CN112857493A - Lead resistance eliminating circuit and thermal mass flowmeter - Google Patents

Lead resistance eliminating circuit and thermal mass flowmeter Download PDF

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Publication number
CN112857493A
CN112857493A CN201911175196.7A CN201911175196A CN112857493A CN 112857493 A CN112857493 A CN 112857493A CN 201911175196 A CN201911175196 A CN 201911175196A CN 112857493 A CN112857493 A CN 112857493A
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Prior art keywords
resistor
lead
capacitor
resistance
thermal
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赵俊奎
邹明伟
张汝纹
李强
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Chongqing Chuanyi Automation Co Ltd
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Chongqing Chuanyi Automation Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
    • G01F1/78—Direct mass flowmeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K3/00—Thermometers giving results other than momentary value of temperature
    • G01K3/08—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
    • G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
    • G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

In the lead resistance eliminating circuit and the thermal mass flowmeter provided by the invention, two thermal resistors (including lead resistances at two ends of the thermal resistor) of a sensor in thermal mass flow are respectively connected in series into two different bridge arms of a bridge through a bridge circuit powered by a constant current source, a feedback circuit formed by combining an operational amplifier is used for carrying out feedback limitation on the potentials of each point of the two bridge arms, and the influence of the lead resistances at two ends of the thermal resistor on a voltage signal reflecting temperature difference can be effectively eliminated by adjusting the resistance values of other resistors connected in series in the bridge arms, so that the response speed of the sensor and the thermal mass flowmeter is greatly improved.

Description

Lead resistance eliminating circuit and thermal mass flowmeter
Technical Field
The invention relates to the technical field of industrial automation, in particular to a lead resistance eliminating circuit and a thermal mass flowmeter.
Background
The thermal gas mass flowmeter can directly measure the mass of the measured gas mediumCompared with gas ultrasonic wave, the flow saves the links of temperature and pressure compensation and saves the cost. The basic principle is that two platinum resistors are adopted as core elements of the sensor, one platinum resistor is used for measuring the temperature of a medium, the other platinum resistor is a heating resistor, and the mass flow of gas flowing through the two platinum resistors conforms to the King's law: p/. DELTA.theta.K1+K2(qm)K3Wherein P is the heating power of the heating resistor, Delta theta is the temperature difference of two platinum resistors, qmIs the flow rate of the fluid, K1、K2、K3Is constant, it can be known that the heating power P and the flow rate q are constant when the temperature difference Deltatheta is constantmA certain mathematical relation is formed, and the flow q can be reflected by measuring the current of the heating resistormA change in (c).
In actual measurement, a bridge circuit is generally adopted to measure a voltage difference between two platinum resistors, in order to improve response speed, resistance values of the heating platinum resistors are small, generally 10 omega-20 omega, for a split-type flowmeter, a sensor lead can be as long as 30 meters, lead resistance reaches 5 omega, and if the lead resistance is not eliminated, a large measurement error is introduced, and measurement accuracy is seriously affected. The traditional three-wire platinum resistance measuring circuit is characterized in that a constant current source is used for driving a platinum resistor, the voltage of the platinum resistor and the voltage on a lead resistor are respectively measured, then the platinum resistor and the voltage are respectively sent to different sampling channels of an AD converter, the sampling difference value of the two channels is calculated to obtain the voltage of the platinum resistor, and the voltage is divided by the constant current source value to obtain the resistance value of the platinum resistor.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a solution for lead resistance cancellation, which is used to solve the above-mentioned technical problems.
