Loop current control and detection circuit

Abstract

A loop current control and detection circuit disclosed by the present invention comprises a loop current control circuit and a loop current detection circuit, the loop current control circuit and a sensor form a loop, the loop current control circuit comprises a signal conversion module and a current control module, and the loop current control circuit is configured to output PWM waves through an MCU. A digital signal of the sensor is converted into an analog signal through the first amplifier, voltage at the input end and the output end of the fifth amplifier is adjusted so as to adjust the output current of the current control circuit, and the loop current detection circuit and the sensor form a loop. Comprising a difference-to-single-end conversion module, a low-pass filter, a full-wave rectifier and a direct-current offset module, and the loop current detection circuit is configured to be capable of detecting the voltage difference between the two ends of loop impedance at the output end of the loop current control circuit, filtering noise generated by a self-vibration circuit, correcting inherent direct-current offset of a magnetic load, and outputting the corrected direct-current offset. Therefore, the working state of the sensor can be detected, and the detection precision and the reliability of the circuit can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle sensor detection, and in particular to a loop current control and detection circuit of a sensor. Background Art

[0002] In vehicle process control systems, sensors collect data such as pressure, temperature, power, and voltage, and rely on induced current signals to send this data to the controller. The induced current signal can provide long-distance recovery, reliability, anti-noise function, and universal compatibility with each controller. Controlling and detecting the induced current of the sensor can ensure the reliability of the sensor's operation.

[0003] A Chinese patent application with publication number CN 112147401 A discloses a sensor-based current detection circuit, including a power supply module and a detection module. The power supply module is used to supply power to the detection module; the detection module includes a Hall current sensor, a signal adjustment circuit, and a microprocessor; the Hall current sensor is used to generate an induction signal based on the measured current signal, the signal adjustment circuit is used to adjust the induction signal generated by the Hall current sensor into an analog signal that can be adapted to the microprocessor, and the microprocessor is used to convert the analog signal into a digital signal, and then detect the size of the measured current signal based on the digital signal and output it.

[0004] However, existing sensor current detection circuits have low detection accuracy, slow response speed, high cost, and low reliability in sensor control and detection.

[0005] Therefore, how to effectively improve the current control and detection accuracy of the sensor, increase the response speed, and ensure effective control and detection of the sensor has become an urgent problem to be solved in this field. Summary of the Invention

[0006] In view of the defects of the prior art, the object of the present invention is to provide a loop current control and detection circuit with high reliability and high precision.

[0007] In order to achieve the above-mentioned purpose, the loop current control and detection circuit provided by the present invention cooperates with the sensor, including a loop current control circuit and a loop current detection circuit.

[0008] The loop current control circuit forms a loop with the sensor, including a signal conversion module and a current control module. The loop current control circuit is configured to output a PWM wave through the MCU, convert the digital signal of the sensor into an analog signal through the first amplifier, and adjust the voltage at the input and output terminals of the fifth amplifier to adjust the output current of the current control circuit.

[0009] The loop current detection circuit forms a loop with the sensor, including a differential-to-single-ended conversion module, a low-pass filter, a full-wave rectifier, and a DC offset module. The loop current detection circuit is configured to detect the voltage difference across the loop impedance at the output end of the loop current control circuit, filter out the noise generated by the self-oscillation circuit, and correct the DC bias inherent in the magnetic load to detect the operating status of the sensor.

[0010] Furthermore, the PWM wave output by the MCU in the signal conversion module is connected to the first end of the first resistor through the isolation converter, the second end of the first resistor is connected to the same-direction input end of the first amplifier, the reverse input end and the output end of the first amplifier are connected to the first end of the sixteenth resistor, the second end of the sixteenth resistor is respectively connected to the first end of the first capacitor and the seventeenth resistor, and the second end of the first capacitor is grounded.

