JPH1164062A - Flow rate sensor having flowing water switching and fluid temperature detecting functions - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow rate sensor which is not affected by foreign matters existing in a fluid, does not cause pressure loss in the flow of the fluid, has a highly reliable flowing water switching function and/or fluid temperature measuring function, and can be attached to a object as a single attaching unit. SOLUTION: A flow rate sensor is provided with a temperature measuring resistor 19 for comparison which is composed of a resistor, having a resistance-temperature characteristic such that it changes according to the temperature of a fluid to be measured and outputs a divided voltage as a comparative output as the flow rate detecting output of the sensor, a comparator circuit 25 which compares the flow rate detecting output with the comparative output and outputs an 'on' or 'off' signal as a flowing water switching output in accordance with the compared results, a bridge circuit 41 composed of a temperature-measuring resistor 18 for detecting exothermic resistor and a temperature-measuring resistor 19 for comparison, and a means 42 which corrects the nonconformities between the thermistor constants of the resistors 18 and 19 for making the differential voltage of the bridge circuit 41 a flow rate detecting output such that does not substantially depend upon the temperature of the fluid, but only corresponds to the flow rate of the fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor, and more particularly, to an indirectly-heated type suitable for use in private demands (general households), especially for use in water heaters, boilers, water heaters, 24-hour baths, and the like. The flow sensor having a flow switch function and / or a fluid temperature detection function.

[0002]

2. Description of the Related Art FIG. 7 is a schematic view showing a conventional flow sensor. As shown in FIG. 1, the flow sensor includes an impeller 2 made of a plastic magnet provided in a pipe 1 and a hall sensor 3 provided near the impeller 2.

In this configuration, when water flows through the pipe 1 in the direction of arrow 4, the impeller 2 rotates at a rotation speed corresponding to the flow rate of the water. The Hall sensor 3 detects magnetism that changes according to the rotation of the impeller 2 and outputs a pulse signal at intervals according to the rotation speed of the impeller 2. At this time, as shown in FIG. 8, the flow rate of water and the number of output pulses per unit time have a linear relationship. Therefore, the flow rate can be obtained by referring to the relationship and the number of output pulses of the Hall sensor 3 per unit time.

FIG. 9 is a schematic view showing a conventional water switch. This water switch is a vertically oriented tube 1
A flow detecting rod 6 rotatably provided between a horizontal position and an upright position around a shaft 5 at one end;
Magnet 7 provided at the other end of flow detection rod 6
And a reed switch 8 that is turned on by the magnetic force of the magnet 7 at the upright position of the flow detecting rod 6.

In this configuration, when the flow rate of the water flowing in the pipe 1 in the direction of arrow 4 (upward) increases and reaches a predetermined value, the rod 6 at the horizontal position stands upright and the reed switch 8 is turned on. . Thereafter, when the flow rate decreases to a predetermined value or less, the rod 6 falls down and becomes horizontal, and the reed switch 8 is turned off. FIG. 10 shows the relationship between the flow rate and the on / off output of the reed switch 8 at this time. As shown in the figure, the flow rate when turning on is larger than the flow rate when turning off. That is, there is a dead zone for the flow rate of the switch output, which prevents chattering of the switch.

In many cases, a thermistor 9 for detecting the temperature of the water flowing in the pipe 1 is independently provided in the flow sensor or the flow switch.

[0007]

However, according to the conventional flow rate sensor described above, the impeller 2 causes a problem of pressure loss in the water flow, and the impeller is in proportion to the flow rate due to entrapment or entanglement of foreign matter. There is a problem that the rotation speed is no longer indicated.

Further, according to the above-mentioned conventional water switch,
Rotation of the rod 6 may not be performed smoothly due to hair, scale, or abrasion of the mounting portion, and may cause malfunction. Such a malfunction of the running water switch may lead to a steam explosion due to empty cooking in the water heater.

[0009] These flow sensors and water switches are used in different standards.
There is also a disadvantage that the water switch and the thermistor for detecting the water temperature described above must be separately installed.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a highly reliable water switch function and / or a fluid temperature measurement function that does not cause a pressure loss in a fluid flow. It is an object of the present invention to provide a flow sensor which can be mounted as one mounting unit.

