Full-bridge strain gauge sensor signal acquisition and signal processing module device

Abstract

The embodiment of the utility model relates to a signal acquisition and signal processing module device for a full-bridge strain gauge sensor, and the device comprises a power input unit which is used for supporting an external power supply voltage; the input anti-reverse connection protection circuit unit is connected with the power supply input unit and is used for preventing input short circuit and reverse connection; the first reference power supply unit is used for providing negative voltage in dual-supply voltage for a dual-input differential amplifier of the analog signal amplification system; the second reference power supply unit is used for providing working voltage for the full-bridge strain gauge; the full-bridge strain gauge unit is used for sensing external stress and reflecting the external stress as voltage difference output; and the analog signal amplification unit is used for amplifying the differential signal output by the full-bridge strain gauge unit into an analog signal which is easy to observe by a user, and outputting the analog signal from an output port. The embodiment of the utility model has the advantages of low price and complete functions, is convenient to use and expand a strain gauge sensor signal acquisition and signal processing system, and is convenient for multi-scene application.

Description

Technical Field

[0001] This utility model relates to the field of sensor technology, specifically to a signal acquisition and signal processing module device for a full-bridge strain gauge sensor. Background Technology

[0002] This section introduces background technology that may be related to various aspects of the embodiments of this utility model, which is believed to provide useful background information to help readers better understand the various aspects of the embodiments of this utility model. Therefore, it is understood that the description in this section is for the above purposes and does not constitute an admission of the prior art.

[0003] Strain gauge sensors are sensors that measure the strain generated by the deformation of an object under stress. Stress measurement is widely used in fields such as machinery, aerospace, automotive, construction, electronics, and medicine. When a strain gauge sensor is subjected to strain or deformation, it produces a change in resistance. By converting this change in resistance into a voltage signal, it can be well integrated into circuit control systems for automated control, signal acquisition, and other applications.

[0004] In education, the popularity of circuit interest groups and circuit innovation competitions has encouraged students to develop more functions for strain gauge sensors. However, the high price and complex operation of the equipment can dampen their enthusiasm. Commercial and industrial methods for converting strain gauge resistance changes into voltage signals involve specialized dynamic and static strain acquisition instruments. These instruments are dedicated precision equipment, costly, and unsuitable for large-scale use. In the low-cost sector, existing strain gauge sensor modules offer basic strain sensing capabilities, but there remains a market demand for strain gauge sensor modules with high usability, ease of operation, and protection mechanisms. Utility Model Content

[0005] The technical problem to be solved is how to provide a signal acquisition and signal processing module device for a full-bridge strain gauge sensor.

[0006] To address the shortcomings of existing technologies, this utility model provides a full-bridge strain gauge sensor signal acquisition and signal processing module device, which can effectively improve the application scenarios of strain gauge sensors.

[0007] In a first aspect, embodiments of this utility model provide a signal acquisition and signal processing module device for a full-bridge strain gauge sensor, comprising:

[0008] Power input unit, used to support external power supply voltage;

[0009] The input reverse connection protection circuit unit connected to the power input unit is used to prevent input short circuit and reverse connection, provide an indicator light when the input is connected in the correct direction, and cut off the power supply to the functional circuit when the input is short circuit or reverse connection.

[0010] The first reference power supply unit, connected to the input reverse connection protection circuit unit, is used to provide the negative voltage in the dual power supply voltage for the dual-input differential amplifier of the analog signal amplification system.

[0011] The second reference power supply unit, connected to the input reverse connection protection circuit unit, is used to provide operating voltage for the full-bridge strain gauge.

[0012] The full-bridge strain gauge unit connected to the second reference power supply unit is used to sense external stress and reflect it as a voltage difference output.

[0013] An analog signal amplification unit, which is connected to the full-bridge strain gauge unit, the input reverse connection protection circuit unit, and the first reference power supply unit respectively, is used to amplify the differential signal output by the full-bridge strain gauge unit into an analog signal that is easy for the user to observe, and output it from the output port.

