JP2003315129A - Thermal flow meter - Google Patents

Abstract

(57) [Problem] To provide a thermal type flow measurement device capable of performing high-accuracy flow measurement in a wide flow range without being affected by a change in ambient temperature. SOLUTION: The heat generation temperature of a heater element of a flow sensor provided with first and second resistance temperature sensors in a flow direction of a fluid with a heater element interposed therebetween is set to the first and second resistance temperature sensors. The heater control means controls the average value of the measured temperature of the element to be higher than the rise in the ambient temperature measured by the ambient temperature resistance element provided in the heater element. Enables high-precision flow measurement,
In addition, the heater control means controls the difference between the heat generation temperature and the ambient temperature in accordance with the change in the ambient temperature, reduces the change in the flow rate sensor sensitivity due to the temperature change, and provides a high-precision flow rate regardless of the ambient temperature change Perform measurement.

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 rate measuring device capable of performing highly accurate flow rate measurement in a wide flow rate range regardless of changes in ambient temperature.

[0002]

2. Description of the Related Art A flow rate sensor which constitutes a thermal type flow rate measuring apparatus has a heater element Rh formed of a heating resistor provided on a silicon substrate B as shown in FIG. A pair of temperature sensors R consisting of resistance temperature detectors
It has an element structure in which u and Rd are provided. In this thermal type flow rate measuring device, the temperature distribution in the flow direction F of the fluid (hereinafter referred to as "heater peripheral temperature distribution") generated by the heat generated by the current supplied to the heater element Rh changes depending on the flow velocity of the fluid. By utilizing the temperature sensor R
The flow rate of the fluid is detected from the change in resistance value of u and Rd depending on the temperature.

As for the specific temperature distribution around the heater, 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. In addition, the temperature on the downstream side becomes higher than the temperature on the upstream side. Therefore, the thermal type flow rate measuring device detects the temperature difference between the downstream side and the upstream side as the output of the flow rate sensor from the temperature measurement results of the temperature sensor Rd on the downstream side of the flow passage and the temperature sensor Ru on the upstream side of the flow passage. It measures Q. In addition, R in FIG.
Reference numeral r is a temperature sensor that forms an ambient temperature measuring resistance element provided at a position distant from the heater element Rh, and is used to measure the ambient temperature (the temperature of the fluid to be measured).

In such a thermal type flow rate measuring device, the temperature difference between the heater element Rh and the ambient temperature ((temperature of the heater element Rh)-(ambient temperature), hereinafter "(heater temperature-ambient temperature)"
There is one that drives and controls the heater element Rh so as to always keep constant (denoted as "DT"). However, in such a thermal type flow rate measuring device, as shown in the flow rate measuring characteristic of FIG. 6, it is known that the output of the flow rate sensor decreases (the sensitivity of the flow rate sensor decreases) as the ambient temperature rises ( The temperature in FIG. 6 indicates the ambient temperature). Further, 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. Therefore, as the flow rate Q increases, the rate of increase in the temperature difference between the temperature sensors Rd and Ru decreases, and the curve representing the flow rate measurement characteristic decreases in slope with the increase in the flow rate Q and finally saturates. This not only lowers the accuracy of flow rate measurement in the high flow rate region, but also narrows the flow rate measurement range of the thermal type flow rate measuring device.

On the other hand, as the (heater temperature-ambient temperature) DT is increased, the change in the heater ambient temperature distribution with respect to the flow direction F is increased, and the sensitivity of the flow rate sensor is improved. Therefore, as disclosed in Japanese Utility Model Publication No. 7-51618,
As shown in the solid line in FIG. 7A, the higher the ambient temperature, the larger the heater temperature-ambient temperature DT, and the thermal type flow rate measuring device that reduces the decrease in the sensitivity of the flow rate sensor due to the temperature rise. It is provided.

[0006]

However, as the ambient temperature rises (heater temperature-ambient temperature) DT is increased, it is possible to reduce the decrease in the sensitivity of the flow sensor due to the rise in ambient temperature, and the flow rate Q It cannot be reduced that the slope of the flow rate measurement characteristic curve becomes smaller with the increase.