[0011]

SUMMARY OF THE INVENTION In order to provide a flow sensor which has a highly reliable flow switch function and can be mounted as one mounting unit, the present invention provides a temperature sensor which changes in accordance with the flow rate and temperature of a fluid. Heat generating resistor,
A heating resistor for detecting a heating resistor provided adjacent to the heating resistor, wherein a voltage divided by the heating resistor for detecting a heating resistor is changed according to a flow rate and a temperature of the fluid. In the indirectly heated flow rate sensor having a flow rate detection output, a resistance temperature sensor whose resistance-temperature characteristic changes according to the temperature of the fluid, and a voltage divided thereby,
A comparison resistance bulb for obtaining as a comparison output with respect to the flow rate detection output, the flow rate detection output is compared with the comparison output, and an ON / OFF signal is output as a flow switch output according to the comparison result. A comparison circuit, a bridge circuit including the heating resistor detection temperature measuring resistor and the comparison temperature measuring resistor as components, and a differential voltage of the bridge circuit substantially depends on a temperature of the fluid. A means for correcting a mismatch of the thermistor constant between the heating resistor detection temperature measuring resistor and the comparison temperature measuring resistor for a flow detection output according to only the flow rate without performing. I do. However, "water" in the "flow switch" does not mean that the target of "fluid" is limited to water. The “fluid” includes a liquid and a gas other than water.

[0012] According to this, an electric circuit based on an indirectly heated flow sensor and using a circuit including a heating resistor and a temperature measuring resistor without using mechanical elements such as the impeller and the rod described above. Unlike the flow rate sensor of FIG. 7, the flow rate detection output and the flowing water switch output are obtained only by the dynamic processing, so that the flow rate detection output can be obtained without causing pressure loss or rotation failure due to foreign matter in the fluid. The output of the water flow switch can be obtained without causing a malfunction due to hair, scale, etc. as in the water flow switch of FIG. In addition, since the heating resistor, each temperature measuring resistor, and necessary circuit elements can be easily and compactly formed and arranged by a thin film / thick film forming technique, etc., the flow rate detection function and the flow switch function are provided. A sensor having a complex function is easily and compactly realized as one attachment unit.

In the comparison circuit, it is easy to provide the dead zone as described above with reference to FIG. 10 in order to prevent chattering at the output of the flowing water switch. Therefore, while utilizing the advantage of the indirectly heated flow sensor, that is, the advantage of not causing the influence of foreign matter in the liquid or causing pressure loss, the flow switch function is added to this.
It enables integration while satisfying both specifications.

In a more specific embodiment, as described above, the flow rate sensor having the flowing water switch function is a bridge having the heating resistor detecting resistor and the comparative resistor as components. Circuit, and a difference voltage between the bridge circuit and the flow rate detection output according to only the flow rate without substantially depending on the temperature of the fluid. It is characterized by comprising means for correcting mismatch of the thermistor constant between the resistance temperature detectors.

In this case, the output from the bridge circuit on the side of which the voltage is divided by the heating resistor detecting temperature measuring resistor (the flow rate detection output that is not temperature compensated) changes in accordance with the flow rate and temperature of the fluid. The characteristics for the flow rate differ depending on the temperature of the fluid. The output on the side divided by the resistance bulb for comparison is in accordance with the temperature of the fluid. And the difference between these outputs (differential voltage of the bridge circuit) depends only on the flow rate without depending on the temperature of the fluid,
As shown in FIG. 2, the temperature-compensated flow rate detection output is substantially represented by one characteristic curve.

However, it is very difficult to set the resistance temperature characteristics of the comparative resistance temperature detector so that the temperature compensation is perfectly performed. Therefore, it is necessary to adjust in advance the means for correcting the mismatch of the thermistor constant so that the difference voltage of the bridge circuit becomes a flow rate detection output corresponding to only the flow rate without substantially depending on the temperature of the fluid. is there. This correction means adjusts the resistance temperature characteristic (gradient of the characteristic curve, that is, the thermistor constant) of the heating resistor detecting temperature measuring resistor by adjusting the heating value of the heating resistor. It can be constituted by a variable resistor connected in series to the body or by means for varying the voltage applied to the heating resistor. By performing this adjustment in advance, the difference voltage of the bridge circuit can be a flow rate detection output corresponding to only the flow rate without substantially depending on the temperature of the fluid.