[0011] Furthermore, the current control module includes a fifth amplifier, a twenty-second resistor, a nineteenth resistor and a twentieth resistor, the first end of the twenty-second resistor is connected to the positive pole of the power supply, the second end is respectively connected to the second end of the seventeenth resistor and the non-inverting input end of the fifth amplifier, the first end of the nineteenth resistor is respectively connected to the second end of the seventeenth resistor and the non-inverting input end of the fifth amplifier, the second end of the nineteenth resistor is respectively connected to the fifth capacitor and the first end of the twentieth resistor, the second ends of the fifth capacitor and the twentieth resistor are connected to each other and connected to the first end of the eighteenth resistor, and the second end of the eighteenth resistor is connected to the reverse input end of the fifth amplifier.

[0012] Furthermore, the output end of the fifth amplifier is connected to the base of the third switch through the twenty-first resistor, the emitter of the third switch is connected to the first end of the twenty-fifth resistor, the second end of the twenty-fifth resistor is connected to the second end of the eighteenth resistor, the collector of the third switch is connected to the first end of the second capacitor and the second resistor, the first end of the second capacitor is also connected to the negative electrode of the power supply, and the second ends of the second capacitor and the second resistor are connected to the first end of the eighteenth resistor.

[0013] Furthermore, the second resistor is a loop load of the loop current control circuit.

[0014] Furthermore, the differential output voltage signal of the sensor load resistor in the differential-to-single-ended conversion module is respectively connected to the first ends of the fifth resistor and the fourth resistor, the second end of the fifth resistor is connected to the first end of the third resistor, the third resistor and the second end are respectively connected to the first ends of the third capacitor, the seventh resistor and the ninth resistor, the second ends of the seventh resistor and the ninth resistor are respectively connected to the two ends of the seventh capacitor and grounded, the second end of the seventh resistor is also connected to the non-inverting input end of the second amplifier, the second end of the fourth resistor is respectively connected to the second end of the third capacitor, the first end of the sixth resistor and the eighth resistor, the second end of the sixth resistor is respectively connected to the first end of the fourth capacitor and the output end of the second amplifier, the second end of the eighth resistor is respectively connected to the second end of the fourth capacitor and the inverting input end of the second amplifier, and the output end of the second amplifier is also connected to the first end of the tenth resistor.

[0015] Furthermore, the fifth resistor is a load resistor of the sensor, and the differential output voltage signal of the load resistor of the sensor is the voltage across the second resistor.

[0016] Furthermore, the first end of the sixth capacitor in the low-pass filter is respectively connected to the second end of the tenth resistor, the first end of the twelfth resistor and the first end of the eleventh resistor, the second end of the sixth capacitor is grounded, the second ends of the twelfth resistor and the eleventh resistor are respectively connected to the two ends of the eighth capacitor, and the second end of the eleventh resistor is also connected to the inverting input terminal of the third amplifier.

[0017] Furthermore, the full-wave rectifier is composed of an eighth rectifier diode and a ninth rectifier diode. The positive input end of the fourth amplifier in the DC offset module is connected to the output end of the third amplifier. The reverse input end of the fourth amplifier is respectively connected to the positive electrode of the eighth rectifier diode and the first end of the thirteenth resistor. The second end of the thirteenth resistor is respectively connected to the first end of the fourteenth resistor and the reverse input end of the sixth amplifier. The second end of the fourteenth resistor is connected to the output end of the sixth amplifier. The output end of the fourth amplifier is connected to the negative electrode of the eighth rectifier diode and to the positive electrode of the ninth rectifier diode. The negative electrode of the ninth rectifier diode is respectively connected to the first end of the thirty-first resistor and the positive input end of the sixth amplifier. The second end of the thirty-first resistor is grounded.

