JPH1194617A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow sensor that is seldom affected by variations in the resistance value of each temperature-measuring resistor. SOLUTION: The flow sensor 1 includes a heating element 2 placed in a flow passage, a first temperature-measuring element 3 placed on the upstream side from the heating element 2 within the flow passage, and a second temperature-measuring element 4 placed on the downstream side from the heating element 2. A heating device 5 has a current source 6 supplying a constant current I 2 to the heating element 2 to heat the same. The non-inverted input terminal and inverted input terminal of a temperature measuring circuit (differential amplifier) 7 are connected, respectively, to (d) and (e) points at both of the terminals of the heating element 2 to detect the voltage between the terminals of the heating element 2 to detect the temperature of the heating element 2. The first temperature-measuring element 3 and the second temperature- measuring element 4 are connected in series with each other, and a constant current I 1 is supplied thereto by a constant current source 9. A voltage difference detecting device 10 includes a comparator 11 detecting the voltage between the terminals of the first temperature-measuring element 3, a comparator 12 detecting the voltage between the terminals of the second temperature-measuring element 4, and a comparator 13 comparing the output voltage of the comparators 11, 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor used for a gas flow meter, a flow meter, and the like.

[0002]

2. Description of the Related Art Japanese Utility Model Publication No. Hei 8-6269 discloses that a heater, an upstream temperature sensor disposed on the upstream side of a fluid flow from the heater, and a fluid flow from the heater are provided on the semiconductor substrate. There is disclosed a technique of forming a downstream temperature sensor disposed on the downstream side and measuring the presence / absence of fluid flow based on a change in resistance value of the upstream and downstream temperature sensors.

In this technique, a bridge circuit having upstream and downstream temperature sensors as circuit elements is used to detect a difference in resistance between an upstream temperature sensor and a downstream temperature sensor. Are connected to the inverting and non-inverting input terminals of a differential amplifier, and the output of this differential amplifier is obtained as a sensor output.

[0004]

However, since the bridge circuit has high sensitivity with respect to the resistance value, the output of the differential amplifier has a large value due to the variation in the resistance value generated in the upstream and downstream temperature sensors constituting the bridge circuit. That makes a difference.

[0005] In order to solve this problem, the prior art attempts to compensate for the variation in the resistance value by taking the difference between the output of the bridge circuit in a state where the heater is heated and a state in which the heater is not heated.

However, since the differential amplifier cannot be used in a state where the output of the differential amplifier is saturated, it is necessary to suppress variations in the resistance values generated in the upstream and downstream temperature sensors constituting the bridge circuit. However, there is a problem that this leads to an increase in manufacturing cost.

[0007] Further, in the above-mentioned conventional technique, there is also a problem that a difference occurs in a measurement result due to a fluctuation in temperature of a fluid.

An object of the present invention is to provide a flow sensor which is hardly affected by variations in the resistance value of a resistance temperature detector.

Another object of the present invention is to provide a flow sensor having a simple circuit configuration.

Another object of the present invention is to provide a flow sensor which can easily operate the differential amplifier even if the differential amplifier is used for detecting the voltage between the terminals of the resistance temperature detector.

Another object of the present invention is to provide a flow sensor capable of reducing the temperature dependency at the time of measurement and improving the accuracy of measurement.

Another object of the present invention is to provide a flow sensor which can easily be matched with another device.

Another object of the present invention is to provide a flow sensor in which zero output can be easily adjusted.

Another object of the present invention is to provide a flow sensor capable of adjusting the zero output without making the fluid flow rate zero.

Another object of the present invention is to provide a flow sensor in which the influence of the temperature of the fluid is corrected to improve the accuracy of the sensor output.

[0016]

According to a first aspect of the present invention, there is provided a heating element disposed in a fluid flow path and generating heat, and a first measurement element disposed upstream of the heating element and the flow path. A first resistor connected in series with a temperature resistor, a second resistor connected in series with the first resistor in a downstream side of the flow path from the heating element, and a second resistor connected in series with the first resistor; And a current source for supplying a constant current to the second resistance temperature detector, and a difference detecting a difference between a terminal voltage of the first resistance temperature detector and a terminal voltage of the second resistance temperature detector. And a voltage detecting device.

Therefore, instead of the conventional bridge circuit, the first and second temperature measuring resistors connected in series and supplied with a constant current are used. Even if the variation is larger than before, it can be used.

Further, since the first and second resistance temperature detectors are connected in series and flow the same current, the influence of the output fluctuation of the current source on the detection of the difference between the voltages at both terminals can be reduced.

Further, since the circuit configuration can be relatively simplified, the stability of the circuit can be improved.

According to a second aspect of the present invention, there is provided a voltage stabilizing device for maintaining a constant potential between the first and second resistance temperature detectors.

Therefore, by maintaining the potential between the first and second resistance temperature detectors constant, the potential of the lower terminal of the first or second resistance temperature detector having the lower potential is reduced. It can be prevented from becoming zero.

According to a third aspect of the present invention, the voltage stabilizer maintains the potential between the first and second resistance temperature detectors at a GND level.

Therefore, by maintaining the potential between the first and second resistance temperature detectors at the GND level, the potential of the positive terminal of the first or second resistance temperature detector having the higher potential is determined. Can be suppressed only to the voltage between the terminals of the first or second resistance temperature detector. When both positive and negative power supplies can be used for the power supply of the differential amplifier, the negative side power supply voltage can be effectively used. Thus, it is possible to suppress the magnitude of the potential of the higher potential plus terminal and the potential of the lower minus terminal of the first or second resistance temperature detector.

Also, by adding the potential of the positive terminal side of the first resistance temperature detector and the potential of the negative terminal side of the second resistance temperature detector, the difference between the voltages between the two terminals can be detected. An adder can be used.

According to a fourth aspect of the present invention, in the differential voltage detecting device, the addition is performed by adding the potential on the plus terminal side of the first resistance temperature detector and the potential on the minus terminal side of the second resistance temperature detector. It is characterized by having a vessel.