[0014] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some embodiments provided.

[0015] The input reverse connection protection circuit unit includes:

[0016] Interconnected reverse connection current non-conducting mechanism and forward connection indication mechanism;

[0017] The reverse connection current non-conducting mechanism comprises: a first field-effect transistor Q1, a second field-effect transistor Q2, and a resistor R11;

[0018] The D terminal of the first field-effect transistor Q1 is connected to the power input unit and the resistor R11, wherein the other end of the resistor R11 is connected to the power ground of the power input unit.

[0019] The S terminal of the first field-effect transistor Q1 is connected to the output power ground, and the G terminal is connected to the resistor R12 and the D terminal of the second field-effect transistor Q2. The other end of the resistor R12 is connected to the output power ground, and the G terminal of the second field-effect transistor Q2 is connected to the power ground of the power input unit, and the S terminal is connected to the input voltage of the power input unit.

[0020] The positive connection indication mechanism consists of a resistor R9 and an indicator light D1; the positive terminal of the indicator light D1 is connected to the power input unit, the negative terminal is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the output power ground.

[0021] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0022] The first reference power supply unit also includes a voltage conversion chip U4, and surrounding capacitors C1, C5, and C7;

[0023] The capacitors C7 and C5 are respectively connected to the input voltage and ground and the output voltage and ground of the voltage conversion chip U4, and the capacitor C1 is connected to the external capacitor port of the voltage conversion chip U4.

[0024] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0025] The second reference power supply unit includes:

[0026] A controllable precision voltage regulator and a voltage divider resistor are provided. The cathode and reference terminal of the controllable precision voltage regulator are connected to the voltage divider resistor, and the other end of the voltage divider resistor is connected to the input positive voltage. The anode of the controllable precision voltage regulator is connected to the output power ground, and the reference terminal of the controllable precision voltage regulator is the output reference voltage.

[0027] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0028] The second reference power supply unit includes:

[0029] Controllable precision voltage regulator, resistor R10, capacitor C8;

[0030] The cathode and reference terminal of the controllable precision voltage regulator are short-circuited and connected to the resistor R10 and the capacitor C8. The other end of the resistor R10 is connected to the power input unit, and the other end of the capacitor C8 is connected to the output power ground. The anode of the controllable precision voltage regulator is connected to the output power ground.

[0031] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0032] The full-bridge strain gauge unit comprises a strain gauge group consisting of four small strain gauges connected in series in a full-bridge structure.

[0033] The strain gauge assembly includes four connection points: the upper connection point is connected to the second reference power supply unit, the lower connection point is connected to the output power ground, and the differential voltage output from the left and right connection points is respectively connected to the differential input port of the first stage amplifier in the analog signal amplification unit.

[0034] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0035] The analog signal amplification unit includes:

[0036] The first operational amplifier module and the second operational amplifier module are connected in sequence.

[0037] The input terminal of the first operational amplifier module is connected to the full-bridge strain gauge unit; the output terminal of the first operational amplifier module is connected to the positive input terminal of the second operational amplifier module.

[0038] The negative input terminal of the second operational amplifier module is grounded, and the output voltage of the second operational amplifier module is the overall output.

[0039] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0040] The first operational amplifier module includes: resistors R1, R2, R3, and R4, capacitor C2, first potentiometer RP1, and first operational amplifier U1;

[0041] One of the output ports of the full-bridge strain gauge unit is connected in series with resistor R1 and resistor R3, and the node between resistor R1 and resistor R3 serves as the negative input of the first operational amplifier U1.

[0042] Another output port of the full-bridge strain gauge unit is connected in series with resistors R2 and R4, and then connected to the output of the first operational amplifier U1. The node between resistors R2 and R4 serves as the positive input of the first operational amplifier U1. The capacitor C2 is connected between the bipolar power supply pins of the first operational amplifier U1, and the potentiometer RP1 is connected between the offset voltage control pins of the first operational amplifier U1.

