JP2656669B2 - Thermal air flow meter that also functions as a temperature measurement meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow meter which also serves as an air temperature meter.

[0002]

2. Description of the Related Art A thermal air flow meter used for measuring an intake air flow rate of an engine is a heating resistor having a temperature dependency in an air flow (a typical example thereof is a hot wire resistance.
Heat resistance is described as an example) , and the heat transfer phenomenon between the heat resistance and air is applied.

That is, when a constant current is applied to the hot wire resistance in an air flow to generate heat, the greater the flow rate of air passing through, the more heat is removed, and the temperature rise of the hot wire resistance becomes small. Therefore, if the heating current flowing through the hot wire resistor is controlled so as to keep the heating temperature Th (resistance Rh) of the hot wire resistance having a positive temperature coefficient of resistance constant, the control current becomes a value corresponding to the air flow rate.

[0004] Since the heating temperature of the heating wire is affected by the temperature of the air, temperature compensation is required. Therefore, the temperature of air is sensed by a temperature-sensitive resistance for temperature compensation, and the heating temperature (resistance value of the hot-wire resistance) is controlled so that the difference between the temperature of the hot-wire resistance and the air temperature becomes constant. The heating current Ih at this time is detected and converted into an air flow rate signal (voltage), and then amplified by an amplifier circuit.
Output to the outside as an air flow signal.

When controlling the engine, for example, in order to calculate the weight flow rate of the intake air, it is necessary to measure the temperature of the intake air in addition to measuring the intake air flow rate.

Recently, as a means for measuring the temperature of the intake air, a device using a temperature-sensitive resistor for temperature compensation of a thermal air flow meter without using a dedicated temperature sensor has been proposed. and are (for example, those described in JP-a 1-100423 JP). This utilizes the fact that the value of the temperature compensation resistor for temperature compensation changes according to the temperature of the intake air, and for example, the voltage across the temperature compensation resistor for temperature compensation, or a resistor ( Normally, the voltage generated at the fixed resistor is detected to calculate the intake air temperature.

[0007]

As described above, when the thermal air flow meter also serves as a temperature measuring instrument, the cost of the product can be reduced.

[0008] However, the voltage across the temperature-sensitive resistor and the voltage induced in the resistor connected in series with the temperature-sensitive resistor are affected by the variation in the resistance connected in series with the temperature-sensitive resistor. The variation referred to here includes, in addition to the variation generated in the manufacturing process, a phenomenon in which the resistance value fluctuates depending on the temperature during use.

Among them, the former variation can be adjusted by adjusting the output of the amplifier, but the latter variation is difficult to correct by adjustment.

In the case of an automobile, a signal detecting section for measuring temperature and an engine control device (generally constituted by a microcomputer) for performing calculations are connected by wires of several meters. The voltage change taken out from the temperature resistor or the fixed resistor is a minute level.
Therefore, if the transmission distance between the signal detection unit and the arithmetic unit is relatively large as described above, the input signal used for the arithmetic operation is affected by electromagnetic waves and the like, becomes a noisy signal, and adversely affects the measurement accuracy. .

The present invention has been made in view of the above points, and an object of the present invention is to measure a resistance (temperature-sensitive resistance and a temperature-sensitive resistance) used when measuring air temperature using a thermal air flow meter. An object of the present invention is to improve the temperature measurement accuracy even if the resistance value of a series-connected resistance element fluctuates due to temperature, without being affected by the fluctuation.

Still another object of the present invention is to provide a thermometer which is hardly affected by noises such as external electromagnetic waves in addition to the above objects.

[0013]

In order to achieve the above object, the present invention basically proposes the following means for solving the problems.

That is, the air flow rate set in the air flow path
For measurementHeating resistorAnd its temperature-sensitive resistor for temperature compensationbody
And the saidHeating resistorConnected in seriesHeating resistorCurrent detection
Voltage generated at the output resistance and the temperature-sensitive resistancebodyConnected in series
Input the voltage generated in the resistor andHeating resistorHeating temperature
The temperature to maintain a predetermined temperature difference with respect to the air temperature.Fever
antibodyA differential amplifier circuit for controlling the amount of current flow,Departure
Thermal resistorThe air flow rate from the amount of electricityThermalAir flow meter
The output voltage Va of the differential amplifier circuit and the temperature sensitivity
resistancebodyDivided by the voltage Vb generated in the resistor connected in series
To obtain the ratio of Va and Vb.
Means for detecting a change in the amplification factor of the differential amplifier)
The output of this division circuit (change in the amplification factor of the differential amplifier)
) Is output as an air temperature measurement signal.
Was.