Therefore, the difference between the voltages between the two terminals is detected by an adder that adds the potential on the plus terminal side of the first resistance temperature detector and the potential on the minus terminal side of the second resistance temperature detector. be able to.

According to a fifth aspect of the present invention, there is provided a dividing means for dividing an output of the differential voltage detecting device by a voltage between terminals of the first or second resistance temperature detector. .

Therefore, by dividing the output of the differential voltage detecting device by the voltage between the terminals of the first or second resistance temperature detector, it is possible to obtain a sensor output at zero flow rate which does not change with the temperature of the fluid. .

[0029] The invention according to claim 6 is characterized in that it comprises subtraction means for subtracting a predetermined constant from the output of the division means.

Therefore, the sensor output when the flow rate of the fluid is zero can be arbitrarily set.

The invention according to claim 7 is characterized in that the subtraction means performs subtraction with a value equal to the output of the division means when there is no fluid flow as a predetermined constant.

Therefore, the sensor output can be made zero.

The invention according to claim 8 is provided with a heat generation stopping device for stopping heat generation of the heating element, wherein the subtraction means sets a value equal to an output of the division means when the heating element does not generate heat as a predetermined constant. It is characterized by performing subtraction.

Accordingly, the heat generation of the heating element can be stopped, and the sensor output can be reduced to zero.

According to a ninth aspect of the present invention, there is provided a temperature sensor disposed in the flow path for detecting the temperature of the fluid, and a correction means for correcting the output of the subtraction means based on the detection signal of the temperature sensor. It is characterized by having.

Therefore, the temperature of the fluid can be detected, and the output after the subtraction can be corrected based on the detected signal.

According to a tenth aspect of the present invention, the heating element generates heat when supplied with electric power, and includes a voltage sensor for detecting a voltage between terminals of the heating element, and a detection signal of the voltage sensor. Correction means for correcting the output of the subtraction means based on the correction value.

Therefore, by detecting the voltage between the terminals of the heating element, the output after the subtraction can be corrected without separately detecting the temperature of the fluid.

According to the eleventh aspect of the invention, there is provided a correction means for correcting the output of the subtraction means based on the voltage between at least one of the first and second resistance temperature detectors. It is assumed that.

Accordingly, the voltage between the terminals of the first and second resistance temperature detectors contains information on the temperature fluctuation of the fluid,
The output after the subtraction can be corrected based on this signal.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a circuit diagram of a flow sensor 1 according to a first embodiment of the present invention.

The flow sensor 1 includes a heating element 2 disposed in a flow path of a fluid to be measured, a first temperature measuring element 3 disposed upstream of the heating element 2 in the flow path, And a second temperature measuring element 4 disposed downstream of the heating element 2.

The heating element 2 and the first and second temperature measuring elements 3 and 4 are installed at a place where they are thermally coupled with the fluid. The place thermally coupled to the fluid is a place where there is a correspondence between the temperature of the fluid and the temperatures of the heating element 2 and the first and second temperature measuring elements 3 and 4. For example, the surface of a flow path using a metal such as copper, aluminum, or iron stainless steel having good heat conductivity in a fluid or a flow path of the fluid.

The first and second temperature measuring elements 3 and 4 are
It is arranged at a place thermally coupled to the heating element 2. Heating element 2
The location thermally coupled to the first location is a location where a corresponding relationship occurs between the temperatures of the first and second temperature measuring elements 3 and 4 and the temperature of the heating element 2. For example, in the vicinity of the heating element 2 where the heat of the heating element 2 is transmitted to the first and second temperature measuring elements 3 and 4 by the heat transfer of the fluid or the flow path material.

The heating element 2 forms a circuit element of the heating device 5.
The heating device 5 includes a current source 6 that supplies a constant current I2 to the heating element 2 to generate heat. Further, a non-inverting input terminal and an inverting input terminal of a temperature measuring circuit (differential amplifier) 7 are connected to points d and e (ground side) on both terminals of the heating element 2, respectively.
The temperature of the heating element 2 can be detected by detecting the voltage between the terminals of the heating element 2.

The first and second temperature measuring elements 3 and 4 have relatively high resistance temperature coefficients and form circuit elements of the temperature measuring device 8. The temperature measuring device 8 connects the first temperature measuring body 3 and the second temperature measuring body 4 in series, and supplies a constant current I1 from a constant current source 9.

The non-inverting input terminal and the inverting input terminal are connected to points a and b on both terminal sides of the first temperature measuring element 3, respectively. A comparator 11 for detecting a voltage between the terminals, and points b and c on both terminals of the second temperature measuring element 4
A non-inverting input terminal and an inverting input terminal are connected to the
And the output terminals of the comparators 11 and 12 are connected to an inverting input terminal and a non-inverting input terminal, respectively, and compare the output voltages of the comparators 11 and 12. And a comparator 13.

Next, the operation of the flow sensor 1 will be described.

The heat generated by the heating element 2 is transmitted to the first and second resistance temperature detectors 3 and 4. If the first and second resistance temperature detectors 3 and 4 have a positive temperature coefficient of resistance, the first
And the resistance values Rs1, Rs2 of the second resistance temperature detectors 3, 4
Rises. Since the current flowing through the first and second resistance temperature detectors 3 and 4 is constant, the first and second resistance temperature detectors 3 and 4
4, the voltage between the terminals increases.

When a flow is generated in the fluid, the heat of the first and second resistance temperature detectors 3 and 4 is taken by the fluid. The amount of heat taken is correlated with the flow velocity of the fluid. Then, the resistance value of the first and second resistance temperature detectors 3 and 4 decreases due to the deprivation of heat. Then, the voltage between the terminals of the first and second resistance temperature detectors 3 and 4 decreases.

FIG. 2 shows the positions of the fluid flow paths (from the left to the right of the horizontal axis, from upstream to downstream of the fluid flow paths), and the temperatures of the first and second resistance temperature detectors 3 and 4. 6 is a graph showing the relationship of.

