Contactor contact screening circuit

Abstract

The invention provides a contactor contact screening circuit which comprises an MCU circuit, the MCU circuit comprises a chip U4, PC7-PC9 pins of the chip U4 are connected with a contact coil power supply circuit, a PE5 pin of the chip U4 is connected with an excitation power supply circuit, a PA4 pin of the chip U4 is connected with a 5A constant-current power supply circuit and a middle screening excitation circuit, PG12, PG11, PD6 and PD5 pins are connected with an RS232 communication circuit, the PA4 and PA5 pins are connected with a middle screening circuit, and the chip U4 is connected with the middle screening circuit. A PC8 pin and a PC9 pin are connected with the low screening excitation circuit, and the middle screening circuit is further connected with the low screening excitation circuit; key technologies such as precise measurement, automatic control, visual data display, intelligent fault judgment and the like are integrated through the system, and low-level signals such as voltage, current, contact resistance and the like of the auxiliary contact of the contactor can be rapidly acquired and analyzed with high precision.

Description

Technical Field

[0001] The present invention relates to a contactor contact screening circuit. Background Art

[0002] Contactor contact screening is a key technical means to improve the performance of contactors. By real-time monitoring and screening of contactor contact signals, abnormal signals can be effectively identified and excluded, reducing the incidence of system failures. Especially under harsh working conditions, the screening technology can capture minute signal changes in real time and effectively eliminate false triggering and misjudgment caused by factors such as noise and interference, thus ensuring the reliability and safety of contactors. To improve the performance of contactor contacts, the assistance of a screening system is also required. Contact screening can test and verify contactors with new materials and new structures, providing experimental data for the improvement direction of contactor contacts.

[0003] Currently, the testing and screening of contactor contacts are carried out by separate instruments and equipment. First, the contact voltage drop parameters are measured on the testing equipment, then transferred to the screening equipment for screening, and then back to the testing equipment for testing. The conversion of the testing equipment takes time, which means that the testing and screening are separated, and the contact parameters measured are no longer the data during multiple operations of the contacts, and cannot effectively simulate the actual working conditions of the contacts. Currently, the screening equipment does not record the specific parameters during the screening process and cannot reflect the change trend and drift trend of contact parameters during multiple on-off processes. For example, a contactor contact logic detection system and its detection method disclosed in CN116679194A include a testing PLC, a sampling resistor, and a contactor to be tested; the present invention controls and tests the contacts of the contactor through the PLC and relays, and can set the corresponding on-off ratio for mechanical aging according to the product structure and working conditions of the contactor, and real-time detect the on-off logic of the contacts during mechanical aging. When the on-off logic is incorrect, an alarm will be given to remind the operator to screen out qualified products. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a contactor contact screening circuit.

[0005] The present invention is achieved through the following technical solutions.

[0006] A contactor contact screening circuit provided by the present invention includes an MCU circuit. The MCU circuit includes a chip U4. The PC7-PC9 pins of the chip U4 are connected to a contact coil power supply circuit. The PE5 pin is connected to an excitation power supply circuit. The PA4 pin is respectively connected to a 5A constant current power supply circuit and a medium screening excitation circuit. The PG12, PG11, PD6, and PD5 pins are connected to an RS232 communication circuit. The PA4 and PA5 pins are connected to a medium screening circuit. The PC8 and PC9 pins are connected to a low screening excitation circuit. The medium screening circuit is also connected to the low screening circuit;

[0007] The VBAT, VDD, and VDD33USB pins of the chip U4 are all connected to a 3.3V power supply. The VDDA pin is connected to a 3.3VA power supply. The PG5, PG6, and PG7 pins are respectively connected to an LED tube. The anodes of the LED tubes are connected to the 3.3V power supply.