Therefore, the above-mentioned thermal type flow rate measuring device cannot reduce the change in the sensitivity of the flow rate sensor with respect to the temperature change in a wide flow rate measuring range, and as shown in FIG. Since the flow rate measurement characteristic curves of the respective temperatures can be overlapped only at the flow rate Qx, there is a problem that it is not possible to reduce the influence of the ambient temperature in a wide flow rate range and perform highly accurate flow rate measurement. And FIG.
As shown in (b), with the flow rate Qx as a boundary point, when the flow rate is higher than Qx, the change in the sensor sensitivity due to the temperature increase decreases, and when the flow rate is lower than Qx, the change in the sensor sensitivity due to the temperature increase increases. There is also a problem in that temperature compensation of a large flow rate measurement characteristic curve is generally complicated and difficult or costly.

[0008] Further, although there is a household gas meter as an example of the above-mentioned thermal type flow rate measuring device, in the household gas meter, from a viewpoint of fairness of gas charges, what amount of gas is consumed in any time zone. Also, the error of the actual charge paid by the consumer is kept within a predetermined error range (percentage) based on the true gas charge according to the true amount of gas consumed (corresponding to the true gas flow rate). Is required.

However, in a general flow meter, since the accuracy of the flow rate measurement is defined with reference to the full span of the flow rate measurement (hereinafter referred to as "% FS"), the allowable error with respect to the true flow rate increases at the flow rate of less than the full span. . For example 1
With a flow meter with an accuracy of% FS, an allowable error at a flow rate of 10% of full span is 1% of a full span flow rate, that is, an error of (1%) / (10%) = 10% is allowed. . Then, in the household gas meter, the accuracy of measuring the gas consumption amount of the consumer who consumes a small amount of gas for a long time is deteriorated, which is not preferable from the viewpoint of maintaining the fairness of the gas charge.

The present invention has been made in order to solve the above-mentioned problems, and it is
Moreover, it is an object of the present invention to provide a thermal type flow rate measuring device capable of performing highly accurate flow rate measurement in a wide flow rate range.

[0011]

In order to achieve the above object, a thermal type flow rate measuring device according to claim 1 of the present invention is provided with a heater element and a heater element provided in the fluid flow direction. A first flow rate sensor having the first and second resistance temperature measuring elements and an ambient temperature resistance measuring element for detecting the ambient temperature thereof; The heater control means for controlling the heater temperature so as to maintain the average value of the temperature measured by the first and second temperature measuring resistance elements higher than the temperature increase by the ambient temperature measuring resistance element, and the first temperature measuring means. Temperature resistance element and second
Flow rate measuring means for measuring the flow rate of the fluid flowing through the flow rate sensor from the temperature difference between the temperature measuring resistance element and the temperature measuring resistance element.

The heater control means makes the (heater temperature-ambient temperature) DT larger than the increase in the ambient temperature based on the result of measuring the ambient temperature by the ambient temperature resistance measuring element, so that the flow rate accompanying the rise in temperature is increased. It is possible to reduce the decrease in the sensitivity of the sensor. Further, the heater control means, based on the measurement result of the average value of the temperature measurement temperatures of the first and second temperature measurement resistance elements, when the ambient temperature is constant, even if the flow rate of the flowing fluid increases, By controlling the driving of the heater element, the average value of the temperature measured by the first and second temperature measuring resistance elements can be maintained at a constant value. Therefore, when the ambient temperature is constant, even if the amount of heat flowing out from the flow rate sensor increases as the flow rate Q increases, the influence of the amount of heat flowing out on the first temperature measuring resistance element and the second temperature measuring resistance element is affected. Is reduced. Then, as the flow rate Q increases, the decrease in the increase rate of the temperature difference between the temperature sensors Rd and Ru caused by the heat generated by the heater element Rh flowing out of the flow rate sensor together with the fluid is reduced, and the flow rate Q increases. As a result, the inclination of the flow rate measurement characteristic curve is reduced, and the saturation of the curve representing the flow rate measurement characteristic in the high flow rate region is also reduced.

That is, the heater control means reduces the decrease in the sensitivity of the flow rate sensor due to the temperature rise and the decrease in the slope of the flow rate measurement characteristic curve as the flow rate Q increases. A thermal type flow rate measuring device is realized which is capable of performing highly accurate flow rate measurement in a wide flow rate range regardless of changes. Further, there is no need to perform temperature compensation which is complicated or costs up because a specific flow rate is used as a boundary point.

