresponds to the velocity of the fluid. That is, when the heat is taken away by the fluid, the resistance values of the first and second heating resistors 22 and 23 decrease corresponding to the amount of heat taken, so the resistance values of the first and second heating resistors 22 and 23 are reduced. Therefore, the fluid flow rate can be known.

  However, even with such a flow rate measuring device 241, there is still room for improvement when examined in detail. This point will be described in detail below. First, in the flow rate measuring device 241, constant currents Iu and Id are supplied from separate current sources to the first and second heating resistors 22 and 23, as illustrated in FIG. Here, a description will be given of the measurement results as to what kind of influence the current values supplied to the first and second heating resistors 22 and 23 change.

  In this measurement example, as the first and second heating resistors 22 and 23, those having the same resistance value of about 500Ω and having the same value with a resistance temperature coefficient of about 3300 ppm / ° C. were used. The same current was applied to these first and second heating resistors 22 and 23 at 2 mA. Now, the fluid temperature was kept at 25 ° C., and the fluid flow rate was changed. At this time, it is measured how the differential voltage Vdu is affected when the current on the first heating resistor 22 side or the current on the second heating resistor 23 side is changed. The amplification factor of the operational amplifier 36 functioning as a subtracter was set to 1.

  FIG. 24 shows how the differential voltage Vdu changes when the current Iu on the first heating resistor 22 side is changed. According to this measurement example, when the current Iu is 0.002 A, the output of the differential voltage Vdu corresponding to the fluid flow 0 [L / H], 100 [L / H], and 200 [L / H] corresponds to the current Iu. It turns out that it changes by the change of. When the current Iu changes to 0.00205 A, the value of the differential voltage Vdu when the current Iu is equivalent to 100 [L / H] is smaller than the value of the differential voltage Vdu when the current Iu is 0.002 A and equivalent to 0 [L / H]. It has become. Thus, the change of the current Iu greatly affects the value of the differential voltage Vdu.

  Next, FIG. 25 shows a measurement example when the currents Iu and Id change equally. That is, the output of the differential voltage Vdu when I = Iu = Id and I changes is shown. Comparing the measurement results of FIG. 24 and FIG. 25, it can be seen that the change in the differential voltage Vdu in FIG. 25 is smaller. That is, when the current sources for the first and second heating resistors 22 and 23 are separate in the configuration as shown in FIG.

Therefore, in the flow rate measuring device 311 of the present embodiment, when the flow rate of the fluid is measured based on the change in the resistance value of the first and second heating resistors exposed to the fluid, the influence of the current value on the measurement result. It is comprised so that measurement precision can be made small and measurement accuracy can be improved. First, first and second heating resistors 22 and 23 are provided that generate heat upon receiving power. These heating resistors 22 and 23 have a large resistance temperature coefficient, and are both disposed in a fluid flow path, that is, installed at a place where there is a thermal coupling of fluid. For example, the first heating resistor 22 is on the upstream side. These first and second heating resistors 22 and 23 are connected in series together with a constant current source 312 for supplying a constant current I. Thus, a resistor array 313 is formed in which the first and second heating resistors 22 and 23 are connected in series in terms of current. Further, a voltage measuring device 314 is provided as a first voltage measuring means for measuring the terminal voltage V ₁ based on the voltages V _A and V _B at the points A and B of the first heating resistor 22. That is, the voltage measuring device 314 calculates the difference between the voltages V _A and V _B and outputs the terminal voltage V ₁ corresponding to the voltage between the points A and B of the first heating resistor 22. Similarly, a voltage measuring device 315 is provided as second voltage measuring means for measuring the terminal voltage V ₂ based on the voltages V _B and V _C at the points B and C of the second heating resistor 23. That is, the voltage measuring device 315 calculates the difference between the voltages V _B and V _C and outputs a terminal voltage V ₂ corresponding to the voltage between the points B and C of the second heating resistor 23. Here, the input impedances of these voltage measuring devices 314 and 315 are set to a sufficiently large value as compared with the impedances of the first and second heating resistors 22 and 23.

