JP2002090195A - Flow velocity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flow velocity signal having a good linearity even in a high flow velocity area by giving linearity to output characteristics of a heat- sensing flow velocity sensor in a low velocity area to the high velocity area. SOLUTION: This device comprises a heat-sensing type flow velocity sensor FS, in which there are provided a first temperature sensor UTP and a temperature sensor DTP each disposed at the upstream side and downstream side of the flow passage F through a heater H and a third temperature sensor TP3 in which a level of an outputted voltage V3 varies depending upon a flow velocity of a fluid, voltage generating means 1 for generating a driving voltage of the heater H, a voltage detecting means 2 for detecting generated voltage of the third temperature sensor TP3, and a voltage supply means 3 for adding the voltage V3 detected by the third temperature sensor TP3 to a heater driving voltage Vh generated by the voltage generating means 1 to increase the heater driving voltage Vh to supply it to the heater H.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity measuring apparatus, and more particularly, to a flow velocity measuring apparatus having a function of correcting the linearity of an output of a thermopile type flow sensor disposed in a fluid passage such as a gas meter. .

[0002]

2. Description of the Related Art Conventionally, as shown in FIG.
The heaters H are located upstream and downstream of the fluid in the gas passage F of FIG.
Upstream thermopile UT arranged at a predetermined interval via
For example, there is a flow sensor FS that measures the flow velocity of gas or the like based on the difference between the thermoelectromotive force due to the voltage of P and the downstream thermopile DTP. In this flow sensor FS, the heat released from the heater H is transferred at a speed lower than the speed of transmission to the downstream thermopile DTP at the upstream thermopile UTP.
Is transferred to the upstream thermopile UPT by the speed difference, and the heat from the heater H is transferred to the downstream thermopile DPT.
It is cooled and transmitted more than TP. As a result, the voltage of the generated electromotive force is lower than that of the downstream thermopile DTP. Then, as the temperature reaches the high flow velocity region, as shown in FIG. 7A, the amount of heat transferred from the heater H is removed by the fluid, and the thermal electromotive force decreases.

[0003] The downstream thermopile DTP is located downstream of the heater H in the gas flow direction.
Is released to the downstream thermopile DTP at a rate obtained by adding the gas flow rate to the heat transfer rate of the gas. However, as the flow velocity becomes higher, more heat is taken away by the fluid than transmitted heat, and the thermoelectromotive force becomes saturated and gradually decreases.

[0004] Upstream and downstream thermopile UPT, D
Assuming that the difference ([DTP-UTP]) in the output (thermoelectromotive force) of TP is (OUT) and the change is determined along the flow velocity, the output change in the low flow velocity region is obtained as shown in FIG. (ΔOU
T1 / ΔF), the output change (ΔOUT2) in the high flow velocity region
/ ΔF), and ΔOUT2 / ΔF <ΔOUT1 / ΔF
Becomes Therefore, in the flow sensor, the higher the flow velocity region, the smaller the change ΔOUT of the sensor output with respect to the change in the flow velocity, and the worse the linearity. Therefore, conventionally, the linearity of the flow sensor output has been corrected by a correction calculation of the sensor output by the microcomputer.

[0005]

As described above, conventionally,
In order to correct the output of the flow sensor, the output of the flow sensor was corrected by calculation by a microcomputer. However, there is a problem that the calculation is complicated, the load on the correction calculation of the microcomputer is large, and the time required for the calculation may accelerate the consumption of the battery built in the gas meter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a flow velocity measuring device having a function of correcting the linearity of a flow sensor output without performing a complicated correction operation by a microcomputer. The purpose is to gain.

[0007]

As shown in the basic configuration diagram of FIG. 1, a flow rate measuring device according to the present invention has a first sensor disposed upstream and downstream of a flow path via a heater. A thermo-sensitive flow rate sensor including a temperature element, a second temperature-sensitive element, and a third temperature-sensitive element whose voltage level changes according to the flow rate of the fluid; and a voltage generating means for generating a heater drive voltage. A voltage detecting means for detecting a voltage generated by the third temperature sensing element; and a heater driving voltage generated by the voltage generating means, and adding the voltage output from the third temperature sensing element to increase the heater driving voltage. Means for supplying voltage to the heater by increasing the heater drive voltage with an increase in the flow velocity, thereby increasing the output change with respect to the flow velocity change of the first temperature sensitive element and the second temperature sensitive element in the high flow velocity region. The first temperature sensing element and the second temperature sensing element By the difference of the output in the device,
The output characteristics of the heat-sensitive flow sensor from a low flow region to a high flow region have linearity.

