JP2002131107A - Heater control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater with a constant temperature when the heater's ambient temperature varies beyond preset reference temperature, by adding difference in variation of ambient temperature against reference temperature to follow the ambient temperature. SOLUTION: The device is placed on a flow sensor propagating heat from a heater 51 into a temperature-sensitivity element via fluid as a medium to measure flow rate of the fluid based on the output of this temperature-sensitivity element. It is provided with a temperature-measuring structure R with its resistance varied depending on ambient temperature, a voltage detector means 13 detecting voltage drop when constant current flows into this temperature- measuring structure R, and a heater drive means 15 controlling electric power to be supplied to the heater based on the detected voltage drop, allowing supply power of the heater 51 to vary following ambient temperature change to control heater temperature and then temperature-compensate output of the temperature- sensitivity element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermopile mounted on a thermopile type flow sensor disposed in a fluid passage of gas or the like. The present invention relates to a heater control device that performs control by following a temperature.

[0002]

2. Description of the Related Art Conventionally, such a device is used as a heater control device in a flow sensor built in a gas passage or the like of a gas meter, for example. As an example, as will be described later in detail, as shown in FIG. 6, an upstream thermopile (UTP) and a downstream thermopile (D
TP) are disposed on a substrate B constituting the flow sensor FS, with a heater H therebetween in a direction orthogonal to a gas flow direction in a gas passage F in the gas meter GM. Then, the heat generated when the heater H is energized is transmitted to the UTP and the DTP using the gas as a medium, so that the UT is heated.
The flow velocity of the gas is determined based on the difference between the thermoelectromotive forces generated in P and DTP.

As a schematic configuration of a conventional heater control device, there is a constant voltage driving circuit for a heater shown in FIG. In this circuit, the output voltage 3V of the battery B built in the gas meter GM is once charged in the electrolytic capacitor C1, and then input to the stabilized power supply IC constituting the three-terminal regulator, and the voltage is reduced to 1.5V to reduce the capacitor C2. Output to 1.5V
After the ripple component is removed from the voltage, the voltage is applied to the heater H.

The heater H generates heat by applying a voltage, and the heat is transmitted to the DTP and the UTP by a gas, so that the D
Based on the difference [DU] of the thermoelectromotive force generated between TP and UTP, that is, the flow rate of the gas, and subsequently the flow rate, is processed based on the output of the flow sensor to obtain the gas flow rate.

[0005]

As described above, in the conventional heater control device, a predetermined voltage, for example, 1.5 V is applied to the heater to obtain a predetermined heater temperature, for example, 45 ° C. However, as shown in FIG. 7, even when the flow rate of the gas flowing through the flow sensor is constant and the heat generation temperature of the heater is constant, if the ambient temperature of the heater (for example, gas temperature) decreases, the flow sensor output [D −U] increases and [DU] decreases as the ambient temperature increases.

Therefore, in a flow sensor having such characteristics, when the gas flow rate is finally measured from the gas flow rate while the heater heat generation temperature is constant, the measured flow rate varies due to a change in ambient temperature. Therefore, conventionally, it has been necessary to correct the temperature of the flow rate measurement value using the measurement value of the ambient temperature using a microcomputer or the like, and there has been a problem that the correction process is complicated. Conventionally, a flow velocity sensor and a flow velocity measurement device disclosed in, for example, Japanese Patent Application Laid-Open No. 7-174600 have been disclosed that measure a gas flow velocity or a flow rate in consideration of a temperature change of an air temperature due to a gas flow. However, this device is capable of measuring the flow velocity up to the minute flow velocity range and improving the linearity of the large flow velocity range by keeping the temperature difference between the fluid temperature measuring element and the heating element temperature measuring element constant. A technique for stably measuring a gas flow velocity regardless of a change in ambient temperature (gas temperature) is not disclosed.

In addition, the conventional apparatus consumes not only the flow rate measurement but also a microcomputer to take in the difference between the thermoelectromotive force of the DTP and the UTP and the ambient temperature to correct the measured value, so that the power consumption of the battery is large as a whole. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to reduce the power consumption of a battery and to control the heater temperature in accordance with a change in the ambient temperature, thereby controlling the ambient temperature. It is an object of the present invention to provide a heater control device capable of performing a stable flow rate measurement regardless of a change.