In such a configuration, the constant current I from the constant current source 312 flows from the point A to the first heating resistor 22 and from the point B to the second heating resistor 23. Therefore, an equal constant current I flows through the first and second heating resistors 22 and 23. Therefore, the voltages V _A , V _B , and V C at the points _A , _B , and _C are represented by the resistance values of the heating resistors 22 and 23 as R ₁ and R ₂ , respectively.
V _A = I × (R ₁ + R ₂ )
V _B = I × R ₂
V _C = 0
It becomes. Therefore, the voltage measuring device 314 obtains V _A −V _B , for example,
V ₁ = I × R ₁
The terminal voltage V ₁ is output. Similarly, the voltage measuring device 315 obtains V _B −V _C , for example,
V ₂ = I × R ₂
The terminal voltage V ₂ is output. That is, the terminal voltage V ₁ has a voltage value corresponding to the resistance value of the first heating resistor 22, and the terminal voltage V ₂ has a voltage value corresponding to the resistance value of the second heating resistor 23.

Therefore, according to the present embodiment, the first and second heating resistors 22 and 23 generate heat by the constant current I, but since they are exposed to the fluid, this heat is taken away by the fluid. At this time, the heat taken away corresponds to the flow velocity of the fluid. On the other hand, since the resistance values of the first and second heating resistors 22 and 23 change depending on the temperature, the terminal voltages V ₁ and V ₂ corresponding to the resistance values of the first and second heating resistors 22 and 23 are used. Becomes a value corresponding to the flow velocity of the fluid, so that the flow rate can be obtained. At this time, since the first and second heating resistors 22 and 23 are connected in series as the resistor row 313 in current, the constant current source 312 always supplies the heating resistors 22 and 23 to each other. An equal current can be flowed, so that the influence of the current value on the flow rate measurement can be reduced, and the measurement accuracy can be improved.

The eleventh embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 321 of the present embodiment, a subtracting device 322 is added as a subtracting means for calculating a difference voltage V ₃ between the terminal voltages V ₁ and V ₂ that is an output voltage of the voltage measuring devices 314 and 315. The subtracting device 322 is structurally similar to the voltage measuring devices 314 and 315.

Therefore, the subtracting device 322 has V ₃ = V ₁ −V ₂ = I × (R ₁ −R ₂ ).
The difference voltage V ₃ is output. Therefore, the difference voltage V ₃ also has a value corresponding to the difference between the resistance values of the first and second heating resistors 22 and 23. Therefore, by adding the subtracting device 322, the measurement accuracy of the difference between the resistance values of the first and second heating resistors 22 and 23 is improved.

  A twelfth embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 331 of the present embodiment, a resistor array 333 is formed that is connected in series in terms of current with a resistor 332 interposed between the first and second heating resistors 22 and 23. Here, unlike the heating resistors 22 and 23, the resistor 332 has a small resistance temperature coefficient, and is disposed at a location that is not thermally related to the fluid.

In the present embodiment, the first and second heating resistors 22 and 23 are provided connected to the feedback loops of the operational amplifiers 334 and 335, respectively. That is, the point D at one end of the first heating resistor 22 is connected to the output terminal of the operational amplifier 334, and the point E at the other end is connected to the negative input terminal of the operational amplifier 334. Similarly, the G point at one end of the second heating resistor 23 is connected to the output terminal of the operational amplifier 335, and the F point at the other end is connected to the negative input terminal of the operational amplifier 335. The resistor 332 interposed between the heating resistors 22 and 23 is connected to the negative input terminal of the operational amplifier 334 at the point E at one end, and connected to the negative input terminal of the operational amplifier 335 at the point F at the other end. Constant voltage sources 336 and 337 are connected to the + input terminals of the operational amplifiers 334 and 335 so that the voltages V _H and V _I are input thereto. Point J is the zero voltage point of the reference voltage of the circuit. As a result, as will be described later, the three resistors 22, 23, 332 are connected in series in terms of the paths D, E, F, G, and any of the points E to F. This is the zero potential point.

  Here, the input impedance of the operational amplifier is large, and no current flows through its input terminal. Therefore, the current from the output of the operational amplifier 334 flows from the point D to the first heating resistor 22. The current flowing through the first heating resistor 22 flows toward point E. At this time, no current flows from the point E to the negative input terminal of the operational amplifier 334. Therefore, the current flowing from the first heating resistor 22 to the point E flows through the resistor 332 to the point F. Also in this case, no current flows from the point F to the negative input terminal of the operational amplifier 335. Therefore, the current flowing from the resistor 332 to the point F flows through the second heating resistor 23 and to the point G, and thus to the output terminal side of the operational amplifier 335. Therefore, the three resistors 22, 23, and 332 are connected in series in terms of current in the paths D, E, F, and G.