Further, based on the above basic problem solving means (first problem solving means), the following problem solving means is proposed.

One is that the dividing circuit used for measuring the air temperature and the amplifying circuit for amplifying the output of the dividing circuit are constituted by one monolithic IC together with the amplifying circuit for measuring the air flow rate (this is a second monolithic IC). This will be referred to as problem solving means).

The other is that after converting the output of the division circuit used for measuring the air temperature into a pulse signal having a frequency corresponding to the output, various control devices (for example, an engine control device)
(This is referred to as a third problem solving means).

[0018]

[Action] The first heating current (applied voltage) to the working ... heating resistor SUMMARY differential amplifier for controlling heating resistor
A voltage generated in the heating resistor current detection resistor connected in series with the body and a voltage generated in the resistor connected in series with the temperature compensation resistor for temperature compensation are input.

As a result, the heating resistor is generated from the differential amplifier.
A heating resistor applied voltage Va is output such that the heating temperature of the body maintains a predetermined temperature difference with respect to the air temperature, and a corresponding heating current (heating current with temperature compensation) flows through the heating resistor .

The power supply amount for the heat generating resistor is detected from the voltage produced for example heating resistor current sensing resistor. This detection voltage is used as an air flow measurement signal,
For example, it is used as a variable of a fuel amount calculation formula for engine control, or is digitally calculated as an air flow value in various measurement fields and then displayed on a meter.

[0021] Incidentally, the temperature sensitive resistors, when the resistance value in proportion to the change of the air temperature changes, that act to regulate the amplification factor of the differential amplifier. As a result, the output voltage Va of the differential amplifier is generated from the differential amplifier such that the heating temperature of the heating resistor maintains a constant temperature difference from the air temperature, and the temperature compensation function operates.

Therefore, means for detecting a change in the amplification factor of the heating resistor control circuit (differential amplifier) [for example, Va and Vb
And a dividing circuit for calculating the ratio (Va / Vb) to the air temperature can be measured.

According to such an air temperature measurement, FIG.
Resistor is connected to the temperature sensing resistor 2 in series for temperature compensation R8 and the R7 molecules as Equation 3 described based on the temperature measurement and the intake air flow meter of Figure 1 in the Examples section, the denominator since arranged, offset resistance variation with temperature change of the resistors R8 and R7 each other, to capture without being affected by a change in the temperature sensing resistor 2 of the resistance value Rc resistor R8, R7 temperature variation Can be. Vt in Equation 3 is the amplification factor of the differential amplifier for controlling the heating current (for controlling the amount of current flowing through the heating resistor ).
It is represented by Va / Vb. VT (Va / Vb) is output as a temperature measurement signal.

The temperature measurement signal Vt is used together with the air flow rate measurement signal as, for example, a variable for calculating a fuel amount for engine control, or is digitally calculated in various measurement fields and displayed as a specific numerical value.

Function of the second means for solving the problem: If the dividing circuit used for measuring the air temperature and the amplifying circuit for amplifying the output of this dividing circuit are constituted by one monolithic IC, the output from the dividing circuit becomes closer. After being amplified at the specified position, it is transmitted to an engine control unit and various other temperature calculation devices. Therefore, the influence of noise on the transmission path of the temperature measurement signal can be significantly reduced.

Operation of the third problem-solving means: The output of the division circuit used for the temperature measurement is converted into a pulse signal having a frequency corresponding to the output, and then transmitted to an engine control unit and various other temperature calculation devices. Therefore, it is not affected by external electromagnetic waves in the signal transmission process.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is an explanatory diagram showing a circuit according to a first embodiment of the present invention, FIG. 2 is a division circuit used in the first embodiment, and FIG. 3 is an amplifier circuit used in the third embodiment.

In FIG. 1, reference numeral 100 denotes a heating resistor 1
(Hereinafter, referred to as a hot wire resistance) . The hot-wire current control circuit 100 includes a detection unit including a bridge circuit of a hot-wire resistor 1, a resistor R1, a temperature-sensitive resistor (hereinafter, referred to as a temperature-sensitive resistor) 2, a resistor R8, and a resistor 7, a differential amplifier Z1, and the like. Is done.