[0009]

A heater control device according to the present invention has a heater 51 as shown in FIG.
Is transmitted to a temperature-sensing element using a fluid as a medium, and is arranged in a flow sensor that measures the flow velocity of the fluid based on the output of the temperature-sensing element. A voltage detecting means 13 for detecting a voltage drop when a constant current flows through the side heating element R, and a heater driving means 16 for controlling electric power supplied to the heater based on the detected voltage drop. When the ambient temperature of the heater is detected to fluctuate based on the voltage drop, the power supply to the heater 51 is controlled so that the heater temperature becomes a temperature obtained by adding the ambient temperature to a preset constant temperature. Is temperature corrected.

[0010] The heater driving means of the heater control device according to the present invention controls the heater so that when the ambient temperature of the heater 51 changes, the heat generation temperature of the heater becomes a temperature obtained by adding a preset reference temperature to the ambient temperature. By controlling the supply power and controlling the heater temperature to follow the ambient temperature,
A stable output can be obtained from the flow sensor regardless of changes in the ambient temperature.

In the heater control device according to the present invention, the heater 51 and the temperature sensing element arranged in the flow sensor are arranged so as to be separated from each other in a direction perpendicular to a gas flow direction in a gas passage in the gas meter. Temperature sensor R is heater 5
By arranging at a position where the influence of the heat generation is avoided, a constant gas flow rate measurement can be performed irrespective of the fluctuation of the ambient temperature.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Next, before describing the operation of the heater control device according to the present embodiment, an outline of a micro flow sensor 31 including a heater to be controlled in the present device will be described. FIG. 2 is an enlarged plan view of a thermopile type micro flow sensor 31, for example.
As shown in the figure, the microflow sensor 31 includes a base 41 made of Si, a diaphragm 41a formed on the base 41 by anisotropic etching, and a diaphragm 4a.
The thermopile 43, 45, 47, 49 on the upstream side, the downstream side, the left side, and the right side for temperature measurement formed on 1a and the micro heater 51 (corresponding to a heater) for heating, and the base outside the diaphragm 41a. And a platinum temperature sensor 53 formed on the base 41 portion.
The platinum temperature sensor 53 is 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 thermopile 47, 49 on the left and right sides are respectively disposed at equal intervals from the micro heater 51 at 41 bases on the upstream side and the downstream side with the gas flow direction A of the gas flowing through the gas passage 29 interposed therebetween. The bases are arranged at equal intervals from the microheater 51 at 41 bases on both left and right sides of the microheater 51 in the width direction orthogonal to each other.

Then, each thermopile 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 platinum temperature measuring element 53 is also a cold junction 43b, 45b, 45b of each thermopile 43, 45, 47, 49.
Like 47b 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 the energization of the micro heater 51 is applied to the upstream, downstream, left, and right thermopiles 43 using the gas in the gas passage 29 as a medium. , 45,
When it reaches the vicinity of 47 and 49, each thermopile 4
3, 45, 47, and 49 are provided with hot junctions 43a, 45a, and 47 each having a temperature corresponding to the heat transmitted from the micro heater 51.
a, 49a and a cold junction 4 having substantially the same temperature as the base 41.
An electromotive force of a voltage corresponding to the temperature difference between 3b, 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 micro-heater 51 in the gas flow direction A 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: The temperature 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 29.

Therefore, the magnitude of the electromotive force signal output from the output terminal 39 of the micro flow sensor 31 in accordance with 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. , Gas passage 29
It depends on the flow velocity of the gas flowing inside.

An embodiment of the heater control device according to the present embodiment will be described below with reference to FIG. In the figure, reference numeral 53 denotes a platinum temperature measuring element as a reference element for measuring an ambient temperature. A battery voltage Vbt-Tens, for example, 3 V is applied from one end of the platinum temperature measuring element 53 to a battery through a parallel body of resistors R71 and 72, and the other end of the platinum temperature measuring element 53 has a collector of a transistor Q1. Is connected. Note that the combined resistance value of the parallel body of the resistors R71 and R72 is a platinum temperature sensor 5 at an ambient temperature of 20 ° C.
3 as a resistance value.