As shown in FIG. 2A, when there is no fluid flow, heat is equally transmitted to the upstream side and the downstream side of the heating element 2. Therefore, the temperatures at the position (A) of the first resistance temperature detector 3 and the position (B) of the second resistance temperature detector 4 are substantially equal, and the first resistance temperature detector 3 and the second temperature measurement element are equal. The voltage between the terminals of the thermal resistor 4 also becomes equal, and the output voltage from the output terminal 14 of the comparator 13 becomes substantially zero.

As shown in FIG. 2B, when there is a flow of the fluid, the heat of the heating element 2 is transferred to the first upstream side of the flow path of the fluid.
The second resistance thermometer 4 downstream of the resistance thermometer 3
Many are transmitted to. Therefore, the temperature at the position (B) of the second resistance temperature detector 4 becomes higher than the position (A) of the first resistance temperature sensor 3. The solid line in FIG. 2B shows the case where there is a fluid flow, and the imaginary line shows the case where there is no fluid flow. As a result, the resistance value Rs1 of the first resistance temperature detector 3
The resistance value Rs2 of the temperature measuring resistor 4 becomes higher, and the voltage between the terminals of the second temperature measuring resistor 4 becomes higher than the voltage between the terminals of the first temperature measuring resistor 3. A voltage corresponding to the difference is output from the output terminal 14.

Since the temperature difference between the first and second resistance temperature detectors 3 and 4 changes according to the flow velocity of the fluid, the output terminal 14
Can be used as a fluid velocity signal. Then, if the step area and cross-sectional shape of the flow path are known, the flow rate of the fluid can be known from the flow velocity signal.

The flow sensor 1 is replaced with a conventional bridge circuit, and is connected in series and has a first current I1.
Since the first and second resistance temperature detectors 3 and 4 are used, the first and second resistance temperature detectors 3 and 4 can be used even if the variation is larger than in the related art.

When the current I1 of the current source 9 fluctuates, the voltage between the terminals of the first and second resistance temperature detectors 3 and 4 also fluctuates. For detection, it is necessary to suppress the fluctuation of the current I1. However, the flow sensor 1 includes the first and second resistance temperature detectors 3,
4 are connected in series and the same current I1 is flowing, so that the voltage between the terminals of the first and second resistance temperature detectors 3 and 4 fluctuates in phase. Therefore, the in-phase voltage fluctuation is canceled in the difference voltage detection device 10, and the influence of the fluctuation of the current I1 of the current source 9 on the output of the difference voltage detection device 10 can be reduced.

Since the circuit configuration is relatively simple,
The stability of the circuit can be improved.

The heating element 2 is supplied with a constant current I2 to generate heat. However, the heating element 2 may be heated by supplying a low voltage or a constant power. Further, heat may be generated by driving at a low temperature that is controlled to be higher by a certain temperature than the temperature of the fluid.

[Second Embodiment of the Invention] FIG. 3 is a circuit diagram of a flow sensor 1 according to a second embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the first embodiment, and detailed description is omitted.

This flow sensor 1 includes a voltage stabilizer 21
And a voltage source 22.

The voltage stabilizer 21 has resistors 23 and 24 and a differential amplifier 25 connected in series.
The non-inverting input terminal of the differential amplifier 25 is connected to a point f, which is a connection point between the resistors 23 and 24, and the inverting input terminal is connected to a point b. The output terminal of the differential amplifier 25 is connected to point c.

The voltage source 22 uses a battery such as a lithium battery, supplies a constant voltage V to the resistors 23 and 24 connected in series, and serves as a power source for each amplifier and current source.

The difference voltage detecting device 10 includes an adder 27 connected in a negative feedback loop with a resistor 26 interposed.
A voltage follower 2 is connected to the inverting input terminal of the adder 27.
8. The voltage at point a is input via the resistor 29. Also,
The voltage at point c is input via the resistor 30. The voltage at point f is input to the non-inverting input terminal of the adder 27.

The temperature measuring circuit 7 has a negative feedback connection instead of grounding the inverting input terminal.

Next, the operation of the flow sensor 1 according to this embodiment will be described.

A constant voltage V is supplied to the resistors 23 and 24 connected in series, and this voltage V is applied to the resistors 23 and 24.
Is divided into a value proportional to the magnitude of the voltage, and the point f is maintained at a constant voltage obtained by subtracting the voltage drop by the resistor 23 from the voltage V. When the resistances of the resistors 23 and 24 are equal and R1, the voltage at the point f becomes V / 2. The differential amplifier 25 is the second
The negative input terminal and the non-inverting input terminal thereof are virtually grounded through the negative feedback connection via the temperature measuring element 4 of FIG. That is, the voltages at the points f and b are controlled to be equal to V / 2.

Since the input impedance of the operational amplifier is large, no current flows from the point b to the inverting input terminal of the differential amplifier 25. Also, no current flows from the point a to the non-inverting input terminal of the voltage follower 28. Therefore, the same current flows through the first and second temperature measuring elements 3 and 4.

The resistance value R of the first and second temperature measuring elements 3 and 4
s1 and Rs2 change according to the flow of the fluid. But b
Since the voltage at the point is maintained at V / 2, the voltage at the point a becomes the value “V / 2 + Rs1 × I1” obtained by adding the voltage between the terminals of the first temperature measuring element 3 to the voltage V / 2 at the point b. . Further, the voltage at point c is a value “V” obtained by subtracting the terminal voltage of Rs2 from the voltage V / 2 at point b.
/ 2−Rs2 × I1 ″.

The adder 27 of the difference voltage detecting device 10 adds the values at the points a and c based on the voltage V / 2 at the point f.
As a result, the output of the differential voltage detector 10 output from the output terminal 31 becomes “Rs2 × I1−Rs1 × I1”, and the difference between the voltages of the first and second temperature measuring elements 3 and 4 is detected. can do. The output of the differential voltage detecting device 10 is V / 2 when there is no fluid flow. If there is a flow of the fluid, it swings from V / 2 to the plus side or the minus side depending on the direction and the flow velocity.