To achieve the above and other related objects, the present invention provides a lead resistance cancellation circuit for canceling lead resistance of a sensor in a thermal mass flowmeter, the sensor including a first thermal resistance, a second thermal resistance, a first lead resistance, and a second lead resistance, the lead resistance cancellation circuit comprising: a bridge circuit and a feedback circuit;
the bridge circuit comprises a first bridge arm and a second bridge arm which are arranged in parallel, one end of the first bridge arm is connected with a constant current source, the other end of the first bridge arm is grounded, the first bridge arm at least comprises a first lead resistor, a first thermal resistor and a second lead resistor which are sequentially connected in series along the direction from the constant current source to the ground, and the second bridge arm at least comprises a second thermal resistor, a first resistor and a second resistor which are sequentially connected in series;
a first detection point is arranged at one end of the first lead resistor close to the constant current source, and a second detection point is arranged at one end of the second thermal resistor close to the constant current source;
the end of the first thermal resistor, which is far away from the constant current source, is connected with the feedback circuit, the end of the first resistor, which is far away from the constant current source, is connected with the feedback circuit, and the feedback circuit performs feedback limitation on the potential.
Optionally, the resistance value of the first lead resistor is equal to the resistance value of the second lead resistor, and the resistance value of the first resistor is equal to the resistance value of the second resistor.
Optionally, the first bridge arm further includes a third resistor, the first lead resistor, the first thermal resistor, and the second lead resistor are sequentially connected in series along a direction from the constant current source to ground, and the first detection point is disposed at a common end of the third resistor and the first lead resistor.
Optionally, the second bridge arm further includes a fourth resistor and a fifth resistor, the fourth resistor, the fifth resistor, the second thermal resistor, the first resistor and the second resistor are sequentially connected in series along a direction from the constant current source to ground, and the second detection point is disposed at a common end of the fourth resistor and the fifth resistor.
Optionally, the sensor further comprises a third lead resistor, and the feedback circuit comprises an operational amplifier, a sixth resistor and a seventh resistor; one end of the third lead resistor is connected with the common end of the first thermal resistor and the second lead resistor, and the other end of the third lead resistor is grounded after passing through the sixth resistor; one end of the seventh resistor is connected with the common end of the third lead resistor and the sixth resistor, and the other end of the seventh resistor is connected with the non-inverting input end of the operational amplifier; and the inverting input end of the operational amplifier is connected with the common end of the first resistor and the second resistor.
Optionally, the feedback circuit further includes an eighth resistor and a PNP type triode, the output terminal of the operational amplifier is connected to the base of the PNP type triode after passing through the eighth resistor, the collector of the PNP type triode is connected to the negative power supply, and the emitter of the PNP type triode is connected to the common terminal of the second thermal resistor and the first resistor.
Optionally, the operational amplifier includes a dual-power operational amplifier, a positive power pin of the dual-power operational amplifier is connected to a positive power, and a negative power pin of the dual-power operational amplifier is connected to the negative power.
Optionally, the feedback circuit further includes a unidirectional transient suppression diode, an anode of the unidirectional transient suppression diode is connected to the negative power supply, and a cathode of the unidirectional transient suppression diode is connected to a common end of the second thermal resistor and the first resistor.
Optionally, the lead resistance cancellation circuit further includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, and a seventh capacitor; one end of the first capacitor is grounded, and the other end of the first capacitor is connected with the common end of the first resistor and the second resistor; the first capacitor is connected with the common end of the first resistor and the second resistor, and the other capacitor is connected with the common end of the first resistor and the second resistor; one end of the third capacitor is connected with the common end of the first resistor and the second resistor, and the other end of the third capacitor is connected with the output end of the operational amplifier; one end of the fourth capacitor is connected with the positive power supply, and the other end of the fourth capacitor is grounded; one end of the fifth capacitor is connected with the negative power supply, and the other end of the fifth capacitor is grounded; one end of the sixth capacitor is connected with the non-inverting input end of the operational amplifier, and the other end of the sixth capacitor is grounded; one end of the seventh capacitor is connected with the common end of the sixth resistor and the seventh resistor, and the other end of the seventh capacitor is grounded.