[0043] In other embodiments of the full-bridge strain gauge sensor signal acquisition and signal processing module device described in this specification, there are some additional embodiments.

[0044] The second operational amplifier module includes: resistors R5, R6, and R8; capacitors C3 and C6; a second potentiometer RP7; and a second operational amplifier U2.

[0045] The output of the first operational amplifier module is connected in series with resistor R5 and then to the positive input of the second operational amplifier U2. Simultaneously, capacitor C6 is connected in series between the positive input and the output power ground of the second operational amplifier U2. Resistor R6 and potentiometer RP7 are connected in series and then to the output of the second operational amplifier U2. The output of the second operational amplifier U2 is connected in series with resistor R8 as the overall output. The node between resistor R6 and RP7 serves as the negative input of the second operational amplifier U2. Capacitor C3 is connected between the bipolar power supply pins of the second operational amplifier U2, and the offset voltage pin is left floating.

[0046] As can be seen from the above technical solution, the full-bridge strain gauge sensor signal acquisition and signal processing module device provided by this utility model has the advantages of low price and complete functions. It is an easy-to-use and expandable strain gauge sensor signal acquisition and signal processing system, and has a reverse connection protection mechanism to avoid module input reverse connection or short circuit due to improper operation or other accidents, which would lead to module damage. It also has zero-point adjustment and amplification adjustment functions, which are convenient for multi-scenario applications. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the overall structure of a full-bridge strain gauge sensor signal acquisition and signal processing module device in one embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of the circuit structure of a full-bridge strain gauge sensor signal acquisition and signal processing module device in one embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the second reference power supply unit structure of a full-bridge strain gauge sensor signal acquisition and signal processing module device in one embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram of the analog signal amplification unit structure of a full-bridge strain gauge sensor signal acquisition and signal processing module device in one embodiment of the present invention;

[0052] Figure 5 This is a schematic diagram of the overall structure and module connection of a full-bridge strain gauge sensor signal acquisition and signal processing module device in one embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0054] like Figures 1 to 5 As shown, this utility model embodiment provides a full-bridge strain gauge sensor signal acquisition and signal processing module device, including: a power input unit 7 for supporting external power supply voltage; an input reverse connection protection circuit unit 3 connected to the power input unit 7 for preventing input short circuits and reverse connections, providing an indicator light when the input is positively connected, and cutting off the power supply to the functional circuit when the input is short-circuited or reverse-connected; a first reference power supply unit 1 connected to the input reverse connection protection circuit unit 2 for providing the negative voltage in the dual power supply voltage; a second reference power supply unit 2 connected to the input reverse connection protection circuit unit 3 for providing the working voltage; a full-bridge strain gauge unit 6 connected to the second reference power supply unit 2 for sensing external stress and converting the sensed external stress into a voltage difference output; and an analog signal amplification unit 8 connected to the full-bridge strain gauge unit 6, the input reverse connection protection circuit unit 3, and the first reference power supply unit 4 respectively, for amplifying the weak differential signal output by the full-bridge strain gauge unit 6 into an analog signal that is easy for the user to observe, and outputting it from the output port. The following is a detailed description of the full-bridge strain gauge sensor signal acquisition and signal processing module device provided in the embodiments of this utility model.

[0055] like Figures 1 to 2 As shown in the embodiment of this utility model, the power input unit 7 is the power source for the entire system; the power input unit 7 externally inputs a +5V voltage and an input ground signal (IN_GND).

