CN-121677858-B - Thermal flowmeter sensor driving circuit, thermal flowmeter and flow measuring method

CN121677858BCN 121677858 BCN121677858 BCN 121677858BCN-121677858-B

Abstract

The invention relates to the technical field of fluid measurement and discloses a thermal flowmeter sensor driving circuit, a thermal flowmeter and a flow measuring method, comprising a constant current source module, a constant current source module and a control module, wherein the constant current source module is connected to a serial branch and used for providing constant excitation current for the serial branch; the system comprises a series branch, a virtual bridge arm module, a signal control and acquisition module and a control and acquisition module, wherein the two input ends of the virtual bridge arm module are respectively connected to a first end and a second end and are used for responding to voltages at two ends of the series branch so as to generate and output a fixed reference voltage, and the signal control and acquisition module is used for enabling the voltage of the second input end of the signal control and acquisition module to be equal to the reference voltage in a steady state through internal negative feedback of the signal control and acquisition module and outputting a voltage signal, wherein the magnitude of the voltage signal represents the unbalance degree of resistance values of a first sensing resistor and a second sensing resistor. The full current flows through the sensor, the signal intensity is high, no additional amplification is needed, the noise introduced by an amplifying circuit is avoided, and the signal acquired by the ADC is more stable.

Inventors

LI CHUNBING
Ran longxiang
HE LIANGWU
LIU LIFENG
HU DINGJUN
Shang Congjian
Cun Xining
HUANG WENJIE

Assignees

成都睿宝电子科技有限公司

Dates

Publication Date: 20260512
Application Date: 20260211

Claims (9)