In addition, in order to achieve the above and other related objects, the present invention further provides a thermal mass flowmeter, including the lead resistance cancellation circuit described in any one of the above, the thermal mass flowmeter further includes a constant voltage and constant current control chip, a gain circuit, and an inverse proportion circuit, the constant voltage and constant current control chip is used as the constant current source, an output end of the constant voltage and constant current control chip outputs a constant current to the outside, two input ends of the gain circuit are respectively connected to the first detection point and the second detection point, an output end of the gain circuit is connected to an input end of the inverse proportion circuit, and an output end of the inverse proportion circuit is connected to an input end of the constant voltage and constant current control chip.
As described above, the lead resistance cancel circuit according to the present invention has the following advantageous effects:
two thermal resistors (including lead resistors at two ends of the thermal resistor) in the thermal mass flow meter sensor are respectively connected in series into two different bridge arms of a bridge through a bridge circuit powered by a constant current source, then the potentials of each point of the two bridge arms are subjected to feedback limitation by combining a feedback circuit, and the influence of the lead resistors at two ends of the thermal resistor on a voltage signal reflecting the temperature difference can be effectively eliminated by adjusting the resistance values of other resistors connected in series in the bridge arms, so that the response speed of the sensor and the thermal mass flow meter is greatly improved.
Drawings
Fig. 1 is a diagram showing a sensor circuit of a thermal mass flowmeter with a lead resistance elimination circuit according to an embodiment of the present invention.
Description of the reference numerals
C1 first capacitor
C2 second capacitor
C3 third capacitor
C4 fourth capacitor
C5 fifth capacitor
C6 sixth capacitor
C7 seventh capacitance
R1 first resistor
R2 second resistor
R3 third resistor
R4 fourth resistor
R5 fifth resistor
R6 sixth resistor
R7 seventh resistor
R8 eighth resistor
RL1 first lead resistor
RL2 second lead resistor
RL3 third lead resistor
RT1 first thermal resistor
RT2 second thermal resistor
Q1 PNP type triode
TVS1 unidirectional transient suppression diode
U1 operational amplifier
VDD Positive Power supply
VEE negative power supply
Current flowing in the first leg of I1
Current flowing in the second arm of I2
First detection Point potential of V1
Second detection Point potential of V2
V3 common terminal potential of the first resistor and the second resistor
1 output terminal of operational amplifier
2 inverting input terminal of operational amplifier
3 non-inverting input terminal of operational amplifier
4 negative power supply pin of operational amplifier
8 positive power supply pin of operational amplifier
Detailed Description
As mentioned in the background, in the existing thermal mass flowmeter, the resistance value of the platinum resistor for measuring the speed is generally about 10 Ω, and at this time, the lead resistance of the platinum resistor (thermal resistor) cannot be ignored no matter the structure is a split structure or an integrated structure; the traditional three-wire system measurement adopts two AD sampling channels, and the difference value of the resistances of the two channels is calculated to be used as an effective signal; the method needs a series of processes such as AD sampling and holding, AD conversion, singlechip reading, filtering and the like, and has a complex structure and long response time. Therefore, it is necessary to design a lead resistance cancellation circuit to cancel the influence of the lead resistance on the thermal mass flow meter sensor and improve the response time thereof.
Based on this, the invention provides a technical scheme for eliminating lead resistance, which comprises the following steps: firstly, a first thermal resistor (not limited to a platinum resistor) and lead resistors at two ends of the first thermal resistor are connected in series into a first bridge arm of a bridge, a second thermal resistor (not limited to the platinum resistor) is connected in series into a second bridge arm of the bridge, the first bridge arm and the second bridge arm are connected in parallel, one end of the first bridge arm is connected with a constant current source, and the other end of the first bridge arm is grounded; secondly, introducing a feedback circuit (such as a feedback circuit formed by an operational amplifier) between the first bridge arm and the second bridge arm, and performing feedback limitation on the potentials of all points on the first bridge arm and the second bridge arm; finally, a suitable detection point is found on each of the first bridge arm and the second bridge arm, the potential difference value between the two detection points is a voltage signal of the sensor for representing the temperature difference, and the resistance values of other resistors connected in series in the first bridge arm or the second bridge arm are adjusted, so that the influence of lead resistors at two ends of the first thermal resistor on the measurement result can be eliminated.
