JP2003247876A - Thermal flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal flowmeter that enables flow measurement with high accuracy by using one flow sensor with low power consumption in a wide flow rate measuring range. <P>SOLUTION: The flow sensor is provided with a first and a second temperature detecting sensor element with a heater element between them in a fluid conducting direction, and an ambient temperature detecting sensor element detecting ambient temperature thereof. A first heater control means maintains the heater temperature of the heater element at a fixed temperature degree higher than the ambient temperature to measure the flow rate with low consumption. A second heater control means maintains the mean value of detected temperatures measured by the first and second temperature detecting sensor elements at a fixed temperature degree higher than the ambient temperature to improve the flow rate measurement in a high flow area and expand the flow rate measuring range in response to the change of the ambient temperature. Then a switch means alternatively uses the first or second heater control means in response to the flow rate of the fluid, and then a flow rate measuring means measures the flow rate of the fluid from the difference between the detected temperatures of the first and second temperature detecting sensors. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter capable of highly accurate flow rate measurement regardless of changes in the flow rate of fluid.

[0002]

2. Description of the Related Art A thermal type flow meter for measuring the flow rate of fluid is
For example, there is a battery used as a power source for household gas meters and the like. The flow rate sensor constituting such a thermal type flow meter has a resistance temperature detector in the fluid flow direction F with a heater element Rh formed of a heat generation resistor provided on a silicon substrate B in between, as shown in FIG. The device structure has a pair of temperature sensors Ru and Rd. In this thermal type flow meter, as shown in FIG. 8, the temperature distribution in the flow direction F of the fluid generated by the heat generated by the current supplied to the heater element Rh (hereinafter referred to as “heater peripheral temperature distribution”) is The flow rate of the fluid is detected from the change in the resistance value of the temperature sensors Ru and Rd, which are temperature measuring resistance elements, depending on the change in the flow rate of the fluid.

In FIG. 7, the heater control means uses an ambient temperature temperature measuring resistance element Rr which is provided at a position distant from the heater element Rh and which constitutes an ambient temperature temperature measuring sensor element. The temperature difference between the heater element Rh and the ambient temperature ((temperature of the heater element Rh) is measured.
-(Ambient temperature), hereafter "(Heater temperature-Ambient temperature) D
(Displayed as “T”) is kept constant.
The voltage is applied to.

The specific temperature distribution around the heater is
As shown by the solid line in FIG. 8, when the flow rate Q of the fluid is zero, the temperature on the downstream side in the flow direction is the same as the temperature on the upstream side in the flow direction, and when the flow rate Q of the fluid is not zero. , Fig. 8
As indicated by the broken line in the middle, the temperature on the downstream side becomes higher than the temperature on the upstream side. Therefore, the thermal type flow meter detects the temperature difference between the downstream side and the upstream side as the output of the flow rate sensor based on the temperature measurement results of the temperature sensor Rd on the downstream side of the flow and the temperature sensor Ru on the upstream side of the flow. To measure.

However, as the flow rate Q increases, the heat generated by the heater element Rh flows out of the flow rate sensor together with the fluid,
The increase rate of the temperature difference between the temperature sensors Rd and Ru decreases. As shown in FIG. 9, the slope of the curve representing the flow rate measurement characteristic becomes smaller as the flow rate Q increases, and finally becomes saturated. Then, not only the accuracy of the flow rate measurement in the high flow rate region is lowered, but also the flow rate measurement range of the thermal type flow meter is narrowed.

Therefore, the present inventors increase the amount of heat generated by the heater element to compensate for the amount of heat flowing out from the flow rate sensor as the flow rate Q increases, and the temperature sensor R with respect to the ambient temperature.
It was considered to control the average value of the measured temperature in d and Ru so that the temperature was increased by a constant temperature. By performing such control, it is possible to reduce the increase rate of the temperature difference between the temperature sensors Rd and Ru with the increase of the flow rate Q, reduce the inclination decrease of the flow rate measurement characteristic curve in the high flow rate region, and reduce the increase in the high flow rate region. The accuracy of flow rate measurement can be improved and the range of flow rate measurement can be expanded.

Alternatively, in order to widen the flow rate measuring range,
A thermal type flow meter that selectively uses two flow rate sensors for low flow rate measurement and high flow rate measurement according to the flow rate is also conceivable.

[0008]

However, the flow rate Q
In the control for increasing the amount of heat generated by the heater element to compensate for the amount of heat flowing out of the flow sensor due to the increase in the temperature, even if the ambient temperature is constant, the temperature of the heater element is increased according to the flow rate. The power consumption of the flow sensor increases as compared with the conventional thermal flow meter that maintains the ambient temperature) DT constant. Such an increase in power consumption cannot be denied in a thermal type flow meter using a battery as a power source, which accelerates discharge of the battery.