A 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 RV6 is connected to the ground. When the applied voltage is set to 3 V based on the adjustment of the variable resistor RV6, the OP amplifier OP1 and the transistor Q1 have the resistance value of the platinum temperature sensor 53 in the normal temperature state and the resistance value of the parallel body of the resistors R71 and R72. A constant current (100
A constant current circuit for supplying μA) is formed. Therefore, when the resistance value of the platinum temperature measuring element 53 changes due to a change in the ambient temperature, the voltage drop that occurs in the resistance series circuit of the parallel configuration of the platinum temperature measuring element 53 and the resistors R71 and R72 changes due to the change in 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. Platinum temperature sensor 53 and transistor Q
The connection point 1 is connected to the negative input terminal of the OP amplifier OP2 through an input resistance (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 the 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. As a result, from the OP amplifier OP2, a voltage corresponding to the resistance change of the resistance temperature detector 53 excluding the effect of the battery voltage is 20.
It is amplified twice and output as Vtmp.

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 150
It is connected to a negative input terminal through a negative feedback 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 has a positive input terminal applied with a reference voltage of 1.5V.
It is connected to the negative input terminal of P4 through an input resistor R83 of 100 KΩ. Therefore, the OP amplifier OP4 is a positive direction inversion type error amplifier with a gain of 1. The output terminals of the OP amplifiers OP3 and OP4 are connected by a variable resistor (potentiometer) RV5. This variable resistor R
V5 is adjusted to adjust the voltage applied to the heater 51 in the range of 0V to 3V.

The variable output of the variable resistor RV5 is connected to a positive input terminal of an OP amplifier OP5 constituting a voltage follower circuit constituted by connecting a negative input terminal and an output terminal. One end of the heater 51 is connected to the output terminal of the OP amplifier OP5. The other end of the heater 51 is connected to the source of the field effect transistor Q8. The drain of the field effect transistor Q8 is connected to the ground. A bias resistor R86 is connected between the gate and the drain of the field-effect transistor Q8, and an H-level signal having a width of 20 msec is passed through the resistor R85 to the gate once every 1 sec. ht).

The operation of the heater control device according to this embodiment will be described. The platinum temperature sensor 53 is normally driven at a constant current of 100 μA in accordance with the resistance value at normal temperature, but the variable resistor RV6 is adjusted so that a current of 100 μA flows by absorbing the individual difference of the platinum temperature sensor 53. As a result, the OP amplifier O
When a current is passed through a parallel circuit of the resistors R71 and R72 and a resistance series circuit of the platinum temperature measuring element 53 by a constant current circuit composed of P1, a transistor Q1, and the like, the gas path in the gas meter is in a normal temperature state (20 ° C.). In this case, the voltage generated between the resistance series circuit of the parallel body of the resistors R71 and R72 and the platinum temperature sensor 53 is 747 mV in the normal temperature state.

As an operation, when a reference voltage of, for example, 0.5 V is input to the OP amplifier OP1 constituting the voltage follower circuit, the transistor Q1 is turned on, and 1s.
In the ec cycle, the current becomes higher than the resistance R71 and R
72, a platinum temperature sensor 53, a transistor Q1, a resistor R74, and a variable resistor RV6. When the current flowing through the transistor Q1 decreases, the output voltage (base voltage) of the OP amplifier OP1 increases and a constant current flows by increasing the current value.

In a normal temperature state, a constant current flows, and the voltage drop between the parallel body of the resistors R71 and R72 and the resistance series circuit of the platinum temperature sensor 53 and the applied battery voltage V
b is input to the OP amplifier OP2 constituting the differential amplifier, and the difference voltage Vtmp obtained by canceling the battery voltage from the voltage drop is multiplied by 20 and output to the error amplifier at the subsequent stage as 747 mV. In the error amplifier, the signal is input to a first OP amplifier OP3 whose gain is set to 1.5 times, and is input to an OP amplifier Q4 whose gain is set to 1 after being amplified. The output voltage from each of the OP amplifiers OP3 and OP4 is applied to both ends of the variable resistor RV5. By adjusting the slider of the variable resistor RV5, the output voltage of 1.5V can be changed to an OP amplifier O which constitutes a volatile follower circuit.
The voltage is applied to one end of the heater 51 through P5.