In general, an operational amplifier cannot process a voltage close to its power supply voltage. For example ± 1
When 2V is used as the power supply, output of about + 11V or more and about-
It cannot handle voltages higher than 12V. The same applies to the case where a battery is used as a power source as in this embodiment. Assuming that the voltage of the battery is 3.5 V, a voltage of about 3 V or more and about 0.5 V or less cannot be handled.
In the case of the first embodiment, if the battery is used as a power source, the point c in FIG. 2 becomes 0 V, so that the comparator 12 including the operational amplifier cannot operate. It is necessary to use a rail-to-rail operational amplifier that considers the use of a battery as a power supply. However, this rail-to-rail operational amplifier corrects so that an area where a general operational amplifier cannot be used can be actively handled, so that accuracy and stability are inferior, and the cost of the operational amplifier increases.

In order to avoid such a problem, a configuration may be adopted in which the voltage range in which the operation of the operational amplifier is difficult is not required. Therefore, in this embodiment, the connection point b of the first temperature measuring elements 3 and 4 is set to the center V / 2 of the battery voltage as described above. Thereby, it is possible to prevent point c from becoming 0V. Also, since the voltage at point b does not move,
Considering the point b as the center, the first and second thermometers 3, 4
Are in opposite directions of positive and negative. Therefore, as described above, the difference voltage detection device 10 can be configured using the adder 27, and a plurality of comparators (differential amplifiers) 11, 12, 13 as in the first embodiment. The circuit can be simplified as compared with the case where is used.
Thereby, the stability of the circuit is improved, the cost can be reduced, and a single power supply such as a battery can be used as the power supply.

In this embodiment, the voltage of the voltage stabilizer 21 is set to V / 2.
V / 2 if within the operable voltage of the voltage follower 28
However, the present invention is not limited to this, and another voltage value may be set.

[Third Embodiment of the Invention] FIG. 4 is a circuit diagram of a flow sensor 1 according to a third embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the second embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment is different from the second embodiment in the circuit configuration in that the resistance 2
3 and 24 are omitted, the non-inverting input terminal of the differential amplifier is grounded and this is set to point f, and the non-inverting input terminal of the adder 27 is grounded via the first temperature measuring element 34; Further, both positive and negative power supplies using voltage sources 32 and 33, which are batteries such as lithium batteries, are used as power supplies for the amplifiers and current sources instead of the voltage source 22.

In the above circuit configuration, since the input terminal of the differential amplifier 25 is virtually grounded, the voltages at the points b and f are controlled so as to be equal to the ground voltage.

Incidentally, in the first embodiment, c
Since the point is the ground voltage, the voltage at point a is a voltage obtained by adding the inter-terminal voltage of the first temperature measuring element 3 and the inter-terminal voltage of the second temperature measuring element 4. That is, the voltage at the point a is close to the positive power supply voltage when the current I1 is a positive current, and close to the negative power supply voltage when the current I1 is a negative current. Then the second
As described in the embodiment, the operating voltage range of the voltage follower (op-amp) 28 must be considered.

However, in this embodiment, the connection point b between the first temperature measuring elements 3 and 4 is set to the ground voltage.
Thus, the voltage at point a can be suppressed to only the voltage between the terminals of the first temperature measuring element 3. Further, the voltage sources 32 and 33
Since both positive and negative power supplies are used, the negative power supply voltage can be used effectively, and the magnitudes of the voltages at points a and c can be suppressed.

Further, since the voltage at the point b is constant, the voltage between the terminals of the first and second temperature measuring elements 3 and 4 is in the opposite positive and negative directions when the point b is considered as the center. For this reason, the difference voltage detection device 10 can be configured using the adder 27, and can simplify the circuit configuration compared to the case where a plurality of comparators (differential amplifiers) are used as in the first embodiment. Therefore, it is possible to improve the stability of the circuit and reduce the cost.

[Fourth Embodiment of the Invention] FIG. 5 is a circuit diagram of a flow sensor 1 according to a fourth embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the third embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment is different from the third embodiment in the circuit configuration in that an output terminal of a voltage follower 28 is connected to an amplifier 41 having an amplification factor A1 and an adder 27 is provided. Amplifier 42 with an amplification factor of A2
Is connected to the output terminals of the amplifiers 41 and 42, and a dividing device 43 for realizing the dividing means of the present invention is connected. In this dividing device 43, "the output of the amplifier 42 ÷ the output of the amplifier 41"
Is performed, and the result is output from the output terminal 44.

In the above circuit configuration, if the voltages between the terminals of the first and second temperature measuring elements 3 and 4 are Vrs1 and Vrs2, respectively, the output voltage Vg of the voltage follower 28 becomes “Vg =
(Vrs2-Vrs1) ", the output voltage Vh of the adder 27
Is “Vh = Vrs1”.

That is, the output Vi of the dividing device 43 is "V
i = (A2 × Vg) / (A1 × Vh) = A2 × (Vrs
2−Vrs1) / (A1 × Vrs1) ”.

When the flow velocity of the fluid is zero, "V
rs2 / Vrs1 ″ is 1. The resistance value R
Considering the variation of s1 and Rs2, this value is 1.0
Various values such as 1, 0.98 can be taken.

Here, a change in the temperature of the fluid will be considered. When the temperature changes, the values of the voltages Vrs1 and Vrs2 change at a rate according to the resistance temperature coefficients of the first and second temperature measuring elements 3 and 4. However, since the rate of change between the voltages Vrs2 and Vrs1 becomes the same, if the division of "Vrs2 / Vrs1" is performed, the temperature change is reduced to about the same, and the result of this division is not affected. Even if the temperature coefficients of the first and second temperature measuring elements 3 and 4 vary, and even if they are slightly different, the voltage Vrs
1. The magnitude of the change of Vrs2 with temperature is the voltage Vrs.
1, the influence is small because it is smaller than the magnitude of Vrs2.
Even in the case of platinum having a relatively large temperature coefficient of resistance, the temperature coefficient of resistance is about 3000 ppm / ° C. in this way,
When the flow velocity of the fluid is zero, the value of “Vrs2 / Vrs1” is hardly affected by a change in the temperature of the fluid.

