JPH0676898B2 - Thermal flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermal type flow meter, and more particularly, to a fluid flow region in a flow path in which a fluid flows and a fluid stationary region communicating with the fluid flow region. Each relates to a thermal type flow meter provided with a temperature sensitive body.

[Conventional technology]

As the flow meter, for example, US Pat. No. 2,859,617 is known. FIGS. 5 and 6 show the outline of the flowmeter according to this US patent. One sensor 52 is provided in the fluid flow region 51 in which the fluid F flows inside the flow passage 50, and the fluid flow region 51 is also provided. The other sensor 55 is provided in the fluid stationary area 44 shielded by the baffle 53 so that the fluid F does not act directly on the sensor. The both sensors 52, 55 are led out by the leads 56, 57 and the resistors 58, 59 are provided. Together with this, a bridge circuit WS is configured so that the voltage E is applied to the bridge circuit WS via the conductors 60 and 61. Reference numeral 62 is a resistor for zero balance adjustment.

The flowmeter configured in this way has the advantage that the temperature change of the fluid can be compensated and the zero point can be effectively corrected.

[Problems to be solved by the invention]

However, in the above conventional technique, two sensors are used.
52 and 55 are incorporated in one bridge circuit WS and are not configured to be individually temperature-controlled, so that they have drawbacks such as poor responsiveness and particularly poor responsiveness to gas. In addition, there is a drawback that the sensitivity changes depending on the temperature of the fluid to be measured, so that it is necessary to calibrate the fluid temperature.

The present invention has been made in consideration of the above matters, and an object of the present invention is to have an excellent responsiveness and to perform an accurate measurement without changing the sensitivity depending on the temperature of a fluid to be measured. To provide a thermal type flow meter.

[Means for solving problems]

In order to achieve the above-mentioned object, the thermal type flow meter according to the present invention senses each of the temperature sensitive bodies provided in a fluid flow area in a flow path of a fluid and a fluid static area communicating with the fluid flow area. The temperature sensitive resistors and the heater are provided, and two constant temperature control circuits each including the temperature sensitive resistors are independently provided, and the constant temperature control circuits keep the temperatures of both the temperature sensitive elements equal and constant. Mass flow rate of the fluid in the flow path based on a value obtained by dividing the difference between the energies applied to the temperature sensitive bodies by the energy applied to the temperature sensitive bodies provided in the fluid stationary region. It is characterized in that it is designed to measure.

[Action]

In the above-mentioned configuration, the constant temperature control circuits each including two temperature sensitive resistors are composed of a bridge circuit and an arithmetic circuit, and each constant temperature control circuit keeps the temperature of the two temperature sensitive elements equal to each other. It is controlled to be constant. The output of each constant temperature control circuit shows the energy required to keep each temperature sensitive body at a constant temperature,
By dividing the difference by the energy given to the temperature sensing element provided in the stationary region of the fluid, an output proportional to the mass flow rate of the fluid in which the temperature influence is compensated can be obtained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 show a schematic structure of a thermal type flow meter according to the present invention. In both figures, 1 is a block made of metal such as stainless steel or plastic, and conduits 2, 2 are provided at both ends thereof.
Is connected, and the flow path 3 through which the fluid F of the gas or liquid to be measured flows through the block body 1 and the conduits 2 and 2.
Are formed.

4 is an opening 5 formed in a part of the peripheral surface of the block body 1,
It is a ceramic base body that is detachably provided via a rubber O-ring 6.

Reference numerals 7 and 8 denote two temperature-sensing bodies, which are chip-shaped bodies held by the base body 4, and these temperature-sensing bodies 7 and 8 have the same configuration as each other
For example, a silicon single crystal wafer is used as a substrate, and a temperature sensitive resistor and a heater are formed on this wafer by a thin film resistor pattern. One temperature sensitive body 7 is provided in the fluid flow region 9 of the flow path 3 through which the fluid F flows, and the other temperature sensitive body 8
Is provided in a fluid stationary region 11 which is communicated with the fluid flow region 9 and shielded by a partition wall 10 so that the fluid F does not act directly.

12 and 12 are lead frames for supporting the temperature sensitive bodies 7 and 8, 13
... are lead wires made of gold wire, and 14 are external connection wires.