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the electronic components related to the present invention rather than being drawn according to the type, number and layout of the components in actual implementation, and the type, number and layout of each electronic component in actual implementation may be changed randomly, and the layout type may be more complicated. The structural form, number and layout of the electronic components shown in the drawings attached to this specification are only used for matching the content disclosed in the specification, so that those skilled in the art can understand and read the electronic components, and do not limit the limitation conditions that the present invention can be implemented, so that the electronic components do not have the essential technical significance. In addition, the terms "close" and "far" are used in the present specification for clarity of description, and are not intended to limit the scope of the present invention, and changes or modifications of the relative relationship may be made without substantial technical changes.
In this embodiment, as shown in fig. 1, the present invention provides a lead resistance cancellation circuit for canceling lead resistance of a sensor in a thermal mass flowmeter, the sensor including a first thermal resistor RT1, a second thermal resistor RT2, a first lead resistance RL1, and a second lead resistance RL2, the lead resistance cancellation circuit comprising: a bridge circuit and a feedback circuit;
the bridge circuit comprises a first bridge arm and a second bridge arm which are arranged in parallel, one end of the first bridge arm is connected with a constant current source, the other end of the first bridge arm is grounded, the first bridge arm at least comprises a first lead resistor RL1, a first thermal resistor and a RT1 second lead resistor RL2 which are sequentially connected in series, and the second bridge arm at least comprises a second thermal resistor RT2, a first resistor R1 and a second resistor R2 which are sequentially connected in series;
a first detection point is arranged at one end, close to the constant current source, of the first lead resistor RL1, and a second detection point is arranged at one end, close to the constant current source, of the second thermal resistor RT 2;
one end of the first thermal resistor RT1, which is far away from the constant current source, is connected with a feedback circuit, one end of the first resistor R1, which is far away from the constant current source, is connected with the feedback circuit, and the feedback circuit performs feedback limitation on the potentials of each point on the first bridge arm and the second bridge arm.
The current flowing through the first bridge arm is I1, and the current flowing through the second bridge arm is I2; the resistance value of the first lead resistor RL1 is equal to the resistance value of the second lead resistor RL2, and the resistance value of the first resistor R1 is equal to the resistance value of the second resistor R2.
In detail, as shown in fig. 1, the first arm further includes a third resistor R3, the third resistor R3, the first lead resistor RL1, the first thermal resistor RT1 and the second lead resistor RL2 are connected in series in sequence along the direction from the constant current source to the ground, and the first detection point is provided at a common end of the third resistor R3 and the first lead resistor RL 1.
In detail, as shown in fig. 1, the second arm further includes a fourth resistor R4 and a fifth resistor R5, the fourth resistor R4, the fifth resistor R5, the second thermal resistor RT2, the first resistor R1, and the second resistor R2 are sequentially connected in series along a direction from the constant current source to the ground, and the second detection point is disposed at a common end of the fourth resistor R4 and the fifth resistor R5.
In detail, as shown in fig. 1, the sensor further includes a third lead resistor RL3, and the feedback circuit includes an operational amplifier U1, a sixth resistor R6, and a seventh resistor R7; one end of the third lead resistor RL3 is connected with the common end of the first thermal resistor RT1 and the second lead resistor RL2, and the other end of the third lead resistor RL3 is grounded after passing through the sixth resistor R6; one end of the seventh resistor R7 is connected with the common end of the third lead resistor RL3 and the sixth resistor R6, and the other end of the seventh resistor R7 is connected with the non-inverting input end 3 of the operational amplifier U1; the inverting input terminal 2 of the operational amplifier U1 is connected to the common terminal of the first resistor R1 and the second resistor R2.
In more detail, as shown in fig. 1, the feedback circuit further includes an eighth resistor R8 and a PNP transistor Q1, the output terminal 1 of the operational amplifier U1 is connected to the base of the PNP transistor Q1 through the eighth resistor R8, the collector of the PNP transistor Q1 is connected to the negative power VEE, and the emitter of the PNP transistor Q1 is connected to the common terminal of the second thermal resistor RT2 and the first resistor R1.