[0008] In the thermal flow sensor of the flow velocity measuring apparatus according to the present invention, the voltage output from the third temperature-sensitive element is added to the heater driving voltage as the flow velocity increases, and the heater driving voltage rises. By increasing the heat transferred to the first temperature sensing element and the second temperature sensing element and increasing the output voltage, a large sensor output characteristic can be obtained even in a high flow velocity region.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Next, before describing the operation of the flow velocity measuring device according to the present embodiment, an outline of a micro flow sensor to which the present invention is applied will be described. FIG.
Is, for example, a thermopile type micro flow sensor 31
FIG. As shown in the figure, the microflow sensor 31 has a base 41 made of Si, and a diaphragm 41a formed on the base 41 by anisotropic etching.
And thermopile 43, 4 on the upstream, downstream, left, and right sides for temperature measurement formed on the diaphragm 41a.
5, 47, 49 and a heating micro-heater 51 (corresponding to a heater), and a base 41 separated from the diaphragm 41a.
And a temperature measuring resistor 53 formed in the portion. The micro heater 51 and the temperature measuring resistor 53 are made of platinum or the like.

The upstream, downstream, left, and right thermopiles 43, 45, 47, and 49 are p ++-S
I and Al, of which the upstream and downstream thermopiles 43 and 45 are provided with a micro heater 51 in the flow direction A of the gas flowing through the gas passage 29.
The thermopiles 47, 49 on the left and right sides are arranged at equal intervals from the microheater 51 at the bases 41 on the upstream side and the downstream side, respectively, with the gas flowing through the gas passage (F in FIG. 6). In the width direction orthogonal to the flow direction A, the micro-heater 51 is interposed between the bases 41 at the left and right sides of the micro-heater 51 at equal intervals.

Then, each of the thermopiles 43, 45, 4
The hot junctions 43a, 45a, 47a, 49a of 7, 49 are placed on the diaphragm 41a, and the cold junctions 43b, 45b, 47
b and 49b are arranged on the base 41 other than the diaphragm 41a, respectively, and the temperature measuring resistor 53 is also connected to the cold junctions 43b, 45b and 4 of the thermopiles 43, 45, 47 and 49.
Like 7b and 49b, they are arranged on the base 41 other than the diaphragm 41a.

In the micro flow sensor 31 configured as described above, the heat generated by energization of the micro heater 51 uses the gas in the gas passage as a medium, and the upstream, downstream, left, and right thermopiles 43, 45, 47,
When it reaches near 49, each of the thermopiles 43, 4
5, 47, and 49 have hot junctions 43a, 45a, 47a, and 4 having a temperature corresponding to the heat transmitted from the micro heater 51.
9a and a cold junction 43b having a temperature substantially the same as that of the base 41,
An electromotive force of a voltage corresponding to the temperature difference between 45b, 47b, and 49b is generated.

Therefore, when the micro-heater 51 is heated, the upstream thermopile 43 located on the upstream side of the gas flow direction A with respect to the micro-heater 51 has a speed obtained by subtracting the gas flow speed from the gas heat propagation speed. Then, the heat released from the microheater 51 is transmitted, and the downstream thermopile 45 located downstream of the microheater 51 in the gas flow direction A has a speed obtained by adding the gas flow rate to the heat transfer speed of the gas. Thus, the heat released from the micro heater 51 is transmitted.

However, when the gas flows in the gas passage 29, the heat released from the micro heater 51 is transmitted to the upstream thermopile 43 at a lower speed than the transmission speed to the downstream thermopile 45, and Since the heat from the micro heater 51 is cooled and transmitted to the upstream thermopile 43 by the speed difference more than the downstream thermopile 45, the voltage of the electromotive force generated in each of the upstream and downstream thermopiles 43, 45 is: It differs depending on the temperature difference of heat transmitted from the micro heater 51 by the gas flowing in the gas passage 29, that is, according to the flow velocity of the gas flowing in the gas passage.

Therefore, the magnitude of the electromotive force signal output from the output terminal 39 of the micro flow sensor 31 according to the voltage difference between the electromotive forces generated in the thermopiles 43 and 45 depends on the temperature of the heat emitted from the micro heater 51 and And the flow velocity of the gas flowing in the gas passage.