More specifically, the adjusting means for correcting the mismatch between the thermistor constants (B constants) adjusts the amount of heat generated by the heating resistor so that the apparent temperature measuring resistor for detecting the temperature of the heating resistor can be adjusted. This is for adjusting the B constant. This apparent B constant B 'is represented by B as the true B constant and the absolute temperature T of the fluid.
And (T + ΔT) and (T ₀ + ΔT), the absolute temperature of the heating resistor when it is increased by heat generation with respect to T ₀ (ie, the absolute temperature of the heating resistor temperature detecting resistor). The resistance value of the resistance bulb for temperature detection is R
And R ₀ are defined by the following equation.

[0018]

(Equation 1) That is, the apparent B constant B 'can be said to be the B constant based on the absolute temperature of the fluid, and its value is ΔT
It changes according to. The temperature compensation by the water temperature compensating resistor is performed by detecting the fluid temperature, so that the apparent B constant of the heating resistor temperature detecting temperature measuring resistor matches the B constant of the water temperature compensating resistor. If the heating value of the heating resistor is adjusted in advance, the temperature compensation can be performed satisfactorily.

When the flow rate is obtained from the flow rate detection output that is not temperature-compensated, data indicating the characteristic of the flow rate detection output with respect to the flow rate for each required temperature is stored in a memory in advance, and when measuring the flow rate, this enormous amount is obtained. It is necessary to perform a process of comparing the measured data with the detected temperature and the flow detection output to obtain the flow. On the other hand, when obtaining the flow rate from the flow rate detection output temperature-compensated, it is sufficient to store the data of the characteristic substantially represented by one curve, so that the memory capacity for storing the characteristic data is small. Very little,
Therefore, the process for obtaining the flow rate is very small.

Further, the temperature compensated flow detection output is obtained by subtracting the output change corresponding to the fluid temperature from the flow compensation output which is not temperature compensated, and is thus unified. The possible value and range of the voltage in the characteristic curve are smaller than the possible values and range of the voltage of the characteristic curve group for the flow rate of the flow rate detection output that is not temperature compensated. Therefore, assuming that the range of possible values and the resolution when expressing the flow rate detection output in the data showing the characteristic curve are constant, a relatively large rate of amplification can be achieved for the temperature compensated flow rate detection output. Even if applied, it falls within the expressible range of the characteristic data. On the other hand, if a large rate of amplification is applied to the flow rate detection output that is not temperature-compensated, the amplification rate cannot easily be increased because it exceeds the range in which characteristic data can be easily expressed. Therefore, when the flow rate detection output with temperature compensation is used, amplification at a larger rate is performed and the flow rate measurement with high accuracy is performed than when the flow rate detection output without temperature compensation is used.

On the other hand, in order to provide a flow rate sensor having a function of measuring a fluid temperature, the present invention further divides a constant voltage supplied from a constant voltage generating circuit for driving the flow rate sensor. It is characterized by comprising a temperature measuring resistor for temperature detection for outputting a temperature detection output voltage corresponding to the temperature of the fluid.

According to this, conventionally, a temperature measuring resistor such as a thermistor for measuring a fluid temperature has been separately mounted from the flow sensor, but a constant voltage generating circuit for driving the flow sensor. Is also used to drive this temperature measuring resistor, so that the temperature measuring resistor can be used as an indirectly heated flow sensor that is compactly formed by thin film / thick film forming technology as described above. On the other hand, it is easily implemented as a chip. In addition, since the temperature detection output is output by dividing the constant voltage from the constant voltage generation circuit, the temperature detection output is supplied to a microcomputer for performing A / D conversion of the temperature detection output as it is to obtain a flow rate. There is also the advantage that it can be done.

[0023]

FIG. 1 is a circuit diagram of an indirectly heated flow sensor having a flow water switch function according to an embodiment of the present invention. As shown in FIG. 1, the flow rate sensor includes a heating resistor 11 whose temperature changes according to the flow rate and temperature of a fluid, and a heating resistor detecting temperature measuring resistor provided adjacent to the heating resistor 11. And the voltage divided by the heating resistor detecting temperature measuring resistor 18 is used as a flow detection output according to the flow rate and temperature of the fluid. This flow rate sensor is also a temperature measuring resistor whose resistance-temperature characteristic changes in accordance with the temperature of the fluid, and converts a voltage divided thereby by:
A comparison resistance temperature detector 19 for obtaining a comparison output with respect to the flow rate detection output, the flow rate detection output is compared with the comparison output, and an ON / OFF signal as a flow switch output is output according to the comparison result. Comparator circuit 2
5 is provided.