Optionally, operational amplifier U1 includes a dual power supply operational amplifier with positive power supply pin 8 connected to positive power supply VDD and negative power supply pin 4 connected to negative power supply VEE.
The positive power supply VDD can provide +15V voltage, and the negative power supply VEE can provide-5V voltage, and the voltage can be flexibly selected according to actual conditions and requirements.
Optionally, as shown in fig. 1, the feedback circuit further includes a unidirectional transient suppression diode TVS1, an anode of the unidirectional transient suppression diode TVS1 is connected to the negative power source VEE, and a cathode of the unidirectional transient suppression diode TVS1 is connected to a common terminal of the second resistor RT2 and the first resistor R1. The PNP transistor Q1 is protected by the unidirectional transient suppression diode TVS1, so that the PNP transistor Q1 is protected from various surge pulses.
Optionally, as shown in fig. 1, the lead resistance elimination circuit further includes a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, and a seventh capacitor C7; one end of the first capacitor C1 is grounded, and the other end is connected with the common end of the first resistor R1 and the second resistor RT 2; the second capacitor C2 has one end connected to the common end of the first resistor R1 and the second resistor R2 and the other end connected to the common end of the first resistor R1 and the second resistor RT 2; one end of the third capacitor C3 is connected with the common end of the first resistor R1 and the second resistor R2, and the other end is connected with the output end 1 of the operational amplifier U1; one end of the fourth capacitor C4 is connected to the positive power supply VDD, and the other end is grounded; one end of the fifth capacitor C5 is connected with the negative power supply VEE, and the other end is grounded; one end of the sixth capacitor C6 is connected with the non-inverting input end 3 of the operational amplifier U1, and the other end is grounded; the seventh capacitor C7 has one end connected to the common end of the sixth resistor R6 and the seventh resistor R7, and the other end connected to ground.
In the present embodiment, as shown in fig. 1, the difference between the voltage V1 at the first detecting point and the voltage V2 at the second detecting point is a voltage signal representing the temperature difference in the sensor; specifically, the lead resistance canceling circuit operates on the following principle:
1) when the circuit is stable, according to the principle of 'virtual interruption', the currents of the non-inverting input end 3 and the inverting input end 2 of the operational amplifier U1 are both zero, and the potential of the non-inverting input end 3 of the operational amplifier U1 is the common end potential of the third lead resistor RL3 and the sixth resistor R6; in practical application, the resistance of the third lead resistor RL3 is very small (on the order of 0.1 Ω), and the resistance of the sixth resistor R6 is very large (on the order of 100k Ω), so that the common terminal potential of the third lead resistor RL3 and the sixth resistor R6 is approximately the common terminal potential between the first thermal resistor RT1 and the second lead resistor RL2, that is, the potential of the non-inverting input terminal 3 of the operational amplifier U1 is approximately the common terminal potential between the first thermal resistor RT1 and the second lead resistor RL2, and the value of the potential is I1 × RL 2;
2) when the circuit is stable, according to the principle of 'virtual short', the potentials of the non-inverting input terminal 3 and the inverting input terminal 2 of the operational amplifier U1 are equal, so that the common terminal potential of the first resistor R1 and the second resistor R2 is equal to I1 × RL 2; in addition, since the resistances of the first resistor R1 and the second resistor R2 are equal (i.e., R1 is equal to R2) and the same current I2 flows through the first resistor R1 and the second resistor R2, the common terminal potential V3 of the first resistor R1 and the second resistor RT2 is equal to 2I 1 RL 2;
3) according to the circuit, the potential V1 at the first detection point is I1 (RL1+ RT1+ RL2), and the potential V2 at the second detection point is V3+ I2 (R5+ RT 2); meanwhile, the resistance of the first lead resistor RL1 is equal to the resistance of the second lead resistor RL2, that is, RL1 is RL 2;
4) the above equations are combined and calculated
V3＝2*I1*RL2 (1)
V1＝I1*(RL1+RT1+RL2) (2)
V2＝V3+I2*(R5+RT2) (3)
RL1＝RL2 (4)
Calculated from equations (1) to (4): V1-V2 ═ I1 × RT1-I2 × (R5+ RT2), it can be seen that the voltage value of the voltage signal representing the temperature difference in the sensor is independent of the resistance values of the lead resistors (the first lead resistor RL1, the second lead resistor RL2 or the third lead resistor RL3) at the two ends of the first thermal resistor RT1, so that the influence of the first lead resistor RL1, the second lead resistor RL2 or the third lead resistor RL3 on the measurement result is effectively eliminated, and the response speed of the sensor in the thermal mass flowmeter is greatly improved.