[0008] The contactor coil power supply circuit includes an opto-isolation chip U1, an opto-isolation chip U2, and an opto-isolation chip U3. The positive input terminal of the opto-isolation chip U1 is connected to the PC9 pin of the chip U4 and is connected to the 3.3V power supply through a resistor R1. The negative input terminal of the opto-isolation chip U1 is grounded, and a capacitor C1 is connected in parallel between the negative input terminal and the positive input terminal. The output terminal of the opto-isolation chip U1 is connected to the V_COIL_IN terminal through a resistor R2 and is connected to the cathode of a diode D2. The V_COIL_IN terminal is also connected to a resistor R3. The resistor R3 is respectively connected to the anode of a light-emitting diode D1 and the cathode of a light-emitting diode D3. The cathode of the light-emitting diode D1, the anode of the light-emitting diode D3, the anode of the diode D2, and the negative output terminal of the opto-isolation chip U1 are all connected to the V_COIL terminal. A fuse F1 is provided between the V_COIL_IN terminal and the V_COIL terminal;

[0009] The positive output terminals of the opto-isolation chip U2 and the opto-isolation chip U3 are both connected to the 3.3V power supply, and the negative output terminals are respectively connected to the PC8 and PC7 pins of the chip U4 through resistors;

[0010] The positive input terminal of the opto-isolation chip U2 is connected to a resistor R6. The other end of the resistor R6 is respectively connected to the anode of a voltage stabilizing diode D4, a resistor R4, and the gate of a MOS transistor Q1. The cathode of the voltage stabilizing diode D4, the other end of the resistor R4, and the source of the MOS transistor Q1 are connected to the V_COIL terminal. The drain of the MOS transistor Q1 is connected to the cathode of a diode D6. The anode of the diode D6 is grounded at the negative input terminal of the opto-isolation chip U2.

[0011] The positive terminal of the input end of the optoelectronic isolation chip U3 is connected to the resistor R7. The other end of the resistor R7 is respectively connected to the anode of the voltage stabilizing diode D5, the resistor R5, and the gate of the MOS transistor Q2. The cathode of the voltage stabilizing diode D5, the other end of the resistor R5, and the source of the MOS transistor Q2 are connected to the V_COIL terminal. The drain of the MOS transistor Q2 is connected to the cathode of the diode D7. The anode of the diode D7 and the negative terminal of the input end of the optoelectronic isolation chip U3 are grounded.

[0012] The excitation power supply circuit includes a MOS transistor Q3. The gate of the MOS transistor Q3 is respectively connected to the resistor R10, the anode of the voltage stabilizing diode D8, and the resistor R12. The cathode of the voltage stabilizing diode D8, the other end of the resistor R10, and the source of the MOS transistor Q3 are connected to the 28V power supply. The 28V power supply is also connected to the resistor R11. The other end of the resistor R11 and the drain of the MOS transistor Q3 are connected to the A0 terminal. The other end of the resistor R12 is connected to the collector of the triode Q3. The base of the triode Q4 is connected to the resistors R17 and R18. The other end of the resistor R17 is connected to the PE4 pin of the chip U4. The resistor R18 and the emitter of the triode Q4 are grounded.

[0013] The 5A constant current power supply circuit includes an operational amplifier U27B. The positive terminal of the input end of the operational amplifier U27B is connected to the PA4 pin of the chip U4. The output end of the operational amplifier U27B is connected to the resistor R19. The resistor R19 is connected to the base of the triode Q5. The collector of the triode Q5 outputs the IMAX5A power supply. The emitter of the triode Q5 and the negative terminal of the input end of the operational amplifier U27B are both grounded through the parallel-connected capacitor C23, resistor R20, and resistor R21.

[0014] The RS232 communication circuit includes an RS232 chip U5. The 9th, 10th, 11th, and 12th pins of the RS232 chip U5 are respectively connected to the PG11, PG12, PD5, and PD6 pins of the chip U4. The 7th, 8th, 13th, and 14th pins are respectively grounded through a TVS tube. Capacitors C27 and C29 are respectively connected between the 1st and 3rd pins and between the 4th and 5th pins. The 16th pin is connected to the 3.3V power supply and grounded through the capacitor C28. The 2nd and 6th pins are respectively grounded through the capacitors C30 and C33.

[0015] The screening circuit includes amplifiers U7 and U8. The 1st and 4th pins of the amplifiers U7 and U8 are respectively connected to the low screening circuit through resistors. A resistor and a capacitor are also connected in parallel between the 1st and 4th pins and are respectively grounded through capacitors. The 7th pins of the amplifiers U7 and U8 are respectively connected to the PA4 and PA5 pins of the chip U4 through resistors, and are connected to the 3.3V power supply through diodes and grounded through capacitors.

