JPH0633375Y2 - Thermal flow sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a heat-sensitive flow sensor for detecting a flow rate of a fluid by using a heat-sensitive resistor (heating resistor).

[Conventional technology]

A flow rate sensor of the type that detects a flow rate from a thermal equilibrium state of a bridge including a heat sensitive resistor (heating resistor) disposed in a fluid has been conventionally used. A conventional air flow sensor using a platinum wire as a heating resistor will be described below.

FIG. 6 (a) is a vertical sectional side view showing the structure of a heat-sensitive air flow sensor using a platinum wire as a heating resistor, and FIG. 6 (b) is a front view thereof. In FIGS. 6 (a) and 6 (b), the support member 3 is provided at a predetermined position in the housing 1 which serves as a main passage for the fluid.
The measurement pipe line 2 is provided by the above, a plurality of heat ray supports 4 are provided on the inner surface of the measurement pipe line 2, and the heat ray R _H is stretched through the heat ray support member 4 in a plane orthogonal to the flow of air. It is equipped.

Further, an air temperature sensor R _C is arranged in the measuring pipe line 2. The leads for electrical connection of each of the heat ray R _H and the air temperature sensor R _C are provided on the outer periphery of the housing 1 through through holes (not shown) provided in each of the housing 1, the measurement pipe line 2 and the support member 3. It communicates with the inside of the control circuit installation unit 5 and is connected to the control circuit installed inside the control circuit installation unit 5. Further, a protective net 6a is provided at the opening of the housing 1.
And 6b are installed.

FIG. 7 is a diagram showing a bridge including the heating wire R _H and the air temperature sensor R _C and a temperature control circuit 10 for controlling the temperature so that the bridge maintains thermal equilibrium. The resistances R ₁ , R ₂ , the heating wire R _H and A bridge is formed by the air temperature sensor R _C , both input terminals of the differential amplifier 101 are connected to the connection points b and f of the bridge, and the output of the differential amplifier 101 is connected to the base of the transistor 102, and The emitter is connected to one end a of the bridge, and the collector of the transistor 102 is connected to the positive electrode of the DC power supply 103.

Next, the operation will be described. Since the operation of the temperature control circuit is well known, detailed description thereof will be omitted, but when the voltages at the connection points b and f become equal, this circuit reaches an equilibrium state, and at this time, the heating wire R _H corresponds to the flow rate. A current I _H flows and the voltage V _{H at the} point b is represented by I _H · R ₂ , and this voltage is used as a flow rate signal.

In order to correct the detection variation due to the resistance value and resistance temperature coefficient of the heating wire R _H and the air temperature sensor R _{C or} the resistance variation of the resistors R ₁ and R ₂ , adjust the resistance value of the resistor R ₂ to detect the flow rate characteristics. Is changed in parallel to adjust the detection output value at a predetermined flow rate (usually a relatively low flow rate) to a target value.

Figure 8 is a detection flow characteristic diagram for explaining the correction, adjusting the resistance value of the resistor R ₁ to enter the range of the target value x unadjusted characteristic curve a at a given flow rate Q ₁ at the resistor R ₁ .

In the thermosensitive flow rate sensor including the temperature control circuit 10 described above, the resistance value of the resistor R ₁ is adjusted to improve the measurement accuracy (by detecting the flow rate characteristic in parallel as shown in FIG. Although the characteristics are adjusted), variations in the dimensions of the housing 1 and the measuring pipe 2 and in relative positions between the two, variations in the central axis of the measuring pipe 2 with respect to the flow direction, and heat rays R _H mounting position, etc.
The inclination of the flow rate characteristic (the flow rate dependency of the deviation from the median of the detection characteristics at each flow rate ... hereafter referred to as the characteristic inclination), which is mainly caused by the structural / dimensional variation / deviation, cannot be adjusted. The measurement accuracy is not improved at flow rates other than the adjusted flow point Q ₁ , especially at flow rates far away from the adjusted flow point Q ₁ . Therefore, in addition to the adjustment by the resistance R ₁ , the inclination of the characteristic is adjusted.