In addition, in this embodiment, as shown in fig. 1, the present invention further provides a thermal mass flowmeter, which includes the above lead resistance cancellation circuit, and further includes a constant voltage and constant current control chip, a gain circuit and an inverse proportion circuit, where the constant voltage and constant current control chip is used as a controlled constant current source, an output end of the constant voltage and constant current control chip outputs a constant current to the outside, two input ends of the gain circuit are respectively connected to the first detection point and the second detection point, an output end of the gain circuit is connected to an input end of the inverse proportion circuit, and an output end of the inverse proportion circuit is connected to an input end of the constant voltage and constant current control chip.
In summary, in the lead resistance canceling circuit and the thermal mass flowmeter provided by the present invention, the bridge circuit powered by the constant current source respectively connects two thermal resistors (including the lead resistances at the two ends of the thermal resistor) in the thermal mass flowmeter sensor in series to two different bridge arms of the bridge, and then the feedback circuit formed by the operational amplifier performs feedback limitation on the potentials of the points of the two bridge arms, and the influence of the lead resistances at the two ends of the thermal resistor on the voltage signal representing the temperature difference can be effectively eliminated by adjusting the resistance values of the other resistors connected in series to the bridge arms, thereby greatly improving the response speed of the sensor and the thermal mass flowmeter.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (10)

1. A lead resistance cancellation circuit for cancellation of sensor lead resistance in a thermal mass flow meter, the sensor including a first thermal resistance, a second thermal resistance, a first lead resistance and a second lead resistance, the lead resistance cancellation circuit comprising: a bridge circuit and a feedback circuit;
the bridge circuit comprises a first bridge arm and a second bridge arm which are arranged in parallel, one end of the first bridge arm is connected with a constant current source, the other end of the first bridge arm is grounded, the first bridge arm at least comprises a first lead resistor, a first thermal resistor and a second lead resistor which are sequentially connected in series along the direction from the constant current source to the ground, and the second bridge arm at least comprises a second thermal resistor, a first resistor and a second resistor which are sequentially connected in series;
a first detection point is arranged at one end of the first lead resistor close to the constant current source, and a second detection point is arranged at one end of the second thermal resistor close to the constant current source;
the end of the first thermal resistor, which is far away from the constant current source, is connected with the feedback circuit, the end of the first resistor, which is far away from the constant current source, is connected with the feedback circuit, and the feedback circuit performs feedback limitation on the potential.
2. The lead resistance cancellation circuit according to claim 1, wherein a resistance value of the first lead resistance is equal to a resistance value of the second lead resistance, and a resistance value of the first lead resistance is equal to a resistance value of the second lead resistance.
3. The lead resistance cancellation circuit according to claim 1 or 2, wherein the first bridge arm further includes a third resistor, the first lead resistor, the first thermal resistor and the second lead resistor are sequentially connected in series along a direction from the constant current source to ground, and the first detection point is provided at a common end of the third resistor and the first lead resistor.
4. The lead resistance cancellation circuit of claim 3, wherein the second leg further comprises a fourth resistor and a fifth resistor, the fourth resistor, the fifth resistor, the second thermal resistor, the first resistor and the second resistor are sequentially connected in series along a direction from the constant current source to ground, and the second detection point is disposed at a common terminal of the fourth resistor and the fifth resistor.