[0016] The low screening circuit includes an AD converter U9. The 11th and 10th pins of the AD converter U9 are respectively connected to the 4th and 1st pins of the amplifier U7 through a resistor R53 and a resistor R55. The 7th and 6th pins are respectively connected to the 4th and 1st pins of the amplifier U8 through a resistor R56 and a resistor R54. The 4th, 1st, 7th, and 6th pins of the AD converter U9 are respectively connected to the 5VA1 power supply through diodes and are respectively grounded through capacitors.

[0017] The low screening excitation circuit includes a triode Q12. The base of the triode Q12 accesses the excitation signal LCON1 through a resistor R65. The base of the triode Q12 is grounded through a resistor R68 to its emitter. The collector of the triode Q12 is respectively connected to the model terminals of solid-state relays U11, U12, U13, and U14 through resistors. The solid-state relays U11, U12 and the solid-state relays U13, U14 are respectively in series. The positive poles of the output ends of the solid-state relays U11 and U12 are connected to the A0 terminal. The negative poles of the output ends of the solid-state relays U13 and U14 are respectively grounded through resistors.

[0018] The medium screening excitation circuit includes an operational amplifier U10B and an operational amplifier U10A. The positive poles of the input ends of the operational amplifier U10B and the operational amplifier U10A are both connected to the PA4 pin of the chip U4 and are respectively grounded through capacitors. The output ends of the operational amplifier U10B and the operational amplifier U10A are respectively connected to the bases of the triodes Q10 and Q11 through resistors. The collectors of the triodes Q10 and Q11 are respectively connected to the negative poles of the output ends of the solid-state relays U11 and U12. The emitters of the triodes Q10 and Q11 and the negative poles of the input ends of the operational amplifier U10B and the operational amplifier U10A are grounded through a parallel combination of a capacitor and a resistor.

[0019] The beneficial effects of the present invention are as follows: By integrating key technologies such as precise measurement, automatic control, visual data display, and intelligent fault judgment, the system can quickly and accurately collect and analyze low-level signals such as voltage, current, and contact resistance of the auxiliary contacts of the contactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the MCU circuit principle of the present invention;

[0021] Figure 2 It is a schematic diagram of the contactor coil power supply circuit principle of the present invention;

[0022] Figure 3 It is a schematic diagram of the excitation power supply circuit principle of the present invention;

[0023] Figure 4 It is a schematic diagram of the 5A constant current power supply circuit principle of the present invention;

[0024] Figure 5 This is the schematic diagram of the principle of the RS323 communication circuit of the present invention;

[0025] Figure 6 This is the schematic diagram of the principle of the screening circuit in the present invention;

[0026] Figure 7 This is the schematic diagram of the principle of the low screening circuit of the present invention;

[0027] Figure 8 This is the schematic diagram of the principle of the low screening excitation circuit of the present invention;

[0028] Figure 9 This is the schematic diagram of the principle of the medium screening excitation circuit of the present invention. Detailed implementation manners

[0029] The following further describes the technical solution of the present invention, but the scope of protection is not limited thereto. A contactor contact screening circuit includes an MCU circuit. The MCU circuit includes a chip U4. The PC7-PC9 pins of the chip U4 are connected to a contact coil power supply circuit, the PE5 pin is connected to an excitation power supply circuit, the PA4 pin is respectively connected to a 5A constant current power supply circuit and a medium screening excitation circuit, the PG12, PG11, PD6, and PD5 pins are connected to the RS232 communication circuit, the PA4 and PA5 pins are connected to the medium screening circuit, the PC8 and PC9 pins are connected to the low screening excitation circuit, and the medium screening circuit is also connected to the low screening circuit;

[0030] The VBAT, VDD, and VDD33USB pins of the chip U4 are all connected to a 3.3V power supply. The VDDA pin is connected to a 3.3VA power supply. The PG5, PG6, and PG7 pins are respectively connected to an LED tube, and the anodes of the LED tubes are connected to the 3.3V power supply.