[0018] The loop current control and detection circuit provided by the present invention uses a loop current control circuit and a loop current detection circuit to respectively form a loop circuit with a sensor to control the sensor current, which can effectively improve the current control accuracy and response speed. At the same time, when performing current detection, the loop current detection circuit filters out the noise generated by the self-oscillation circuit and corrects the DC bias inherent in the magnetic load, which can effectively improve the detection accuracy and thus improve the reliability of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 A system block diagram of the loop current control and detection circuit provided by the present invention;

[0021] Figure 2 is the overall circuit diagram of the loop current control in the present invention;

[0022] Figure 3 This is the circuit diagram of the signal conversion module in the present invention;

[0023] Figure 4 This is the circuit diagram of the current control module in the present invention;

[0024] Figure 5 This is the overall circuit diagram of loop current detection in the present invention;

[0025] Figure 6 This is a circuit diagram of a differential to single-ended conversion module in the present invention;

[0026] Figure 7 This is a circuit diagram of a low-pass filter in the present invention;

[0027] Figure 8 This is a circuit diagram of a full-wave rectifier and a DC offset module in the present invention;

[0028] Figure 9 Schematic diagram of transient simulation results of the full-wave rectifier and DC offset module in the present invention.

[0029] Reference numerals:

[0030] 1. Loop current control circuit; 11. Signal conversion module; 12. Current control module;

[0031] 2. Loop current detection circuit; 21. Differential to single-ended conversion module; 22. Low-pass filter; 23. Full-wave rectifier; 24. DC offset module. DETAILED DESCRIPTION

[0032] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific illustrations.

[0033] See also Figure 1 , which shows an example of the loop current control and detection circuit provided by the present invention.

[0034] As can be seen from the figure, the loop current control and detection circuit of this example cooperates with the sensor, and mainly includes a loop current control circuit 1 and a loop current detection circuit 2.

[0035] The loop current control circuit 1 forms a loop with the sensor, including a signal conversion module 11 and a current control module 12. The loop current control circuit 1 is configured to output a PWM wave through the MCU, convert the digital signal of the sensor into an analog signal through the first amplifier, and adjust the voltage at the input and output ends of the fifth amplifier to adjust the output current of the current control circuit. At the same time, the loop current detection circuit 2 forms a loop with the sensor, including a differential to single-ended conversion module 21, a low-pass filter 22, a full-wave rectifier 23 and a DC offset module 24. The loop current detection circuit 2 is configured to detect the voltage difference between the two ends of the loop impedance at the output end of the loop current control circuit 1, while filtering out the noise generated by the self-oscillation circuit and correcting the DC bias inherent in the magnetic load to detect the working state of the sensor, thereby improving the detection accuracy and reliability.

[0036] Among them, the signal conversion module 11 of the loop current control circuit 1 can convert the digital signal of the sensor into an analog signal, so that the subsequent current control module 12 can control the output current of the loop current control circuit 1 based on the adjustment of the analog signal to control the current of the sensor.

[0037] Combine Figure 2 and Figure 3 Specifically, the PWM wave output by the MCU in the signal conversion module 11 is provided as input to the first amplifier U1 through the isolation converter A4. In this example, the PWM wave output by the MCU is represented by V2. V2 is a simulation device for emitting PWM waves, which can emit PWM waves of different frequencies and duty cycles. Based on the inverse Fourier transform, PWM generates a sinusoidal analog wave. Analog waves of different amplitudes can provide different feedback voltages for the subsequent first amplifier U1.

[0038] Here, the isolation converter A4 isolates the PWM wave from the first amplifier U1 and isolates it from the analog reference through digital noise, so that the PWM waveform is not affected and is input to the first amplifier U1.

[0039] Furthermore, V2 is connected to the first end of the first resistor R1 through the isolation converter A4, the second end of the first resistor R1 is connected to the same-direction input end of the first amplifier U1, the reverse input end and the output end of the first amplifier U1 are connected to the first end of the sixteenth resistor R16, the second end of the sixteenth resistor R16 is respectively connected to the first end of the first capacitor C1 and the seventeenth resistor R17, and the second end of the first capacitor C1 is grounded.

[0040] In this way, the digital signal of the sensor is converted into an analog signal through the conversion output of the first amplifier U1 , and the sixteenth resistor R16 , the first capacitor C1 and the seventeenth resistor R17 form a filtering protection circuit, which can ensure the stability of the signal conversion module 11 .