In such a configuration, since the operational amplifiers 334 and 335 are feedback-controlled by the heating resistors 22 and 23, respectively, the + input terminal and the −input terminal are virtually grounded and become equipotential. That is, the voltage at the point E connected to the negative input terminal of the operational amplifier 334 is equal to the voltage V _H, and similarly, the voltage at the point F connected to the negative input terminal of the operational amplifier 335 is equal to the voltage V _I.

As a result, the current I flowing through the resistor 332 from point E to point F follows Ohm's law,
I = (V _H −V _I ) / R ₃
It becomes. At this time, since the resistors 22, 23, and 332 are connected in series in terms of current, the current I flows out from the operational amplifier 334 and flows to the operational amplifier 335 through the paths of points D, E, F, and G.

If the voltages V _H and V _I are constant voltages and the resistance value of the resistor 332 is not changed, the current I becomes a constant current. Thereby, a constant current can always flow through the first and second heating resistors 22 and 23. Therefore, in the case of the present embodiment, a constant current source 338 is formed by a combination of constant voltage sources 336 and 337 that supply constant voltages V _H and V _I and operational amplifiers 334 and 335.

At this time, the voltage V _D at the point _D and the voltage V G at the point _G are respectively V _D = I × R ₁ + V _H
V _G = −I × R ₂ + V _I
It becomes. Here, for example, when V _H = 1V and V _I = −1V, in order to obtain a current I = 2 mA,
R ₃ = (1-(-1)) / 0.002 = 1000
Thus, the resistance value of the resistor 332 may be set to 1 kΩ.

When such a constant current I flows, the first and second heating resistors 22 and 23 generate heat. Here, since these heating resistors 22 and 23 have a large resistance temperature coefficient, the resistance value varies depending on the environmental temperature, the temperature of the fluid, and the flow of the fluid. When resistors having a resistance change range of about 500 to 750Ω are used, a voltage of 2 to 2.5 V appears at point D, and a voltage of −2 to −2.5 V appears at point G. Appear. Therefore, when subtracting the constant voltage V _H from the voltage V _D at point D, the voltage corresponding to the terminal voltage across the first heating resistor 22 is determined. Similarly, when subtracting the constant voltage V _I from the voltage V _G of the G point, the voltage corresponding to the terminal voltage across the second heating resistor 23 is determined.

Incidentally, in the present embodiment, V _H = 1V and V _I = −1V, but the voltage is lowered to V _H = 0.5V and V _I = −0.5V, and the resistance value of the resistor 332 is 500Ω. Then, the voltage range of the voltage V _{D at} the point _D is 1.5 to 5 V, and the voltage range of the voltage V _{G at} the point G is −1.5 to −2 V. If V _I = 0V, the point F becomes 0V. Thereby, the constant voltage source 337 can be omitted. At this time, if V _H = 1V and the resistance value of the resistor 332 is 500Ω, the voltage range of the voltage V _{D at} the point _D is 2 to 2.5 V, and the voltage range of the voltage V _{G at} the point _G is − 1 to -1.5V.

  Thus, by making the voltage at the point E positive and the voltage at the point F negative, a zero potential point can be provided between the paths EF connecting the heat generating resistors 22 and 23, and the heat generating resistors 22, The magnitude of the voltage required for measuring the terminal voltage of 23 can be kept low. This is a great merit in, for example, a battery-driven gas meter or the like.

In the present embodiment, any of the first and second heating resistors 22 and 23 may be upstream (the same applies to the following embodiments), and the positive and negative _values of V _H and V _I are the same. Contrary to negative, the V _H side may be negative and the V _I side may be positive.

A thirteenth embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 341 of the present embodiment, an adder 342 is added as an adding means for adding V _D and V _G that are output voltages of the operational amplifiers 334 and 335. V _D means a terminal voltage having a larger absolute value among terminal voltages at both ends of the first heating resistor 22, and V _G represents an absolute value among terminal voltages at both ends of the second heating resistor 23. Means the larger terminal voltage. The adder 342 includes an operational amplifier 343 and a plurality of resistors 344 to 347 for input and feedback to the operational amplifier 343.

In such a configuration, when the resistance values of the resistors 344 and 345 are made equal, and the voltages V _H and V _I have a relationship of V _H = −V _I , the voltage V _D at the point _D and the voltage V _{G at the} point _G are From the above formula,
V _D = I × R ₁ + V _H
V _G = −I × R ₂ −V _H
It becomes.