5. The lead resistance cancellation circuit of claim 4, wherein the sensor further comprises a third lead resistance, the feedback circuit comprising an operational amplifier, a sixth resistance, and a seventh resistance; one end of the third lead resistor is connected with the common end of the first thermal resistor and the second lead resistor, and the other end of the third lead resistor is grounded after passing through the sixth resistor; one end of the seventh resistor is connected with the common end of the third lead resistor and the sixth resistor, and the other end of the seventh resistor is connected with the non-inverting input end of the operational amplifier; and the inverting input end of the operational amplifier is connected with the common end of the first resistor and the second resistor.
6. The lead resistance cancellation circuit according to claim 5, wherein the feedback circuit further includes an eighth resistor and a PNP transistor, the output terminal of the operational amplifier is connected to the base of the PNP transistor through the eighth resistor, the collector of the PNP transistor is connected to the negative power supply, and the emitter of the PNP transistor is connected to the common terminal of the second thermal resistor and the first resistor.
7. The lead resistance cancellation circuit of claim 6, wherein said operational amplifier comprises a dual power supply operational amplifier having a positive power supply pin coupled to a positive power supply and a negative power supply pin coupled to said negative power supply.
8. The lead resistance cancellation circuit of claim 6, wherein the feedback circuit further comprises a one-way transient suppression diode, an anode of the one-way transient suppression diode being connected to the negative power supply, a cathode of the one-way transient suppression diode being connected to a common terminal of the second thermal resistor and the first resistor.
9. The lead resistance cancellation circuit of claim 7, wherein the lead resistance cancellation circuit further comprises a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, and a seventh capacitor; one end of the first capacitor is grounded, and the other end of the first capacitor is connected with the common end of the first resistor and the second resistor; the first capacitor is connected with the common end of the first resistor and the second resistor, and the other capacitor is connected with the common end of the first resistor and the second resistor; one end of the third capacitor is connected with the common end of the first resistor and the second resistor, and the other end of the third capacitor is connected with the output end of the operational amplifier; one end of the fourth capacitor is connected with the positive power supply, and the other end of the fourth capacitor is grounded; one end of the fifth capacitor is connected with the negative power supply, and the other end of the fifth capacitor is grounded; one end of the sixth capacitor is connected with the non-inverting input end of the operational amplifier, and the other end of the sixth capacitor is grounded; one end of the seventh capacitor is connected with the common end of the sixth resistor and the seventh resistor, and the other end of the seventh capacitor is grounded.
10. A thermal mass flowmeter comprising the lead resistance cancellation circuit according to any one of claims 1 to 9, and further comprising a constant-voltage constant-current control chip, a gain circuit, and an inverting proportional circuit, wherein the constant-voltage constant-current control chip is used as the constant current source, an output terminal of the constant-voltage constant-current control chip outputs a constant current to the outside, two input terminals of the gain circuit are respectively connected to the first detection point and the second detection point, an output terminal of the gain circuit is connected to an input terminal of the inverting proportional circuit, and an output terminal of the inverting proportional circuit is connected to an input terminal of the constant-voltage constant-current control chip.
CN201911175196.7A 2019-11-26 2019-11-26 Lead resistance eliminating circuit and thermal mass flowmeter Pending CN112857493A (en)

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CN201911175196.7A CN112857493A (en) 2019-11-26 2019-11-26 Lead resistance eliminating circuit and thermal mass flowmeter

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Application Number Priority Date Filing Date Title
CN201911175196.7A CN112857493A (en) 2019-11-26 2019-11-26 Lead resistance eliminating circuit and thermal mass flowmeter

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CN112857493A true CN112857493A (en) 2021-05-28

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CN201911175196.7A Pending CN112857493A (en) 2019-11-26 2019-11-26 Lead resistance eliminating circuit and thermal mass flowmeter

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CN (1) CN112857493A (en)

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