[0056] like Figures 1 to 5As shown in the embodiment of this utility model, the input reverse connection protection circuit unit 3 includes: a reverse connection current non-conducting mechanism 31 and a forward connection indication mechanism 32 connected to each other; the reverse connection current non-conducting mechanism 31 includes: a first field-effect transistor Q1, a second field-effect transistor Q2, and a resistor; the drain (D) terminal of the first field-effect transistor Q1 is connected to the power input unit 7 (power ground input) and the resistor R11, wherein the other end of the resistor R11 is connected to the power input unit 7 (external input voltage +5V voltage); the source (S) terminal of Q1 is connected to the output power ground, and the gate (G) terminal is connected to the resistor R12 and the drain (D) terminal of the second field-effect transistor Q2, wherein the other end of the resistor R12 is connected to the output power ground, the gate (G) terminal of the second field-effect transistor Q2 is connected to the input power input unit 7 (power ground input), and the source (S) terminal of the second field-effect transistor Q2 is connected to the power input unit 7 (external input voltage +5V voltage). The forward connection indication mechanism 32 consists of a resistor R9 and an indicator light D1 (LED light-emitting diode). The positive terminal of indicator light D1 is connected to the power input unit, and the negative terminal is connected to one end of resistor R9. The other end of resistor R9 is connected to the output power ground. In this embodiment of the invention, the first field-effect transistor Q1 can be a KIA8205. The second field-effect transistor Q2 can be an AO3407.

[0057] like Figures 1 to 5 As shown in the embodiment of this utility model, the first reference power supply unit 1 includes a voltage conversion chip U4 and surrounding capacitors C1, C5, and C7; wherein capacitors C7 and C5 are respectively connected to ground for the input voltage and ground for the output voltage of the voltage conversion chip U4, and capacitor C1 is connected to the external capacitor port of the voltage conversion chip U4. The voltage conversion chip U4 can be an ICL7660. The first reference power supply unit 1 generates a -5V voltage, providing the negative voltage of the dual power supply voltage for the dual-input differential amplifier of the analog signal amplification system.

[0058] like Figures 1 to 5As shown in the embodiment of this utility model, the second reference power supply unit 2 includes: a controllable precision voltage regulator and a voltage divider resistor R10. The cathode and reference terminal of the controllable precision voltage regulator are connected to the voltage divider resistor, and the other end of the voltage divider resistor is connected to the power input unit 7 (external input voltage +5V). The anode of the controllable precision voltage regulator is connected to the output power ground, and the reference terminal of the controllable precision voltage regulator is the output reference voltage. The +2.5V reference power supply unit provides the working voltage for the full-bridge strain gauge; the controllable precision voltage regulator U3 can be a TCL431. The second reference power supply unit 2 also includes a capacitor C8; wherein the cathode and reference terminal of U3 are short-circuited and connected to the resistor R10 and the capacitor C8. The other end of the resistor R10 is connected to the power input unit 7 (external input voltage +5V), and the other end of the capacitor C8 is connected to the output power ground; the negative terminal of U3 is connected to the output power ground. The second reference power supply unit 2 outputs a +2.5V reference connected to the full-bridge strain gauge unit 6.

[0059] like Figures 1 to 5 As shown in the embodiment of this utility model, the full-bridge strain gauge unit 6 includes a strain gauge group consisting of four small strain gauges connected in series in a full-bridge structure; the strain gauge group includes four connection points, the upper connection point is connected to the second reference power supply unit 2, the lower connection point is connected to the output power ground, and the differential voltage output from the left and right connection points is respectively connected to the differential input port of the first stage amplifier in the analog signal amplification unit.

[0060] like Figures 1 to 5 As shown in the embodiment of this utility model, the analog signal amplification unit 8 includes: a first operational amplifier module 81 and a second operational amplifier module 82 connected in sequence; the input terminal of the first operational amplifier module 81 is connected to the full-bridge strain gauge unit 6; the output terminal of the first operational amplifier module 81 is connected to the positive input terminal of the second operational amplifier module 82; the negative input terminal of the second operational amplifier module 82 is connected to the output power ground. The first operational amplifier module 81 and the second operational amplifier module 82 constitute a positive proportional amplifier circuit structure, and the output voltage of the second operational amplifier module 82 is the overall output.

