A screening device for a sensor

Abstract

A sensor screening device comprises: a constant current circuit, a comparison circuit, a sequence judgment circuit, an alarm circuit and a power supply circuit; the constant current circuit provides a positive and negative constant voltage for the sensor to be detected; the comparison circuit compares the test voltage on the sensor to be detected with the set voltage, and outputs the result to the sequence judgment circuit; the sequence judgment circuit receives the output results of the constant current circuit and the comparison circuit, and outputs the result to the alarm circuit in the order of the input of the output results of the constant current circuit and the comparison circuit; the alarm circuit gives an alarm when the sensor to be detected is unqualified; the power supply circuit provides power for the constant current circuit, the comparison circuit, the sequence judgment circuit and the alarm circuit; wherein the constant current circuit comprises an external foot switch, and the external foot switch provides a positive or reverse constant voltage when it is in different states.

Description

Technical Field

[0001] The present application belongs to the field of automobile sensor manufacturing, and in particular, relates to a sensor screening device. Background Art

[0002] Hall sensors are widely used in the automotive industry, including power, body control, traction control, and anti-lock braking systems. Hall sensors may cause varying degrees of damage to the chip during chip molding, spot welding, and other manufacturing processes. At the same time, when the cable and the connecting piece are riveted, it may also cause the core wire to short-circuit, and the crimping is not firm to form an open circuit. Therefore, in order to screen and remove these defective products before the sensor is injected to reduce the scrap of finished products, it is important to invent a sensor skeleton component screening device that can identify multiple bad conditions. Summary of the invention

[0003] The purpose of this application is to provide a sensor skeleton component screening device to solve the problem that existing Hall sensors may cause varying degrees of damage to the chip during the chip molding, spot welding and other manufacturing processes and cannot be detected.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] The present invention discloses a sensor screening device, comprising:

[0006] The constant current circuit provides a constant positive and negative voltage for the sensor to be detected;

[0007] A comparison circuit compares the test voltage on the sensor to be detected with the set voltage and outputs the result to the sequence judgment circuit;

[0008] A sequence judgment circuit receives the output results of the constant current circuit and the comparison circuit, and outputs the results to the alarm circuit in the order of the input of the output results of the constant current circuit and the comparison circuit; and

[0009] An alarm circuit is used to alarm when the sensor to be tested fails to meet the requirements;

[0010] A power supply circuit, which provides power to the constant current circuit, the comparison circuit, the sequence judgment circuit and the alarm circuit;

[0011] Wherein, the constant current circuit includes an external foot switch, and the external foot switch provides a forward or reverse constant voltage when it is in different states.

[0012] Optionally, the constant current circuit is provided with a positive electrode test access terminal and a negative electrode test access terminal; the external foot switch includes a first relay, and the first relay includes: a fixed connection terminal, a first port, and a second port; wherein, when the first relay is in a first state, the fixed connection terminal is connected to the first port, and when the first relay is in a second state, the fixed connection terminal is connected to the second port.

[0013] The fixed connection end includes a first sub-fixed connection end and a second sub-fixed connection end, and the first sub-fixed connection end and the second sub-fixed connection end are respectively connected to the input end of the sensor to be detected; the first port includes: a first sub-port and a second sub-port; the first sub-port is connected to the positive test access end, and the second sub-port is connected to the negative test access end; the second port includes a third sub-port and a fourth sub-port; the third sub-port is connected to the positive test access end, and the fourth sub-port is connected to the negative test access end;

[0014] The screening device further comprises a digital voltmeter and a first switch connected in series; the other end of the digital voltmeter is connected to the positive electrode test access terminal, and the other end of the first switch is connected to the negative electrode test access terminal;

[0015] The constant current circuit is provided with a first optical coupler output unit, one end of the first optical coupler output unit is connected to the constant current circuit, and the other end is connected to the positive electrode test access terminal;

[0016] The sequence judgment circuit receives the optical signal of the first optical coupling output unit, converts it into an electrical signal and outputs it to the alarm circuit.

[0017] Optionally, the comparison circuit configuration includes a first comparison circuit and a second comparison circuit; an input terminal of the first comparison circuit and an input terminal of the second comparison circuit are respectively connected to the positive electrode test access terminal;

[0018] The first comparison circuit is provided with a second optical coupler output unit, one end of the second optical coupler output unit is connected to the output end of the first comparison circuit, and the other end is grounded;

[0019] The second comparison circuit is provided with a third optical coupler output unit, one end of the third optical coupler output unit is connected to the output end of the second comparison circuit, and the other end is grounded;

[0020] The sequence judgment circuit receives the optical signal of the second optical coupling output unit and the optical signal of the third optical coupling output unit, converts them into electrical signals and outputs them to the alarm circuit.