If two flow rate sensors for low flow rate measurement and high flow rate measurement are used, the power consumption of the thermal type flow meter increases, and the cost and size of the thermal type flow meter increase. . The present invention has been made in order to solve the above problems, and provides a thermal type flow meter capable of highly accurate flow rate measurement in a wide flow rate measurement range with low power consumption by one flow rate sensor. With the goal.

[0010]

In order to achieve the above object, according to claim 1 of the present invention, a flow rate sensor is provided with a heater element and a first heater element in the fluid flow direction F with the heater element interposed therebetween. And a second temperature measuring sensor element, and an ambient temperature measuring sensor element for detecting the ambient temperature.

In order to measure the flow rate of the fluid with low power consumption, the first heater control means determines the heater temperature of the heater element according to the temperature measured by the ambient temperature temperature measuring sensor element. By maintaining the temperature higher than the temperature measured by the element, it is possible to measure the temperature upstream and downstream of the fluid flow direction by the first and second temperature sensor elements. On the other hand, in order to improve the accuracy of flow rate measurement and to expand the flow rate measurement range in the high flow rate region, the second heater control means sets the first and first heaters according to the temperature measured by the ambient temperature temperature sensor element. The average value of the temperature measured by the second temperature measuring sensor element is kept higher than the ambient temperature by the temperature measuring sensor element by a constant temperature, and the flow direction of the fluid by the first and second temperature measuring sensor elements is maintained. Enables temperature measurement upstream and downstream.

As described above, the heater control means activates the heater elements, and the first and second temperature measuring sensor elements measure the temperature in the upstream and downstream of the fluid flow direction, whereby these temperature measuring sensor elements are operated. The flow rate measuring means can measure the flow rate of the fluid flowing through the flow rate sensor based on the temperature difference. According to the flow rate of the fluid measured in this way, the switching means is
The flow rate sensor is selectively connected to the heater control means or the second heater control means, and the thermal type flow meter measures the flow rate of the fluid.

Therefore, the flow rate sensor is driven by the first heater control means to realize flow rate measurement with low power consumption,
In addition, the flow rate sensor can be driven by the second heater control means to improve the accuracy of flow rate measurement in the high flow rate region and expand the flow rate measurement range. In the invention of claim 2, first and second thermopiles (thermocouples) are used for the first and second temperature measuring sensor elements. Therefore, when a temperature measuring resistance element is used for each temperature measuring sensor element, the temperature of each temperature measuring sensor element rises due to self-heating caused by the current flowing through each temperature measuring resistance element, causing an error in flow rate measurement. Can be prevented, and the flow rate measurement can be made more accurate.

According to the third aspect of the invention, when the flow rate of the fluid is low, the first heater control means is used to drive the heater element, and when the flow rate of the fluid is high, the second heater control means is operated. Since the heater element is driven by using a specific flow rate, the flow rate below the threshold value is set as the low flow rate, and the flow rate above the threshold value is set as the high flow rate, while reducing the power consumption of the thermal type flow meter while increasing the high flow rate. It is possible to improve the accuracy of flow rate measurement in a region and expand the flow rate measurement range.

In particular, a thermal type flow meter which operates with a battery as a power source and usually has a low flow rate of a fluid, such as a household gas meter, can operate with a battery for a long period of time. It is possible to realize a thermal type flow meter capable of improving the accuracy of flow rate measurement in a high flow rate region and expanding the flow rate measurement range.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A thermal flow meter according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an essential part of an embodiment of a thermal type flow meter according to the present invention. A flow rate sensor 11 included in the thermal type flow meter 10 shown in FIG.
Are configured in the same manner as the flow rate sensor shown in FIG. 7, and the temperature sensor Ru (first temperature measuring sensor) on the upstream side of the flow, the temperature sensor Rd (second temperature measuring sensor) on the downstream side of the flow, and the heater element It has Rh and an ambient temperature resistance measuring element Rr (ambient temperature measuring sensor).

The flow rate sensor 11 is selectively operated by the switching operation of the switching means 14 to the first heater control means 12 when measuring a low flow rate and to the second heater control means 13 when measuring a high flow rate. Connected to. The flow rate of the fluid flowing through the flow rate sensor 11 is the flow rate measuring means 15
Is output as an electric signal, and this electric signal is input to the arithmetic unit 16. Further, the arithmetic unit 16 controls the switching operation of the switching means 14, and the switching means 14 has switches SW14a to 14c.
It has three switches.