[0031] The contactor coil power supply circuit includes an opto-isolation chip U1, an opto-isolation chip U2, and an opto-isolation chip U3. The positive input terminal of the opto-isolation chip U1 is connected to the PC9 pin of the chip U4 and is connected to the 3.3V power supply through a resistor R1. The negative input terminal of the opto-isolation chip U1 is grounded, and a capacitor C1 is connected in parallel between the negative input terminal and the positive input terminal. The output terminal of the opto-isolation chip U1 is connected to the V_COIL_IN terminal through a resistor R2 and is connected to the cathode of a diode D2. The V_COIL_IN terminal is also connected to a resistor R3. The resistor R3 is respectively connected to the anode of a light-emitting diode D1 and the cathode of a light-emitting diode D3. The cathode of the light-emitting diode D1, the anode of the light-emitting diode D3, the anode of the diode D2, and the negative output terminal of the opto-isolation chip U1 are all connected to the V_COIL terminal. A fuse F1 is provided between the V_COIL_IN terminal and the V_COIL terminal;

[0032] The anodes of the output terminals of the opto-isolation chips U2 and U3 are both connected to the 3.3V power supply, and the cathodes are respectively connected to the PC8 and PC7 pins of the chip U4 through resistors;

[0033] The anode of the input terminal of the opto-isolation chip U2 is connected to the resistor R6, and the other end of the resistor R6 is respectively connected to the anode of the zener diode D4, the resistor R4, and the gate of the MOS transistor Q1. The cathode of the zener diode D4, the other end of the resistor R4, and the source of the MOS transistor Q1 are connected to the V_COIL terminal. The drain of the MOS transistor Q1 is connected to the cathode of the diode D6, and the anode of the diode D6 is grounded to the negative terminal of the input of the opto-isolation chip U2.

[0034] The anode of the input terminal of the opto-isolation chip U3 is connected to the resistor R7, and the other end of the resistor R7 is respectively connected to the anode of the zener diode D5, the resistor R5, and the gate of the MOS transistor Q2. The cathode of the zener diode D5, the other end of the resistor R5, and the source of the MOS transistor Q2 are connected to the V_COIL terminal. The drain of the MOS transistor Q2 is connected to the cathode of the diode D7, and the anode of the diode D7 is grounded to the negative terminal of the input of the opto-isolation chip U3.

[0035] The excitation power supply circuit includes a MOS transistor Q3. The gate of the MOS transistor Q3 is respectively connected to the resistor R10, the anode of the zener diode D8, and the resistor R12. The cathode of the zener diode D8, the other end of the resistor R10, and the source of the MOS transistor Q3 are connected to the 28V power supply. The 28V power supply is also connected to the resistor R11. The other end of the resistor R11 and the drain of the MOS transistor Q3 are connected to the A0 terminal. The other end of the resistor R12 is connected to the collector of the triode Q3. The base of the triode Q4 is connected to the resistors R17 and R18. The other end of the resistor R17 is connected to the PE4 pin of the chip U4. The resistor R18 and the emitter of the triode Q4 are grounded.

[0036] The 5A constant current power supply circuit includes an operational amplifier U27B. The anode of the input terminal of the operational amplifier U27B is connected to the PA4 pin of the chip U4. The output terminal of the operational amplifier U27B is connected to the resistor R19. The resistor R19 is connected to the base of the triode Q5. The collector of the triode Q5 outputs the IMAX5A power supply. The emitter of the triode Q5 and the negative terminal of the input of the operational amplifier U27B are both grounded through the parallel-connected capacitor C23, resistor R20, and resistor R21.

[0037] The RS232 communication circuit includes an RS232 chip U5. The 9th, 10th, 11th, and 12th pins of the RS232 chip U5 are respectively connected to the PG11, PG12, PD5, and PD6 pins of the chip U4. The 7th, 8th, 13th, and 14th pins are respectively grounded through a TVS tube. Capacitors C27 and C29 are respectively connected between the 1st and 3rd pins and between the 4th and 5th pins. The 16th pin is connected to the 3.3V power supply and grounded through the capacitor C28. The 2nd and 6th pins are respectively grounded through the capacitors C30 and C33.

[0038] The screening circuit includes amplifiers U7 and U8. The 1st and 4th pins of the amplifiers U7 and U8 are respectively connected to the low screening circuit through resistors. A resistor and a capacitor are also connected in parallel between the 1st and 4th pins and are respectively grounded through capacitors. The 7th pins of the amplifiers U7 and U8 are respectively connected to the PA4 and PA5 pins of the chip U4 through resistors, connected to the 3.3V power supply through diodes, and grounded through capacitors.