FIG. 3 is a circuit diagram showing the electrical connection relationship of the above-mentioned thermal type flow meter. In FIG. 3, reference numerals 15 and 16 denote temperature sensitive resistors 7S and 8S of the temperature sensitive bodies 7 and 8 of the bridge circuits 17 and 18, respectively. In the constant temperature control circuit including each component, both constant temperature control circuits 15 and 16 are configured by the same part so as to have the same characteristics, and the heaters 7H and 8H of the temperature sensitive bodies 7 and 8 are appropriately respectively. By generating heat, the temperature of the temperature sensitive bodies 7 and 8 is controlled so that they are always equal and constant.

That is, one of the constant temperature control circuit 15 has a temperature sensing resistor 7S and a resistor.
The bridge circuit 17 is composed of 19, 21 and 23, a control circuit 25 such as an operational amplifier, a switching element 27 such as a transistor, and DC power supplies 29 and 31. The other constant temperature control circuit 16 includes a bridge circuit 18 including a temperature sensitive resistor 8S and resistors 20, 22, and 24, a control circuit 26 such as an operational amplifier, a switching element 28 such as a transistor, and a DC power supply. It is composed of 30,32. The resistors 19 to 24 have a temperature coefficient sufficiently smaller than that of the temperature sensitive resistors 7S and 8S.

33 and 34 are connection points between the temperature sensitive resistors 7S and 8S and the resistors 19 and 20, respectively, and the potentials V _A1 and V _A2 thereof are inputted as one input signal of the control circuits 25 and 26, respectively. 35 and 36 are resistors 2 respectively
At the connection points of 1 and 23, 22 and 24, the potentials V _B1 and V _B2 are input as the other input signals of the control circuits 25 and 26, respectively. The control circuits 25 and 26 compare the input signals V _A1 and V _B1 , respectively, and compare the input signals V _A2 and V _B2, and output control signals S ₁ and S ₂ when there is a difference. . Switching element 2
7, 28 perform a switching operation based on the control signals S ₁ and S ₂ . By this switching operation, the power supply from the power sources 29, 30 to the temperature sensitive resistors 7S, 8S is ON / OFF controlled. The outputs P ₁ and P ₂ appearing at the connection points 37 and 38 between the switching elements 27 and 28 and the heaters 7H and 8H are the heaters 7 and
Represents the energy supplied to H and 8H, respectively.

Reference numeral 39 is a subtractor to which the outputs P ₁ and P ₂ are input and which performs a calculation of (P ₁ −P ₂ ). The output of the subtraction circuit 39 (P ₁ -P ₂₎
Is the temperature sensing element 7 located in the fluid flow region 9 and the fluid flow region 10
Since the temperature sensing element 8 located at is always at the same temperature and at a constant temperature, it represents the difference in energy supplied from the power sources 29, 30 to the heater 7H of the temperature sensing element 7 and the heater 8H of the temperature sensing element 8, respectively. And is proportional to the fluid flow rate of the fluid F flowing through the flow path 3 at the same time.

40 receives the output (P ₁ −P ₂ ) and the output P ₂ and outputs (P ₁
−P ₂ ) / P ₂ is a divider that performs the operation. This calculator 40
Output (P ₁ −P ₂ ) / P ₂ indicates the accurate mass flow rate of the fluid F with the temperature effect of the fluid F removed.

Next, the operation of the thermal type flow meter having the above configuration will be described.

First, when the fluid F is not flowing in the flow path 3, the temperature sensing resistors 7S and 8S are connected to the power source 3 via the bridge circuits 17 and 18, respectively.
Power is supplied from 1,32, and both temperature-sensitive resistors 7S and 8S have resistance 1
It is kept at the temperature determined by 9,20 respectively. And since the temperature characteristics of the resistors 19 and 20 are equal to each other,
The temperature of the temperature sensitive resistors 7S and 8S becomes equal, and therefore the output P ₁ ,
P ₂ becomes equal. As a result, the output of the calculator 40 becomes zero, and it can be seen that the fluid F does not flow.