When measuring a low flow rate, the amplifier AMP12 and the transistor TR are used to measure the flow rate of the fluid with low power consumption.
The first heater control means 12 including the resistance elements R12a, R12b, and R12c controls the temperature of the heater element Rh of the flow rate sensor 11 in accordance with the ambient temperature measurement of the flow rate sensor 11 by the ambient temperature measurement resistance element Rr. Is configured to control.

The temperature of the heater element Rh is controlled by the resistance element R12a and the ambient temperature measuring resistance element Rr connected in series.
To the resistor element R12b and the heater element Rh connected in series.
By paralleling a first heater control bridge circuit formed by connecting in parallel. More specifically, the switch SW14a included in the switching means 14 is used to connect the connection point N1 which is one end of the ambient temperature measuring resistance element Rr.
Is selectively connected to one end of the resistance element R12a, and the switch SW14b of the switching means 14 selectively connects the connection point N2, which is one end of the heater element Rh, to one end of the resistance element R12b. The other ends of the ambient temperature measuring resistance element Rr and the heater element Rh are grounded, and a current is supplied to the other ends of the resistance element R12a and the resistance element R12b from the collector of the transistor TR12.

One end of the resistance element R12a has an amplifier AMP1.
2 is connected to the inverting input terminal, and one end of the resistance element R12b is connected to the non-inverting input terminal of the amplifier AMP12. The output voltage of the amplifier AMP12 is input to the base of the transistor TR12 whose emitter is connected to the power supply line Vc via the resistance element R12c. Therefore, the collector current of the transistor TR12 is controlled by the output voltage of the amplifier AMP12.

When the first heater control bridge circuit configured as described above is in equilibrium with the potentials at the connection points N1 and N2 being the same, the voltage across the ambient temperature measuring resistance element Rr and the heater element Rh are balanced. Will be equal to the voltage across. Here, the resistance elements R12a and R12b, the ambient temperature measuring resistance element Rr, and the heater are arranged so that the first heater control bridge circuit is in the equilibrium state when the heater temperature is higher than the ambient temperature by a constant value. The resistance value of the element Rh is set.

Therefore, when the resistance value of the ambient temperature measuring resistance element Rr increases as the ambient temperature rises, the voltage across the ambient temperature measuring resistance element Rr also increases and the voltage applied to the heater element Rh becomes the first value. Is increased by the heater control means of (heater temperature-ambient temperature) and DT is maintained at a constant value. When the flow rate sensor 11 is driven by the first heater control means 12, the temperature sensors Ru and R connected in series forming a flow rate measurement bridge circuit described later.
The connection point N3, which is one end side of d, is alternatively connected to the power supply line Vc by the switch SW14c.

Next, the driving of the flow rate sensor 11 by the second heater control means 13 will be described. In order to measure the flow rate of the fluid at the time of high flow rate measurement, as shown in FIG.
The second heater control unit 13 including the MP13 and the resistance elements R13a and 13b averages the temperature measured by the temperature sensors Ru and Rd according to the ambient temperature measured by the temperature sensor resistance element Rr of the flow sensor 11. The value is configured to be higher than the ambient temperature measured by the ambient temperature resistance measuring element Rr by a certain value.

The temperature control of the heater element Rh is performed by connecting the resistance element R13a and the ambient temperature measuring resistance element Rr connected in series.
Is connected in series to the resistance element R13b and the temperature sensor Ru.
And a second heater control bridge circuit formed in parallel with the temperature sensor Rd. More specifically, the connection point N1 which is one end of the ambient temperature measuring resistance element Rr is selectively connected to one end of the resistance element R13a by the switch SW14a included in the switching means 14, and the temperature sensor Rd and the temperature sensor Rd are connected in series. One end (connection point N3) of the temperature sensor Ru is selectively connected to one end of the resistance element R13b by the switch SW14c included in the switching means 14. The other ends of the resistance element R13a and the resistance element R13b are connected to the power supply line Vc so that current is supplied to the second heater control bridge circuit.

One end of the resistance element R13a has an amplifier AMP1.
3 is connected to the non-inverting input terminal of the resistor element R13b, and one end of the resistor element R13b is connected to the inverting input terminal of the amplifier AMP13.
At this time, the heater element Rh is selectively connected to the output terminal of the amplifier AMP13 by the switch SW14b and driven by the amplifier AMP13. In the temperature sensor Rd and the temperature sensor Ru connected in series, the temperature sensor Ru is connected to the connection point N3 side and the temperature sensor Rd is connected to the ground side.