[0041] Combine Figure 2 and Figure 4 Furthermore, the current control module 12 includes a fifth amplifier U5, a twenty-second resistor R22, a nineteenth resistor R19, and a twentieth resistor R20. The first end of the twenty-second resistor R22 is connected to the positive power supply VDD, and the second end is respectively connected to the second end of the seventeenth resistor R17 and the non-inverting input terminal of the fifth amplifier U5. The first end of the nineteenth resistor R19 is respectively connected to the second end of the seventeenth resistor R17 and the non-inverting input terminal of the fifth amplifier U5. The second end of the nineteenth resistor R19 is respectively connected to the first end of the fifth capacitor C5 and the first end of the twentieth resistor R20. The second ends of the fifth capacitor C5 and the twentieth resistor R20 are connected to each other and connected to the first end of the eighteenth resistor R18. The second end of the eighteenth resistor R18 is connected to the inverting input terminal of the fifth amplifier U5.

[0042] At the same time, the output end of the fifth amplifier U5 is connected to the base of the third switch Q3 via the twenty-first resistor R21. The emitter of the third switch Q3 is connected to the first end of the twenty-fifth resistor R25. The second end of the twenty-fifth resistor R25 is connected to the second end of the eighteenth resistor R18. The collector of the third switch Q3 is connected to the first end of the second capacitor C2 and the second resistor R2. The first end of the second capacitor C2 is also connected to the negative power supply electrode VEE. The second ends of the second capacitor C2 and the second resistor R2 are connected to the first end of the eighteenth resistor R18.

[0043] The second resistor R2 is the loop load of the loop current control circuit 1 , including the inductive resistor and the resistive impedance of the sensor.

[0044] In this way, the twenty-second resistor R22, the nineteenth resistor R19 and the twentieth resistor R20 constitute a voltage divider resistor, which jointly controls the voltage of the same-direction input terminal and the reverse input terminal of the fifth amplifier U5, so that the analog signal is adjusted through the voltage of the same-direction input terminal and the reverse input terminal to adjust the current of the sensing resistor of the sensor of the loop current control circuit 1. At the same time, the voltage drop of the eighteenth resistor R18 is the same as the voltage of the same-direction input terminal of the fifth amplifier U5, thereby controlling the output current of the loop current control circuit 1.

[0045] Furthermore, the output end of the fifth amplifier U5 is connected to the third switch Q3 , which can close the third switch Q3 to drive the loop current control circuit 1 .

[0046] The loop current control circuit 1 thus constructed forms a loop with the sensor, converts the digital signal of the sensor into an analog signal, and adjusts the inductive resistor current of the sensor by adjusting the analog signal, thereby controlling the sensor current.

[0047] Combine Figure 1 and Figure 5Furthermore, after the sensor current stabilizes, the loop current detection circuit 2 detects the current. The loop current detection circuit 2 includes a differential to single-ended conversion module 21, a low-pass filter 22, a full-wave rectifier 23, and a DC offset module 24. The loop current detection circuit 2 is configured to detect the voltage difference between the two ends of the loop impedance at the output end of the loop current control circuit 1, while filtering out the noise generated by the self-oscillation circuit and correcting the DC bias inherent in the magnetic load to detect the working state of the sensor, thereby improving the detection accuracy.

[0048] Specifically, the differential-to-single-ended conversion module 21 converts the differential signal on the sensor load resistor into a single-ended signal, simplifying subsequent signal conditioning.

[0049] Combine Figure 5 and Figure 6 The differential output voltage signal V1 of the sensor load resistor in the differential-to-single-ended conversion module 21 is respectively connected to the first ends of the fifth resistor R5 and the fourth resistor R4, the second end of the fifth resistor R5 is connected to the first end of the third resistor R3, the third resistor R3 and the second end are respectively connected to the first ends of the third capacitor C3, the seventh resistor R7 and the ninth resistor R9, the second ends of the seventh resistor R7 and the ninth resistor R9 are respectively connected to the two ends of the seventh capacitor C7 and grounded, the second end of the seventh resistor R7 is also connected to the non-inverting input end of the second amplifier U2, the second end of the fourth resistor R4 is respectively connected to the second end of the third capacitor C3, the sixth resistor R6 and the first end of the eighth resistor R8, the second end of the sixth resistor R6 is respectively connected to the first end of the fourth capacitor C4 and the output end of the second amplifier U2, the second end of the eighth resistor R8 is respectively connected to the second end of the fourth capacitor C4 and the inverting input end of the second amplifier U2, and the output end of the second amplifier U2 is also connected to the first end of the tenth resistor R10.