The heating resistance detecting temperature measuring resistor 18 and the comparative temperature measuring resistor 19 are connected together with a fixed resistor 12 and a variable resistor 13 connected in series via connection points 15 and 16, respectively. 41. The flow sensor also detects the differential voltage of the bridge circuit 41,
Inconsistency in the thermistor constant between the heating resistor detecting temperature measuring resistor 18 and the comparative temperature measuring resistor 19 for obtaining a flow rate detection output corresponding to only the flow rate without substantially depending on the temperature of the fluid. Is provided. Here, this means is constituted by a variable resistor 12 connected in series to the heating resistor 11.

The flow sensor further outputs a voltage obtained by dividing the constant voltage supplied from the constant voltage generating circuit 23 for driving the flow sensor by the fixed resistor 10 as a temperature detection output corresponding to the temperature of the fluid. Temperature measuring resistor 17 for measuring the temperature. The constant voltage generation circuit 23 also supplies a constant voltage to the heating resistor 11 and the bridge circuit 41.

In FIG. 1, reference numeral 21 denotes an operational amplifier whose non-inverting input is connected to the connection point 15 and whose inverting input is grounded, and reference numeral 22 denotes an operational amplifier whose non-inverting input is connected to the connection point 16 and whose inverted input is grounded. , 24 are proportional amplification circuits 24 for proportionally amplifying the difference between the output of the operational amplifier 21 and the output of the operational amplifier 22. The comparator circuit 25 includes the operational amplifier 2
1 and the output of the operational amplifier 22 are input.

In this configuration, the heating resistor 11 generates heat when a constant voltage is applied by the constant voltage generating circuit 23, and the temperature of the heating resistor 11 becomes constant according to the flow rate and temperature of the fluid. A constant output according to the flow rate and the temperature is output via the connection point 15, and an output according to the temperature of the fluid is output via the connection point 16. These outputs are output to operational amplifiers 21 and 22 respectively.
, And their difference is further amplified by the proportional amplification circuit 24.
And is output as a flow rate detection output substantially independent of the temperature of the fluid (temperature compensated). However, in order to actually obtain such a flow rate detection output independent of the fluid temperature, the
It is necessary to adjust the amount of heat generated by the heating resistor 11 to adjust the thermistor constant of the temperature measuring resistor 18 for detecting the heating resistor.

FIG. 2 is a graph showing the characteristics of the flow rate detection output (output voltage) with respect to the flow rate at respective temperatures of 10 ° C., 30 ° C., and 50 ° C. As shown in the figure,
It can be seen that the characteristic curves at each temperature are almost the same, and the characteristics are substantially independent of the temperature of the fluid. In addition, the slope of the characteristic curve shows that the operational amplifier 2 not temperature-compensated.
1 (not particularly shown). That is, the output voltage-flow rate characteristic can be represented as one characteristic curve having a larger slope with very little data as compared with a conventional indirectly heated flow rate sensor in which temperature compensation is not performed.

In the actual flow rate measurement, the microcomputer processes the data based on such data obtained in advance and the output voltage of the proportional amplification circuit 24 by A / D conversion, thereby achieving quick and accurate measurement. The flow rate can be obtained.

When the comparative resistance bulb 19 is formed of a thermistor, a thermistor having an optimum characteristic for obtaining an output voltage excluding the above-mentioned temperature dependence is obtained due to a variation in thermistor constant. It is difficult to do.

Therefore, it is necessary to correct in advance the variation of the thermistor constant between the temperature measuring resistor 18 for detecting the heating resistor and the temperature measuring resistor 19 for comparison by the variable resistor 42. That is, by adjusting the variable resistor 42, the amount of heat generated by the heating resistor 11 is adjusted to change the characteristics of the heating resistor detecting temperature measuring resistor 18 (the slope in the resistance temperature characteristic, that is, the thermistor constant). Thereby, the characteristics of the heating resistor detecting temperature measuring resistor 18 can be more adapted to the compensation characteristics of the comparative temperature measuring resistor 19.

It is also necessary to adjust the characteristics of the comparative resistance bulb 19 in accordance with the variation in the characteristics of the comparative resistance bulb 19, the method of attaching to the piping, the diameter of the piping to which the sensor is attached, and the like. May occur.