In the connection paths D, E, F, and G, the zero potential point exists between the points E to F. Therefore, the absolute value of the voltage at points D and E at both ends of the first heating resistor 22 is larger at the point D. Similarly, the absolute value of the voltage at points F and G at both ends of the second heating resistor 23 is larger at the point G. Therefore, the adder 342 adds the voltage V _D at the point _D and the voltage V _{G at the} point G, and outputs the result as an added voltage V _K. This added voltage V _K is V _K = −R ₆ × (V _D / R ₄ + V _G / R ₅ )
It becomes. Therefore, substituting the previous formula,
V _K = −R ₆ / R ₄ × {I × R ₁ + V _H + (I × R ₂ ) −V _H }
= −R ₆ / R ₄ × I × (R ₁ −R ₂ )
It becomes.

As a result, the voltage V _H, when a constant value of V _I, the current I becomes a constant current. Then, it can be seen from this equation that the added voltage V _K of the adder 342 becomes an output proportional to the difference between the resistance values of the first and second heating resistors 22 and 23. Therefore, only the difference component between the resistance values of the heating resistors 22 and 23 can be extracted from the output of the adder 342, and the measurement accuracy is improved.

A fourteenth embodiment of the present invention will be described with reference to FIG. The flow rate measuring device 351 of the present embodiment is configured by connecting the second heating resistor 23 in the resistor row 313 as shown in FIG. 22 to the feedback loop of the operational amplifier 352. That is, the connection point B of the heating resistors 22 and 23 is connected to the negative input terminal of the operational amplifier 352, and the point C on the other end side of the heating resistor 23 is connected to the output terminal of the operational amplifier 352. Thereby, the connection point B of the heating resistors 22 and 23 is virtually grounded by the operational amplifier 352. An arbitrary constant voltage V _L is applied to the + input terminal of the operational amplifier 352.

  In such a configuration, the constant current I from the constant current source 312 flows from the point A to the first heating resistor 22 and further toward the point B. The current flowing to the point B does not flow to the negative input terminal of the operational amplifier 352 having a large input impedance, flows to the second heating resistor 23, and moves to the point C. Here, the first and second heating resistors 22 and 23 are connected in series in terms of current.

At this time, since the operational amplifier 352 is feedback-controlled by the second heating resistor 23, the ground between the − input terminal and the + input terminal is a virtual ground and is equipotential. That is, the voltage at point B is equal to the constant voltage V _{L at} point _L. Therefore, the voltage V _A at point _A and the voltage V _{C at} point _C are
V _A = I × R ₁ + V _L
V _C = −I × R ₂ + V _L
It becomes. Thus, it can be seen that the voltages V _A and V _C are proportional to the resistance values of the respective heating resistors 22 and 23.

Therefore, according to the present embodiment, when the constant current I is supplied, the first and second heating resistors 22 and 23 generate heat. Here, since these heating resistors 22 and 23 have a large resistance temperature coefficient, the resistance value varies depending on the environmental temperature, the temperature of the fluid, and the flow of the fluid. When resistors whose resistance value changes are about 500 to 750Ω each, a constant voltage V _L = 0 V and a constant current I = 2 mA, a voltage of 1 to 1.5 V appears at point A. , A voltage of −1 to −1.5 V appears at point C. The flow of fluid can be known from these voltage changes. As a result, even when the heating resistors 22 and 23 are connected in series and a constant current flows, there is no need for a resistor or the like for providing a zero potential point as in the resistor 332 in FIGS. The circuit can be operated at a lower voltage.

A fifteenth embodiment of the present invention will be described with reference to FIG. In the flow rate measuring device 361 of the present embodiment, an adder 362 that is an adding means for adding the voltage across the resistor array 313, that is, the voltage V _A at the point _A and the voltage V _{C at the} point _C is added. ing. The adder 362 is structurally the same as the adder 342 and includes an operational amplifier 343 and a plurality of resistors 344 to 347 for input and feedback to the operational amplifier 343. Therefore, the addition voltage V _K output from the adder 362 is
V _K = −R ₆ × (V _A / R ₄ + V _C / R ₅ )
It becomes. Now, if V _L = 0V and the resistance values of the resistors 344 and 345 are equal, the above equation is
V _K = −R ₆ / R ₄ × {I × R ₁ + (− 1) × R ₂ }
= −R ₆ / R ₄ × I × (R ₁ −R ₂ )
It becomes.

Therefore, if the current I is constant, the addition output V _K of the adder 362 becomes a value proportional to the difference between the resistance values of the first and second heating resistors 22 and 23. Therefore, only the difference component between the resistance values of the heating resistors 22 and 23 can be extracted by the output of the adder 362, and the measurement accuracy is improved.

  A sixteenth embodiment of the present invention will be described with reference to FIG. In the flow measurement device 371 of the present embodiment, in addition to the configuration shown in FIG. 30, an operational amplifier 373 functioning as impedance conversion means 372 is interposed between the point A and the + input side of the adder 362 by a voltage follower. ing.

In such a configuration, first, a case where there is no operational amplifier 373 (in the case of the configuration of FIG. 30) will be considered. In this case, a part of the current I from the constant current source 312 flows from the point A toward the adder 362 side. Since this branch current depends on the input impedance of the adder 362, the current flowing from the point A toward the first and second heating resistors 22 and 23 does not become the constant current I and decreases. Further, the voltage V _A at the point _A varies depending on the resistance value of the first heating resistor 22. When the voltage V A at the point _A changes, the current flowing from the point A to the adder 362 also changes. Here, in order to accurately measure the flow rate, it is necessary to accurately measure the change in resistance value of the first and second heating resistors 22 and 23, but the change in current leaking from the point A to the adder 362 is required. Causes a measurement error of the resistance values of the first and second heating resistors 22 and 23.

In this regard, such an inconvenience is avoided by interposing the operational amplifier 373 in the input stage of the adder 362 as in the present embodiment. That is, the input impedance of the impedance converting means 372 is defined by the input impedance of the operational amplifier 373. The input impedance of the operational amplifier 373 is ideally infinite, and even in an actual product, about 10 ⁶ to 10 ⁹ Ω. Things exist. Therefore, for example, if the resistance value of the first heating resistor 22 is about 10 ³ Ω and the operational amplifier 373 has a large input impedance, the current flowing from the point A to the operational amplifier 373 can be ignored. Can be reduced to a small extent. Therefore, the influence of the adder 362 on the current I flowing through the first and second heating resistors 22 and 23 can be reduced by the large input impedance of the operational amplifier 373.

The seventeenth embodiment of the present invention will be described with reference to FIG. As can be seen from the illustrated example, the flow measurement device 381 of the present embodiment is structurally the same as the flow measurement device 371 shown in FIG. 31, but the three flow measurement devices used in this configuration are the same. The operational amplifiers 343, 352, and 373 are formed on the same silicon wafer and sealed in the same package. Specifically, it can be easily realized by using three operational amplifiers as four operational amplifiers 343, 352, and 373 such as OPA404 manufactured by BURR-BROWN and LT1179 manufactured by LINEAR TECHNOLOGY. In this case, the resistance values of the resistors 344, 345, and 346 in the adder 362 are made equal.
The reason why such an operational amplifier of the same package is used is that an offset voltage existing in the operational amplifier is taken into consideration. That is, there is an offset voltage in the operational amplifier, and it is actually difficult to set the same voltage between the −input terminal and the + input terminal even in the virtual ground operation state. Therefore, consider the offset voltage of the operational amplifier. Assuming that the offset voltages of the three operational amplifiers 343, 352, and 373 are V _O1 , V _O2 , and V _O3 , the voltage V _B at the connection point _B is
V _B = −V _O1
It becomes. When the current I flows from the constant current source 312, the voltages V _A and V _{C at the} points _A and _C are
V _A = V _B + I × R ₁ = I × R ₁ −V _O1
V _C = V _B −I × R ₂ = −I × R ₂ −V _O1
It becomes. The output voltage V _A ′ of the operational amplifier 373 is
V _A '= V _A -V _O2
= I × R ₁ −V _O1 −V _O2
It becomes.

Here, since the resistance values of the resistors 344, 345, and 346 are equal, when R ₄ = R ₅ = R ₆ = R, the added voltage V _K output from the adder 362 is
V _K = V _O3 − {(V _A ′ −V _O3 ) / R + (V _C −V _O3 ) / R} × R
= -3 × V _O3 −V _A ′ −V _C
= −3 × V _O3 + 2 × V _O1 + V _O2 −I × (R ₂ −R ₁ )
It becomes. That is, the offset voltage V _O1 , V _O2 , V _O3 components of the operational amplifiers 343, 352, 373 other than the difference component of the resistance values of the first and second heating resistors 22, 23 remain in the added voltage V _K. .

  For example, in the case of LT1179 manufactured by LINEAR TECHNOLOGY, an offset voltage of about 100 μV may be generated at an environmental temperature of 25 ° C. Furthermore, the offset voltage changes even if it is affected by the environmental temperature and the time.

In this regard, if the offset voltages of the three operational amplifiers 343, 352, and 373 are equal and V _O1 = V _O2 = V _O3 = V _O ,
V _K = −I × (R ₂ −R ₁ )
Thus, it is not affected by the offset voltage.

  Here, it is very difficult to produce operational amplifiers having completely the same offset voltage, but if those formed on the same silicon wafer are used, it is possible to prepare the ones having very close offset voltages. For example, if three circuits of four operational amplifiers such as the above-mentioned BUPA-BROWN OPA404 or LINEAR TECHNOLOGY LT1179 are used as the operational amplifiers 343, 352, 373, the difference in offset voltage between the operational amplifiers Can be minimized. In particular, if the ones enclosed in the same package are used, the three operational amplifiers 343, 352, and 373 can be thermally brought into the same state. As a result, the change in offset voltage of the three operational amplifiers 343, 352, and 373 can be arranged in the same tendency with respect to the temperature change in the offset voltage, and the resistance values of the first and second heating resistors 22 and 23 can be measured. The effect of the applied offset voltage can be minimized.

  In implementation, the circuit is not limited to the two illustrated IC product examples and is not limited to the operational amplifier IC, and the entire circuit is fabricated on a silicon wafer and enclosed in the same package as shown in the figure. It may be.

  The eighteenth embodiment of the present invention will be described with reference to FIG. The flow rate measuring device 391 of the present embodiment is applied to, for example, the flow rate measuring device 381 having the configuration shown in FIG. 32, and a power source 392 such as a battery for operating the circuit 382 of the flow rate measuring device 381 is provided. A switch 393 is provided as switch means for intermittently supplying power from the power source 392 to the circuit 382. This switch 393 can be opened and closed automatically at an arbitrary time by a control circuit from the outside.

  In such a configuration, when measuring the flow rate, the switch 393 is closed and power is supplied from the power source 392 to the circuit 382. As a result, the circuit 382 can perform the operation as described above, and a current is supplied to the first and second heating resistors 22 and 23. On the other hand, when it is not necessary to measure the flow rate, the power supply from the power source 392 to the circuit 382 is stopped by opening the switch 393. As a result, the circuit 382 cannot operate, and no current flows to the first and second heating resistors 22 and 23. In this way, when it is not necessary to perform flow rate measurement, it is possible to reduce wasteful power consumption by setting the current value to zero. In particular, when the power source 392 is a battery, the period during which the measurement operation can be performed without battery replacement can be extended.

  Note that the power supply to the circuit 382 is cut off by the switch 393 in order to make the current flowing to the first and second heating resistors 22 and 23 zero when there is no need to perform the measurement. This current may be made zero by cutting the connection path from the resistor to the resistor row 313. The circuit 382 to which this embodiment is applied is not limited to the circuit as shown in FIG. 32, and any of the tenth to sixteenth embodiments described above can be applied in the same manner. .

It is a block diagram which shows the flow volume measuring apparatus of 1st embodiment of this invention. It is a characteristic view which shows the change of the heat generation temperature by the flow volume of the 1st, 2nd heat generating resistor. It is a characteristic view which shows the relationship between the calculation result of flow volume, and actual flow volume. It is a block diagram which shows the flow measuring device of one modification. It is a block diagram which shows the flow volume measuring apparatus of 2nd embodiment of this invention. It is a block diagram which shows the flow volume measuring apparatus of 3rd embodiment of this invention. It is a block diagram which shows the flow volume measuring apparatus of 4th embodiment of this invention. It is a block diagram which shows the flow volume measuring apparatus of 5th embodiment of this invention. It is a block diagram which shows the flow volume measuring apparatus of a 1st modification. It is a block diagram which shows the flow volume measuring apparatus of a 2nd modification. It is a block diagram which shows the flow volume measuring apparatus of the 6th Embodiment of this invention. It is a characteristic view which shows the relationship between the change of the flow volume of a fluid, and the change of the both-ends voltage of the 1st, 2nd heating resistor. It is a characteristic view which shows the relationship between the change of the flow volume of a fluid, and a measurement result. It is a characteristic view which shows the measurement result of the flow volume in three types of temperatures. It is a characteristic view which shows the state which correct | amended the measurement result of the flow volume in three types of temperature with the predetermined multiplier. It is a characteristic view which shows the state which changed the multiplier. Furthermore, it is a characteristic view which shows the state which changed the multiplier. Furthermore, it is a characteristic view which shows the state which changed the multiplier. It is a block diagram which shows the flow measuring device of 7th Embodiment of this invention. It is a block diagram which shows the flow measuring device of 8th Embodiment of this invention. It is a block diagram which shows the flow measuring apparatus of 9th Embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 10th Embodiment of this invention. It is a circuit diagram which shows the structure for examination. It is a Vdu-Iu characteristic figure which shows the measurement result. It is a Vdu-Iu characteristic figure which shows the measurement result at the time of changing the conditions. It is a circuit diagram which shows the flow measuring device of 11th Embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 12th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 13th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 14th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 15th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 16th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 17th embodiment of this invention. It is a circuit diagram which shows the flow volume measuring apparatus of 18th embodiment of this invention. It is a block diagram which shows the flow volume measuring apparatus of a 1st prior art example. It is a block diagram which shows the flow volume measuring apparatus of the 2nd prior art example. It is a circuit diagram which shows the flow volume measuring apparatus of a 3rd prior art example. It is a circuit diagram which shows the flow volume measuring apparatus of a 4th prior art example.

Explanation of symbols

22 First heating resistor 23 Second heating resistor 24 First measuring means 25 Second measuring means 26 First feeding means 27 Second feeding means 36 Subtraction processing means 122 First heating resistor 123 Second heating resistor 124, 125 Power supply means 126, 127 Temperature measuring means 133, 142 Division processing means (arithmetic processing means)
152 Drive power supply (power supply means)
163 Current detection means 164, 165 Temperature measurement means, resistance measurement means 172 Third resistor 173 Third power supply means 174 Third measurement means 182 Power supply means 183 Resistance storage means 192, 193 Power supply means 196, 197 Current detection means 205, 206 Temperature measurement means 207 Third measurement means 228 A / D converter 230 Coefficient multiplication means 231 Subtraction processing means 232 Division processing means 242 Coefficient multiplication means 243 Addition processing means 244 Multiplication processing means 252 First power supply means 253 First Second power supply means 254 First measurement means 255 Second measurement means 256 Subtraction processing means 257 m-th power processing means 258 n-th power processing means 259 Multiplication processing means 262 Digital addition means 263 m-th power processing means 312 Constant current sources 313 and 333 Resistor array 338 Constant current source 342 Adder 362 Adder 393 Switch means 314 First voltage measurement means 315 Second voltage measurement means 322 Subtraction means 342 Addition means 343 Operational amplifier 352 Operational amplifier 362 Addition means 372 Impedance conversion means 373 Operational amplifier

Claims (3)

A first heating resistor having a large resistance temperature coefficient disposed in the fluid flow path;
A second heating resistor having a large resistance temperature coefficient disposed downstream of the first heating resistor;
First power supply means for supplying electric power with constant voltage and constant current to the first heating resistor;
A second power supply means for supplying a constant current with a variable voltage to the second heating resistor;
First measuring means for measuring a voltage across the first heating resistor;
Second measuring means for measuring a voltage across the second heating resistor;
Coefficient multiplication means for multiplying the measurement voltage of the first measurement means by a predetermined correction coefficient;
Subtraction processing means for subtracting the multiplication result from the measurement voltage of the second measurement means;
Division processing means for dividing the subtraction result by the measurement voltage of the first measurement means;
A flow rate measuring device comprising: In the coefficient multiplying means, a numerical value obtained as a result of dividing the resistance value of the second heating resistor in the reference state of the flow rate “0” at a predetermined temperature by the resistance value of the first heating resistor is set as a correction coefficient. The flow rate measuring apparatus according to claim 1. The coefficient multiplier means that the numerical value resulting from dividing the measurement voltage of the second measurement means by the measurement voltage of the first measurement means in the reference state of the flow rate “0” at the predetermined temperature is set as the correction coefficient. The flow rate measuring device according to claim 1, wherein

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