In the second heater control bridge circuit formed as described above, when the potentials at the connection points N1 and N3 become equal and equilibrate, the ambient temperature measuring resistance element R
The voltage across r is equal to the voltage across temperature sensor Rd and temperature sensor Ru connected in series. The resistance element R13 is arranged so that the second heater control bridge circuit is in an equilibrium state when the average value of the temperature measured by the temperature sensors Rd and Ru is higher than the ambient temperature by a certain value.
a, 13b, ambient temperature measuring resistance element Rr, temperature sensor R
Resistance values of u and Rd are set.

The temperature sensors Rd and Ru are connected in series, and a voltage corresponding to the total value of the temperature measured by each temperature sensor is generated at both ends thereof. In this case, the total value is the average value. Since it is twice, the total value of the temperature measurement temperatures can be treated as an average value by appropriately setting the gain for the non-inverting side input and the gain for the inverting side input of the amplifier AMP13.

Thus, the flow rate increases and the heater element R
Even when the amount of heat generated by h increases to the outside of the flow rate sensor, according to the temperature measured by the ambient temperature temperature measuring resistance element Rr,
The voltage applied to the heater element Rh is controlled by the second heater control means, and the average value of the temperature measured by the temperature sensor Rd and the temperature sensor Ru is maintained at a temperature higher than the ambient temperature by a certain value.

The flow rate measuring means 15 has an amplifier AMP15 and resistance elements 15a and 15b connected in series, and the resistance elements 15a and 15b are connected in parallel with temperature sensors Rd and Ru connected in series in the flow rate sensor 11. Form a flow measurement bridge circuit. And the temperature sensor R
The connection point of d and Ru forms a connection point N4, and the resistance element 15
The connection point of a and 15b forms the connection point N5, and the resistance element 15
It is assumed that a is connected to the connection point N3, the resistance element 15b is grounded, and the resistance elements 15a and 15b have the same resistance value.

The connection points N4 and N5 form the output terminal (sensor output terminal) of the flow rate measurement bridge circuit, the connection point N4 is connected to the non-inverting input terminal of the amplifier AMP15, and the connection point N5 is the inverting input terminal of the amplifier AMP15. It is connected to the. Therefore, when the flow rate of the fluid is zero, the resistance values of the temperature sensors Rd and Ru become equal, the flow rate measurement bridge circuit is balanced, the output of the flow rate sensor becomes zero (V), and the output voltage of the output terminal of the amplifier AMP15 also becomes. It becomes zero (V).

On the other hand, when the flow rate is not zero, the temperature measured by the temperature sensor Rd (resistance value) becomes higher than the temperature measured by the temperature sensor Ru (resistance value), so that the connection point N4. Is higher than the potential of the connection point N5, and the sensor output of the flow rate measurement bridge circuit can be obtained as a positive voltage from the output terminal of the amplifier AMP15 by setting the gain of the amplifier AMP15.

The arithmetic unit 16 transmits the flow rate of the fluid to an external device based on the output voltage of the amplifier AMP15, and each switch SW14a-1 of the switching means 14
4c switching control is performed. The arithmetic unit 16 has a central arithmetic unit (hereinafter referred to as "CPU") 16a, an input interface 16b and an output interface 16c. And the input interface 16b is AD
It has a converter (analog / digital converter, not shown). The CPU 16a is, for example, a ROM including an electrically erasable read-only memory (EEPROM).
Controlled by a program stored in 16f, the output voltage of the amplifier AMP15 is converted from analog to digital to measure the flow rate of the fluid and transmitted to an external device. Also,
Based on this flow rate measurement, the CPU 16a causes the flow rate sensor 1 to
The switches SW14a to 14c of the switching means 14 are switched so that 1 is selectively driven by the first heater control means 12 or the second heater control means 13. Reference numeral 16d in FIG. 1 is an output terminal for a switching control signal of each of the switches SW14a to 14c of the switching means 14, and 16e is a flow rate measurement output terminal.

As shown in FIG. 3, the CPU 16 controls the driving of the flow rate sensor 11 by the first heater control means 12 or the second heater control means 13 by the arithmetic unit 16.
16a is performed in the following procedure. In the following procedure, the measurement mode 1 means a state in which the flow rate sensor 11 is driven by the first heater control means 12 by the switching operation of the switching means 14 and the thermal flow meter 10 measures the flow rate. Say. On the other hand, the measurement mode 2 is the switching means 1
The state in which the flow rate sensor 11 is driven by the second heater control means 13 by the switching operation of No. 4 and the thermal type flow meter 10 measures the flow rate. Further, Y in FIG. 3 is affirmative and N is negative for the determination condition.