In view of this point, the resistor 13 is a variable resistor having a small temperature coefficient of resistance, and is used when the characteristics of the comparative resistance thermometer 19 do not always match the characteristics of the heating resistance detecting temperature detector 18. However, by adjusting the resistance value of the variable resistor 13, the characteristic of the output from the connection point 16 with respect to the temperature is corrected, so that there is substantially no dependence on the temperature of the fluid, as shown in FIG. , A flow rate detection output can be obtained. The variable resistor may be connected in parallel to the comparative resistance bulb 19, or the connection point 16 and the comparative resistance bulb 19 may be connected.
The same effect can also be obtained by inserting the variable resistor between them and adjusting the resistance value of the variable resistor.

On the other hand, the outputs of the operational amplifiers 21 and 22 input to the comparator circuit 25 are compared in the comparator circuit 25, and the difference between them is
When the flow rate increases, the output becomes the flow switch output when the flow rate becomes equal to or more than the predetermined value T1, and when the flow rate decreases, the output becomes off when the flow rate becomes equal to or less than the predetermined value T2. The value T1 is larger than the value T2, thereby preventing chattering in the flow switch output.

FIG. 3 is a graph illustrating the output of the comparator circuit 25 when the open collector system is used for a part of the circuit. The horizontal axis of the graph indicates the flow rate value, which corresponds to the difference between the outputs of the operational amplifiers 21 and 22. The vertical axis indicates the output of the comparator circuit 25 based on the resistance value. In this case, T1 ≒ 4.0 (liter / liter)
Min), and T2 ≒ 3.5 (liter / min). As described above, it is preferable that the output of the flowing water switch from the comparator circuit 25 be a resistance value because the output can be directly replaced with the output of the conventional flowing water switch having the resistance value shown in FIGS. 9 and 10. .

On the other hand, the voltage is divided by the fixed resistor 10 and the heating resistor temperature measuring resistor 17 which is output via a connection point 14 between the fixed resistor 10 and the heating resistor temperature measuring resistor 17. The temperature detection output shows a characteristic as shown in FIG. 4 with respect to the temperature of the fluid. Therefore, if data representing such characteristics is stored in a memory in advance, the temperature of the fluid can be determined by A / D converting the temperature detection output and processing the data with reference to the data by a microcomputer. it can.

FIG. 5 is a schematic sectional view showing the flow sensor of FIG. 1 attached to the pipe 34, and FIG. 6 is a plan view showing a state of the bottom of the cap. In these figures, 31 is a flow rate detecting unit formed by chipping the above-described heating resistor 11, the heating resistor detecting temperature measuring resistor 18, the fixed resistor 12, and the like, and 32 is the temperature measuring resistor 17, the fixed resistor 10 And a temperature compensator 33 formed by chipping the comparative resistance temperature detector 19, the variable resistor 13 and the like. These chips are formed at the bottom of a stainless steel cap 30. Then, as shown in FIG.
Are located. That is, the portion corresponding to these chips is the one-dot chain line portion 20 in FIG. The arrow 36 in FIG. 5 indicates the direction of the water flow in the pipe 34.

Reference numeral 26 denotes the operational amplifier 2 shown in FIG.
1, 22, a comparator circuit 25, a proportional amplifier circuit 24,
A printed circuit board on which the constant voltage generating circuit 23 and the like are formed, 27 is a waterproof lid for protecting each chip in the cap 30 and the printed circuit board 26 and the like, 29 is a connection between each chip in the cap 30 and the printed circuit board 26 Reference numeral 28 denotes a wiring for connecting the printed board 26 to the outside. Wiring 29
Is a wiring extracting portion 35 provided at the bottom of the cap 30.
Is connected to each chip via a.

As described above, the flow rate sensor according to the present embodiment easily integrates the flow rate detection function, the flow water switch function, and the fluid temperature detection function into the pipe 34 in a form that is compactly integrated as one mounting unit. Can be attached.

[0040]

As described above, according to the present invention, based on the indirectly heated flow rate sensor, the flow rate detection output depending on the flow rate and temperature of the fluid and the resistance-temperature characteristic depending on the temperature of the fluid are obtained. Compared with the voltage divided by the changing resistance thermometer for comparison, the on / off signal as the output of the water switch is output according to the comparison result, so that it is affected by foreign matter in the fluid. Thus, a flow sensor that can detect a flow rate without causing a pressure loss in a fluid and has a highly reliable flow switch function can be easily provided as one compact mounting unit. Further, since it is easy to provide a dead zone for preventing chattering with the output of the flowing water switch in an electric circuit, the advantage of the indirectly heated flow sensor, that is, the advantage of being compact and causing no pressure loss, is utilized. On the other hand, the function of the flowing water switch can be easily integrated while satisfying both specifications.