The heating wire 1 and the resistor R1 in the bridge circuit
Are connected in series, the intermediate point is connected to the non-inverting input terminal of the differential amplifier Z1, and the other end of the resistor R1 is grounded.

The temperature-sensitive resistor 2 and the fixed resistors R8 and R7 are connected in series, an intermediate point between the resistors R8 and R7 is connected to the inverting input terminal of the differential amplifier Z1, and the other end of the resistor R7 is grounded. I have. The output terminal 3 of the differential amplifier Z1 is connected to the hot wire resistor 1 and the temperature sensitive resistor 2.

Further, the inverting input terminal 4 of the differential amplifier Z1
And the output terminal 3 of the differential amplifier Z1 are connected to the input terminals of the division circuit A1, respectively.
Is connected to the input terminal of the amplifier A2, the output terminal 6 of the amplifier A2 serves as the output terminal of the air temperature detector, and is connected to a control unit (not shown, which is an engine control unit, which is a microcomputer). I have.
The division circuit A1 and the amplifier A2 are used for temperature measurement.

Although not shown in FIG. 1, the terminal voltage V2 generated at the resistor R1 is input to the engine control unit as an air flow rate measurement signal via an amplifier.

Next, the operation of this embodiment will be described.

The hot wire resistance 1 is a heat generating resistor having a positive temperature coefficient, and the temperature changes due to a heat transfer phenomenon according to the intake air flow rate. Therefore, the resistance value changes according to the intake air flow rate. .

When the intake air flow rate increases, the heat ray resistance 1
The amount of heat deprived of the circuit increases, and the equilibrium condition of the circuit shown in Expression 1 is broken. Here, the resistance value of the heating wire is Rh, the resistance value Rc of the temperature-sensitive resistor, and the resistance values of the fixed resistors R1, R7, R8 are R1, R7, R8 as they are.

[0037]

## EQU1 ## A voltage Va is output from the differential amplifier Z1 so as to satisfy the equilibrium condition of the equation (1), and the voltage Va is applied to the bridge circuit including the hot wire resistance 1 so as to satisfy the equilibrium condition of the equation (1). , A heating current Ih sufficient to compensate for the amount of heat taken by the hot wire resistance 1 is supplied, and the resistance value of the hot wire Rh
Is controlled to be constant. The heating current of the hot wire resistance 1 is Ih, the air flow rate is Q, the hot wire temperature is Th, and the air temperature is Ta.
Then, there is a relationship represented by Equation 2 between the resistance value Rh of the hot wire resistance 1 and the air flow rate Q.

[0038]

(Equation 2)

Here, A, B and n are constants. This heating current Ih is converted into a voltage signal (air flow rate measurement signal) V2 by the resistor R1 and output.

The temperature-sensitive resistor 2 is disposed in the air passage similarly to the hot wire 1, has a positive temperature coefficient, and changes its resistance value according to the intake air temperature.

When the value of the temperature-sensitive resistor 2 changes in accordance with the intake air temperature, the output voltage V2 is subjected to temperature compensation by the equilibrium equations of the equations (1) and (2). Heating current I so as to maintain a constant temperature difference
h flows.

Further, in this embodiment, in addition to the above-described measurement of the intake air flow rate, the input voltage Vb of the differential amplifier Z1 is
(The voltage generated in the fixed resistor R7) and the output voltage Va of the differential amplifier Z1 are input to the division circuit A1 of the air temperature measurement system, and the division circuit A1 calculates the ratio of Va and Vb (Va / V
By taking b), that is, by determining the amplification factor, a signal proportional to the intake air temperature is obtained.

The input voltage Vb of the differential amplifier Z1 is the same as the output voltage V2 of the air flow, and the output voltage Va of the amplifier Z1 is expressed by the following equation (3).

[0044]

(Equation 3)

That is, assuming that the ratio of the output voltage Va of Z1 to the input voltage Vb of the differential amplifier Z1, that is, the amplification factor is Vt, it can be expressed by equation (4).

[0046]

(Equation 4)

When the value Rc of the temperature-sensitive resistor 2 changes according to the air temperature, the output voltage Vt of the division circuit A1 changes. The output voltage Vt is amplified by the amplifier A2, and the output voltage signal Vto corresponding to the air temperature change is generated. Obtainable. The output voltage signal Vto is sent to the engine control unit as a temperature measurement signal.