The relationship between the resistances Rs1 and Rs2 and the grounding of the heating element Rh is specific to the flow sensor 1. That is, “Vr” when the flow rate of one flow sensor 1 is zero.
The change of the value of s2 / Vrs1 ″ depending on the temperature is small.

When a fluid flows, the resistance value Rs1 of the first temperature measuring element 3 becomes smaller than the resistance value Rs2 of the second temperature measuring element 4, and the ratio thereof corresponds to the flow velocity. That is, "Vr
The value of s2 / Vrs1 "becomes larger than when the flow rate is zero. When the fluid flows backward, it becomes smaller than when the flow rate is zero.

Then, when the value of “Vrs2 / Vrs1-1” is obtained, when there is no flow in the fluid, it takes a constant value for each device, and when there is a flow of the fluid, it becomes a large value according to the flow velocity. By transforming this equation, "(Vrs2-Vrs
1) / Vrs1 ". Therefore, since the amplification factors A1 and A2 of the amplifiers 41 and 42 are constants, the output of the divider 43 becomes substantially constant regardless of the temperature of the fluid when there is no flow of the fluid. In addition, when the fluid has a flow, an output corresponding to the flow velocity is output, and in the case of a backflow, the value has an opposite sign.

As described above, when the output of the divider 43 is used as a flow velocity signal, the state of zero flow velocity can be accurately measured regardless of the fluid temperature.

In the above example, the difference voltage detecting device 10
Is divided by the terminal voltage Vrs1 of the first temperature measuring element 3, but may be divided by the terminal voltage Vrs2 of the second temperature measuring element 4.

The dividing device 43 can be constituted by, for example, a microcomputer operated by a predetermined program.

[Fifth Embodiment of the Invention] FIG. 6 is a circuit diagram of a flow sensor 1 according to a fifth embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the fourth embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment differs from the fourth embodiment in terms of the circuit configuration in that a constant E is subtracted from the output of the divider 43 and output from the terminal 46. The difference is that a subtraction device 45 for realizing the subtraction means is provided.

In the above circuit configuration, the output of the terminal 46 becomes substantially constant when the flow velocity of the fluid is zero. If this value is set in advance as a constant E, the output of the terminal 46 can be made zero. In other words, when the fluid velocity is zero,
The output of the flow sensor 1 can be made zero. The output of the terminal 46 can be set to an arbitrary value by selecting the value of the constant E.

The subtraction device 43 can be realized by, for example, a microcomputer that operates according to a predetermined program.

[Sixth Embodiment of the Invention] FIG. 7 is a circuit diagram of a flow sensor 1 according to a sixth embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the fifth embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment differs from the fifth embodiment in the circuit configuration in that the output terminal of the divider 43 is connected to the constant part 47 of the subtractor 45 and Is that the constant E can be replaced with the output value of the divider 43.

In the above circuit configuration, when the flow velocity of the fluid is zero, the output of the flow sensor 1 can be made zero by replacing the constant E of the subtraction device 45 with the output value of the division device 45. That is, the zero output can be adjusted. In particular, after the flow sensor 1 is manufactured, the apparatus is first placed in a state where the flow velocity of the fluid is zero, and the constant E is replaced, whereby the zero output can be easily adjusted. Further, even during the use of the flow sensor 1, the flow sensor 1 is periodically set to the zero state, and the constant E is replaced, whereby the zero output fluctuation over time can be corrected, and accurate flow velocity measurement can be performed.

[Seventh Embodiment of the Invention] FIG. 8 is a circuit diagram of a flow sensor 1 according to a seventh embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the sixth embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment is different from the sixth embodiment in terms of circuit configuration in that the heat-generating device 5 is provided with a cut-off device 51 for realizing the heat-generating stop device of the present invention. is there. The current I2 generated by the current source 6 due to the switching of the cutoff device can be applied to the heating element 2 or can flow to the resistor 52.

In the above circuit configuration, the shut-off device 51
By stopping the power supply to the heating element 2, the temperature of the first and second temperature measuring elements 3, 4 can be made equal to the temperature of the fluid.
Even if there is a flow of the fluid, the temperatures of the first and second thermometers 3 and 4 do not change because both the first and second thermometers 3 and 4 have the same temperature as the fluid. Therefore, in a state in which the heating element 2 does not generate heat, the output of the flow sensor 1 does not change even if the flow velocity of the fluid is zero. Here, the flow sensor 1
Is almost unaffected by the temperature of the heating element 2 when the flow rate is zero, just as it is not affected by the temperature of the fluid when the flow velocity is zero. That is, the output of the flow sensor 1 when the heating element 2 does not generate heat is substantially equal to the output of the flow sensor 1 when the heating element 2 generates heat and the flow velocity is zero.

The output of the flow sensor 1 can be made zero by making the heat generating element 2 not generate heat by the cutoff device 51 and replacing the value of the constant E of the subtraction device 45.
At this time, regardless of whether or not the fluid has a flow, the output at zero flow velocity can be made zero.

In some cases, it is difficult for the flow sensor 1 to create a zero flow state during use. For example, in an application such as a home gas meter, once it is installed, it is hardly removed and recalibrated. Even in such use condition,
By cutting off the current to the heating element 2, it is possible to adjust the output when the flow velocity is zero.

In the above example, the path of the current source 6 to the heating element 2 is cut off by switching. However, it may be performed by adjusting the current value I2 generated by the current source 6 to zero. Good.

[Eighth Embodiment of the Invention] FIG. 9 is a circuit diagram of a flow sensor 1 according to an eighth embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the seventh embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment differs from the sixth embodiment in the circuit configuration in that it has a temperature sensor 61 and a correction device 65. The temperature sensor 61 includes a temperature measuring resistor 63 having a large resistance temperature coefficient.
And a current source 6 for supplying a constant current I3 to the resistance bulb 63.
2 and a temperature measuring circuit 64. The positive terminal side of the temperature measuring resistor 63 is connected to the non-inverting input terminal of the temperature measuring circuit 64, and the inverting input terminal and the output terminal of the temperature measuring circuit 64 are connected in negative feedback. The output of the subtraction device 45 and the temperature measurement circuit 64 are included in the correction device 65 for realizing the correction means of the present invention.
Is input.