According to a second aspect of the present invention, there is provided a thermal type flow rate measuring device for setting a resistance temperature coefficient, which is connected in parallel with a series circuit including the first and second temperature measuring resistance elements and / or an ambient temperature measuring resistance element. Of the resistance element. Therefore, the resistance temperature coefficient of the combined resistance of the ambient temperature resistance measuring element and the resistance element for resistance temperature coefficient setting (hereinafter referred to as “first resistance element”) connected in parallel to the ambient temperature measuring resistance element, and / Alternatively, the resistance of the combined resistance of the series circuit of the first and second temperature measuring resistance elements and the resistance element for setting the temperature coefficient of resistance (hereinafter “second resistance element”) connected in parallel to these temperature measuring resistance elements The temperature coefficient can be set arbitrarily.

Thus, by setting the resistance temperature coefficients, the average value of the temperature measured by the first and second temperature measuring resistance elements is maintained higher than the temperature measured by the ambient temperature temperature measuring resistance element by a predetermined temperature. When the ambient temperature rises, the heater control means for controlling the heater temperature as described above is based on the measurement of the temperature measured by the ambient temperature resistance measuring element (heater temperature-
The ambient temperature) DT can be controlled to be larger than the increase in the ambient temperature, and the decrease in the sensitivity of the flow sensor due to the increase in the temperature can be reduced.

According to a third aspect of the thermal type flow rate measuring device, the resistance temperature coefficient of the combined resistance of the parallel connection of the ambient temperature measuring resistance element and the first resistance element is the first and the second. Is larger than the temperature coefficient of resistance of the combined resistance of the temperature measuring resistance element and the second resistance element connected in parallel. Therefore, if the resistance temperature coefficient of each resistance element is set to a positive value, when the ambient temperature rises, the ambient temperature measurement is performed against the increase in the resistance value on the first and second temperature measurement resistance element sides connected in series. The increase in the resistance value on the temperature resistance element side is larger. The heater control means can increase the voltage applied to the heater element by detecting the difference in the increase in the resistance value (the increase in the resistance value on the side of the ambient temperature measuring resistance element being larger) as the voltage. Yes, if the ambient temperature rises,
(Heater temperature-ambient temperature) DT can be made larger than the increase in ambient temperature, and the decrease in the sensitivity of the flow sensor can be reduced.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A thermal type flow rate measuring device 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 rate measuring device according to the present invention. This thermal type flow rate measuring device 1 has a flow rate sensor 10 having the structure shown in FIG. 5, an amplifier 11 and a transistor 12 which are heater control means, and a first bridge circuit which is a flow rate measurement means. The first bridge circuit includes an upstream temperature sensor Ru (first temperature measuring resistance element included in the flow rate sensor 10) and a downstream temperature sensor Rd.
(Second temperature measuring resistance element included in the flow sensor 10), a resistance Ra and a resistance Rb.

The first bridge circuit, which constitutes the flow rate measuring means, includes a series circuit of temperature sensors Ru and Rd, a resistor Ra,
Rb series circuit is connected in parallel, temperature sensor Rd
And one end of the first bridge circuit to which the resistor Rb is connected are grounded, and the other end of the first bridge circuit is connected to the resistor R1.
Is connected to the power supply line Vc via. And the resistance R
The connection point N1 between a and the resistance Rb and the connection point N2 between the temperature sensor Ru and the temperature sensor Rd are outputs of the first bridge circuit. The potential at the connection point N1 is the resistances Ra and Rb.
Of the temperature sensors Ru and Rd, and the potential of the connection point N2 is determined by the resistance value of each of the temperature sensors Ru and Rd.

For example, when the resistance values of the resistors Ra and Rb are set equal, and when the resistance values of the temperature sensors Ru and Rd are equal, the first bridge circuit is balanced and the connection point N
The potential difference between 1 and N2 is zero (V). On the other hand, when the resistance values of the temperature sensors Ru and Rd are not equal, the first sensor
The bridge circuit is not balanced, and a potential difference occurs between the connection points N1 and N2. In this way, the difference between the temperature measurement temperatures of the temperature sensors Ru and Rd can be detected from the potential difference between the connection points N1 and N2, and the connection points N1 and N2 are flow sensor output terminals.