The dividing circuit A1 used in this embodiment can be realized by a circuit configuration as shown in FIG. 2, for example.

In FIG. 2, an FET is connected to the input terminal 3 of Va.
7 and the resistor R101 are connected.
Is connected to the resistor R102 and the gate of the FET7,
The source of the FET 7 is connected to the inverting input terminal of the differential amplifier Z7 and the resistor R103, the other end of the resistor R103 is connected to the output terminal 5 of the differential amplifier Z7, and the non-inverting input terminal of the differential amplifier Z7 is grounded. I have.

The input terminal 4 of Vb is connected to the drain of the FET 8 and the resistor R104, and the other end of the resistor R104 is connected to the resistor R105 and the gate of the FET 8,
8 is connected to the inverting input terminal of the differential amplifier Z8, and the constant voltage VS is supplied to the differential amplifier Z8 via the resistor R106.
, The non-inverting input terminal of the differential amplifier Z8 is grounded, and the output terminal of the differential amplifier Z8 is connected to the resistor R102 and the resistor R105.

Next, the operation of the division circuit A1 will be described.
When the voltage applied to the input terminal 3 is Va, the voltage applied to the input terminal 4 is Vb, the resistance values of the resistors R101 to R106 are R101 to R106, the current flowing through the resistor R106 is I ₁ , and the constant voltage VS is 1V, first, Differential amplifier Z
The output 8 operates so as to establish an imaginary short between its input terminals, and adjusts the gate voltage of the FET 8.

In this state, if the resistance between the source and the drain of the FET 8 is Rt8, the input of the differential amplifier becomes 0V.
From the condition, the current I ₁ flowing through the resistor R106 is expressed by the following equation (5).
Expression.

[0053]

I ₁ = VS / R106 = 1 / R106 Further, the resistance value Rt8 between the source and the drain of the FET 8 can be expressed by the following equation (6).

[0054]

Rt8 = −Vb / I ₁ = −Vb · R106 At this time, assuming that the resistance of the FET 7 is also substantially the same as the resistance Rt8 of the Rt8, the output of the differential amplifier Z7 with respect to the input voltage Va is expressed by the following equation (7). It can be expressed like an equation.

[0055]

(Equation 7)

The resistance values Rt7 and Rt between the source and the drain
8 are substantially equal and the resistance values of the resistor R103 and the resistor R106 are equal, the output voltage Vt is expressed by the following equation (8) from the equations (6) and (7).

[0057]

Vt = Va / Vb In other words, a voltage signal Vt proportional to a value obtained by dividing the input voltage Va by Vb is obtained at the output terminal 5.

Next, the amplifier A2 used in this embodiment can be realized, for example, by a circuit configuration as shown in FIG.

The input terminal 5 of Vt in FIG. 3 is connected to the non-inverting input terminal of the differential amplifier Z9, the constant voltage VE is connected to the resistor R107, and the other end of the resistor R107 is connected to R108 and grounded. , Resistor R107 and resistor R1
The contact 08 is connected to the resistor R109 and connected to the inverting input terminal of the amplifier Z9, and the inverting input terminal is connected to the output terminal 6 of the amplifier Z9 via the resistor R110.

The voltage Vt input to the input terminal 5 is converted to a predetermined voltage width by adjusting the voltage serving as a reference point by adjusting the resistors R107 and R108, and adjusting the resistors R109 and R110. it can.

According to this embodiment, in addition to the measurement of the air flow rate, the temperature can be measured from the voltage ratio between two points by using the division circuit A1. The resistors R8 and R7 connected in series with the temperature-sensitive resistor 2 are arranged in the numerator and the denominator, so that the resistance value fluctuations due to the temperature changes of the resistors R8 and R7 cancel each other out, and The change in the resistance value Rc can be detected without being affected by the temperature fluctuation of the resistors R8 and R7. As a result, a high-precision air temperature measurement circuit can be realized with a simple circuit configuration, and can be realized with one monolithic IC by using Bi-CMOS technology.