1. A thermal flowmeter sensor drive circuit for driving and measuring a flow sensor comprising a first sensing resistor R6 and a second sensing resistor R12, wherein the first sensing resistor R6 and the second sensing resistor R12 are connected in series to form a series branch, one end of the first sensing resistor R6 away from the second sensing resistor R12 is a first end a of the series branch, one end of the second sensing resistor R12 away from the first sensing resistor R6 is a second end C of the series branch, and a common connection end of the first sensing resistor R6 and the second sensing resistor R12 is an intermediate node B, the thermal flowmeter sensor drive circuit comprising: a constant current source module connected to the series branch for providing a constant excitation current I1 to the series branch; the two input ends of the virtual bridge arm module are respectively connected to the first end A and the second end C and are used for responding to the voltages at two ends of the serial branch so as to generate and output a fixed reference voltage Vd; The signal control and acquisition module is used for enabling the voltage of the second input end of the signal control and acquisition module to be equal to the reference voltage Vd in a steady state through internal negative feedback of the signal control and acquisition module and outputting a voltage signal Vadc, wherein the magnitude of the voltage signal Vadc represents the unbalance degree of the resistance values of the first sensing resistor R6 and the second sensing resistor R12; The signal control and acquisition module comprises a fourth operational amplifier U2.1, wherein the fourth operational amplifier U2.1 is connected into a voltage follower mode, the non-inverting input end of the fourth operational amplifier U2.1 is connected to the output end D of the virtual bridge arm module, the output end of the fourth operational amplifier U2.1 is used for outputting the buffered reference voltage Vd, and the inverting input end of the fourth operational amplifier U2.1 is connected to the output end of the fourth operational amplifier U2.1; The signal control and acquisition module further comprises a fifth operational amplifier U2.2 and a sixth operational amplifier U2.3, a ninth resistor R9 is connected between the output end of the fifth operational amplifier U2.2 and the inverting input end of the sixth operational amplifier U2.3, and the output end of the sixth operational amplifier U2.3 outputs the voltage signal Vadc.
2. The thermal flowmeter sensor drive circuit of claim 1, wherein the constant current source module comprises a first operational amplifier U1.1, a first MOS transistor Q1, a first sampling resistor R1, a second sampling resistor R2, a first frequency compensation capacitor C1, and a second filter capacitor C2; the drain electrode of the first MOS tube Q1 is connected with a power supply module through the first sampling resistor R1, and the source electrode of the first MOS tube Q1 is connected with the first end A so as to provide the excitation current I1 to the serial branch; The output end of the first operational amplifier U1.1 is connected to the grid electrode of the first MOS tube Q1, the non-inverting input end of the first operational amplifier U1.1 receives the reference voltage VREF, and the inverting input end of the first operational amplifier U1.1 is grounded through a second resistor R2 connected in series; The first frequency compensation capacitor C1 is connected between the output end and the inverting input end of the first operational amplifier U1.1, and the second filter capacitor C2 is connected between the non-inverting input end and the ground of the first operational amplifier U1.1.
3. The thermal flowmeter sensor drive circuit of claim 1, wherein said virtual bridge arm module comprises a summing and scaling circuit comprising an operational amplifier for summing and scaling voltages across said series legs to generate said reference voltage Vd.
4. The thermal flowmeter sensor drive circuit of claim 3, wherein said virtual bridge arm module comprises a second operational amplifier U1.2, a third operational amplifier U1.3, and a fourth operational amplifier U1.4; The second operational amplifier U1.2 and the third operational amplifier U1.3 are both connected in a voltage follower mode, the non-inverting input end of the second operational amplifier U1.2 is connected with the first end A, the output end of the second operational amplifier U1.2 is connected with the inverting input end of the second operational amplifier U1.2, the non-inverting input end of the third operational amplifier U1.3 is connected with the second end C, and the output end of the third operational amplifier U1.3 is connected with the inverting input end of the third operational amplifier U1.3; The fourth operational amplifier U1.4 is connected to an in-phase summing circuit, the in-phase input end of the fourth operational amplifier U1.4 receives the output voltage of the second operational amplifier U1.2 through a fifth resistor R5 connected in series, the in-phase input end of the fourth operational amplifier U1.4 receives the output voltage of the third operational amplifier U1.3 through an eleventh resistor R11 connected in series, and meanwhile, the inverting input end of the fourth operational amplifier U1.4 is connected with the output end of the fourth operational amplifier U1.4 through a fourth resistor R4 serving as a feedback resistor, and the output end of the fourth operational amplifier U1.4 serves as an output node D to output the reference voltage Vd.
5. The sensor driver circuit of claim 4, wherein the fifth resistor R5 and the eleventh resistor R11 have equal resistance values, such that the reference voltage Vd is one half of the sum of the voltage at the first terminal A and the voltage at the second terminal C.
6. The driving circuit of a thermal flowmeter according to claim 1, wherein a non-inverting input terminal of the fifth operational amplifier U2.2 is connected to an output terminal of the fourth operational amplifier U2.1 to receive the buffered reference voltage Vd, an inverting input terminal of the fifth operational amplifier U2.2 is connected to the intermediate node B through an eighth resistor R8, and both ends of the eighth resistor R8 are connected to an output terminal of the fifth operational amplifier U2.2 in a signal transmission direction through a third resistor R3 and a fourth capacitor connected in series, respectively; The non-inverting input end of the sixth operational amplifier U2.3 is connected to the output end of the fourth operational amplifier U2.1 to receive the buffered reference voltage Vd, the inverting input end of the sixth operational amplifier U2.3 is connected to the output end of the fifth operational amplifier U2.2 through a ninth resistor R9 in series, and meanwhile, the inverting input end of the sixth operational amplifier U2.3 is connected with the output end of the sixth operational amplifier U2.3 through a parallel link consisting of a seventh resistor R7 and a third capacitor in series.
7. The driving circuit of a thermal flowmeter sensor according to claim 6, wherein the signal control and acquisition module further comprises a tenth resistor R10, a thirteenth resistor R13, a fifth capacitor C5, a sixth capacitor C6 and a seventh capacitor C7, wherein an output end of the sixth operational amplifier U2.3 forms a voltage signal negative output end ADC-by connecting the tenth resistor R10 in series, an output end of the fourth operational amplifier U2.1 forms a voltage signal positive output end adc+ by connecting the thirteenth resistor R13 in series, the fifth capacitor C5 and the seventh capacitor C7 are connected between the positive output end adc+ and the negative output end ADC-in series, and a series node of the fifth capacitor C5 and the seventh capacitor C7 is grounded, and two ends of the sixth capacitor C6 are respectively disposed between the positive output end adc+ and the negative output end ADC-.
8. A thermal flowmeter comprising a flow sensor comprising a first sense resistor R6 and a second sense resistor R12, and a signal processing circuit, wherein the signal processing circuit is a thermal flowmeter sensor drive circuit according to any of claims 1 to 7.
9. A thermal flowmeter flow measurement method based on the thermal flowmeter sensor drive circuit of any of claims 1-7, comprising the steps of: providing a constant current I1 to a first sensing resistor R6 and a second sensing resistor R12 of the sensor through a constant current source module; Generating a fixed reference voltage Vd through the virtual bridge arm module, wherein the reference voltage Vd is used for balancing the system when the resistance values of the first sensing resistor R6 and the second sensing resistor R12 are equal; Forcing the intermediate node B voltages of the first and second sense resistors R6 and R12 to follow the reference voltage Vd by a signal control and acquisition module; collecting and measuring a voltage signal Vadc output by the signal control and collection module to maintain a voltage following relationship; and calculating a flow value flowing through the flow sensor according to the voltage signal Vadc.