The gate of the field-effect transistor Q2, whose source is connected to the other end of the heater 51, is connected to the gate of the field effect transistor Q2 for 20 m at a time during one second when the battery voltage Vb-Tens is applied.
A heater drive voltage Vb-ht having a pulse width of sec is applied. As a result, the field effect transistor Q2 takes 20 ms.
By turning on during ec and applying a voltage of 1.5 V to the heater, the heat generation amount obtained by adding 20 ° C. (normal temperature) to the ambient temperature from the heater 51 can be transmitted to the thermopile using the gas fluid as a medium.

However, when the voltage applied to the heater 51 is set to 1.5 V at an ambient temperature of about 20 ° C. (normal temperature), if the resistance value of the platinum temperature measuring element 53 increases with an increase in the ambient temperature, the resistance R71 Since a constant current flows through the parallel circuit of the resistor R72 and the resistance series circuit of the platinum temperature sensor 53 by the constant current circuit, the battery voltage Vb and the resistance R71
The difference voltage between the parallel body of R72 and R72 and the resistance series circuit of the platinum temperature sensor 53 increases.

Therefore, the differential voltage output from the OP amplifier OP2 forming the differential amplifier becomes larger than that at the time of the normal temperature state, and is input to the OP amplifier OP3 having a gain of 1.5 forming the first error amplifier circuit. , A negative output voltage that is 1.5 times the difference voltage from the reference voltage 1.5V, and
5 is applied to one end. The negative output voltage is input to a negative input terminal of an error amplifier OP4 having a gain of 1, and the variable output RV5 as a positive difference voltage from the reference voltage 1.5V there.
Is applied to the other end.

The voltage applied to both ends of the variable resistor RV5 is divided by a resistance ratio determined by the position of the slider, and is divided by an OP amplifier OP5 constituting a voltage follower circuit.
1 is applied. When a gate signal having a width of 20 msec is externally applied to the field effect transistor Q2 while a voltage is applied to the heater 51, the field effect transistor Q2
Conducts, and a current flows by the applied voltage to generate heat.

At this time, since the voltage applied to the heater 51 rises following the rise in the ambient temperature, the temperature of the heat generated from the heater 51 becomes a constant temperature following the ambient temperature.
Therefore, initially, at normal temperature, Δ [DU] 25-M
AX)-([DU] 25-0)} = {([DU] H
-MAX)-([DU] H-0)}, the voltage applied to the heater 51 is adjusted in accordance with the ambient temperature by adjusting the variable resistor RV5.

Here, {([DU] 25-MAX)-
([DU] 25-0)｝ = ｛([DU] H-MA
X)-([DU] H-0)} is, for example, DTP in the case of a maximum flow rate (MAX) in a normal temperature state (25 ° C.).
The difference between the (downstream thermopile) output and the UPT (upstream thermopile) output and the DTP (downstream thermopile) output and UPT (upstream thermopile) output at zero flow rate (0) at normal temperature (25 ° C.). The difference in the difference is the DTP at the maximum flow rate in the high temperature state (H).
The difference between the (downstream thermopile) output and the UPT (upstream thermopile) output and the difference between the DTP (downstream thermopile) output and the UPT (upstream thermopile) output when the flow rate is 0 in the high temperature state (H). But FIG.
Are equal.

That is, if the flow rate is constant, even if the gas temperature (ambient temperature) changes from the normal temperature state 25 ° C. to the high temperature state H, the output change of the downstream thermopile DTP (shown by hatching) and the upstream thermopile The output change of UTP (shown by hatching) is equivalent, and
The flow sensor output [DU] 25-0 at 5 ° C. and the flow sensor output [DU] H-0 in the high temperature state H are equivalent. This state is the same even when the flow rate MAX is constant, and the output change (shown by hatching) of the downstream thermopile DTP and the output change (shown by hatching) of the upstream thermopile UTP are equivalent, and therefore, the normal temperature Flow sensor output [D-
U] 25-max and the flow sensor output [DU] H-max in the high temperature state H are equivalent.