Next, an example of the conventional characteristic inclination adjustment will be described. FIG. 3 is a circuit diagram of a conventional heat-sensitive flow sensor for adjusting the inclination of the related art. In FIG.
In the temperature control circuit shown in the figure, 11 is resistors R ₃ , R ₄ , R ₅ , R ₆ , R
₁₄ , a subtraction circuit composed of the operational amplifier 104, the (+) input end of the operational amplifier 104 is grounded via the resistor R ₄ , and the connection point b of the bridge circuit of the temperature control circuit is connected via the resistor R _3. It is connected to the.

Of the operational amplifier 104 (-) input terminal, the setting voltage Vref resistor R ₅
This operational amplifier is designed to be applied via
A resistor R ₆ is connected between the (-) input end and the output end of 104, and the output end is grounded via the resistor R ₁₄ . Further, the output V ₁ at the output end is connected to the operational amplifier 10 via the resistor R ₇ in the voltage dividing circuit 12.
It is connected to the (+) input terminal of 5.

This voltage dividing circuit 12 is composed of resistors R ₇ , R ₈ , R ₉ , and R ₁₅ operational amplifier 105, and the (+) input terminal of the operational amplifier 105 is a resistor.
It is grounded via R ₈ and has a resistor R between the output and (-) input.
₉ is connected, and the output end is grounded via a resistor R ₁₅ . The output V ₂ of the operational amplifier 105 is connected to the (+) input terminal of the operational amplifier 106 via the resistor R ₁₀ in the operational circuit 13.

This arithmetic circuit 13 includes resistors R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and an operational amplifier 106.
The (-) input terminal of the operational amplifier 106 is grounded through the resistor R _12, and the resistor R ₁₂ is connected between the output terminal and this (-) input terminal.
₁₃ are connected. Further, the (+) input terminal is connected to the connection point b of the bridge circuit of the temperature control circuit 10 via the resistor R ₁₁ . The output V ₀ is output from the output terminal of the operational amplifier 106.

In FIG. 3, the subtracting circuit 11 is an operational amplifier 104.
By subtracting a predetermined set voltage Vref from the output voltage V _H of the temperature control circuit 10, the voltage divider circuit 12 is determined the output voltage V ₁ of the from the subtraction circuit 11 in each of the resistance values of the resistors R _7, R ₈ And the arithmetic circuit 13 is configured to add the output voltage V _H of the temperature control circuit 10 and the output voltage V ₂ of the voltage dividing circuit 12.

Next, the operation of FIG. 3 will be described with reference to FIG. The output voltage V ₁ of the subtraction circuit 11 is the resistance value R ₃ of each of the resistors R ₃ , R ₄ , R ₅ , and R ₆ .
Depending on R ₄ , R ₅ , R ₆ Relationship becomes a value satisfying the resistance value appropriate value, setting for example _{(R 3 = R 4, R} 5 = R 6), a V ₁ = V _H -Vref.

Since running in the positive electrode only in the power supply voltage of the operational amplifier 104, the output voltages V ₁ does not become a negative value, V _H <Vref
In this case, V ₁ = 0 and the characteristic V ₁ shown in FIG. 5 (a) is obtained.

The voltage dividing circuit 12 receives the output voltage V ₁ of the subtracting circuit 11, and the output voltage V ₂ of the voltage dividing circuit 12 according to the resistance values R ₇ and R ₈ of the resistors R ₇ and R ₈ , respectively. Relationship becomes a value satisfying, varying the resistance value R ₇ or R _8, FIG. 5 a predetermined voltage as indicated by the characteristic V ₂ of (a) V
With ref as a base point, its slope changes according to the output voltage V _H of the temperature control circuit 10.