In the flow sensors 1 of the sixth and seventh embodiments, the temperature dependence of the flow velocity output in the zero flow velocity state is suppressed, but if there is a flow rate, the temperature dependence occurs. That is, when the temperature of the fluid is three different temperatures T1, T2, and T3, the output of the circuit changes according to the temperature of the fluid as shown in FIG. In this case, a different flow velocity value is output depending on the temperature of the fluid. To correct this, it is necessary to measure the temperature of the fluid.

Therefore, the temperature measuring resistor 63 is installed in a place where it is not thermally coupled with the fluid. The place thermally coupled to the fluid is a place where there is a correspondence between the temperature of the fluid and the temperature of the resistance bulb 63. For example, the surface of a flow channel using a metal such as copper, aluminum, iron, or stainless steel having good heat conductivity in a fluid or a flow channel of the fluid.

The resistance temperature detector 63 is installed in a place where it is not thermally coupled to the heating element 2. The location that is not thermally coupled to the heating element 2 is a location where there is no correspondence between the heating temperature of the heating element 2 and the temperature of the temperature measuring resistor 63. For example, the heating element 2 is located far away from the heating element 2 so that the heat of the heating element 2 is not transmitted to the temperature measuring resistor 63 due to the heat transfer of the fluid or the flow path material.

In the above circuit configuration, the current source 62 supplies power so that the resistance bulb 63 does not generate heat. Since the resistance temperature detector 63 is thermally coupled to the fluid, the resistance temperature detector 63
Is a temperature corresponding to the temperature of the fluid. Temperature measurement circuit 6
4 outputs an output corresponding to the resistance value Rs3 of the resistance bulb 63. Since the resistance temperature detector 63 has a large temperature coefficient of resistance,
It changes according to the temperature of the resistance bulb 63. That is, the output of the temperature measurement circuit 64 is an output corresponding to the temperature of the fluid. Since the temperature of the fluid can be known from the output of the temperature measuring circuit 64, the correcting device 65 corrects the output of the subtracting device 45 based on the temperature signal of the fluid and converts the output to an accurate flow rate.

Specifically, the output of the subtraction device 45 is Vj,
Assuming that the output of the temperature measuring circuit 7 is Vu1, the flow rate signal F whose temperature has been corrected can be obtained by the following equation (1).

[0111]

(Equation 1)

The correction device 65 can be constituted by a microcomputer or the like that operates according to a predetermined program.

The value of n is determined by the first and second thermometers 3,
4. There is an optimum value depending on the material of the heating element 2, the installation method, the shape of the flow path, and the like. To determine its value: First, the first and second temperature measuring elements 3 and 4 and the heating element 2
Is installed in the flow path, and the temperature and the flow velocity of the fluid are changed, and FIG.
And the output Vu1 that can create a graph as shown in FIG. The value of n is temporarily set to 1, and the value of F is calculated for each measurement data. Taking the calculated F on the vertical axis, a graph as shown in FIG. 10 is created. Next, n
Is recalculated by setting the value of F to a value other than 1, for example, 2 or the like. Then, the graph is re-created. When the difference between the temperatures T1, T2, and T3 (see FIG. 10) is larger when the value of n is 2 than when the value of n is 1, the value of n is reset to a value less than 2, and the difference between the two is changed. N becomes smaller when
Is made larger than 2 and a graph is created. This operation is repeated until the difference between the temperatures T1, T2 and T3 falls within the temperature error range required for the flow velocity measurement. Then, the last value after the repetition is determined as an optimum value, and is set in advance in (the ROM of) the correction device 65.

As described above, by correcting the output of the subtraction device 45 based on the fluid temperature signal, the flow rate can be converted to an accurate flow rate.

[Ninth Embodiment of the Invention] FIG. 11 is a circuit diagram of a flow sensor 1 according to a ninth embodiment of the present invention. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the eighth embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment differs from the eighth embodiment in terms of circuit configuration in that the temperature sensor 61 is not provided and a correction device 65 is used instead of the output signal of the temperature measurement circuit 64. Is that the output signal of the temperature measurement circuit 7 is input.

In the eighth embodiment, the output Vj of the subtraction device 45 is an output corresponding to the flow velocity of the fluid. Since this output changes depending on the temperature of the fluid, the temperature sensor 61
However, this increases the number of circuit elements and increases the cost.

To correct the temperature of the output Vj, information on the temperature of the fluid is required. Since the heating element 2 is thermally coupled to the fluid, the output Vu2 of the temperature measuring circuit 7 includes the temperature information of the fluid. Therefore, in this embodiment, the output Vj is corrected by the output Vu2 in the correction device 65, and is converted into an accurate flow velocity.

More specifically, a flow rate signal F whose temperature has been corrected is obtained by the calculation according to the following equation (2). In this equation, k is a predetermined constant.

[0120]

(Equation 2)

The value of k is determined by the first and second thermometers 3,
4. There is an optimum value depending on the material of the heating element 2, the installation method, the shape of the flow path, and the like. To determine its value: First, the first and second temperature measuring elements 3 and 4 and the heating element 2
Is installed in the flow path, and the temperature and the flow velocity of the fluid are changed, and FIG.
The output Vj data and the output Vu2 that can create a graph as shown in FIG. The value of k is temporarily set to 1, and the value of F is calculated for each measurement data. Taking the calculated F on the vertical axis, a graph as shown in FIG. 10 is created. Next, k
Is recalculated by setting the value of F to a value other than 1, for example, 2 or the like. Then, the graph is re-created. When the difference between the temperatures T1, T2, and T3 (see FIG. 10) is larger when k is 1 than when k is 1, the value of k is reset to a value less than 2, and the difference between the two is changed. K becomes smaller when
Is made larger than 2 and a graph is created. This operation is repeated until the difference between the temperatures T1, T2 and T3 falls within the temperature error range required for the flow velocity measurement. Then, the last value after the repetition is determined as an optimum value, and is set in advance in (the ROM of) the correction device 65.