Before giving a detailed description of the flow velocity measuring device according to the present invention, in the micro flow sensor (abbreviated as “flow sensor” hereinafter) configured as described above, a straight line of the sensor output is used without using a microcomputer. An outline of a method for correcting the gender will be described. As described in the related art, when the flow velocity of the fluid in the gas passage increases, the amount of heat taken by the fluid in both the upstream thermopile (UTP) and the downstream thermopile (DTP) increases, and the [DTP-UTP] output is saturated. State.

Therefore, the heater voltage is increased to increase the UTP, D
By increasing the heat transferred to the TP and shifting the high flow velocity region in which the [DTP-UTP] output is saturated to a higher flow velocity region, a low flow velocity capable of maintaining the linearity of the [DTP-UTP] output The width of the high flow velocity region widens from the region.

To detect an increase in the flow velocity, output information of the right thermopile 47 (TP3) constituting the flow sensor is used. TP3 is a micro heater 5 as shown in FIG.
The output due to the thermoelectromotive force generated by the slightly transmitted heat, which is not on the axial flow with that of No. 1, decreases when the flow rate increases, because the fluid is deprived of the heat. Therefore, by applying the output of TP3 to the input terminal of the output amplifier at the last cut in the heater control circuit described later, the output voltage of TP3 is added to the output voltage of the output amplifier and added to the micro heater 51.

As a result, the driving power of the micro-heater 51 is raised and the amount of heat generated increases, and the heat transmitted to the UTP and DTP increases. Then, the [DTP-UTP] output characteristic in the high flow velocity region shown by the curve A in FIG. 5 has its linearity corrected from the saturated state to the output characteristic in the high flow velocity region shown by the curve A ′ in FIG. Is done.

Next, the operation of the flow velocity measuring device according to this embodiment will be described with reference to the drawings. This apparatus comprises a flow velocity detecting circuit shown in FIG. 3 and a heater control circuit shown in FIG. In this flow velocity detection circuit, OP6 is the right thermopile T
A voltage follower circuit for outputting the output voltage of P3 to the subsequent stage,
OP7 is an OP amplifier constituting the error amplifier.

The OP amplifier OP7 has a negative input terminal connected to the output terminal of the voltage follower circuit OP6 through a 10K input resistor R42, a reference voltage of 1.5 V is applied to the positive input terminal, and the output terminal and the negative input terminal are connected to a capacitor. A parallel circuit of (for oscillation prevention) and a negative feedback resistor of 10K is connected.

A negative input terminal of the OP amplifier OP7 is connected to a series circuit of a resistor R43 to which a reference voltage of 2.2 V is applied at one end and a variable resistor RV1, and a voltage follower circuit OP6.
Are connected as a level shift circuit that raises the output to 1.5V. OP8 is an OP amplifier constituting an error amplifier. This OP amplifier OP8 has a negative input terminal of 10
It is connected to the output terminal of the OP amplifier OP7 through the input resistor R42 of K, a reference voltage of 1.5 V is applied to the positive input terminal, and the output terminal and the negative input terminal are capacitors (for preventing oscillation) and 5K and 20K. A parallel circuit with a series circuit of a variable resistor is connected. The output terminal of the OP amplifier OP8 is input to the input terminal of the final output circuit of the heater control circuit shown in FIG.

FIG. 4 shows a heater control circuit according to the present embodiment. In the figure, reference numeral 53 denotes a temperature measuring resistor as a reference element for measuring an ambient temperature. This temperature measuring resistor 5
The battery voltage Vbt-Tens, for example, 3 from one end of the battery 3 through a parallel circuit of resistors R71 and R72.
V is applied, and the other end of the temperature measuring resistor 53 is connected to the collector of the transistor Q1. Note that the resistor R71
The combined resistance value of the parallel circuit composed of the resistors 72 and 72 is the resistance value of the temperature measuring resistor 53 at an ambient temperature of 20 ° C.

The resistor R73 is connected to the base of the transistor Q1.
Amplifier OP that constitutes a voltage follower circuit
1 output terminal, and the emitter is an OP amplifier OP1.
And a parallel circuit in which a capacitor C25 is connected in parallel to a series body of the resistor R74 and the variable resistor RV3 is connected to the ground.

The OP amplifier OP1 and the transistor Q1 are
When the applied voltage is 3 V, the resistance value of the resistance bulb 53 and the resistance value of the resistance R7 in the normal temperature state are adjusted based on the adjustment of the variable resistance RV3.
A constant current circuit is formed such that a constant current (100 μA) corresponding to a combined resistance value of the resistance values of the parallel bodies of 1 and 72 flows.

Accordingly, the resistance of the temperature measuring resistor 5 is changed by the change of the ambient temperature.
When the resistance value of No. 3 changes, the voltage drop generated in the resistance series circuit of the parallel connection of the temperature measuring resistor 53 and the resistors R71 and R72 changes according to the change of the ambient temperature.