The arithmetic circuit 13 inputs the output voltage V _H of the temperature control circuit 10 and the output voltage V ₂ of the voltage dividing circuit 12, and inputs the resistance values R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ of the resistors R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , respectively. Depending on R ₁₂ and R ₁₃ , the output voltage V ₀ is If the respective resistance values are set to appropriate values, for example, R ₁₀ = R ₁₁ , R ₁₂ = R ₁₃ , then V ₀ = V _H + V ₂ and the above voltages V ₁ , V _The output voltage V ₀ is calculated from the relational expressions of ₂ , V _H and V ref. Therefore, when V _H <Vref, the output voltage V ₀ is independent of the resistances R ₇ and R _8, and when V ₀ = V _H , V _H > Vref, the resistance value R ₇ becomes the value of (V _H −Vref). , A value obtained by multiplying the voltage division ratio according to R ₈ becomes a voltage added to the output voltage V _H , and has the characteristic shown by V ₀ in FIG. 5 (a).

FIG. 5 (b) is a diagram showing the relationship between the air flow rate and the output voltage V _H of the temperature control circuit 10 and the output voltage V ₀ of the arithmetic circuit 13, and FIG. 5 (c) is the air flow rate and each of the above-mentioned respective values. Output voltage of V _H , V ₀
FIG. 6 is a diagram showing the relationship of the detection error of the air flow meter due to the above. As shown in FIG. 5 (b), the output voltage of the arithmetic circuit 13 is a resistance value only when the flow rate is equal to or higher than the air flow rate Qref corresponding to the set voltage Vref. The characteristics are set in the addition direction according to R ₇ and R ₈ .

Therefore, as shown in FIG. 5 (c), the detection error due to the output voltage V _H of the temperature control circuit 10 changes the resistance value R ₇ or R _{8 due} to the detection error on the (-) side at the flow rate higher than the set flow rate Qref. Be adjusted.

The inclination adjustment operation by the configuration of the subtraction circuit 11, the voltage dividing circuit 12, and the arithmetic circuit 13 shown in FIG. 3 is as described above.
The detection error on the (-) side can be adjusted for flow rates above Qref, but the detection error on the (+) side cannot be adjusted.To adjust the detection error on the (+) side, the output voltage V of the temperature control circuit 10 must be adjusted. _It is necessary to subtract the output voltage V ₂ of the voltage dividing circuit 12 from _H to obtain V ₀ = V _H -V _{2. In} this case, the output voltage V ₂ of the voltage dividing circuit 12 is calculated as shown in FIG. It is necessary to change the connection so that the signal is input to the (-) input terminal of the operational amplifier 106 included in 13. The relationship of each voltage at this time is Therefore, similar to the description of the operation of FIG. 3, R ₁₀ = R ₁₁ , R ₁₂ =
With R ₁₃ And the set flow rate Qr according to the resistance value R ₇ or R _8.
The characteristics above ef are adjusted in the subtraction direction.

[Problems to be solved by the device]

Since the conventional thermal type flow sensor that adjusts the inclination of the characteristic is configured as described above, it is not possible to adjust the detection variations on the (+) side and the (-) side in the same circuit, and the temperature control circuit 10 After determining the direction of deviation of the output voltage V _H from the median characteristic value, it is determined which circuit in FIG. 3 or FIG. 4 is to be used, and the connection between the voltage dividing circuit 11 and the arithmetic circuit 12 is switched. There is a problem that the tilt needs to be adjusted above.

This invention was made to solve the above-mentioned problems, and it is possible to adjust the variation in both the (+) side and the (-) side with the same circuit. The purpose is to obtain a sensor.

[Means for Solving the Problems]

A thermal flow sensor according to the present invention comprises a voltage divider circuit for dividing an output voltage of a subtraction circuit, an amplifier circuit for amplifying the divided voltage, an output voltage of the amplifier circuit and an output voltage from a temperature control circuit. And an arithmetic circuit for subtracting the output voltage of the subtraction circuit from the added voltage.

[Action]

The voltage divider circuit according to the present invention divides the output voltage of the subtraction circuit, amplifies the divided voltage with an amplifier circuit, adds the output voltage of the amplifier circuit and the output voltage of the temperature control circuit with an arithmetic circuit, and By subtracting the output voltage of the subtraction circuit from the voltage of the addition result and changing the voltage division ratio of the voltage division circuit, it works so that the detection error can be adjusted in either the (+) side or the (-) side. .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment thereof, 10 is a temperature control circuit, 11 is a subtraction circuit, 12 is a voltage dividing circuit composed of resistors R ₇ and R ₈ , 13 is an arithmetic circuit, and 14 is a resistor. This is an amplifier circuit composed of R ₁₆ , R ₁₇ , and an operational amplifier 107.