First, the measurement mode 1 in which the flow rate sensor 11 driven by the first heater control means 12 measures the flow rate in the low power consumption state will be described as an initial state. The control by the arithmetic unit 16 is started from step S20, and it is determined in step S21 whether the thermal type flow meter 10 is operating in the measurement mode 1. In the initial state above,
The measurement mode 1 is determined and the process proceeds to step S22.

Then, when the flow rate is low (when the flow rate is not higher than Q1), the following is performed.
Flow rate sensor 11 driven by first heater control means 12
Measures the flow rate in the low power consumption state. In step S22, the thermal type flow meter 10 measures the flow rate in the measurement mode 1. Based on this flow rate measurement, it is determined in step S23 whether the flow rate is equal to or greater than the predetermined value Q1.

When it is determined in step S23 that the measured flow rate is not equal to or higher than the predetermined flow rate Q1, the arithmetic unit 16
Outputs the flow rate measurement result (low flow rate) measured in the measurement mode 1 to the external device in step S22, proceeds to step S24, ends the control, and returns to step S2.
Control starts from 0. Furthermore, the determination of the flow rate change when the flow rate changes from the low flow rate to the high flow rate (the flow rate is Q1 or more) during the flow rate measurement in the measurement mode 1 will be described.

When it is determined in the above step S23 that the measured flow rate is equal to or greater than the predetermined value Q1, the control proceeds to step S25, and the thermal flow meter 10 is set to the measurement mode 1
In this state, the flow rate is continuously measured, and the arithmetic unit 16 determines whether or not the flow rate Q1 or more is maintained for T seconds. The determination in step S25 described above is that, when the measurement mode is switched using Q1 as a threshold value, the measurement mode is frequently switched due to a minute change in the flow rate near the threshold value, and the flow rate measurement becomes unstable. It is done to prevent. Therefore, when the flow rate measurement result maintains Q1 or more for T seconds, the control is performed in step S
In step 26, the measurement mode is switched from the measurement mode 1 to the measurement mode 2. Further, the control is completed by shifting from step S26 to step S24, and the control is started again from step S20 in the state of the measurement mode 2.

On the other hand, when the flow rate Q1 or more is not maintained for T seconds, the control shifts to step S24 and ends, and the measurement mode is set to 1 again to step S20.
The control starts from. Next, the case where the flow rate sensor 11 driven by the second heater control means is in the measurement mode 2 for measuring the flow rate with high accuracy even for a high flow rate will be described.

The control by the arithmetic unit 16 is step S20.
Starting from step S21, it is determined in step S21 whether the thermal type flow meter 10 is operating in the measurement mode 1. In the above case, it is determined that the measurement mode 1 is not set, and the control advances to step S27. In step S27, the thermal type flow meter 10 measures the flow rate in the measurement mode 2. As a result of this flow rate measurement, whether or not the flow rate is less than the predetermined value Q1 is step S28.
It is judged by.

When it is determined in step S28 that the flow rate is not less than the predetermined value Q1 (when the flow rate is high), the arithmetic unit 16 outputs the flow rate measurement result measured in step S27 to the external device, and step S24 Then, the control is ended and the control is started again from step S20 in the measurement mode 2 state. Next, the determination of the flow rate change when the flow rate changes from the high flow rate to the low flow rate (the flow rate is less than Q1) during the flow rate measurement in the measurement mode 2 will be described.

When it is determined in step S28 that the flow rate is less than the predetermined value Q1, the arithmetic unit 16
In step S29, the flow rate is continuously measured in the measurement mode 2, and it is determined whether the flow rate is less than Q1 for T seconds. When the flow rate does not remain below Q1 for T seconds (when the flow rate is high), step S27
The flow rate measurement result (high flow rate) measured in step 3 is output to an external device, and the process proceeds to step S24 to end the control,
The control is started again from step S20.

Only when the flow rate remains below Q1 for T seconds (when the flow rate is low), the control proceeds to step S3.
In 0, the measurement mode is switched from the measurement mode 2 to the measurement mode 1, the process further shifts to step S24 and ends, and the control from step S20 is started again in the state of the measurement mode 1. The reason why the continuation of the flow rate for T seconds is determined in step S29 is for the same reason as in step S25.

In this manner, the thermal type flow meter 10 uses the flow rate Q1 as a threshold value and uses the flow rate sensor 11 as the first heater control means 12 when measuring a low flow rate and the flow rate sensor 11 when measuring a high flow rate. Second heater control means 13
Can be alternatively connected by the switching operation of the switching means 14. For example, as shown in FIG. 4 (a), the flow rate Q 1 is set to the flow rate measurement characteristic curve of the flow rate sensor 11 driven by the first heater control means 12 (FIG. 4 (a)).
The flow rate sensor 11 is set to the first heater control means 12 so that the gradient of the flow rate measurement characteristic curve of the flow rate sensor 11 does not decrease even when the flow rate is equal to or higher than the flow rate Q1. Driven by the second
The heater control means 13 is switched to drive.