[0039] The low screening circuit includes an AD converter U9. The 11th and 10th pins of the AD converter U9 are respectively connected to the 4th and 1st pins of the amplifier U7 through the resistors R53 and R55. The 7th and 6th pins are respectively connected to the 4th and 1st pins of the amplifier U8 through the resistors R56 and R54. The 4th, 1st, 7th, and 6th pins of the AD converter U9 are respectively connected to the 5VA1 power supply through diodes and are respectively grounded through capacitors.

[0040] The low screening excitation circuit includes a triode Q12. The base of the triode Q12 accesses the excitation signal LCON1 through the resistor R65. The base of the triode Q12 is grounded to its emitter through the resistor R68. The collector of the triode Q12 is respectively connected to the model terminals of the solid-state relays U11, U12, U13, and U14 through resistors. The solid-state relays U11, U12 and the solid-state relays U13, U14 are respectively in series. The positive poles of the output ends of the solid-state relays U11 and U12 are connected to the A0 terminal. The negative poles of the output ends of the solid-state relays U13 and U14 are respectively grounded through resistors.

[0041] The middle screening excitation circuit includes operational amplifiers U10B and U10A. The positive terminals of the inputs of operational amplifiers U10B and U10A are both connected to the PA4 pin of chip U4 and are grounded through capacitors respectively. The output terminals of operational amplifiers U10B and U10A are connected to the bases of transistors Q10 and Q11 through resistors respectively. The collectors of transistors Q10 and Q11 are connected to the negative outputs of solid-state relays U11 and U12 respectively. The emitters of transistors Q10 and Q11 and the negative inputs of operational amplifiers U10B and U10A are grounded through a parallel combination of a capacitor and a resistor.

[0042] Chip U4 serves as the main control unit and is connected to each sub-circuit through different pins to achieve system-level coordination. PC7 - PC9 pins: Connect the contact coil power supply circuit, drive the coil through opto-isolation chips (U1, U2, U3) to achieve high-voltage and low-voltage isolation and stable power supply.

[0043] PE5 pin: Controls the excitation power supply circuit, regulates the 28V power output through MOS transistor Q3 and zener diode D8 to ensure the stability of the high-voltage excitation signal.

[0044] PA4 / PA5 pins: Are respectively connected to the 5A constant-current power supply circuit and the middle screening excitation circuit, and achieve precise current control and signal amplification through operational amplifiers (U27B, U10A / B).

[0045] PG / PD series pins: Are connected to the RS232 communication circuit, and achieve reliable data transmission and anti-interference protection through RS232 chip U5.

[0046] The contactor coil power supply circuit uses a combination of opto-isolation chips (U1 - U3) and MOS transistors (Q1 / Q2), realizes signal isolation and surge protection through a resistor and capacitor network, and uses light-emitting diodes (D1 / D3) to provide status indication at the same time.

[0047] The excitation power supply circuit consists of MOS transistor Q3 and transistor Q4 to form a switching control loop, combined with zener diode D8 and voltage-dividing resistors (R10 - R12) to achieve dynamic regulation and overvoltage protection of the 28V power supply.

[0048] Screening circuit, middle screening circuit: Amplify and filter the signal through amplifiers U7 / U8, and eliminate high-frequency noise by combining a resistor-capacitor network.

[0049] Low screening circuit: Uses an AD converter U9 to digitize the analog signal, and isolates power supply interference through a diode and capacitor network to improve the signal acquisition accuracy.

[0050] Solid-state relay drive:

[0051] The low / mid screening excitation circuit drives the solid-state relays (U11 - U14) through transistors (Q10 - Q12) to achieve fast switching and isolation control of the load.

[0052] The application of the opto-isolation chip and TVS diodes effectively isolates high and low voltage signals, prevents electromagnetic interference (EMI) and surge impacts, and improves system stability.

[0053] The configuration of the fuse F1 and zener diodes (D4 / D5 / D8) provides overcurrent and overvoltage protection, reducing the risk of hardware damage.

[0054] The 5A constant current power supply circuit ensures a constant output current through the closed-loop control of the operational amplifier U27B and the transistor Q5, and is suitable for driving high-precision loads.

[0055] The screening circuit combines AD conversion and amplification filtering technologies to significantly improve the signal-to-noise ratio (SNR) and enhance the system detection sensitivity.