[0021] Optionally, the sequence determination circuit includes: a first optical coupler access circuit, a second optical coupler access circuit, a third optical coupler access circuit, and a first switch circuit, a second switch circuit and a third switch circuit connected in series;

[0022] The first optocoupler access circuit receives an optical signal from the first optocoupler output unit and converts it into an electrical signal input to the first switch circuit, the second optocoupler access circuit receives an optical signal from the second optocoupler output unit and converts it into an electrical signal input to the second switch circuit, and the third optocoupler access circuit receives an optical signal from the third optocoupler output unit and converts it into an electrical signal input to the third switch circuit;

[0023] The alarm circuit includes a constant current indication module, a forward-measurement voltage indication module and a reverse-measurement voltage indication module, wherein the constant current indication module is connected to the output end of the first switch circuit, the forward-measurement voltage indication module is connected to the output end of the second switch circuit, and the reverse-measurement voltage indication module is connected to the output end of the third switch circuit.

[0024] The beneficial effects of the present invention are as follows: the sensor includes a chip with a Hall sensor as the core. In order to detect whether the sensor skeleton is in a bad state, the present application connects the Hall chip to the access end of the screening device, uses the constant current circuit of the screening device to provide a constant voltage, and measures and determines the constant current resistance and forward and reverse virtual resistance of the Hall chip respectively, and outputs the results to the sequence judgment circuit. The sequence judgment circuit judges the detection results of the constant current resistance, forward virtual resistance, and reverse virtual resistance in turn. If the sequence is qualified and the constant current resistance and the forward and reverse virtual resistance are all qualified, the alarm circuit displays qualified; if one of the constant current resistance and the forward and reverse virtual resistance is unqualified, the alarm circuit displays unqualified.

[0025] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a screening device for a sensor according to the present invention;

[0027] Figure 2 A circuit schematic diagram of a constant current circuit of the present invention connected to a Hall chip via a positive and negative electrode test input terminal;

[0028] Figure 3 A circuit diagram of a comparison circuit of the present invention;

[0029] Figure 4 is a circuit diagram of another comparison circuit of the present invention;

[0030] Figure 5 The present invention is a circuit diagram of a sequence judgment circuit and an alarm circuit.

[0031] 10. Screening device; 20. Sensor; 100. Constant current circuit; 100a. Positive electrode test access terminal; 100b. Negative electrode test access terminal; 110. External foot switch; 111. First relay; 112. Fixed terminal; 112a. First sub-fixed connection terminal; 112b. Second sub-fixed connection terminal; 113. First port; 113a. First sub-port; 113b. Second sub-port; 114. Second port; 114a. Third sub-port; 114b. Fourth sub-port; 120. Digital voltmeter; 130. First optical coupler output unit; 200. Comparison circuit; 210. First comparison circuit; 211. Second optical coupler output unit; 212. The first comparator; 213, the second comparator; 214, the first constant current unit; 215, the second constant current unit; 220, the second comparison circuit; 221, the third optical coupler output unit; 230, the third comparison circuit; 240, the fourth comparison circuit; 300, the sequence judgment circuit; 310, the first optical coupler access circuit; 320, the second optical coupler access circuit; 330, the third optical coupler access circuit; 340, the first switch circuit; 350, the second switch circuit; 360, the third switch circuit; 400, the alarm circuit; 410, the constant current indication module; 420, the forward voltage indication module; 430, the reverse voltage indication module; 440, the alarm; 500, the power supply circuit. DETAILED DESCRIPTION

[0032] like Figure 1 As shown, a screening device 10 for sensor 20 bone components is disclosed, comprising: a constant current circuit 100, a comparison circuit 200, a sequence judgment circuit 300, an alarm circuit 400 and a power supply circuit 500; the constant current circuit 100 provides a positive and negative constant voltage for the sensor 20 to be detected; the comparison circuit 200 compares the test voltage on the detected sensor 20 with the set voltage, and outputs the result to the sequence judgment circuit 300; the sequence judgment circuit 300 receives the output result of the constant current circuit 100 and the comparison circuit 20 ... The result is outputted to the alarm circuit 400 in the order of the input of the output results of the constant current circuit 100 and the comparison circuit 200; the alarm circuit 400 gives an alarm when the sensor 20 to be detected is unqualified; the power supply circuit 500 provides power for the constant current circuit 100, the comparison circuit 200, the sequence judgment circuit 300 and the alarm circuit 400; wherein the constant current circuit 100 includes an external foot switch 110, and the external foot switch 110 provides a forward or reverse constant voltage when it is in different states.