Thus, in the flow rate region below the flow rate Q1, the solid flow rate measurement characteristic curve in FIG. 4A (the flow rate measurement characteristic curve of the flow rate sensor 11 driven by the first heater control means 12) can be obtained. On the other hand, on the other hand, in the flow rate region equal to or higher than the flow rate Q1, the flow rate measurement characteristic curve of the broken line in FIG.
The flow rate measurement characteristic curve of the flow rate sensor 11 driven by the heater control means 13 can be obtained. FIG. 4B shows the flow rate measurement characteristics obtained by driving the flow rate sensor 11 by switching the heater control means 12 and 13 in this way.

Thus, one flow sensor has low power consumption,
In addition, a thermal flow meter that enables highly accurate flow rate measurement in a wide flow rate measurement range is realized. Next, FIG. 5 shows a first modified embodiment of the thermal type flow meter according to the present invention. The present modified embodiment is a modification of the thermal type flow meter 10 described above with respect to the flow rate sensor 11 and the flow rate measuring means 15.
The components having the same functions as those of the above-described thermal type flow meter 10 are designated by the same reference numerals, and the description thereof will be omitted and the description of the arithmetic unit 16 will be omitted.

In the first modified embodiment, the flow sensor 11
Has an element structure in which a pair of thermopiles (thermocouples) Tpu and Tpd are provided in the fluid flow direction F in place of the pair of temperature sensors Ru and Rd formed of resistance temperature detectors. When the heater ambient temperature distribution changes according to the flow rate of the fluid, the flow rate of the fluid is detected from the change in the electromotive force of the thermopiles Tpu and Tpd.

Specifically, when the flow rate Q of the fluid is zero, the electromotive forces of the thermopiles Tpu and Tpd are equal, and when the flow rate Q is not zero, the downstream thermopile Tp.
The flow rate Q is measured by utilizing the fact that the thermoelectromotive force of d is higher than the thermoelectromotive force of the thermopile Tpu on the upstream side. The flow rate measuring means 15 includes high input impedance amplifiers AMP15c and 15d and a subtraction circuit AMP15e.
have. In the first modified embodiment, since the flow rate measurement bridge circuit is not formed, the upstream thermopile T
The thermoelectromotive force of pu is amplified by the amplifier AMP15c and input to the inverting input terminal of the subtractor AMP15e, while the thermoelectromotive force of the thermopile Tpd on the downstream side is amplified by the amplifier AMP15.
The signal is amplified by d and input to the non-inverting input terminal of the subtractor AMP15e. Then, the subtractor AMP15e subtracts the thermoelectromotive force of the thermopile Tpu from the thermoelectromotive force of the thermopile Tpd on the downstream side, and outputs it to the input interface 16b of the CPU 16a.

Thus, the temperature distribution around the heater of the flow rate sensor 11 which changes depending on the flow rate of the fluid is the thermopile Tp.
It can be measured by u and Tpd, and the flow rate of the fluid can be measured. On the other hand, the pair of temperature sensors Ru and Rd included in the flow rate sensor 11 of the heat flow meter 10 described above are
The temperature sensor Ru is composed of a resistance temperature detector, and a current is supplied to the temperature sensors Ru and Rd to convert a resistance value into a voltage value.
It is necessary to detect the change in resistance value of Rd depending on the temperature. Then, it is undeniable that the above-mentioned current causes self-heating of the temperature sensors Ru and Rd, which causes an error in the heater peripheral temperature distribution measurement of the flow rate sensor 11.

On the other hand, in a thermal flow meter for measuring temperature by thermoelectromotive force generated by the thermopiles Tpu and Tpd, the temperature distribution around the heater of the flow sensor 11 can be measured without the above self-heating. It is possible to further improve the accuracy of the thermal type flow meter. If a thermopile is used instead of the ambient temperature measuring resistance element Rr, an error caused by self-heating of the ambient temperature measuring resistance element Rr can be prevented, and the accuracy of the thermal type flow meter can be further improved.

Also in FIG. 5, the flow rate sensor 11
Is driven by the first heater control means 12,
(Heater temperature-ambient temperature) DT is maintained at a constant value.
When the flow rate sensor 11 is driven by the second heater control unit 13, the total value (average value) of the electromotive forces of the thermopiles Tpu and Tpd is maintained higher than the ambient temperature by a constant temperature.