Description

Thermal flowmeter sensor driving circuit, thermal flowmeter and flow measuring method Technical Field The invention relates to the technical field of fluid measurement, in particular to a thermal flowmeter sensor driving circuit, a thermal flowmeter and a flow measurement method. Background The thermal flowmeter measures the fluid flow according to the heat conduction principle, two groups of metal wires which are sensitive to temperature are wound on a capillary channel in a flow sensor, the two groups of metal wires are heated to keep a certain temperature, when fluid passes through the thermal flowmeter, the heat balance between the two groups of metal wires is broken, the heat of one group of metal wires can be transferred to the other group of metal wires along with the fluid, the resistance difference between the two groups of metal wires is changed, and the flow flowing through the capillary channel can be obtained by measuring the resistance value change between the two groups of metal wires and carrying out corresponding change. For measuring the resistance change between two sets of wires, there are two general methods, one is to collect the voltage at a single end, i.e. directly collect the voltage at the middle point of the two sets of wires, and the other is composed of a wheatstone bridge. The first method is to directly collect the voltage value change between two groups of metal wires, but because the accuracy of the flowmeter is guaranteed and the fluid flowing into the pipeline of the flowmeter tends to be in a laminar flow state, the fluid entering the thermal flowmeter can be separated by a shunt in the pipeline to a great extent, and only a small part of the fluid flows into a capillary pipeline in a sensor, at this time, the voltage value change value between the two groups of metal wires is directly measured, an ADC collecting chip with higher resolution is needed for the flowmeter with larger flow, a signal amplifying circuit is needed to be added subsequently, the voltage value change value between the two groups of metal wires is amplified, but some extra noise is introduced, and the voltage value collected by a final control chip is more jittery. The other is to use a Wheatstone bridge to measure the resistance change between two groups of wires, as shown in FIG. 1, since the Wheatstone bridge consists of four resistors R 1~R4, each two are one bridge arm, for a thermal flowmeter, two groups of wires on a capillary channel are one bridge arm (R 1、R3), and two resistors are the other bridge arm (R 2、R4) are additionally needed, and the two bridge arms are measured by measuring A, The voltage Vout between the two points B can measure the resistance value change between the metal wires R 1 and R 3 on the sensor, and when the upper and lower resistance values of the bridge arms R 2 and R 4 are changed, A, The voltage Vout between the two points B also changes, and since R 2 and R 4 are connected in parallel with R 1 and R 3, a part of current is divided by R 2 and R 4, so that certain power consumption and heat exist, when the temperature changes, not only the resistance values of the wires R 1 and R 3 on the sensor change, but also the resistance values of the resistors R 2 and R 4 on the other bridge arm change, so that the temperature drift of the flowmeter increases, and meanwhile, when the resistance values of the resistors R 2 and R 4 change, the current flowing through the wires R 1 and R 3 on the sensor also changes. at present, the solution to this is mainly to use a low-temperature drift resistor on the other bridge arm at home and abroad, the price is relatively high, and meanwhile, when the low-temperature drift resistor is used, the condition that one resistor on the other bridge arm drifts in a positive direction and the other resistor drifts in a negative direction possibly occurs, which can lead to the increase of the temperature drift of the flowmeter. Accordingly, there is a need for a low cost thermal flow meter sensor drive scheme that effectively suppresses temperature drift. Disclosure of Invention The invention aims to overcome the defects of the prior art, and provides a thermal flowmeter sensor driving circuit, a thermal flowmeter and a flow measuring method, which solve the problem that the temperature drift of a flowmeter is increased due to the change of resistance on a sensor driving bridge caused by temperature. The invention is realized by the following technical scheme: A thermal flowmeter sensor driving circuit for driving and measuring a flow sensor comprising a first sensing resistor R6 and a second sensing resistor R12, wherein the first sensing resistor R6 and the second sensing resistor R12 are connected in series to form a series branch, one end of the first sensing resistor R6 away from the second sensing resistor R12 is a first end a of the series branch, one end of the second sensing resistor R12 away from the first sensing resistor R6 i