The thermal type flow rate measuring device 1 further uses a second bridge circuit to divide the average value of the temperature measured by the first and second resistance temperature measuring elements and the temperature measured by the ambient temperature resistance measuring element. The heater control means drives the heater element Rh to control the DT (heater temperature-ambient temperature) DT based on the measured difference. In the second bridge circuit, a series circuit of a first bridge circuit (a resistor Rx described later is connected in parallel to the first bridge circuit) and a resistor R1 is an ambient temperature measuring resistance element Rr ( A resistance Ry, which will be described later, is connected in parallel to the ambient temperature measuring resistance element Rr) and a resistor R2 connected in parallel in a series circuit, and the ambient temperature measuring resistance element Rr and one end of the first bridge circuit are connected. One end of the second bridge circuit to which the side is connected is grounded, and the second side to which the resistors R1 and R2 are connected
The other end of the bridge circuit is connected to the power supply line Vc.

The connection point N3 between the first bridge circuit and the resistor R1 and the connection point N4 between the ambient temperature measuring resistance element Rr and the resistor R2 are the outputs of the second bridge circuit, and the connection point N3 is the amplifier 11. Of the amplifier 11 and the connection point N4 is connected to the inverting input terminal of the amplifier 11. The amplifier 11 has a heater element R via a transistor 12 (PNP transistor) whose emitter is connected to the power supply line Vc.
drive h. The second bridge is balanced when the potentials at the connection points N3 and N4 are equal (the amplifier 11 and the transistor 12 are connected to the heater element R so that this balanced state is maintained).
drive h).

The connection point N3 is a temperature sensor Ru, R.
The potential is determined by the resistance value corresponding to the total value of the measured temperature of d, and this potential is input to the non-inverting input terminal of the amplifier 11. In this case, the total value of the temperature measurement temperatures of the temperature sensors Ru and Rd is twice the average value of the temperature measurement temperatures of the temperature sensors Ru and Rd, and the gain on the non-inverting input terminal side of the amplifier 11 and the inverting input of the amplifier 11 are By appropriately setting the relationship with the gain on the terminal side, the total value of the temperature measurement temperatures of the temperature sensors Ru and Rd can be treated as the average value of the temperature measurement temperature of the temperature sensors Ru and Rd.

The operation of the heater control means is stabilized by the negative feedback of the capacitor C, and the resistor R3 is interposed in series between the output terminal of the amplifier 11 and the base of the transistor 12 to cause the base current of the transistor 12 to flow. Is restricted. In the second bridge circuit, the (heater temperature-ambient temperature) DT is increased more than the increase in the ambient temperature. Therefore, the ambient temperature measuring resistance element Rr and the resistance Ry are increased.
The temperature coefficient of resistance of the combined resistance of the parallel connection (hereinafter referred to as “Rr-side temperature coefficient”) is a combination of the parallel connection of the series circuit of the temperature sensors Ru and Rd and the resistance Rx. The resistance temperature coefficient is larger than the resistance temperature coefficient of resistance (hereinafter referred to as “Rud side temperature coefficient”).

For example, at 20 ° C., the resistance value of the ambient temperature measuring resistance element Rr and the resistance value of the resistance Ry are equal, the resistance temperature coefficient of the ambient temperature measuring resistance element Rr is α1, and the resistance temperature coefficient of the resistance Ry is zero. Then, the Rr-side temperature coefficient becomes (α1) / 2, so that the Rr-side temperature coefficient and the Rud
The side temperature coefficient can be set arbitrarily. The resistance values of the resistors Ra and Rb are the same as those of the temperature sensors Ru and Rd.
The resistance value is sufficiently higher than the resistance value of 1 and does not affect the Rud side temperature coefficient.

Next, the operation of reducing the decrease in the slope of the flow rate measurement characteristic curve as the flow rate Q increases will be described. When the flow rate Q is zero and the ambient temperature is 20 ° C., for example, FIG.
As shown in (a), the heater ambient temperature distribution due to the heat generated by the heater element Rh is distributed around the position where the heater element Rh is arranged (indicated by H in the figure), and the temperature sensors Ru, Rd Position where is placed (U and D respectively in the figure)
(Displayed as) is the same, and is the same at 30 ° C., for example. And at this time (heater temperature-ambient temperature)
It is assumed that the temperature of the positions U and D is maintained at 30 ° C. and the temperature of the position H is 65 ° C. at 45 ° C.

When the heater ambient temperature distribution is maintained, the ambient temperature measuring resistance element Rr has a resistance value corresponding to 20 ° C., and the series resistance of the temperature sensors Ru and Rd is the total temperature of the temperature sensors Ru and Rd. Is 60 ° C (average value is 30 ° C)
In the resistance value corresponding to, the second bridge circuit is balanced, and the heater element Rh is driven by the amplifier 11 and the transistor 12 so that this balanced state is maintained.

As described above, when the flow rate Q is zero, the resistance values of the temperature sensors Ru and Rd are equal, so the first bridge circuit is balanced and the flow sensor output terminal (between the connection point N1 and the connection point N2). The electric potential difference becomes zero, and the thermal type flow rate measuring device 1 measures that the flow rate Q is zero. Next, the operation of the heater control means when the flow rate increases to Q1 when the ambient temperature is constant at 20 ° C. will be described.

At this time, tentatively (heater temperature-ambient temperature)
Assuming that DT is constant at 45 ° C., the heat generated by the heater flows out of the sensor element by the flowing fluid. Then, as shown in FIG. 2B, the total temperature of the positions U and D decreases. For example, the temperature at the position U is 27 ° C., the temperature at the position D is 29 ° C., and the temperature sensor Rd,
It seems that the total value of the measured temperature of Ru is 56 ° C. and the average value is 28 ° C.

The reduction of the total value of the positions U and D (decrease of the average value) lowers the potential of the connection point N3, lowers the output voltage of the amplifier 11 and increases the collector current of the transistor 12, and increases the collector current of the heater element Rh. Fever increases. And FIG.
As shown in (c), for example, the temperature at the position U becomes 28 ° C., the temperature at the position D becomes 32 ° C., and the total value of the temperatures at the positions U and D rises to 60 ° C. (average value 30 ° C.). The potential generated at the connection point N3 and the potential generated at the connection point N4 corresponding to the measured temperature of the ambient temperature measuring resistance element Rr of 20 ° C. match and the second bridge circuit is balanced. That is, in order to maintain the average value of the temperatures at the positions U and D at a constant value with respect to the change in the flow rate Q of the fluid (heater temperature-ambient temperature).
It controls the DT.

Thus, in the thermal type flow rate measuring device 1, the average value of the temperatures at the positions U and D in the flow rate sensor 10 is 30 ° C.
Maintained at. Then, as the flow rate Q increases, the decrease in the increase rate of the temperature difference between the temperature sensors Rd and Ru caused by the heat generated by the heater element Rh flowing out of the flow rate sensor together with the fluid is reduced. As shown in a), in the high flow rate region, the inclination of the flow rate measurement characteristic curve is reduced, and the saturation of the curve representing the flow rate measurement characteristic in the high flow rate region is also reduced.

Next, when the ambient temperature rises,
The operation of reducing the decrease in the sensitivity of the flow sensor will be described. Here, the second bridge circuit is Rr as described above.
The side temperature coefficient is set to be larger than the Rud side temperature coefficient. If the Rr-side temperature coefficient and the Rud-side temperature coefficient are equal in the thermal type flow rate measuring device 1 shown in FIG. , Rd is balanced so that the increase in the average value of the measured temperature of Rd and the increase in the potential of the connection point N4 are equal. Therefore, the heater control means drives the heater element Rh so that the average value of the temperature measured by the temperature sensors Ru and Rd becomes equal to the increase in the ambient temperature due to the increase in the ambient temperature. That is, (heater temperature-ambient temperature) DT becomes equal to the increase in ambient temperature.