As described above, by initially setting the voltage of 1.5 V in the normal temperature state to the heater, even if the temperature around the heater rises from the normal temperature of 25 ° C., the voltage is applied to the heater. Voltage rises as the ambient temperature rises. Therefore, the output of the flow sensor [DTP output-UPT output] is temperature-compensated regardless of the heat radiation temperature of the heater due to an increase in the ambient temperature.

The temperature compensation of the DTP-UPT output is as follows.
The CPU always monitors the DTP-UPT output and the ambient temperature by software, instead of using software.
Once in c, only for 20 msec, a voltage of a value based on the ambient temperature change of the heater is applied to the heater to adjust the heating voltage of the heater. Can be measured.

[0038]

According to the present invention, the heat generated by the heater 51 is transmitted to the temperature-sensitive element using the fluid as a medium, and is arranged in the flow sensor for measuring the flow rate of the fluid based on the output of the temperature-sensitive element. A temperature measuring element R whose resistance value changes in accordance with the ambient temperature; voltage detecting means 13 for detecting a voltage drop when a constant current flows through the side temperature element R; and a heater based on the detected voltage drop. Heater driving means 16 for controlling the electric power supplied to the heater 51, and controlling the heater temperature by changing the electric power supplied to the heater 51 in accordance with the change in the ambient temperature, thereby correcting the output of the thermosensitive element. When the ambient temperature of the heater fluctuates from a preset reference temperature, the temperature of the heater is added to the reference temperature by the variation of the ambient temperature, and a constant temperature is always given to the heater following the ambient temperature. It is possible Therefore, there is an effect that it is possible to obtain a stable flow sensor output despite variations in ambient temperature.

According to the present invention, the heater driving means 16
When the ambient temperature of the heater 51 changes, the power supplied to the heater is controlled so that the heat generation temperature of the heater becomes a temperature obtained by adding a preset reference temperature to the ambient temperature, and the heater temperature follows the ambient temperature. By controlling the temperature, it is possible to obtain a more stable sensor output than the flow sensor.

According to the present invention, the heater and the temperature sensing element arranged in the flow sensor are spaced apart from each other in a direction perpendicular to the direction in which the gas flows in the gas passage in the gas meter. By arranging the heater at a position where the influence of the heat generated by the heater is avoided, there is an effect that a constant gas flow rate can be measured irrespective of the fluctuation of the ambient temperature.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a heater control device according to the present invention.

FIG. 2 is an enlarged plan view of a microflow sensor equipped with a resistance temperature sensor and a heater to be controlled in the present embodiment.

FIG. 3 is a configuration diagram of a heater control device according to the present embodiment.

FIG. 4 is a diagram showing a relationship between a sensor output and a change in ambient temperature.

FIG. 5 is a schematic configuration diagram of a conventional heater control device.

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

FIG. 7 is a diagram illustrating a relationship between a sensor output and a change in ambient temperature.

[Explanation of symbols]

 R temperature measuring element 11 constant current circuit 13 voltage detecting means, 15 heater driving means 51 heater

Claims (3)

[Claims] 1. A heat sensor for transmitting heat generated by a heater to a temperature-sensitive element using a fluid as a medium, and disposed in a flow sensor for measuring a flow rate of the fluid based on an output of the temperature-sensitive element. And a voltage detecting means for detecting a voltage drop when a constant current is applied to this side temperature body,
Heater driving means for controlling the power supplied to the heater based on the detected voltage drop, and controlling the heater temperature by changing the power supplied to the heater in accordance with the change in the ambient temperature; A heater control device for correcting the output of a heating element by temperature. 2. The heater driving unit controls power supplied to the heater such that when the ambient temperature of the heater changes, the heat generation temperature of the heater becomes a temperature obtained by adding a preset reference temperature to the ambient temperature. The heater control device according to claim 1, wherein the heater temperature is controlled to a temperature that follows the ambient temperature. 3. A heater and a temperature sensing element arranged in the flow sensor are spaced apart from each other in a direction orthogonal to a gas flowing direction in a gas passage in the gas meter, and the temperature measuring element is configured to generate heat of the heater. The heater control device according to claim 1, wherein the heater control device is arranged at a position to avoid the influence of the heat.