Further, there is an effect that the measurement of the air temperature and the measurement of the air flow rate can be performed by one module without changing the circuit configuration for measuring the air flow rate at all. Further, a calculation is performed by a division circuit (analog circuit) A1, and this air temperature measurement signal is output to the engine control unit.
There is an effect that the influence of noise due to electromagnetic waves or the like can be reduced.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

The hot-wire current control circuit 100 shown in FIG. 4 has a configuration different from that of the first embodiment.

The hot wire resistor 1 is grounded via the resistor R1. A resistor R2 and a resistor R3 are connected in series between both ends of the hot wire resistor 1, a connection point between the resistors R2 and R3 is connected to an inverting input terminal of the differential amplifier Z2, and an output terminal of the differential amplifier Z2. Is connected to the heating wire 1 and the resistor R2.

The connection point between the resistors R3 and R1 is connected to the non-inverting input terminal of the differential amplifier Z3.
The inverting input terminal of the differential amplifier Z3 is grounded via a resistor R7, a resistor R8 and a temperature-sensitive resistor 2 for detecting air temperature are connected in series between the inverting input terminal and the output terminal of the differential amplifier Z3. The output terminal is connected to the non-inverting input terminal of the differential amplifier Z2.

The non-inverting input terminal of the differential amplifier Z3 is the output terminal of the air flow meter.

The operation of this embodiment will be described. In FIG. 4, the resistance value of the hot-wire resistance 1 is Rh, and the resistance value of the temperature-sensitive resistance 2 is R.
c, the resistance values of the resistors R1, R2, R3, R7 and R8
Assuming R1, R2, R3, R7 and R8 as they are, in this case, the hot wire resistance 1 is controlled so that Equation 9 is satisfied.

[0069]

(Equation 9)

On the other hand, as in FIG. 1, the relationship of equation 2 holds. That is, the analog voltage signal V2 obtained by detecting the current Ih of the heating wire 1 with the resistor R1 is the air flow measurement signal.

Also in the air flow meter having such a circuit configuration, the voltage of the inverting input terminal of the differential amplifier Z3 is set to Vb,
Assuming that the voltage at the output terminal of the differential amplifier Z3 is Va, the output voltage Vt is obtained by dividing the two voltages by the divider A1 and taking the ratio in the same manner as in FIG. 1, and this is amplified by the amplifier A2. And an output voltage Vto corresponding to the air temperature can be obtained.

Further, the same effect as in the case of FIG. 1 can be obtained.

FIG. 5 shows a third embodiment of the present invention. The voltage Va of the hot-wire control circuit 100 is exactly the same as the circuit shown in FIG.
And the voltage Vb are ratioed by the divider A1 and amplified by the amplifier A2. The amplified signal Vto is converted into a frequency signal by the voltage-frequency conversion circuit A3 and output.

The voltage-frequency conversion circuit 3 can be realized, for example, by a circuit configuration as shown in FIG. In FIG. 6, a voltage-frequency conversion circuit A3 is connected to an output terminal 6 of an amplifier A2, and a resistor R115 is connected between the output terminal 6 and the ground.
And the resistor R116 are connected in series with each other, and the resistor R11
The connection point of the differential amplifier 5 and the resistor R116 is connected to the non-inverting input terminal of the differential amplifier Z4, and the resistor R117 is connected between the inverting input terminal and the output terminal 6 of the differential amplifier Z4.

A capacitor C1 is connected between the output terminal and the inverting input terminal of the differential amplifier Z4.
Between the inverting input terminal of the inverter and the output terminal of the inverter Z6.
18 are connected.

Then, a voltage of 1/2 Ve is applied to the non-inverting input terminal of the inverter Z6, and the inverting input terminal of the inverter Z6 is connected to the non-inverting input terminal of the comparator Z5 via the resistor R121. The non-inverting input terminal of Z5 is a resistor R120.
Grounded through.

Further, the non-inverting input terminal of the comparator Z5 has
The voltage Ve is applied via the resistor R119, and the inverter Z6
Is connected to the output terminal of the comparator Z5. The output terminal of the differential amplifier Z4 is connected to the comparator Z5.
And the output terminal of the comparator Z5 is the output terminal 12 of the voltage-frequency conversion circuit A3.

The operation of the embodiment having such a configuration will be described below.

Based on the analog voltage signal Vto input to the voltage-frequency conversion circuit A3, the current given by the equation (10) is integrated by the capacitor C1 and the differential amplifier Z4.