[0050] Among them, the fifth resistor R5 is the load resistor of the sensor, and V1 is the differential input signal of the sensor load resistor, specifically the voltage across the second resistor R2 in the loop current control circuit 1, so as to realize the detection of the voltage difference across the loop impedance at the output end of the loop current control circuit 1, so as to detect the working state of the sensor.

[0051] Furthermore, the second amplifier U2 is a differential amplifier. Based on the differential amplifier, the output Vout = -(Vin-)×(R8 / R4)+(Vin+)×(R9 / (R9+R3)) = (Vin+) / 2-(Vin-) can be calculated. Therefore, the third resistor R3, the fourth resistor R4, the eighth resistor R8 and the ninth resistor R9 can adjust the calculated values ​​of the output and input of the second amplifier U2 to enable the second amplifier U2 to amplify the differential input signal.

[0052] At the same time, the voltage shared by the reverse input and the same-direction input of the second amplifier U2 is the common-mode voltage. The second amplifier U2 suppresses the common-mode voltage to accurately amplify the differential input signal, reduce noise interference, and improve system accuracy. The effectiveness of the second amplifier U2 in suppressing the common-mode voltage is the common-mode rejection ratio. The third capacitor C3, the fourth capacitor C4, the sixth capacitor C6, the sixth resistor R6 and the seventh resistor R7 can effectively increase the common-mode rejection ratio of the second amplifier U2, thereby reducing common-mode voltage interference and improving detection reliability.

[0053] In coordination therewith, the low-pass filter 22 can attenuate the self-oscillation frequency and filter out the noise generated by the self-oscillation circuit in the loop current control circuit 1 to prevent false tripping.

[0054] Combine Figure 5 and Figure 7 , wherein the first end of the sixth capacitor C6 in the low-pass filter 22 is respectively connected to the second end of the tenth resistor R10, the first end of the twelfth resistor R12 and the first end of the eleventh resistor R11, the second end of the sixth capacitor C6 is grounded, the second ends of the twelfth resistor R12 and the eleventh resistor R11 are respectively connected to the two ends of the eighth capacitor C8, and the second end of the eleventh resistor R11 is also connected to the inverting input terminal of the third amplifier U3.

[0055] In this way, based on the cut-off frequency formula f=1 / (2×π×R6×R10), the eleventh resistor R11, the twelfth resistor R12 and the eighth capacitor C can filter out noise interference, so that the low-pass filter 22 can filter out the noise generated by the self-oscillation circuit in the loop current control circuit 1 to prevent false tripping.

[0056] Combine Figure 5 and Figure 8 Furthermore, the full-wave rectifier 23 and the DC offset module 24 correct the DC bias inherent in the magnetic load in the loop current control circuit 1. The full-wave rectifier 23 is composed of an eighth rectifier diode D8 and a ninth rectifier diode D9. The positive input terminal of the fourth amplifier U4 in the DC offset module 24 is connected to the output terminal of the third amplifier U3, the negative input terminal of the fourth amplifier U4 is respectively connected to the positive electrode of the eighth rectifier diode D8 and the first end of the thirteenth resistor R13, the second end of the thirteenth resistor R13 is respectively connected to the first end of the fourteenth resistor R14 and the negative input terminal of the sixth amplifier U6, the second end of the fourteenth resistor R14 is connected to the output terminal of the sixth amplifier U6, the output terminal of the fourth amplifier U4 is connected to the negative electrode of the eighth rectifier diode D8 and to the positive electrode of the ninth rectifier diode D9, the negative electrode of the ninth rectifier diode D9 is respectively connected to the first end of the thirty-first resistor R31 and the positive input terminal of the sixth amplifier U6, and the second end of the thirty-first resistor R31 is grounded.