[0056] Each sub-circuit is independently designed and centrally controlled by the MCU, facilitating function expansion and maintenance. For example, the RS232 communication interface supports multi-device interconnection, and the solid-state relay module can adapt to different load types.

[0057] The LED tubes (PG5 - PG7) provide power and communication status indication, facilitating fault troubleshooting and system debugging.

[0058] Composite isolation technology: The combination of opto-isolation and solid-state relays achieves multi-level electrical isolation, taking into account both safety and response speed.

[0059] Dynamic constant current control: Through the collaborative design of the operational amplifier and the transistor, precise adjustment of wide-range current output (such as 5A constant current) is achieved.

Claims

1. A contactor contact screening circuit, characterized in that: It includes an MCU circuit, and the MCU circuit includes a chip U4. The PC7-PC9 pins of the chip U4 are connected to a contact coil power supply circuit, the PE5 pin is connected to an excitation power supply circuit, the PA4 pin is respectively connected to a 5A constant current power supply circuit and a medium screening excitation circuit. The PG12, PG11, PD6, and PD5 pins are connected to an RS232 communication circuit. The PA4 and PA5 pins are connected to a medium screening circuit. The PC8 and PC9 pins are connected to a low screening excitation circuit. The medium screening circuit is also connected to the low screening circuit; The VBAT, VDD, and VDD33USB pins of the chip U4 are all connected to a 3.3V power supply. The VDDA pin is connected to a 3.3VA power supply. The PG5, PG6, and PG7 pins are respectively connected to an LED tube, and the anodes of the LED tubes are connected to the 3.3V power supply.

2. The contactor contact screening circuit according to claim 1, characterized in that: the contactor coil power supply circuit includes an opto-isolation chip U1, an opto-isolation chip U2, and an opto-isolation chip U3. The positive input terminal of the opto-isolation chip U1 is connected to the PC9 pin of the chip U4 and is connected to the 3.3V power supply through a resistor R1. The negative input terminal of the opto-isolation chip U1 is grounded, and a capacitor C1 is connected in parallel between the positive and negative terminals. The output terminal of the opto-isolation chip U1 is connected to the V_COIL_IN terminal through a resistor R2 and is connected to the cathode of a diode D2. The V_COIL_IN terminal is also connected to a resistor R3. The resistor R3 is respectively connected to the anode of a light-emitting diode D1 and the cathode of a light-emitting diode D3. The cathode of the light-emitting diode D1, the anode of the light-emitting diode D3, the anode of the diode D2, and the negative output terminal of the opto-isolation chip U1 are all connected to the V_COIL terminal. A fuse F1 is provided between the V_COIL_IN terminal and the V_COIL terminal; The positive output terminals of the opto-isolation chip U2 and the opto-isolation chip U3 are both connected to the 3.3V power supply, and the negative terminals are respectively connected to the PC8 and PC7 pins of the chip U4 through resistors; The positive input terminal of the opto-isolation chip U2 is connected to a resistor R6. The other end of the resistor R6 is respectively connected to the anode of a voltage stabilizing diode D4, a resistor R4, and the gate of a MOS transistor Q1. The cathode of the voltage stabilizing diode D4, the other end of the resistor R4, and the source of the MOS transistor Q1 are connected to the V_COIL terminal. The drain of the MOS transistor Q1 is connected to the cathode of a diode D6. The anode of the diode D6 is grounded at the negative input terminal of the opto-isolation chip U2. The positive input terminal of the opto-isolation chip U3 is connected to a resistor R7. The other end of the resistor R7 is respectively connected to the anode of a voltage stabilizing diode D5, a resistor R5, and the gate of a MOS transistor Q2. The cathode of the voltage stabilizing diode D5, the other end of the resistor R5, and the source of the MOS transistor Q2 are connected to the V_COIL terminal. The drain of the MOS transistor Q2 is connected to the cathode of a diode D7. The anode of the diode D7 is grounded at the negative input terminal of the opto-isolation chip U3.