The temperature control circuit 10, the subtraction circuit 11, and the arithmetic circuit 13 are configured in the same manner as in FIG. 3, and in the description of the configuration, the same parts as in FIG.

The voltage divider circuit 12 divides the output voltage V ₁ of the subtraction circuit 11 by resistors R ₇ and R ₈ , and the series circuit of the resistors R ₇ and R ₈ is between the output terminal of the subtraction circuit 11 and the ground. It is connected.

Output voltage of voltage divider circuit 12 obtained at the connection point between resistors R ₇ and R _8.
V ₃ is applied to the (+) input terminal of the operational amplifier 107 of the amplifier circuit 14. The (−) input terminal of the operational amplifier 107 is grounded via the resistor R ₁₆ .

In addition, a resistor is placed between the output terminal of the operational amplifier 107 and the (-) input terminal.
R ₁₇ is connected, and this output terminal is grounded via a resistor R ₁₈ .

The output voltage V ₄ of the amplifier circuit 14 is input to the (+) input terminal of the operational amplifier 106 via the resistor R ₁₀ in the arithmetic circuit 13.

The output voltage V ₁ of the subtraction circuit 11 is the resistance R in the arithmetic circuit 13.
It is adapted to be added to the (-) input terminal of the operational amplifier 106 via ₁₂ . The other parts are constructed in the same manner as in FIG.

Next, the operation will be described. The operation of the subtraction circuit 11 is the same as that of the conventional example shown in FIG. 3, and the resistance value is R ₃ = R ₄ , R
By setting ₅ = R _6, the output voltages V ₁ becomes V ₁ = V _H -Vref, except V _H <V ₁ = 0 when the Vref.

The output voltage V ₃ of the voltage dividing circuit 12 is determined according to the resistance values R ₇ and R ₈ of the resistors R ₇ and R ₈ in the voltage dividing circuit 12, Is input to the amplifier circuit 14, and the output voltage of the amplifier circuit 14 becomes
V _4, depending on the respective resistance values R _16, R ₁₇ of resistor R _16, R _17, Becomes

The arithmetic circuit 13 outputs the output voltage V _H of the temperature control circuit 10 and the amplifier circuit 14
Input the output voltage V ₄ and the output voltage V ₁ of the subtraction circuit 11,
Resistors _{R 10, R 11, R 12} , resistance value of each respective _{R 13 R 10, R 11,} R 12, R 13 and the output voltage V ₀ depending on the If the resistance values of each are appropriate values, for example, R ₁₀ = R ₁₁ , R ₁₂ = R ₁₃ , then V ₀ = V _H + V ₄ -V ₁ and the output voltage _{V 1, V 3, V 4} , V H, from each of the relationship set voltage Vref (However, when V _H <V ref, V _O = V _H ). In the above equation, if the resistance values R ₇ , R ₈ , R ₁₆ , R ₁₇ are set to appropriate values, for example, R ₇ = R ₈ , R ₁₇ = R ₁₆ × (1 ± α), V ₀ = V _H + {1/2 x (2 ± α) -1} x (V _H -Vref) = V _H ± 1/2 α (V _H -Vref) (where V ₀ = V _H when V _H <Vref) Becomes

Therefore, the output voltage of the arithmetic circuit 13 is V _H − when V ₀ = V _H , V _H > V ref when V _H <V ref, regardless of the resistance values R ₁₆ and R _17.
The value obtained by multiplying the Vref value by a coefficient according to the ratio of the resistance values R ₁₆ and R ₁₇ is added to or subtracted from V _H. Especially when R ₁₆ = R ₁₇ , V _H
V ₀ = V _H regardless of the magnitude of Vref.