The point of application of the battery voltage to the parallel combination of the resistors R71 and R72 is connected to the positive input terminal of the OP amplifier OP2 through an input resistor (50 KΩ) which is a parallel circuit of the resistors R75 and R76. Temperature measuring resistor 53 and transistor Q1
Is connected to the negative input terminal of the OP amplifier OP2 through an input resistor (50 KΩ) which is a parallel circuit of the resistors R78 and R79.

The positive input terminal of the OP amplifier OP2 is connected to ground through a resistor R77 (1 MΩ). 1 between the output terminal and the negative input terminal of the OP amplifier OP2.
Since the MΩ negative feedback resistor R80 is connected, the OP amplifier OP2 constitutes a differential amplifier having a gain of 20.

The output terminal of the OP amplifier OP2 is 100 KΩ
Is connected to the negative input terminal of the OP amplifier OP3 through the input resistor R81. The output terminal of the OP amplifier OP3 is 200
It is connected to a negative input terminal through a negative feedback resistor (variable resistor) R82 of KΩ. Since a reference voltage of 1.5 V is applied to the positive input terminal of the OP amplifier OP3, the OP amplifier OP3 forms an error amplifier having a gain of 1.5.

The OP amplifier OP3 has a negative input terminal and an output terminal connected to a negative feedback resistor R84 of 100 KΩ, and a positive input terminal to which a reference voltage of 1.5 V is applied. Connected through R83. Therefore, the OP amplifier OP4 becomes an error amplifier having a gain of 1.

The output terminal of the OP amplifier OP4 is connected to the source of the field effect transistor Q2. The heater 51 is connected between the drain of the field effect transistor Q2 and the ground, and the gate is connected to the gate through a resistor R85.
An H-level signal having a width of sec is input as a heater drive control signal (Vb-ht) once per second. The gate is pulled up by a resistor R87.

Hereinafter, the operation of the flow velocity measuring device according to the present embodiment will be described. The temperature measuring resistor 53 is normally driven at a constant current of 100 μA according to the resistance value at normal temperature.
The variable resistor RV3 is adjusted so that a current of 100 μA flows by absorbing the individual difference of 3. As a result, the OP amplifier OP
1. When a current flows through a parallel circuit of resistors R71 and R72 and a resistance series circuit of a temperature measuring resistor 53 by a constant current circuit composed of a transistor Q1 and the like, the parallel connection of the resistors R71 and R72 and the temperature measuring resistor 53 A voltage drop occurs between the series circuits.

The generated voltage drop is input to the negative input terminal of the OP amplifier OP2 constituting the differential amplifier, and the applied battery voltage is input to the positive input terminal of the OP amplifier OP2.

The difference between the battery voltage and the voltage drop is input from the OP amplifier OP2 to the OP amplifier OP3 having a gain of 20. The OP amplifier OP3 amplifies the input voltage to a predetermined magnification by adjusting the variable resistor RV4 and operates the operational amplifier O3.
Input to P4. The operational amplifier OP4 applies the input voltage as a heater drive voltage to the source of the field effect transistor Q2.

The gate of the field effect transistor Q2 has
The heater drive voltage Vb- having a pulse width of 20 msec once during 1 sec when the battery voltage Vb-Tens is applied
ht is applied. Field effect transistor Q2 is 20 m
By turning on for a second and applying a voltage (1.5 V + α) corresponding to the ambient temperature to the heater, the heat generated from the heater 51 can be used as a medium for the upstream thermopile 4 using a gas fluid as a medium.
3 and the downstream thermopile 45.

As a result, an electromotive force is generated from the downstream thermopile 45 and the upstream thermopile at a voltage corresponding to the flow velocity and the transmitted heat value of the heater, and the difference in the electromotive force is the [DTP] of the flow sensor at the flow velocity at that time. −UTP] output.

However, when the thermopile type flow sensor reaches a high flow velocity region, as described above, [DTP-UTP]
Output saturates and decreases. Therefore, in the present invention, the output voltage of TP3 at which the output of heat is reduced by the fluid being deprived of the heating value of the heater as the flow velocity becomes higher is reduced by the OP amplifier O.
After being taken into a level shift circuit through P6, the overall level is raised by 1.5V, and then amplified through an OP amplifier OP7, it is input to an OP amplifier OP8.