In this embodiment, the flow velocity of the fluid can be corrected for the temperature without providing any special means for determining the temperature of the fluid.

[Tenth Embodiment of the Invention] FIG.
Flow sensor 1 according to a tenth embodiment of the present invention
FIG. Hereinafter, the same reference numerals are given to circuit elements and the like corresponding to the case of the ninth embodiment, and detailed description is omitted.

The flow sensor 1 of this embodiment differs from the ninth embodiment in the circuit configuration in that the correction device 65 replaces the output signal of the temperature measurement circuit 7 with the output signal Vu3 of the amplifier 41. Is that you are typing

In this embodiment, the subtraction device 4
5 is corrected by the output Vu3 of the amplifier 41. Specifically, the temperature is corrected by the calculation of the following equation (3). In this equation, m is a predetermined constant.

[0126]

(Equation 3)

The value of m is determined by the first and second thermometers 3,
4. There is an optimum value depending on the material of the heating element 2, the installation method, the shape of the flow path, and the like. To determine its value: First, the first and second temperature measuring elements 3 and 4 and the heating element 2
Is installed in the flow path, and the temperature and the flow velocity of the fluid are changed, and FIG.
The output Vj data and the output Vu3 that can create a graph as shown in FIG. The value of m is temporarily set to 1, and the value of F is calculated for each measurement data. Taking the calculated F on the vertical axis, a graph as shown in FIG. 10 is created. Next, F is recalculated by setting the value of m to a value other than 1, for example, 2 or the like. Then, the graph is re-created. Temperatures T1, T2, T3 when m is 1 compared to when m is 1 (see FIG. 10)
If the difference is larger, the value of m is reset to a value less than 2, and if the difference between the two is smaller, the value of m is made larger than 2, and a graph is created. This operation is repeated until the difference between the temperatures T1, T2 and T3 falls within the temperature error range required for the flow velocity measurement. Then, the last value after the repetition is determined as an optimum value,
(ROM).

The output Vj is equal to the first and second temperature sensors 3 and 4
Is output reflecting the temperature of In the ninth embodiment, the temperature of the output of the subtraction device 45 is corrected by reflecting the temperature of the heating element 2 in addition to the output Vj. On the other hand, in this embodiment, the first and second thermometers 3,
Since the temperature correction is performed only from the temperature information of No. 4, the flow velocity measurement can be performed with the influence of the measurement error reduced.

In the above description, F was obtained using the voltage between the terminals of the first temperature measuring element 3 and the temperature was corrected.
A similar result can be obtained by obtaining F using the voltage between terminals of the second temperature measuring element 4.

[0130]

According to the first aspect of the present invention, there is provided a heating element disposed in a flow path of a fluid and generating heat, and a first temperature measuring resistor disposed upstream of the heating element in the flow path. A second temperature measuring resistor disposed downstream of the heating element in the flow path and connected in series with the first temperature measuring resistor; and the first and second temperature measuring resistors connected in series. A current source for supplying a constant current to the resistance temperature detector, a difference voltage detection device for detecting a difference between a terminal voltage of the first resistance temperature element and a terminal voltage of the second resistance temperature element, Therefore, instead of the conventional bridge circuit, the first and second resistance temperature detectors are connected in series and the first and second resistance temperature detectors are used. It can be used even if the variation of the resistance temperature detector 2 is larger than before. Also, since the first and second resistance temperature detectors are connected in series and the same current flows,
The effect of the output fluctuation of the current source on the detection of the difference between the voltages between the two terminals can be reduced. Further, since the circuit configuration can be relatively simplified, the stability of the circuit can be improved.

According to a second aspect of the present invention, in the first aspect, a voltage stabilizing device for maintaining a constant potential between the first and second resistance temperature detectors is provided. Therefore, by maintaining the potential between the first and second resistance temperature detectors constant, the negative terminal of the lower potential terminal of the first or second resistance temperature detector is maintained. Since the potential can be prevented from becoming zero, even if a differential amplifier is used for detecting the voltage between the terminals of the first or second resistance temperature detector, the operation of the differential amplifier is facilitated. Can be.

According to a third aspect of the present invention, in the second aspect, the voltage stabilizer maintains the potential between the first and second resistance temperature detectors at a GND level. Therefore, by maintaining the potential between the first and second resistance temperature detectors at the GND level, the higher potential of the first or second resistance temperature detector is added. The potential of the side terminal can be suppressed only to the voltage between the terminals of the first or second resistance temperature detector, and if both positive and negative power sources can be used as the power source of the differential amplifier, the negative side power source voltage is It is possible to suppress the magnitude of the potential of the higher potential positive terminal and the potential of the lower potential negative terminal of the first or second resistance temperature detector by effectively utilizing the resistance temperature detector. First
Alternatively, even if a differential amplifier is used for detecting the voltage between the terminals of the second resistance temperature detector, the operation of the differential amplifier can be facilitated. Further, by adding the potential on the plus terminal side of the first resistance temperature detector and the potential on the minus terminal side of the second resistance temperature detector, the difference between the voltages between the two terminals can be detected. Since it can be used, the circuit configuration can be simplified and the operation of the circuit can be stabilized as compared with a circuit configuration using a plurality of differential amplifiers.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the difference voltage detecting device is configured such that the potential on the plus terminal side of the first temperature measuring resistor and the second temperature measuring resistor Is provided with an adder for adding the potential on the negative terminal side of the first resistance thermometer to the potential on the plus terminal side of the first resistance temperature detector and the negative terminal of the second resistance temperature detector. The difference of the voltage between both terminals can be detected by the adder that adds the potential of the terminal to the other side, so that the circuit configuration is simplified and the operation of the circuit is stabilized as compared with a circuit configuration using a plurality of differential amplifiers. be able to.

The invention according to claim 5 is the invention according to claims 1, 2,
The invention according to any one of (3) and (4), further comprising division means for dividing the output of the differential voltage detection device by the voltage between the terminals of the first or second resistance temperature detector. Therefore, by dividing the output of the differential voltage detecting device by the voltage between the terminals of the first or second resistance temperature detector, it is possible to obtain a sensor output at zero flow velocity that does not change with the temperature of the fluid, and thus to perform measurement. In this case, the temperature dependence can be reduced, and the measurement accuracy can be improved.