However, in the thermal type flow rate measuring device 1 shown in FIG. 1, the Rr side temperature coefficient is larger than the Rud side temperature coefficient.
Then, as compared with the case described above, when the ambient temperature rises, the potential increase at the connection point N4 becomes larger than the potential increase at the connection point N3. At this time, in order to balance the second bridge circuit, the temperature sensor Ru,
The increase in the average value of the measured temperature of Rd must be large, and the heater control means acts to increase (heater temperature-ambient temperature) DT more than the increase in ambient temperature. In this way, (heater temperature-ambient temperature) DT becomes larger than the increase in the ambient temperature, so that the decrease in the sensitivity of the flow sensor 10 due to the increase in the ambient temperature is reduced.

Thus, in the thermal type flow rate measuring device 1 shown, the inclination of the flow rate measurement characteristic curve becomes smaller as the flow rate Q increases, and the saturation of the curve showing the flow rate measurement characteristic in the high flow rate region is also reduced. Moreover, as shown in FIG. 3B, the decrease in the sensitivity of the flow sensor 10 due to the increase in the ambient temperature is reduced, so that the flow rate sensor 10 is not affected by the change in the ambient temperature.
In addition, highly accurate flow rate measurement can be performed in a wide flow rate range.

FIG. 4 shows an example of actual measurement of the sensitivity (flow velocity measurement characteristic) of the thermal type flow rate measuring device 1 with respect to the flow velocity.
Good sensitivity is obtained in the flow velocity range of 0 to 16 m / sec, and sensitivity error is well reduced in the flow velocity range in the temperature range of (-20 ° C to 60 ° C). Where the flow rate of the fluid is
Since it is the product of the cross-sectional area of the fluid flow portion and the flow velocity at the flow rate measurement site, a wide flow velocity measurement range is synonymous with a wide flow rate measurement range.

The resistance element for setting the resistance temperature coefficient on the ambient temperature measuring resistance element side and the resistance element for setting the resistance temperature coefficient on the first and second temperature measuring resistance element sides are always used. There is no need to use either one, and the second
On the basis of the bridge circuit output of the above, the heater control unit causes the heater temperature to increase more than the increase in the ambient temperature (heater temperature-ambient temperature) DT.
What is necessary is that it can be controlled so as to increase.

The series circuit of the first and second temperature measuring resistance elements and the connection between the ambient temperature measuring resistance element and the input terminal (non-inverting input terminal, inverting input terminal) of the amplifier are as described above. If the resistance temperature coefficient on the series circuit side of the first and second resistance temperature detectors is made larger than the resistance temperature coefficient on the ambient temperature resistance measurement element side, the same effect can be obtained. can get.

Further, the heater control means may be constituted by a microprocessor or the like. For example, a microprocessor or the like may convert the output of the second bridge circuit (an analog voltage output between the connection points N3 and N4) into an analog-digital signal and set the output of the second bridge circuit to zero (V). It seems that the heater element Rh is driven via a digital-analog converter according to a predetermined program.

As described above, the present invention is not limited to the above-described embodiments, but can be modified and carried out without departing from the spirit of the present invention.

[0039]

As described above, according to the first aspect of the present invention.
According to the thermal type flow rate measuring device described in (1), the heat generated by the heater element disposed between the respective sensors is maintained so as to maintain the average value of the temperature measured by the upstream temperature sensor and the downstream temperature sensor of the flow rate sensor. Since the control is performed, the inclination of the flow rate measurement characteristic curve is reduced as the flow rate Q increases, and the saturation of the curve indicating the flow rate measurement characteristic in the high flow rate region is also reduced.

Further, the heater control means controls the drive of the heater element in accordance with the temperature difference between the average value of the measured temperature of the upstream temperature sensor and the downstream temperature sensor and the measured temperature of the ambient temperature resistance measuring element. Therefore, the (heater temperature-ambient temperature) DT can be made larger than the increase in the ambient temperature, and the decrease in the sensitivity of the flow sensor due to the increase in the ambient temperature is reduced. That is, highly accurate flow rate measurement can be performed over a wide flow rate range regardless of changes in the ambient temperature, and temperature compensation that requires a specific flow rate as a boundary point and that causes complexity or cost increase is not required. Further, in the gas meter for home use, the flow rate of gas can be measured with high accuracy at any flow rate, and the fairness of the gas fee can be easily maintained.