FIG. 2 (a) is a diagram showing the characteristics of each of the above voltages,
The output voltage V ₄ of the amplifier circuit 14 changes based on the characteristic of the output voltage V ₁ of the subtraction circuit 11 depending on the value of α determined by the ratio of the resistors R ₁₆ and R ₁₇ , and the output voltage V of the arithmetic circuit 13 ₀ is V _H <Vref
In case of V ₀ = V _H , and in case of V _H > Vref, it changes with reference to the characteristic of V ₀ = V _H.

2 (b) is a diagram showing the relationship between the air flow rate, the output voltage of the temperature control circuit 10 and the output voltage V ₀ of the arithmetic circuit 13, and FIG.
(c) is a diagram showing the relationship between the air flow rate and the detection error of the air flow meter due to the respective output voltages V _H , V ₀ , and as shown in FIG. 2 (b), the output voltage V _{0 of the} arithmetic circuit 13 Is the resistance value R ₁₇ , only when the flow rate is equal to or higher than the air flow rate Qref corresponding to the set voltage Vref.
The characteristic can be arbitrarily set to the (+) side or the (−) side with the output voltage V _H of the temperature control circuit 10 as the center according to R ₁₈ .

Therefore, as shown in FIG. 2 (c), when the detection error due to the output voltage V _H of the temperature control circuit 10 is on the (−) side at a flow rate larger than the air flow rate Qref, it is on the (+ α) side and on the (+) side. In the case of an error, the same circuit configuration can be easily adjusted on the (-α) side.

In the above embodiment, the respective resistance values are R ₃ = R ₄ , R ₅ = R ₆ , R _{7
= R 8, R 10 = R} 11, R 12 = has been described by setting the R _13, it can be set to other values depending on the required detection characteristics the same effects.

As described above, according to the present invention, the output voltage of the subtraction circuit is divided by the voltage dividing circuit, the output voltage is amplified by the amplification circuit, and the output voltage of the amplification circuit and the temperature control are performed by the arithmetic circuit. The output voltage of the subtraction circuit is subtracted from the addition result with the output voltage of the circuit.Therefore, in the same circuit configuration without switching the connection of the input part of the arithmetic circuit, (+) It is possible to easily adjust the detection errors on the negative and negative sides in proportion to the flow rate, and to obtain a heat-sensitive flow rate sensor with high detection accuracy over the entire flow rate.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a heat-sensitive flow sensor according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of FIG.
3 and 4 are views showing a conventional control circuit, FIG. 5 is a view for explaining the operation of FIG. 3, and FIG. 6 is a structure of a heat-sensitive air flow sensor using a platinum wire as a heating resistor. FIG. 7 is a vertical sectional side view and a front view showing FIG. 7, FIG. 7 is a view showing a temperature control circuit of a heating resistor, and FIG. 8 is a view for explaining an adjusting method in the temperature control circuit of FIG. 10 …… Temperature control circuit, 11 …… Subtraction circuit, 12 …… Voltage divider circuit, 13 …… Calculation circuit, 14 …… Amplification circuit, R _H …… Thermal resistor, R _C …… Air temperature sensor, R ₁ , R ₂ …… Resistance. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] Claim: What is claimed is: 1. A bridge circuit comprising a heat-sensitive resistor arranged in a fluid passage and a plurality of resistors, the bridge circuit controlling the electric current flowing to the heat-sensitive resistor to maintain a predetermined thermal balance. In the thermosensitive flow rate sensor configured to control the flow rate from the state of thermal equilibrium, the temperature control circuit of the temperature control circuit obtained from the terminal voltage of the resistor connected in series with the thermosensitive resistor of the bridge circuit. A subtracting circuit for subtracting a predetermined voltage from the output voltage, a voltage dividing circuit for dividing the output voltage of the subtracting circuit, an amplifier circuit for amplifying the output voltage of the voltage dividing circuit, and an output voltage of the temperature control circuit having a positive voltage. Heat-sensitive flow rate sensor, which is provided with an arithmetic circuit that is input to a positive input terminal so that the output voltage of the subtraction circuit and the output voltage of the amplification circuit have opposite polarities.