Next, when the fluid F is flowing in the flow path 3, the temperature-sensitive body 7 located in the fluid flow region 9 is deprived of heat by the fluid F, but the temperature-sensitive body 8 located in the fluid stationary region 10 is fluidized. Almost no heat is taken away by F. Therefore, in order to make the temperatures of both the temperature sensitive bodies 7 and 8 equal and constant, the switching elements 27 and 2
Energy is supplied from the power sources 29 and 30 via 8 but as described above, the amount of heat taken by the temperature sensitive body 7 is larger than that in the temperature sensitive body, and therefore, as the output of the constant temperature control circuits 15 and 16. At the outputs P ₁ and P ₂ appearing at the connection points 37 and 38, respectively, P ₁ > P ₂ . Difference between the outputs P ₁ and P ₂ (P ₁ −P ₂ )
Is proportional to the size of the fluid F.

Then, the output (P ₁ −P ₂ ) of the subtraction circuit 39 is input as one input signal of the division circuit 40, and the output P ₂ is input to the division circuit 40.
Is input as the other input signal of ( ₁ ) to (P ₁ −P ₂ ) / P ₂ in the division circuit 40. The output (P ₁ −P ₂ ) / P ₂ of the division circuit 40 is the fluid F that compensates for the temperature effect of the fluid F.
Is proportional to the fluid flow rate of, the fluid flow rate of the fluid F in the flow path 3 can be obtained by multiplying this by a constant.

The shape of the partition wall body 10 shown in FIG. 1 is not limited to this, and the rising edge of the partition wall body 10 is appropriately increased depending on the flow rate of the fluid F so that the tip of the partition wall body 10 approaches the base body 4 side. (When the flow rate is several tens / min or more), the rise may be reduced.

FIG. 4 shows another embodiment of the present invention. The difference from that shown in FIG. 3 is that in the constant temperature control circuit 16, the bridge circuit 18 is omitted and the temperature sensitive resistor 8S and the resistor 20 are provided. Connection point
34 is connected to one input terminal of the control circuit 26, and the connection point 35 of the resistors 21 and 23 of the constant temperature control circuit 15 is connected to the other input terminal of the control circuit 26. The operation in the case of such a configuration is the same as that of the above-mentioned embodiment, and therefore its explanation is omitted.

〔The invention's effect〕

As described above, the thermal type flow meter according to the present invention has a temperature-sensitive resistance for each of the temperature-sensing bodies provided in the fluid flow region in the flow path in which the fluid flows and the fluid stationary region communicating with the fluid flow region. Two constant temperature control circuits, each of which is composed of a body and a heater, and which includes the temperature sensitive resistor, are independently provided.
The constant temperature control circuit controls the temperatures of both the temperature sensitive bodies so that they are always equal and constant, and the difference in energy applied to both the temperature sensitive bodies is applied to the temperature sensitive bodies provided in the fluid stationary region. Since the mass flow rate of the fluid in the flow path is measured based on the value divided by the given energy, not only the zero point is skillfully corrected, but also the responsiveness, especially the fluid is a gas. In this case, the responsiveness can be greatly improved. Further, the calibration of the temperature change of the fluid to be measured is minimal, and therefore, the adverse effect caused by the change of the fluid temperature can be eliminated, so that accurate and quick measurement can be performed.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a sectional view of a main part, FIG. 2 is a sectional view taken along line II-II of FIG. 1, FIG. 3 is a circuit diagram, and FIG. FIG. 5 is a circuit diagram according to another embodiment, FIGS. 5 and 6 show a conventional example, FIG. 5 is a sectional view, and FIG. 6 is a circuit diagram. 3 ... Flow path, 7,8 ... Temperature sensor, 7S, 8S ... Temperature sensor, 7
H, 8H: Heater, 9: Fluid flow area, 11: Fluid static area, 15,16: Constant temperature control circuit.

Claims (1)

[Claims] 1. A thermal flow meter in which a temperature sensor is provided in each of a fluid flow region in a flow path of a fluid and a fluid static region communicating with the fluid flow region. Two constant temperature control circuits, each of which is composed of a resistor and a heater, and each of which includes the temperature sensitive resistor, are independently provided, and the constant temperature control circuits keep the temperatures of both the temperature sensitive elements equal and constant. The mass flow rate of the fluid in the flow channel is controlled based on a value obtained by dividing the difference between the energies applied to the temperature sensitive bodies by the energy applied to the temperature sensitive bodies provided in the fluid stationary region. A thermal type flow meter characterized by being adapted to measure.