According to the thermal type flow rate measuring device of the second aspect, the resistance temperature coefficient of the combined resistance of the ambient temperature measuring resistance element and the first resistance element, and the upstream side temperature sensor and the downstream side temperature sensor. The temperature coefficient of resistance of the combined resistance of the series circuit and the second resistance element can be arbitrarily set. Therefore, when the ambient temperature rises due to the setting of each resistance temperature coefficient, the heater control means (heater temperature-ambient temperature)
The DT can be made larger than the increase in the ambient temperature, and the thermal type flow rate measuring device that reduces the decrease in the sensitivity of the flow rate sensor is realized.

According to the thermal type flow rate measuring device of the third aspect, the resistance temperature coefficient of the combined resistance of the ambient temperature measuring resistance element and the first resistance element is the upstream temperature sensor and the second resistance element. It is set to be larger than the temperature coefficient of resistance of the combined resistance of and. Therefore, when the ambient temperature rises, the resistance change on the ambient temperature measuring resistance element side is larger than that on the series resistance side of the upstream temperature sensor and the downstream temperature sensor. Therefore, when the ambient temperature rises, the heater control means can make the (heater temperature-ambient temperature) DT larger than the rise in the ambient temperature, and a thermal type flow rate measuring device that reduces the decrease in the sensitivity of the flow rate sensor is realized. To be done.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an essential part of an embodiment of a thermal type flow rate measuring device according to the present invention.

FIG. 2 is a graph showing an example of a heater surrounding temperature distribution in the thermal type flow rate measuring device.

FIG. 3 is a graph showing an example of flow rate measurement characteristics in the thermal type flow rate measurement device of FIG.

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

FIG. 5 is a diagram showing a schematic configuration of a main part of a flow sensor.

FIG. 6 is a graph showing an example of flow rate measurement characteristics in a conventional thermal type flow rate measurement apparatus that controls (heater temperature-ambient temperature) DT to be constant.

FIG. 7 is a graph showing an example of flow rate measurement characteristics in a conventional thermal type flow rate measurement apparatus in which DT is increased as the ambient temperature becomes higher (heater temperature-ambient temperature).

[Explanation of symbols]

1 Thermal flow meter 10 Flow rate sensor 11 Amplifier (heater control means) 12 transistors (heater control means) Rh heater element Rr Ambient temperature resistance measuring element Ru temperature sensor (first resistance temperature detector) Rd temperature sensor (second resistance temperature detector) Rx resistance (resistive element for setting temperature coefficient of resistance) Ry resistance (resistive element for setting temperature coefficient of resistance)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidenori Hibi             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama (72) Inventor Koichiro Shinkawa             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama (72) Inventor Masao Seo             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama F term (reference) 2F030 CC13 CD15 CE01                 2F035 EA05 EA09

Claims (3)

[Claims] 1. A heater element, first and second temperature measuring resistance elements respectively provided in the fluid flow direction with the heater element interposed therebetween, and an ambient temperature temperature measuring resistance element for detecting an ambient temperature thereof. An average value of the temperature measured by the first and second temperature measuring resistance elements is calculated according to a change in the temperature measured by the flow rate sensor and the ambient temperature measuring resistance element. The heater control means for controlling the heater temperature so as to keep the temperature measurement temperature higher than the temperature measurement temperature rise by the temperature measurement temperature difference between the first temperature measurement resistance element and the second temperature measurement resistance element. A thermal type flow rate measuring device comprising: a flow rate measuring means for measuring a flow rate of a fluid flowing through the flow rate sensor. 2. The thermal type flow rate measuring device according to claim 1, wherein a resistance connected in parallel to the series circuit with the first and second resistance temperature measuring elements and / or the ambient temperature resistance measuring element. A thermal type flow rate measuring device comprising a resistance element for setting a temperature coefficient. 3. The resistance temperature coefficient of the combined resistance of the ambient temperature measuring resistance element and the resistance element for setting the resistance temperature coefficient connected in parallel to the ambient temperature measuring resistance element has a resistance temperature coefficient of the first and second resistance elements. The heat resistance according to claim 2, wherein the resistance temperature coefficient of the combined resistance of the series circuit of the two temperature measuring resistance elements and the resistance element for setting the resistance temperature coefficient connected in parallel to the series circuit is larger than the resistance temperature coefficient. Flow meter.