Further, the temperature difference of the bridge circuit and the temperature measuring resistor for detecting the heating resistor and the measuring resistor for comparison are used to make the flow rate detection output according to only the flow rate substantially independent of the fluid temperature. Since the means for correcting the mismatch between the thermistor constants between the thermal resistance elements is provided, the amount of processing by a microcomputer or the like for obtaining the flow rate and the memory capacity required for processing can be significantly reduced. Further, by amplifying and using the temperature compensated flow detection output, a flow measurement with high accuracy can be performed.

Further, a constant voltage supplied from a constant voltage generating circuit for driving the flow rate sensor is divided by the temperature measuring resistor to output a temperature detection output voltage corresponding to the temperature of the fluid. In addition, the flow sensor having the function of measuring the fluid temperature can be easily provided as one compact mounting unit. In this case, there is also an advantage that the temperature detection output can be directly A / D converted and supplied to the microcomputer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an indirectly heated flow sensor having a flow switch function according to an embodiment of the present invention.

FIG. 2 is a graph showing a temperature-compensated flow detection output (output voltage) -flow characteristic output by the flow sensor of FIG. 1;

FIG. 3 is a graph illustrating an output of a comparator circuit in the flow sensor of FIG. 1;

FIG. 4 is a graph showing a temperature detection output (output voltage) -temperature characteristic in the flow sensor of FIG. 1;

FIG. 5 is a schematic sectional view showing the flow sensor of FIG. 1;

FIG. 6 is a plan view showing a state of a cap bottom of the flow sensor of FIG. 5;

FIG. 7 is a schematic diagram showing a conventional flow sensor.

8 is a graph showing the relationship between the flow rate of water and the number of output pulses per unit time in the flow rate sensor of FIG.

FIG. 9 is a schematic view showing a conventional water switch.

FIG. 10 is a graph showing a relationship between a flow rate and an on / off output of a reed switch in the flow rate switch of FIG. 9;

[Explanation of symbols]

10: fixed resistor, 11: heating resistor, 12: fixed resistor,
13: Variable resistance, 14, 15, 16: Connection point, 17: Heating resistor, RTD for detecting temperature, 18: RTD for detection,
19: comparative resistance thermometer, 20: dashed line portion, 21,
22: operational amplifier, 23: constant voltage generating circuit, 24: proportional amplifier circuit, 25: comparator circuit, 26: printed circuit board, 27: waterproof lid, 28, 29: wiring, 30: cap, 31: flow rate detecting unit, 32 Reference numeral: hot water temperature detector, 33: temperature compensator, 34: pipe, 35: wiring outlet, 36: arrow indicating water flow direction, 41: bridge circuit, 42: variable resistor (adjustment means).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Kawanishi 1333-2 Mitsui Metal Mining Co., Ltd. Shikisha Research Institute

Claims (2)

[Claims] 1. A heating resistor, the temperature of which changes in accordance with the flow rate and temperature of a fluid, and a heating resistor for detecting a heating resistor provided adjacent to the heating resistor. In an indirectly heated flow sensor that uses the voltage divided by the detection resistance temperature detector as a flow detection output according to the flow rate and temperature of the fluid, the resistance-temperature characteristic changes according to the temperature of the fluid. A resistance temperature detector, a voltage divided thereby, a comparison resistance temperature detector for obtaining as a comparison output with respect to the flow rate detection output, and comparing the flow rate detection output and the comparison output, A comparison circuit that outputs an on / off signal as a flow switch output in accordance with the comparison result, a bridge circuit including the heating resistor detection temperature measuring resistor and the comparison temperature measuring resistor as components, Bridge circuit A thermistor between the heating resistor detecting temperature measuring resistor and the comparative temperature measuring resistor for making the difference voltage a flow detection output corresponding to only the flow rate without substantially depending on the temperature of the fluid; A flow sensor having a flow switch function, comprising: means for correcting a mismatch between constants. 2. A temperature sensing resistor for outputting a voltage obtained by dividing a constant voltage supplied from a constant voltage generating circuit for driving the flow rate sensor as a temperature detection output corresponding to the temperature of the fluid. The flow sensor according to claim 1, further comprising: