JPS6236523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot wire pulse flow meter that measures the flow rate of a fluid using a resistance wire heated by an electric current.

The fluid to be measured is heated by a heat pulse on the upstream side of the flow tube of the fluid to be measured, and the heated fluid to be measured is detected at the downstream side of the flow tube at a predetermined distance from the heating position of the fluid to be measured. The flow rate of the fluid to be measured is measured by measuring the time from the time to the time of detection, and the flow rate of the fluid to be measured is measured based on this.

On the other hand, a method is also used in which ultrasonic waves are used, the flow velocity is measured from the propagation time of the ultrasonic waves, and the flow rate is measured based on this flow velocity. However, ultrasonic waves have the disadvantage that their propagation time varies considerably depending on the composition of the fluid. For example, the propagation velocity of ultrasonic waves in He is 19.0×10 ⁴ m ² /S ² at 0° C., and in air it is 11.0×10 ⁴ m ² /S ² . In contrast, hot wire flowmeters can measure flow velocity without being affected by the composition of the fluid being measured, and the detectors are more accurate than those using ultrasonic waves, and the thickness and length of the hot wire can be measured. It is possible to easily obtain a simple structure whose characteristics are determined by the installation position without being affected by the size or the like. In this case, assuming that the flow rate of the fluid to be measured is Lml/sec and the cross-sectional area of the flow tube for measurement is ^Scm2 , the average flow velocity v of the fluid to be measured is given by the following equation.

v=L/S (cm/sec) (1) The distance between the heating part of the fluid to be measured installed on the upstream side of the flow tube and the temperature sensing part installed on the downstream side of the flow tube is d (cm) If T is the time required from the heating of the fluid to be measured in the heating section to the detection of the heated fluid to be measured in the temperature sensing section, then the following equation holds true.

T=1/LS.d (sec) (2) Use a W wire with diameter D and length l as the heating element in the heating section, and the density of the W wire is P (g/cm ³ ) and its thermal conductivity is Cp (cal/g〓) resistance value is R, applied voltage is V
When the current application time is t, the amount of heat ΔT given to the fluid to be measured is given by the following equation.

As is clear from equation (2), as the flow rate L of the fluid to be measured increases, the time T decreases in inverse proportion to this. Therefore, especially in a measurement system where the flow rate of the fluid to be measured changes significantly, it is difficult to set the heating time period of the fluid to be measured in the heating section. That is, if this heating time period is set too long, it will not be possible to perform measurements that accurately follow changes in the flow rate of the fluid to be measured. On the other hand, if the heating time period is made too short, the fluid detected on the downstream side of the flow tube for each unit time will be affected by the heating in the previous time period, making the detection inaccurate.

This invention solves the problems with conventional hot-wire pulse flowmeters, makes it possible to change the heat generation time period in the heating section in response to the flow rate of the fluid being measured, and allows for constant accuracy and efficiency in response to a wide range of flow rate changes. The present invention provides a hot wire pulse flowmeter that can measure flow rates with good accuracy.

In this invention, a heating means is provided for instantaneously heating the fluid to be measured at a predetermined position in the flow path to be measured, and the fluid to be measured heated by the heating means passes through the fluid. A temperature sensitive element is provided. A temperature sensing circuit section is provided which is connected to the temperature sensing element and detects passage of the heated fluid to be measured. Also, measuring the time from heating by the heating means to detection of the temperature sensitive circuit section,
A time setting circuit is provided for driving the heating means after a period of time equal to the measurement time has elapsed since the detection by the temperature sensing circuit, and the temperature of the fluid to be measured is adjusted in accordance with the driving cycle of the heating means by the time setting circuit. Means are provided for measuring the flow rate. Further, a timer means is provided for detecting that the flow rate of the fluid to be measured has become less than a predetermined value, and while the timer means is detecting, the heating means is driven at a constant cycle. (If the flow rate of the fluid to be measured falls below a predetermined value, for example, even if the flow has almost stopped, if the heating means is driven at a constant cycle (for example, about 10 Hz), the flow will suddenly stop.) Even when the flow rate is restarted, the flow rate can be measured immediately.) Hereinafter, the hot wire pulse flow meter of the present invention will be described in detail based on embodiments thereof and with reference to the drawings.

FIG. 1 is a diagram showing the configuration of the present invention, in which a flow tube 11
A fluid F to be measured is introduced into the flow tube 11, and a turbulence generator 12 is provided on the inner peripheral surface of the flow tube 11 at right angles to the flow direction of the fluid F to be measured on the upstream side of the flow tube 11.
The turbulence generator 12 has a structure in which a mesh-like body is formed of metal wire on a surface perpendicular to the flow of the fluid F to be measured, for example.

The fluid F to be measured introduced into the flow tube 11 is generally laminar and has a certain velocity distribution in a plane perpendicular to the flow. The introduced laminar fluid F to be measured becomes a turbulent flow due to the turbulence generator, and has a uniform average velocity in a plane perpendicular to the flow.

A heating element 13 is placed in the flow tube 11 on the downstream side of the turbulence generator 12 in the diametrical direction of the flow tube 11 . The heating element 13 is formed of a W wire having a diameter of 5 μm, for example, and a heat pulse for heating the fluid to be measured is applied from the heating element 13 to the fluid to be measured.
That is, a heat generating circuit section 14 is provided, and in this heat generating circuit section 14, a heating circuit 18 is excited by a heating pulse S _H of a predetermined pulse width generated from a heating pulse width setting circuit 10, and the heated heating circuit 18 is excited. The heating element 13 connected to generates heat, and the fluid to be measured is heated by this heat pulse.

A temperature sensing circuit section 15 is provided downstream of the heat generating circuit section 14 with respect to the flow tube 11 . Temperature sensing circuit section 1
5, a temperature sensing circuit 20 is connected between the output terminals of the temperature sensing element 19, an amplification shaping circuit 21 is connected to the output terminal of this temperature sensing circuit 20, and a filter is connected to the output terminal of this amplification shaping circuit 21. 9 is connected. The pulse corresponding to the heated fluid to be measured detected by the temperature sensing element 19 is amplified and shaped, the DC component is blocked by the filter 9, and the output signal of the filter 9 passes through the positive feedback circuit 8 and is sent to the Schmitt circuit 7.
, and an actuation signal S _D is obtained from the output terminal of the Schmitt circuit 7.

A comparison circuit (not shown) is connected to the output stage of the amplification and shaping circuit 21, and the detection pulse S _S is compared with the reference signal from the reference signal setter given to this comparison circuit, and if this exceeds the reference value, , the Schmitt circuit 7 issues an actuation signal S _D. The time setting circuit 16 is controlled by this operating signal S _D.
is driven, and after a predetermined time, a time setting signal S _T is generated from the time setting circuit 16.

The fluid to be measured includes, for example, that associated with exhalation and inhalation, and the heating circuit section 14 periodically applies heating pulses from the heating element 13 to the fluid to be measured so that measurement can be carried out in either case. heating is carried out. That is, a pulse signal of, for example, 10 Hz is supplied from the pulse generator 5 to the pulse width setting circuit 10 via the switch circuit 6, and the heating pulse S corresponding to the pulse signal of the pulse generator 5 is normally supplied to the heating circuit 18. _H is emitted. A pulse counter arithmetic circuit 3 is connected to the output end of the pulse width setting circuit 10, and a display 2 is connected to the output end of the pulse counter arithmetic circuit ₃ . The structure is such that the flow rate of the fluid to be measured is calculated and displayed.

When the flow rate of the fluid to be measured slightly exceeds the minimum flow rate of the measurement range, the time setting signal S from the matching circuit 26 is activated.
The heating pulse generating circuit section 17 is configured to be driven by _T. That is, the output terminal of the matching circuit 26 is connected to the pulse width setting circuit 10 and also to the timer 4, and the output terminal of the timer 4 is connected to the gate terminal of the switch circuit 6. The timer 4 issues a gate signal S _g to close the gate of the switch circuit 6 when the time setting signal S _T reaches a value slightly smaller than the period corresponding to the required minimum flow rate. For example, the time setting circuit 16 includes:
Pulse width setting circuit 1 of heating pulse generation circuit section 17
An up-down counter 24 is provided, which starts counting by the heating pulse S _H from 0 and counts the oscillation signal of an oscillator 25 having an oscillation frequency of 20 KHz, for example. This up-down counter 24 is
Counting is continued during the time that the fluid to be measured flows between the heating element 13 and the detection element 19, and a down count is performed in response to the activation signal S _D from the temperature sensing circuit section 15. When the coincidence circuit 26 connected to the output terminal of the counter 24 detects that this downcount number matches the count value that has already been completed after counting started with the heating pulse _SH , the time setting circuit 16 A time setting signal S _T is issued from.