3. The contactor contact screening circuit according to claim 1, wherein: The excitation power supply circuit includes MOS transistor Q3. The gate of MOS transistor Q3 is respectively connected to resistor R10, the anode of zener diode D8, and resistor R12. The cathode of zener diode D8, the other end of resistor R10, and the source of MOS transistor Q3 are connected to the 28V power supply. The 28V power supply is also connected to resistor R11. The other end of resistor R11 and the drain of MOS transistor Q3 are connected to terminal A0. The other end of resistor R12 is connected to the collector of transistor Q3. The base of transistor Q4 is connected to resistor R17 and resistor R18. The other end of resistor R17 is connected to the PE4 pin of chip U4. Resistor R18 and the emitter of transistor Q4 are grounded.

4. The contactor contact screening circuit according to claim 1, characterized in that: The 5A constant current power supply circuit includes operational amplifier U27B. The positive input terminal of operational amplifier U27B is connected to the PA4 pin of chip U4. The output terminal of operational amplifier U27B is connected to resistor R19. Resistor R19 is connected to the base of transistor Q5. The collector of transistor Q5 outputs the IMAX5A power supply. The emitter of transistor Q5 and the negative input terminal of operational amplifier U27B are both grounded through the parallel-connected capacitor C23, resistor R20, and resistor R21.

5. The contactor contact screening circuit according to claim 1, characterized in that: The RS232 communication circuit includes RS232 chip U5. The 9, 10, 11, and 12 pins of RS232 chip U5 are respectively connected to the PG11, PG12, PD5, and PD6 pins of chip U4. The 7, 8, 13, and 14 pins are respectively grounded through a TVS tube. Capacitor C27 and capacitor C29 are respectively connected between the 1 and 3 pins and between the 4 and 5 pins. The 16 pin is connected to the 3.3V power supply and grounded through capacitor C28. The 2 pin and the 6 pin are respectively grounded through capacitor C30 and capacitor C33.

6. The contactor contact screening circuit according to claim 1, characterized in that: The middle screening circuit includes amplifier U7 and amplifier U8. The 1 pin and the 4 pin of amplifier U7 and amplifier U8 are respectively connected to the low screening circuit through resistors. A resistor and a capacitor are also connected in parallel between the 1 pin and the 4 pin and are respectively grounded through capacitors. The 7 pins of amplifier U7 and amplifier U8 are respectively connected to the PA4 and PA5 pins of chip U4 through resistors, and are connected to the 3.3V power supply through diodes and grounded through capacitors.

7. The contactor contact screening circuit according to claim 1, wherein: The low screening circuit includes AD converter U9. The 11 and 10 pins of AD converter U9 are respectively connected to the 4 pin and the 1 pin of amplifier U7 through resistor R53 and resistor R55. The 7 pin and the 6 pin are respectively connected to the 4 pin and the 1 pin of amplifier U8 through resistor R56 and resistor R54. The 4 pin, 1 pin, 7 pin, and 6 pin of AD converter U9 are respectively connected to the 5VA1 power supply through diodes and are respectively grounded through capacitors.

8. The contactor contact screening circuit according to claim 1, wherein: The low screening excitation circuit includes a triode Q12. The base of the triode Q12 is connected to the excitation signal LCON1 through a resistor R65. The base of the triode Q12 is grounded to its emitter through a resistor R68. The collector of the triode Q12 is respectively connected to the model terminals of solid-state relays U11, U12, U13, and U14 through resistors. The solid-state relays U11, U12 and the solid-state relays U13, U14 are respectively in series. The positive poles of the output ends of the solid-state relays U11 and U12 are connected to the A0 terminal. The negative poles of the output ends of the solid-state relays U13 and U14 are respectively grounded through resistors.

9. The contactor contact screening circuit according to claim 1, wherein: The medium screening excitation circuit includes an operational amplifier U10B and an operational amplifier U10A. The positive poles of the input ends of the operational amplifier U10B and the operational amplifier U10A are both connected to the PA4 pin of the chip U4 and are respectively grounded through capacitors. The output ends of the operational amplifier U10B and the operational amplifier U10A are respectively connected to the bases of a triode Q10 and a triode Q11 through resistors. The collectors of the triode Q10 and the triode Q11 are respectively connected to the negative poles of the output ends of the solid-state relays U11 and U12. The emitters of the triode Q10 and the triode Q11 and the negative poles of the input ends of the operational amplifier U10B and the operational amplifier U10A are grounded through capacitors and resistors connected in parallel.

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