[0057] In this way, the eighth rectifier diode D8 and the ninth rectifier diode D9 convert the AC signal into DC, but the conduction voltage of the eighth rectifier diode D8 and the ninth rectifier diode D9 will cause the output signal to shift.

[0058] In conjunction with this, the positive signal input in the DC offset module 24 is Vout=Vin, and the negative signal input is Vout / Vin=-R14 / R13=-1. When the negative signal is input, the thirteenth resistor R13 and the fourteenth resistor R14 serve as the load of the fourth amplifier U4 and the sixth amplifier U6. By selecting the thirteenth resistor R13 and the fourteenth resistor R14, the full-wave rectifier 23 can reduce thermal noise and minimize the voltage drop caused by the reverse leakage current of the eighth rectifier diode D8 and the ninth rectifier diode D9.

[0059] At the same time, when a negative signal is input, the thirty-first resistor R31 will bias the in-phase node of the sixth amplifier U6 to ground, and the fourth amplifier U4 can drive the load of the thirty-first resistor R31 when a positive input signal is input to stabilize the operation of the fourth amplifier U4.

[0060] Combine Figure 9 As an example, as shown in the red curve in the figure, when a positive signal is input, the fourth amplifier U4 works and outputs Vout = Vin, which offsets the conduction voltage drop of the eighth rectifier diode D8. As shown in the green curve in the figure, when a negative signal is input, the sixth amplifier U6 works and outputs Vout = -Vin (because the gain -R14 / R13 = -1). Therefore, the thirteenth resistor R13 and the fourteenth resistor R14 are precisely matched, compensating for the reverse voltage drop of the ninth rectifier diode D9, and the correction circuit does not damage the signal integrity.

[0061] Furthermore, the curves in the figure are symmetrical along the time axis (0V reference), indicating that the DC component generated by the magnetic load has been accurately compensated.

[0062] Therefore, the full-wave rectifier 23 and the DC offset module 24 cooperate, and the DC offset module 24 injects a compensation voltage that is equal to the inherent DC bias in the loop current control circuit 1 and has an opposite polarity after the rectified output, and adjusts the compensation amount through the feedback network of the fourth amplifier U4 and the sixth amplifier U6 to correct the loop.

[0063] The loop current detection circuit 2 thus constructed detects the voltage difference across the loop impedance at the output end of the loop current control circuit 1, while filtering out the noise generated by the self-oscillation circuit and correcting the DC bias inherent in the magnetic load to detect the working state of the sensor, which can effectively improve the detection accuracy.

[0064] At the same time, the loop current control circuit 1 and the loop current detection circuit 2 respectively form a loop circuit with the sensor, which can effectively improve the current control and detection response speed and improve the reliability of the circuit.

[0065] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A loop current control and detection circuit, in conjunction with a sensor, characterized in that: Including loop current control circuit and loop current detection circuit, The loop current control circuit forms a loop with the sensor, including a signal conversion module and a current control module. The loop current control circuit is configured to output a PWM wave through the MCU, convert the digital signal of the sensor into an analog signal through the first amplifier, and adjust the voltage at the input and output terminals of the fifth amplifier to adjust the output current of the current control circuit. The loop current detection circuit forms a loop with the sensor, including a differential-to-single-ended conversion module, a low-pass filter, a full-wave rectifier, and a DC offset module. The loop current detection circuit is configured to detect the voltage difference across the loop impedance at the output end of the loop current control circuit, while filtering out the noise generated by the self-oscillation circuit and correcting the DC bias inherent in the magnetic load to detect the operating status of the sensor.

2. The loop current control and detection circuit according to claim 1, characterized in that: The PWM wave output by the MCU in the signal conversion module is connected to the first end of the first resistor through the isolation converter, the second end of the first resistor is connected to the same-direction input end of the first amplifier, the reverse input end and the output end of the first amplifier are connected to the first end of the sixteenth resistor, the second end of the sixteenth resistor is respectively connected to the first end of the first capacitor and the first end of the seventeenth resistor, and the second end of the first capacitor is grounded.