According to a sixth aspect of the present invention, in accordance with the fifth aspect of the present invention, there is provided a subtracting means for subtracting a predetermined constant from the output of the dividing means. Since the sensor output when the flow rate is zero can be arbitrarily set, it is easy to match with other devices.

According to a seventh aspect of the present invention, in the sixth aspect, the subtracting means performs subtraction with a value equal to the output of the dividing means when there is no fluid flow as a predetermined constant. Since the sensor output can be set to zero, it is easy to adjust the zero output.

According to an eighth aspect of the present invention, in accordance with the sixth aspect of the present invention, there is provided a heat generation stopping device for stopping heat generation of the heat generating element, and the subtraction means is provided for the dividing means when there is no heat generation of the heat generating element. Since the subtraction is performed with a value equal to the output as a predetermined constant, the heat generation of the heating element can be stopped and the sensor output can be reduced to zero, so that the fluid flow rate can be reduced to zero. Zero output can be adjusted without it.

According to the ninth aspect of the present invention,
8. The invention according to any one of 8), further comprising a temperature sensor arranged in the flow path for detecting a temperature of the fluid, and a correction unit for correcting an output of the subtraction unit based on a detection signal of the temperature sensor. Since the temperature of the fluid can be detected and the output after the subtraction can be corrected based on the detection signal, the effect of the temperature of the fluid can be corrected to improve the accuracy of the sensor output. be able to.

The invention according to claim 10 is the invention according to claim 6,
In the invention according to any one of 7, and 8, the heating element generates heat when supplied with electric power, and includes a voltage sensor that detects a voltage between terminals of the heating element, and a detection signal of the voltage sensor. Correction means for correcting the output of the subtraction means on the basis of the voltage between the terminals of the heating element. Can be corrected, the influence of the temperature of the fluid can be corrected, the accuracy of the sensor output can be improved, and the circuit configuration can be simplified.

The invention according to claim 11 is the invention according to claim 6,
The invention according to any one of the seventh and eighth aspects, further comprising a correction unit that corrects an output of the subtraction unit based on a voltage between terminals of at least one of the first and second resistance temperature detectors. Since the voltage between the terminals of the first and second resistance temperature detectors includes information on the temperature fluctuation of the fluid, the output after the subtraction can be corrected based on this signal. Therefore, the influence of the temperature of the fluid can be corrected to improve the accuracy of the sensor output.
The circuit configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a flow sensor according to a first embodiment of the present invention.

FIG. 2 is a graph illustrating an operation of the flow sensor.

FIG. 3 is a circuit diagram of a flow sensor according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a flow sensor according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a flow sensor according to a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a flow sensor according to a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram of a flow sensor according to a sixth embodiment of the present invention.

FIG. 8 is a circuit diagram of a flow sensor according to a seventh embodiment of the present invention.

FIG. 9 is a circuit diagram of a flow sensor according to an eighth embodiment of the present invention.

FIG. 10 is a graph illustrating an operation of the flow sensor.

FIG. 11 is a circuit diagram of a flow sensor according to a ninth embodiment of the present invention.

FIG. 12 is a circuit diagram of a flow sensor according to a tenth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow sensor 2 Heating element 3 1st temperature measuring element 4 2nd temperature measuring element 9 Constant current source 10 Difference voltage detecting device 21 Voltage stabilizer 27 Adder 43 Division means 45 Subtraction means 51 Heat generation stopping means 61 Temperature sensor 65 Correction means

Claims (11)

[Claims] A heating element disposed in a flow path of a fluid and generating heat; a first temperature measuring resistor disposed upstream of the heating element with respect to the flow path; A second resistance thermometer arranged downstream and connected in series with the first resistance thermometer; and supplying a constant current to the first and second resistance thermometers connected in series. And a difference voltage detecting device for detecting a difference between a voltage between terminals of the first resistance temperature detector and a voltage between terminals of the second resistance temperature detector. Flow sensor. 2. The flow sensor according to claim 1, further comprising a voltage stabilizer for maintaining a constant potential between the first and second resistance temperature detectors. 3. The flow sensor according to claim 2, wherein the voltage stabilizer maintains the potential between the first and second resistance temperature detectors at a GND level. 4. The differential voltage detecting device according to claim 1, further comprising an adder for adding a potential on a positive terminal side of the first resistance temperature detector and a potential on a negative terminal side of the second resistance temperature detector. The flow sensor according to claim 3, wherein: 5. The output of the differential voltage detecting device is connected to a first or a second
The flow sensor according to any one of claims 1, 2, 3, and 4, further comprising a dividing unit that divides by a voltage between terminals of the temperature measuring resistor. 6. The flow sensor according to claim 5, further comprising subtraction means for subtracting a predetermined constant from the output of the division means. 7. The flow sensor according to claim 6, wherein the subtraction means performs the subtraction with a value equal to the output of the division means when there is no fluid flow as a predetermined constant. 8. A heat generation stopping device for stopping heat generation of the heating element, wherein the subtraction means performs subtraction with a value equal to an output of the division means when there is no heat generation of the heating element as a predetermined constant. The flow sensor according to claim 6, wherein: 9. A temperature sensor disposed in a flow path for detecting a temperature of a fluid, and correction means for correcting an output of the subtraction means based on a detection signal of the temperature sensor. Item 7. A flow sensor according to any one of Items 6, 7, and 8. 10. A heating element for generating heat by receiving power supply, a voltage sensor for detecting a voltage between terminals of the heating element, and an output of a subtraction means based on a detection signal of the voltage sensor. The flow sensor according to any one of claims 6, 7, and 8, further comprising a correction unit configured to perform correction. 11. A correcting means for correcting an output of a subtracting means based on a voltage between at least one terminal of the first and second resistance temperature detectors. 9. The flow sensor according to any one of claims 8 and 9.