As shown in the embodiment of FIG.
An output signal S _n or a time setting signal S _T is applied to the base T _p of the transistor 30, and a heating pulse S _H of a predetermined pulse width is emitted from the pulse width setting circuit 10 by the drive signal S p emitted from the transistor ₃₀ . It will be done. This heating pulse S _H is applied to the base of the transistor 32, and the transistor 3
Transistor 33, whose base is connected to the emitter of transistor 2, becomes conductive, and a heating current instantaneously flows through heating element 13, which is connected between its emitter and ground.

As mentioned above, the output signal S _n of the switch circuit 6 corresponding to the pulse signal from the pulse generator 5 is always
The pulse width setting circuit 10 is driven, and when the time setting signal S _T becomes slightly smaller than the period corresponding to the minimum flow rate, the gate signal S _g causes the switch circuit 6 to close the gate, and the pulse width setting circuit 10 starts setting the time. Driven by signal S _T .

When the heating element 13 is heated, the fluid to be measured flowing through the heating element 13 is heated at the time of heating. When this heated fluid to be measured passes through the temperature sensing element 19, the temperature sensing element 19 is heated and its resistance value increases. A bridge 34 having one side of this temperature sensing element 19 is constructed, and an amplifier 35 is connected between detection terminals of the bridge 34. When the bridge 34 becomes unbalanced due to a temperature change in the fluid to be measured, the amplifier 35 generates a detection signal S _C .

In the embodiment shown in FIG.
The temperature sensing elements 19-1 and 19-2 are arranged with their positions shifted from each other. For example, when measuring exhaled breath, the second temperature sensing element 19-2, which is arranged offset from the first temperature sensing element 19-1, separates and detects the amount of heat given by the human body to the exhaled breath. Therefore, the temperature sensing circuit 20 can perform measurements in which the influence of the amount of heat given by the human body to the fluid to be measured is removed. In addition, when measuring exhalation and inhalation, two sets of temperature sensing elements 19, 1 are placed on both sides of the heating element 13, as shown in FIG.
9' may be provided. This detection signal S _C is
7 and a capacitor 38, and the output of the integrating circuit 36 is fed to a capacitor 39 to block the DC component in the detection signal _S.sub.C. The detection signal S _C with the DC component blocked is sent to the amplifier 4
0,41, and a shaped detection pulse S _C is obtained at the output end of the amplifier 41. This detection pulse S _C is applied to the non-inverting input terminal of the comparison amplifier 42 of the temperature sensing circuit section 15 .

On the other hand, the output terminal of the amplifier 41 is connected to the comparator amplifier 4
3, and is connected to the non-inverting input terminal of the comparison amplifier 43.
The cathode side of the diode 44 is connected to the output terminal of the diode 44 . The anode side of the diode 44 is connected to the capacitor 4
5, and the other end of this capacitor 45 is grounded. The anode side of the diode 44 is connected to the non-inverting terminal of the comparison amplifier 46, and the non-inverting terminals of the comparison amplifiers 43 and 46 are connected to each other. The output terminal of comparison amplifier 46 is connected to the variable terminal of variable resistor 49 via resistors 47 and 48. The connection point between resistors 47 and 48 is connected to the inverting input terminal of comparator amplifier 42.

The anode side of the diode 44 is connected to the cathode side of the diode 50, and the anode side of the diode 50 is connected to the output end of the multivibrator 51. An inverting circuit 52 is connected to the output terminal of the comparison amplifier 42.
is connected.

If the detection pulse S _C obtained at the output terminal of the comparator amplifier 41 has a peak value smaller than a predetermined value, the output signal of the comparator amplifier 43 is smaller than the predetermined value, and the diode 44 is in a conductive state. When the diode 44 is conductive, the charge in the capacitor 45 is discharged, a negative voltage appears at the output terminal of the comparator amplifier 46, and the operating signal S appears at the output terminal of the inverting circuit 52.
_D does not occur.

However, when the peak value of the detection pulse S _C exceeds a predetermined set value, the diode 44 is cut off, a predetermined reference voltage is set at the inverting terminal of the comparator amplifier 42 , and the operating signal S is sent to the output terminal of the inverting circuit 52 . _D occurs. When a reset signal is applied to the excitation terminal _t1 of the multivibrator 51, the capacitor 4
A positive pulse is applied to 5 to perform a reset operation.

The actuation signal S _D is applied to the input terminal of a NOR circuit 60, and the output terminal of the NOR circuit 60 is connected to one input terminal of a NOR circuit 61, as shown in FIG. An output terminal of NOR circuit 61 is connected to another input terminal of NOR circuit 60. NOR circuit 6
1 output terminal is connected to one input terminal of the NOR circuit 62. The output terminal of the NOR circuit 62 is NOR
connected to one input terminal of the circuit 63;
An output terminal of the NOR circuit 63 is connected to another input terminal of the NOR circuit 62. The output terminal of a NAND circuit 64 is connected to the other input terminal of the NOR circuit 63, and one end of a capacitor 65 is connected to one input terminal of this NAND circuit 64.
The other end of 5 is grounded.

A predetermined power supply is applied via a resistor 66 to a terminal of the NAND circuit 64 to which a capacitor 65 is connected. A start switch 67 is connected between the two plates of the capacitor 65. The output terminal of the NOR circuit 62 is connected to the input terminal of an inverting circuit 68, and the output terminal of the inverting circuit 68 is connected to one input terminal of a NAND circuit 69. A 20 KHz reference signal is applied from the oscillator 25 to the other input terminal of the NAND circuit 69. An output terminal of the inverting circuit 68 is connected to one input terminal of a NAND circuit 71 via another inverting circuit 70. A 20 KHz reference signal is applied from the oscillator 25 to the input terminal of this NAND circuit 71.

The respective output terminals of the NAND circuits 69 and 71 are connected to the respective input terminals of the NOR circuit 72. The output terminal of this NOR circuit 72 is connected to the clock terminals of up-down counters 73, 74 and 75 connected in series, respectively. Further, the output terminal of the inverting circuit 68 is connected to each control terminal t _c of the counters 73 , 74 and 75 .

Each output terminal t _p of counters 73, 74 and 75
₁ , t _p2 , t _p3 and each control terminal are connected to the input terminal of the NOR circuit 76, respectively. The output terminal of this NOR circuit 76 is connected to one of the input terminals of the NAND circuit 64 via a NOR circuit 77.

At the time of starting, the switch 67 shown in FIG. 3 is turned on, and at the same time, the output signal S _n of the switch circuit 6 is applied to the base T _p of the transistor 30 shown in FIG.
_H is emitted. Since this heating pulse S _H is applied to the input terminal T ₁ of the NOR circuit 61, the logic value of the signal at the output terminal of the NOR circuit 62 becomes "1".
Each counter 73, 74,
The logical value of the signal at the control terminal _tc of the clock terminal 75 is set to "0", and each counter 73, 74, 75 counts the 20 KHz signal of the oscillator 25 applied to the clock terminal.

The heat pulse given to the fluid to be measured is transmitted to the temperature sensing element 1.
9 and the activation signal S _D is output from the inverting circuit 52.
When the activation signal S D is issued, this activation signal S _D is applied to the input terminal T ₂ of the NOR circuit 60 . When the time comes,
The logic value of the signal at the output terminal of the NOR circuit 62 becomes "0", and the logic value of the signal at the control terminal t _c of each counter 73, 74, 75 becomes "1" via the inverting circuit 68. The counter is controlled to perform a down-count operation, and uses a signal applied to the clock terminal to down-count the already counted value.

When the already counted count value is exhausted and the signals at the output terminals t _p1 , t _p2 , and t _p3 all become logic value "0", the logic value of the signal at the control terminal t _c has already become "0". ”, so this is
It is detected by the NOR circuit 76, and a time setting signal S _T appears at the output terminal of the NOR circuit 76. This time setting signal S _T is given to the timer 4, and when the period of the time setting signal S _T becomes slightly smaller than the period corresponding to the minimum flow rate, the timer 4 issues a gate signal S _g . When this gate signal S _g is generated, it is applied to the switch circuit 6 of FIG. 1 (not shown in FIG. 3), which closes the gate to the pulse generator 5.
The input of the pulse signal from the transistor 3 to the pulse width setting circuit 10 is blocked, and the time setting signal S _T is input to the pulse width setting circuit 10.
This time setting signal S _T is applied as an input signal to the base of the heating pulse generating circuit 17.
is driven, and the fluid to be measured is heated by the heating pulse from the heating circuit 18.

In this embodiment, heating pulses based on the time setting signal S _T are successively emitted at intervals twice the time T from when the heating pulse is emitted until it is detected by the temperature sensitive circuit section 15 . When the period of the time setting signal S _T increases slightly from the period corresponding to the minimum flow rate, the timer 4 opens the gate of the switch circuit 6 by the gate signal S _g , and the heating circuit 18 responds to the pulse signal from the pulse generator 5. It will be heated based on the temperature.

As described above, according to the present invention, the fluid to be measured is regularly heated periodically by the pulse signal of the pulse generator 5, and is in a state that can be used for both exhalation and inspiration flow measurement, and the time setting signal S _T When the cycle becomes equal to or less than a predetermined value, the fluid to be measured is heated at this cycle and detected by the temperature sensing circuit section 15. The time setting signal S _T is set at an interval twice the time T required for detecting the heated fluid in the temperature sensing circuit section 15 by heating the heating element 13, so that it is sufficient for the heating element 13 and the temperature sensing element 19. It is possible to give time for cooling, and the temperature detection of the measured fluid is unlikely to be adversely affected by the temperature of the heating of the previous heating pulse.
Highly accurate flow measurement is always possible even when the flow rate is short, and the dynamic range of high flow areas can be greatly expanded. Figure 4 shows the relationship between the flow rate l obtained with the hot-wire pulse flowmeter of the present invention and the time from heating to detection, and shows that linearity is extremely good over a wide range of flow rates. .

As explained in detail above, according to the present invention, the application interval of heating pulses to the fluid to be measured is automatically changed in accordance with the flow velocity and flow rate of the fluid to be measured, so that fluids with large flow fluctuations, For example, it is possible to efficiently measure the respiratory flow rate.

Therefore, the power consumption is low, and the detection in the temperature sensing circuit is not affected by the previous heating pulse, and is not affected by the type of fluid, temperature, or ambient temperature, and it is possible to accurately measure the flow rate of the fluid to be measured with little error. Measurement becomes possible. Even if the flow rate of the fluid to be measured is below a predetermined value (for example, the minimum value of the measurement range), the heating means is driven at a fixed cycle, so even if the flow rate suddenly changes beyond the predetermined value, the changed flow rate can be measured immediately. can. Therefore, it can also be applied to measurements of expiration and inspiration in which the flow temporarily stops and then suddenly resumes.
Also, calibration during quantitative detection is simple as it depends only on the geometrical dimensions of the detection system. The measured flow rate ranges over a wide range from a low flow rate to a high flow rate, and it is sufficiently possible to measure, for example, human respiratory volume.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the hot-wire pulse flowmeter of the present invention, and FIGS. 2 and 3 are circuit diagrams of the main parts of the embodiment of the hot-wire pulse flowmeter of the present invention, respectively. Fig. 4 is a diagram showing the relationship between the flow rate of the fluid to be measured and the detection time obtained by the hot-wire pulse flowmeter of the present invention, and Fig. 5 is a diagram showing the arrangement of the heating element and the detection body in an embodiment of the hot-wire pulse flowmeter of the present invention. FIG.

Claims (1)

[Scope of Claims] 1. A heating means for instantaneously heating the fluid to be measured at a predetermined position with respect to the fluid to be measured in the flow path to be measured; a temperature sensing element provided at a passing position; a temperature sensing circuit unit connected to the temperature sensing element and detecting passage of the heated fluid to be measured; and detection of the temperature sensing circuit unit from heating by the heating means. a time setting circuit that measures the time from the temperature sensing circuit section and drives the heating means after a period of time equal to the measurement time has elapsed since the detection of the temperature sensing circuit section; means for measuring the flow rate of the fluid to be measured; timer means for detecting when the flow rate of the fluid to be measured falls below a predetermined value; and pulses for driving the heating means at a constant cycle while the timer means is detecting the flow rate of the fluid to be measured. A hot wire pulse flowmeter comprising: a generator;