[0080]

(Equation 10)

The integrated value obtained by the capacitor C1 and the differential amplifier Z4 is detected by the comparator Z5, and the output signal of the comparator Z5 is supplied to the inverting input terminal of the inverter Z6. Is done.

The slope of the integrated output signal of the differential amplifier Z4 is controlled by the output signal of the inverter Z6.

Thus, the analog voltage signal Vto
Is converted to a pulse voltage signal fto.

According to this embodiment, in addition to having the same effects as those of the first embodiment, since the temperature measurement signal transmitted to the engine control unit is further converted into a digital signal fto, noise generated by other devices is generated. Erroneous operation can be suppressed.

[0085]

According to the present invention, in the first means for solving the problems, it is possible to measure the air temperature using a thermal air flow meter, and furthermore, it is connected in series with the temperature-sensitive resistor used for the air temperature measurement. Since the temperature can be measured while minimizing the influence of the variation (fluctuation) due to the temperature change of the resistance, high-precision temperature measurement with few measurement errors is enabled.

In the second means for solving the problem, the temperature measurement signal processing is performed by one module for output, and in the third problem solving means, the temperature measurement signal is converted into a pulse frequency and output. In the signal transmission process from the control unit to various control units such as the engine control unit, the influence of noise on the measurement signal can be reduced, and the measurement accuracy can be further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a division circuit used in the first embodiment.

FIG. 3 is a circuit diagram of an amplifier used in the first embodiment.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a voltage-frequency converter used in a third embodiment.

[Explanation of symbols]

1 ... resistance of the heating resistor (heating resistors) 2 ... input terminal 6 ... air temperature measurement output terminal R7 of the temperature sensitive resistors 3, 4 ... division circuit for temperature compensation, R8 ... temperature sensitive resistors connected in series Z1 ... Differential amplifier 100. Heating resistor (hot wire) current control circuit A1. Divider circuit (Amplification factor detecting means of differential amplifier) A2. Amplifier

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Yoneda 2477 Kashimayatsu, Kata-shi, Ibaraki Pref. Hitachi Automotive Engineering Co., Ltd.

Claims (4)

(57) [Claims] 1. A calling for air flow measurement installed in the air passage
A heat resistor, a temperature-sensitive resistor for temperature compensation thereof , and the heat generation
The voltage generated at the heating resistor current detection resistor connected in series with the resistor and the voltage generated at the resistor connected in series with the temperature-sensitive resistor are input, and the heating temperature of the heating resistor is set to a predetermined value with respect to the air temperature. A differential amplifier circuit for controlling the amount of current supplied to the heating resistor so as to maintain a temperature difference, wherein a thermal air flow meter that obtains an air flow rate from the amount of current supplied to the heating resistor includes an output voltage of the differential amplifier circuit. its V by dividing a voltage Vb generated in the resistor connected in series to the temperature sensing resistor and Va
A thermal air flow meter also serving as a temperature measuring device, comprising a dividing circuit for obtaining a ratio of a and Vb, and having a circuit configuration for outputting an output of the dividing circuit as an air temperature measuring signal. 2. A monolithic IC according to claim 1, wherein said dividing circuit used for measuring said air temperature and an amplifying circuit for amplifying an output of said dividing circuit are constituted together with an amplifying circuit for measuring air flow rate by one monolithic IC. Thermal air flow meter that also serves as a characteristic temperature meter. 3. The temperature measuring device according to claim 1, wherein an output of said dividing circuit is set to be converted into a pulse signal having a frequency corresponding to the output and transmitted. Thermal air flow meter. 4. A calling for air flow measurement installed in the air passage
A heat resistor, a temperature-sensitive resistor for temperature compensation thereof , and the heat generation
A voltage generated at a heating resistor current detection resistor connected in series with a resistor and a voltage generated at a resistor connected in series with the temperature-sensitive resistor are input, and a heating temperature of the heating resistor is set to a predetermined value with respect to an air temperature. A differential amplifying circuit for controlling the amount of current flowing through the heating resistor so as to maintain a temperature difference, wherein a thermal air flowmeter that obtains an air flow rate from the amount of current flowing through the heating resistor includes an amplification factor of the differential amplifier circuit. A thermal air flow meter also serving as a thermometer, wherein a means for detecting a change in the temperature is provided, and the air temperature is set based on the change in the amplification factor.