The OP amplifier OP8 amplifies the input voltage and a final output stage OP in the heater control circuit.
The signal is input to the input terminal of the amplifier OP4 through the resistor R89. At this time, the OP amplifier OP4 adjusts the amplification factor by adjusting the variable resistor RV2, and changes the voltage TP3 to [DTP-UT
P] In order to improve the saturation state of the output, the signal is amplified to a level and output to the heater control circuit.

In the heater control circuit, the input TP3 voltage is input to the input terminal of the OP amplifier OP4, added to the heater driving voltage input to the input terminal, and output to the field effect transistor Q2, thereby obtaining the electric field effect transistor Q2. Transistor Q
2, a heater drive voltage obtained by adding the TP3 voltage to the heater 51 is applied.

As described above, by increasing the level by adding the TP3 voltage to the heater drive voltage, as shown in FIG. 5, the [DTP-UTP] output (A
Curve) is indirectly boosted at the TP3 voltage level, and the [DTP-UTP] output in the high flow velocity region is changed to the [DTP-UTP] 'output indicated by the A' curve to have linearity. As a result, in the [DTP-UTP] output, the width from the low flow velocity region having high linearity to the high flow velocity region is widened, and the flow velocity can be measured in a wide flow velocity region.

[0041]

According to the present invention, the output is made according to the flow rate of the fluid with the first and second temperature-sensitive elements and the second temperature-sensitive element which are respectively disposed on the upstream and downstream sides of the flow path via the heater. Thermal flow sensor provided with a third temperature-sensitive element whose voltage level changes, voltage generating means for generating a heater driving voltage, and voltage detecting means for detecting a voltage generated by the third temperature-sensitive element Voltage supply means for increasing the heater drive voltage by adding the voltage output from the third temperature sensing element to the heater drive voltage generated by the voltage generation means, and supplying the heater drive voltage to the heater. By increasing the heater drive voltage and increasing the output change with respect to the flow rate change of the first and second temperature sensing elements in the high flow rate region, the first temperature sensing element and the second temperature sensing element Low flow rate of thermal flow sensor due to output difference It is possible to have the linearity in the output characteristics of the high flow rate range from, there is an effect that it is possible to obtain a good flow rate signal linearity even at a high flow rate zone.

According to the present invention, the heat-sensitive flow velocity sensor of the flow velocity measuring device has the third heater driving voltage as the flow velocity increases.
The voltage output from the temperature sensing element is added to increase the heater drive voltage, so that the heat transferred to the first temperature sensing element and the second temperature sensing element increases and the output voltage increases. Therefore, since a large sensor output characteristic can be obtained even in a high flow velocity region, the flow velocity can be measured in a wide flow velocity range.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a flow velocity measuring device according to the present invention.

FIG. 2 is an enlarged plan view of a micro flow cell equipped with a temperature measuring resistor and a heater to be controlled according to the present embodiment.

FIG. 3 is a configuration diagram of a flow velocity detection circuit according to the present embodiment.

FIG. 4 is a configuration diagram of a heater control circuit according to the present embodiment.

FIG. 5 is a [DTP-UTP] output characteristic diagram for explaining the operation of the present embodiment.

FIG. 6 is a schematic configuration diagram of a gas meter.

FIG. 7 illustrates a conventional problem [DTP-UT
P] is an output characteristic diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Voltage generation means 2 Voltage detection means 3 Voltage supply means FS Thermal flow sensor F Flow path UTP First temperature sensing element DTP Second temperature sensing element TP3 Third temperature sensing element H Heater

Claims (2)

[Claims] 1. A level of a voltage output in accordance with a flow rate of a fluid with a first temperature sensing element and a second temperature sensing element disposed via a heater on an upstream side and a downstream side of a flow path, respectively. A heat-sensitive flow rate sensor provided with a third temperature-sensitive element, a voltage generating means for generating a drive voltage for the heater;
Voltage detecting means for detecting the voltage generated by the temperature-sensitive element, and adding the voltage detected by the third temperature-sensitive element to the heater driving voltage generated by the voltage generating means to increase the heater driving voltage. And a voltage supply means for supplying a voltage to the heater, increasing the heater drive voltage with an increase in the flow velocity, and increasing an output change with respect to a flow velocity change of the first temperature sensing element and the second temperature sensing element in a high flow rate region. A flow velocity measuring device characterized by the above-mentioned. 2. The thermal flow sensor according to claim 1, wherein the heater drive voltage rises as the flow velocity increases, so that the heat transmitted to the first and second temperature-sensitive elements rises and the output is increased. The flow velocity measuring device according to claim 1, wherein the voltage increases.