[0061] like Figures 1 to 5As shown in this embodiment of the present invention, the first operational amplifier module 81 includes: resistors R1, R2, R3, and R4, capacitor C2, a first potentiometer RP1, and a first operational amplifier U1. One output port of the full-bridge strain gauge unit 6 is connected in series with resistors R1 and R3, and the other end of R3 is connected to the output power ground. The node between resistors R1 and R3 serves as the negative input of the first operational amplifier U1. The other output port of the full-bridge strain gauge unit 6 is connected in series with resistors R2 and R4, and then connected to the output of the first operational amplifier U1. The node between resistors R2 and R4 serves as the positive input of the first operational amplifier U1. Capacitor C2 is connected between the bipolar power supply pins of the first operational amplifier U1, and potentiometer RP1 is connected between the offset voltage control pins of the first operational amplifier U1. Potentiometer RP1 adjusts the zero point of the output voltage.

[0062] like Figures 1 to 5 As shown in this embodiment of the invention, the second operational amplifier module 82 includes: resistors R5, R6, and R8; capacitors C3 and C6; a second potentiometer RP7; and a second operational amplifier U2. The output terminal of the first operational amplifier module 81 is connected in series with resistor R5 and then to the positive input terminal of the second operational amplifier U2. Simultaneously, capacitor C6 is connected in series between the positive input terminal and the output power ground of the second operational amplifier U2. Resistor R6 and the second potentiometer RP7 are connected in series and then to the output of the second operational amplifier U2. The output of the second operational amplifier U2 is connected in series with resistor R8 and serves as the output of the overall circuit system. The node between resistor R6 and the second potentiometer RP7 serves as the negative input of the second operational amplifier U2. Capacitor C3 is connected between the bipolar power supply pins of the second operational amplifier U2, and the offset voltage pin is left floating. The output voltage (Vout) of the second operational amplifier U2 is the output of the overall system. The second potentiometer RP7 adjusts the amplification factor of the strain gauge output.

[0063] In summary, the full-bridge strain gauge sensor signal acquisition and signal processing module device provided by this utility model has the advantages of low price and full functionality. It is an easy-to-use and expandable strain gauge sensor signal acquisition and signal processing system, and has a reverse connection protection mechanism to prevent module input reverse connection or short circuit due to improper operation or other accidents, which could lead to module damage. It also has zero-point adjustment and amplification adjustment functions, which are convenient for multi-scenario applications.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model, and they should all be covered within the scope of the claims and specification of this utility model.

Claims

1. A full-bridge strain gauge sensor signal acquisition and signal processing module apparatus, characterized by, The application relates to a power input unit for supporting external power supply voltage, an input anti-reverse connection protection circuit unit connected with the power input unit for preventing input short circuit and reverse connection, a first reference power unit connected with the input anti-reverse connection protection circuit unit for providing negative voltage in double power supply voltage for a double-input differential amplifier of an analog signal amplification system, a second reference power unit connected with the input anti-reverse connection protection circuit unit for providing working voltage for a full-bridge strain gauge, a full-bridge strain gauge unit connected with the second reference power unit for sensing external stress and reflecting the stress as voltage difference output, and an analog signal amplification unit connected with the full-bridge strain gauge unit, the input anti-reverse connection protection circuit unit and the first reference power unit respectively for amplifying the differential signal output by the full-bridge strain gauge unit into analog signals easy to be observed by users and outputting from an output port. The input anti-reverse connection protection circuit unit comprises a reverse connection current non-conduction mechanism and a forward connection prompting mechanism connected with each other. The reverse connection current non-conduction mechanism comprises a first field effect transistor Q1, a second field effect transistor Q2 and a resistor R11. The D end of the first field effect transistor Q1 is connected with the power input unit and the resistor R11, wherein the other end of the resistor R11 is connected with the power ground of the power input unit. The S end of the first field effect transistor Q1 is connected with an output power ground, and the G end is connected with the resistor R12 and the D end of the second field effect transistor Q2, wherein the other end of the resistor R12 is connected with the output power ground, and the G end of the second field effect transistor Q2 is connected with the power ground of the power input unit, and the S end is connected with the input voltage of the power input unit. The forward connection prompting mechanism comprises a resistor R9 and an indicator lamp D1. The first reference power unit further comprises a voltage conversion chip U4 and surrounding capacitors C1, C5 and C7.