Therefore, the thermal type flow meter according to the first modification of FIG. 5 can also operate in the same manner as the thermal type flow meter 10 described above, and realizes the flow rate measurement characteristic shown in FIG. Therefore, it is possible to realize a thermal type flow meter which has a low power consumption and a highly accurate flow rate measurement in a wide flow rate measurement range with one flow rate sensor. Next, FIG.
2 shows a second modified embodiment of the thermal type flow meter according to the present invention. The components having the same functions as those of the thermal type flow meter 10 described above are designated by the same reference numerals, and the description thereof will be omitted.

The thermal type flow meter 40 of the second modified embodiment is
It does not have the first and second heater control bridge circuits and the flow rate measurement bridge circuit. However, the ambient temperature, the voltage applied to the heater element Rh, and the temperature of the fluid flowing through the flow rate sensor upstream and downstream of the heater element Rh are measured as follows. To measure the ambient temperature, the ambient temperature measuring resistance element Rr of the flow rate sensor is connected to the power supply line V through the resistance element 41a.
This is performed by supplying a current from c and detecting a change in the voltage across the ambient temperature measuring resistance element Rr with temperature. The voltage across the ambient temperature measuring resistance element Rr is the amplifier AMP4.
Input interface 1 of arithmetic unit 16 amplified by 2
It is converted into a digital signal by the AD converter of 6b, and the CPU
By the program control of 16a, the temperature measurement data is obtained by the ambient temperature resistance measuring element Rr.

The voltage across the heater element Rh is determined by the amplifier AM.
It is amplified in P43 and is set as voltage data of the heater element Rh by the program control of the CPU 16a in the same manner as above. Current is supplied to the temperature sensors Ru and Rd from the power supply line Vc through the resistance element 41b, and the voltage across the temperature sensors Rd and Ru connected in series is amplified by the amplifier AMP44, and the program of the CPU 16a is executed in the same manner as above. By the control, the temperature data of the temperature sensors Rd and Ru are summed to obtain total value data. The total value data is the temperature sensors Rd, R
It is converted into the average value data of the temperature measurement temperature of u.

The voltage across the temperature sensor Rd is the amplifier AMP.
The data is amplified by 45 and is used as temperature measurement temperature data of the temperature sensor Rd by the program control of the CPU 16a in the same manner as above. Therefore, even if the first heater control bridge circuit is not formed, the ambient temperature (temperature measurement data by the ambient temperature resistance measuring element Rr) and the voltage of the heater element Rh (voltage data of the heater element Rh) Compare the CPU
16a can be performed by program control. Similarly, the average value of the measured temperatures of the temperature sensors Ru and Rd (average value of the measured temperature of the temperature sensors Rd and Ru) and the ambient temperature (the temperature measured by the ambient temperature resistance measuring element Rr) in the upstream and downstream of the heater element Rh. Data) can be compared by the CPU 16a under program control.

Then, the CPU 16a drives the heater element Rh via the output interface 16c (having a digital / analog converter (not shown)) and the transistor TR46, and the temperature is measured by the ambient temperature resistance measuring element Rr. Accordingly, (heater temperature-ambient temperature) DT can be maintained at a constant value. Further, the CPU 16a keeps the average value of the temperature measured by the temperature sensors Rd, Ru higher than the temperature measured by the ambient temperature resistance measuring element Rr by a certain temperature according to the temperature measured by the ambient temperature resistance measuring element Rr. can do.

Further, the CPU 16a sets the heater element Rh to the ambient temperature and the heater element R according to the procedure shown in FIG.
Either the control based on the comparison with the voltage of h or the control based on the comparison between the average value of the temperature measured by the temperature sensors Ru and Rd and the ambient temperature is selectively switched according to the program. You can choose. And the CPU 16a
Is the total value data of the temperature measured by the temperature sensors Rd and Ru,
From the temperature measurement data of the temperature sensor Rd, the heater element Rh
Since it is possible to calculate the difference in the temperature measurement temperature between the upstream and the downstream, the flow rate of the fluid can be detected.

As described above, the thermal type flow meter 40 of the second modified embodiment operates in the same manner as the thermal type flow meter 10 described above, and one flow rate sensor has low power consumption and high flow rate measurement range. Enables accurate flow rate measurement. The thermal type flow meter according to the present invention is not limited to the above embodiment,
Modifications can be made without departing from the spirit of the invention.

[0058]

As described above, according to the first aspect of the present invention.
According to the thermal type flow meter described in (1), the switching means drives the heater element of the flow rate sensor by selectively using the first heater control means and the second heater control means according to the flow rate of the fluid. Therefore, using one flow rate sensor, it is possible to switch between low flow rate measurement with low power consumption and high flow rate measurement that alleviates that the slope of the flow rate measurement characteristic curve decreases in the high flow rate region, depending on the flow rate of the fluid. It is possible to realize a thermal type flow meter capable of highly accurate flow rate measurement in a wide flow rate measurement range.