3. The loop current control and detection circuit according to claim 2, characterized in that: The current control module includes a fifth amplifier, a twenty-second resistor, a nineteenth resistor and a twentieth resistor. The first end of the twenty-second resistor is connected to the positive electrode of the power supply, and the second end is respectively connected to the second end of the seventeenth resistor and the non-inverting input end of the fifth amplifier. The first end of the nineteenth resistor is respectively connected to the second end of the seventeenth resistor and the non-inverting input end of the fifth amplifier. The second end of the nineteenth resistor is respectively connected to the first end of the fifth capacitor and the first end of the twentieth resistor. The second ends of the fifth capacitor and the twentieth resistor are connected to each other and connected to the first end of the eighteenth resistor. The second end of the eighteenth resistor is connected to the inverting input end of the fifth amplifier.

4. The loop current control and detection circuit according to claim 3, characterized in that: The output end of the fifth amplifier is connected to the base of the third switch through the twenty-first resistor, the emitter of the third switch is connected to the first end of the twenty-fifth resistor, the second end of the twenty-fifth resistor is connected to the second end of the eighteenth resistor, the collector of the third switch is connected to the first end of the second capacitor and the second resistor, the first end of the second capacitor is also connected to the negative electrode of the power supply, and the second ends of the second capacitor and the second resistor are connected to the first end of the eighteenth resistor.

5. The loop current control and detection circuit according to claim 4, characterized in that: The second resistor is the loop load of the loop current control circuit.

6. The loop current control and detection circuit according to claim 5, characterized in that: The differential output voltage signal of the sensor load resistor in the differential-to-single-ended conversion module is respectively connected to the first ends of the fifth resistor and the fourth resistor, the second end of the fifth resistor is connected to the first end of the third resistor, the third resistor and the second end are respectively connected to the first ends of the third capacitor, the seventh resistor and the ninth resistor, the second ends of the seventh resistor and the ninth resistor are respectively connected to the two ends of the seventh capacitor and grounded, the second end of the seventh resistor is also connected to the non-inverting input terminal of the second amplifier, the second end of the fourth resistor is respectively connected to the second end of the third capacitor, the first end of the sixth resistor and the eighth resistor, the second end of the sixth resistor is respectively connected to the first end of the fourth capacitor and the output terminal of the second amplifier, the second end of the eighth resistor is respectively connected to the second end of the fourth capacitor and the inverting input terminal of the second amplifier, and the output terminal of the second amplifier is also connected to the first end of the tenth resistor.

7. The loop current control and detection circuit according to claim 6, characterized in that: The fifth resistor is a load resistor of the sensor, and the differential output voltage signal of the load resistor of the sensor is the voltage across the second resistor.

8. The loop current control and detection circuit according to claim 7, characterized in that: The first end of the sixth capacitor in the low-pass filter is respectively connected to the second end of the tenth resistor, the first end of the twelfth resistor and the first end of the eleventh resistor, the second end of the sixth capacitor is grounded, the second ends of the twelfth resistor and the eleventh resistor are respectively connected to the two ends of the eighth capacitor, and the second end of the eleventh resistor is also connected to the inverting input terminal of the third amplifier.

9. The loop current control and detection circuit according to claim 8, characterized in that: The full-wave rectifier is composed of an eighth rectifier diode and a ninth rectifier diode. The positive input end of the fourth amplifier in the DC offset module is connected to the output end of the third amplifier. The negative input end of the fourth amplifier is respectively connected to the positive electrode of the eighth rectifier diode and the first end of the thirteenth resistor. The second end of the thirteenth resistor is respectively connected to the first end of the fourteenth resistor and the negative input end of the sixth amplifier. The second end of the fourteenth resistor is connected to the output end of the sixth amplifier. The output end of the fourth amplifier is connected to the negative electrode of the eighth rectifier diode and to the positive electrode of the ninth rectifier diode. The negative electrode of the ninth rectifier diode is respectively connected to the first end of the thirty-first resistor and the positive input end of the sixth amplifier. The second end of the thirty-first resistor is grounded.

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