2. The full-bridge strain gauge sensor signal acquisition and signal processing module apparatus of claim 1, wherein, The capacitor C7 and the capacitor C5 are connected with the input voltage and the ground of the voltage conversion chip U4 and the output voltage and the ground of the voltage conversion chip U4 respectively, and the capacitor C1 is connected with the external capacitor port of the voltage conversion chip U4. The second reference power unit comprises a controllable precision voltage stabilizing source and a voltage dividing resistor. The second reference power unit comprises a controllable precision voltage stabilizing source, a resistor R10 and a capacitor C8. ​ ​ ​ 3. The full-bridge strain gauge sensor signal acquisition and signal processing module apparatus of claim 1, wherein, ​ ​ 4. The full-bridge strain gauge sensor signal acquisition and signal processing module apparatus of claim 1, wherein, ​ ​ 5. The full-bridge strain gauge sensor signal acquisition and signal processing module apparatus of claim 1, wherein, ​ ​ The cathode of the controllable precision voltage regulator is shorted with the reference end, and is connected with the resistor R10 and the capacitor C8, the other end of the resistor R10 is connected with the power input unit, and the other end of the capacitor C8 is connected with the output power ground; the anode of the controllable precision voltage regulator is connected with the output power ground.

6. The full-bridge strain gage sensor signal acquisition and signal processing module apparatus of claim 1, wherein, The full-bridge strain gauge unit comprises four small pieces of strain gauges connected in series to form a strain gauge group. The strain gauge group comprises four connection points, the upper end connection point is connected with the second reference power unit, the lower end connection point is connected with the output power ground, and the left and right connection points output differential voltages and are connected to the differential input ports of the first-stage amplifiers in the analog signal amplification unit.

7. The full-bridge strain gage sensor signal acquisition and signal processing module apparatus of claim 1, wherein, The analog signal amplification unit comprises: a first operational amplification module and a second operational amplification module connected in sequence; the input end of the first operational amplification module is connected with the full-bridge strain gauge unit, and the output end of the first operational amplification module is connected to the positive input end of the second operational amplification module; the negative input end of the second operational amplification module is grounded, and the output voltage of the second operational amplification module is the overall output.

8. The full-bridge strain gage sensor signal acquisition and signal processing module apparatus of claim 7, wherein, The first operational amplification module comprises resistors R1, R2, R3, R4, a capacitor C2, a first potentiometer RP1 and a first operational amplifier U1. One of the output ports of the full-bridge strain gauge unit is connected in series with the resistors R1 and R3, and the node between the resistors R1 and R3 serves as the negative input end of the first operational amplifier U1. The other output port of the full-bridge strain gauge unit is connected in series with the resistors R2 and R4, and is then connected to the output of the first operational amplifier U1, wherein the node between the resistors R2 and R4 serves as the positive input end of the first operational amplifier U1, the capacitor C2 is connected between the bipolar power supply pins of the first operational amplifier U1, and the potentiometer RP1 is connected between the offset voltage control pins of the first operational amplifier U1.

9. The full-bridge strain gage sensor signal acquisition and signal processing module apparatus of claim 7, wherein, The second operational amplification module comprises resistors R5, R6, R8, capacitors C3, C6, a second potentiometer RP7 and a second operational amplifier U2. The output end of the first operational amplification module is connected in series with the resistor R5, and then connected to the positive input end of the second operational amplifier U2, while the capacitor C6 is connected in series between the positive input end and the output power ground of the second operational amplifier U2; the resistor R6 and the potentiometer RP7 are connected in series, and then connected to the output of the second operational amplifier U2, the output of the second operational amplifier U2 is connected in series with the resistor R8, and then serves as the overall output; the node between the resistor R6 and the potentiometer RP7 serves as the negative input end of the second operational amplifier U2, the capacitor C3 is connected between the bipolar power supply pins of the second operational amplifier U2, and the offset voltage pin is left unconnected.

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