According to the thermal type flow meter of the second aspect of the present invention, since the thermopile is used for the temperature measuring sensors on the upstream and downstream sides of the flow rate sensor in the flow direction, self-heating of the upstream and downstream temperature measuring sensors does not occur. It is possible to measure the temperature distribution around the heater of the flow rate sensor, and it is possible to further improve the accuracy of the thermal type flow meter. In the thermal type flowmeter according to claim 3 of the present invention, when the flow rate of the fluid is low by the switching means, the first heater control means is used to measure the flow rate with low power consumption and the flow rate is high. In the case of, the second heater control means is used to measure the flow rate while reducing the inclination of the flow rate measurement characteristic curve becoming small in the high flow rate region. Therefore,
The flow rate below the threshold value is set as the low flow rate, the flow rate above the threshold value is set as the high flow rate, and the flow rate above the threshold value is set as the high flow rate. This makes it possible to perform highly accurate flow rate measurement in a wide flow rate measurement range. Further, in the battery-operated thermal type flow meter, it is possible to realize a thermal type flow meter capable of operating on a battery for a long period of time, improving accuracy of flow rate measurement in a high flow rate region, and expanding a flow rate measurement range.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a thermal type flow meter according to the present invention, showing a case where the thermal type flow meter measures a low flow rate.

FIG. 2 shows a case where the thermal type flow meter whose schematic configuration diagram is shown in FIG. 1 measures a high flow rate.

FIG. 3 is a flowchart showing a procedure in the case where the thermal type flow meter shown in FIG. 1 measures the flow rate by switching the heater control means.

FIG. 4 is a graph showing an example of thermal type flow rate measurement characteristics of the thermal type flow meter according to the present invention.

FIG. 5 is a diagram showing a schematic main configuration of a first modified embodiment of a thermal type flow meter according to the present invention.

FIG. 6 is a diagram showing a schematic main configuration in a second modified embodiment of the thermal type flow meter according to the present invention.

FIG. 7 is a diagram showing a schematic main configuration of a flow sensor.

FIG. 8 is a graph showing an example of temperature distribution around a heater of a thermal type flow meter.

FIG. 9 is a graph showing an example of flow rate measurement characteristics of a conventional thermal type flow meter.

[Explanation of symbols]

10, 40 Thermal flow meter 11 Flow rate sensor 12 First heater control means 13 Second heater control means 15 Flow rate measurement means 14 Switching means Rh Heater element Ru Temperature sensor (first temperature measurement sensor) Rd Temperature sensor (first 2 temperature measuring sensor) Rr ambient temperature measuring resistance element (ambient temperature measuring sensor) Tpu thermopile (first temperature measuring sensor) Tpd thermopile (second temperature measuring sensor)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichiro Shinkawa             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama (72) Inventor Osamu Momose             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama F term (reference) 2F035 EA02 EA05 EA08 EA09

Claims (3)

[Claims] 1. A heater element, first and second temperature measuring sensor elements respectively provided in a fluid flow direction with the heater element interposed therebetween, and an ambient temperature temperature measuring sensor element for detecting an ambient temperature thereof. According to the temperature sensor equipped with a flow rate sensor and the ambient temperature temperature sensor element,
First heater control means for controlling the heater temperature of the heater element so as to maintain the heater temperature of the heater element at a constant temperature higher than the temperature measured by the ambient temperature measuring sensor element; Depending on the temperature measured by the temperature sensor element,
The heater temperature of the heater element is controlled so that the average value of the temperature measured by the first and second temperature measuring sensor elements is maintained higher than the temperature measured by the ambient temperature measuring sensor element by a constant temperature. Heater control means, flow rate measurement means for measuring the flow rate of the fluid flowing through the flow rate sensor from the temperature measurement temperature difference between the first temperature measurement sensor element and the second temperature measurement sensor element, and this flow rate measurement Based on the flow rate measured by the means, the first
And a switching means for driving the heater element by selectively using the heater control means and the second heater control means. 2. The thermal type flow meter according to claim 1, wherein first and second thermopiles are used for the first and second temperature measuring sensor elements. 3. The switching means, when the flow rate measured by the flow rate measuring means is low,
When the heater element is driven by using the first heater control unit, and the flow rate measured by the flow rate measurement unit is high,
The thermal type flow meter according to claim 1 or 2, wherein the heater element is driven by using the second heater control means.