[0033] In the present application, the sensor 20 component includes a chip with the Hall sensor 20 as the core. In order to detect whether the sensor 20 component is in a bad state, the present application connects the Hall chip to the access end of the screening device 10, uses the constant current circuit 100 of the screening device 10 to provide a constant voltage, and measures and determines the constant current resistance and the forward and reverse virtual resistance of the Hall chip respectively, and outputs the result to the sequence judgment circuit 300. The sequence judgment circuit 300 judges the detection results of the constant current resistance, the forward virtual resistance, and the reverse virtual resistance in turn. If the sequence is qualified and the constant current resistance and the forward and reverse virtual resistance are qualified, the alarm circuit 400 displays qualified. If one of the constant current resistance and the forward and reverse virtual resistance is unqualified, the alarm circuit 400 displays unqualified.

[0034] like Figure 2 As shown, it is a schematic diagram of a constant current circuit 100 connected to a Hall chip through positive and negative test input terminals; wherein the constant current circuit 100 is provided with a positive test access terminal 100a and a negative test access terminal 100b; the external foot switch 110 includes a first relay 111, and the first relay 111 includes: a fixed connection terminal, a first port 113 and a second port 114; wherein, when the first relay 111 is in a first state, the fixed connection terminal is connected to the first port 113, and when the first relay 111 is in a second state, the fixed connection terminal is connected to the second port 114.

[0035] The fixed connection end includes a first sub-fixed connection end 112a and a second sub-fixed connection end 112b, and the first sub-fixed connection end 112a and the second sub-fixed connection end 112b are respectively connected to the input end of the sensor 20 to be detected; the first port 113 includes: a first sub-port 113a and a second sub-port 113b; the first sub-port 113a is connected to the positive electrode test access end 100a, and the second sub-port 113b is connected to the negative electrode test access end 100b; the second port 114 includes a third sub-port 114a and a fourth sub-port 114b; the third sub-port 114a is connected to the positive electrode test access end 100a, and the fourth sub-port 114b is connected to the positive electrode test access end 100a. Port 114b is connected to the negative pole test access terminal 100b; the screening device also includes a digital display voltmeter 120 and a first switch K1 connected in series; the other end of the digital display voltmeter 120 is connected to the positive pole test access terminal 100a, and the other end of the first switch K1 is connected to the negative pole test access terminal 100b; a first optical coupler output unit 130 is provided on the constant current circuit 100, one end of the first optical coupler output unit 130 is connected to the constant current circuit 100, and the other end is connected to the positive pole test access terminal 100a; the sequence judgment circuit 300 receives the optical signal of the first optical coupler output unit 130, and converts it into an electrical signal and outputs it to the alarm circuit 400.

[0036] The first switch K1 is a single-pole double-throw switch, the fixed end 112 of the first switch K1 is connected to a resistor R11, the other end of the resistor R11 is connected to the digital voltmeter 120, the first port 113 of the first switch K1 is connected to a test end test, and the second port 114 of the first switch is connected to a setting end, the setting end can adjust the set voltage, and the voltage range of different types of Hall chips is different. Therefore, when comparing the constant current voltage measurement, the comparison is performed through the adjustable set voltage. In order to adjust the digital voltmeter 120, an adjustable resistor R12 and a resistor R13 are arranged in parallel with the digital voltmeter 120 to adjust the appropriate parameters of the digital voltmeter 120.

[0037] Figure 2 In the embodiment, the first optical coupler output unit 130 is an optical coupler 4N35, and the constant current circuit 100 also includes resistors R14, R15, an adjustable resistor R16, and N-type transistors N11, N12, an optical coupler 4N351 and a constant current Y-LED lamp. The adjustable resistor R16 can adjust the resistance to adjust the constant current value. One end of the resistor R14 is connected to the input end of the transistor N11 and is connected to the power supply circuit 500. The resistor R14 and the adjustable resistor R16 are connected in series, one end is connected to the input end of the transistor N11, and the other end is connected to the control end of the transistor N11; the control end of the transistor N11 is connected to the input end of the transistor N12, the output end of the transistor N11 is connected to the control end of the transistor N12, and the output end of the transistor N12 is connected in series to the constant current Y-LED lamp in sequence, and the optical coupler 4N35 is connected to the positive electrode test access terminal 100a.

[0038] like Figure 3 , shows a schematic diagram of a comparison circuit 200, wherein the comparison circuit 200 includes a first comparison circuit 210 and a second comparison circuit 220; the input end of the first comparison circuit 210 and the input end of the second comparison circuit 220 are respectively connected to the positive test access end 100a; the first comparison circuit 210 is provided with a second optical coupler output unit 211, one end of the second optical coupler output unit 211 is connected to the output end of the first comparison circuit 210, and the other end is grounded; the second comparison circuit 220 is provided with a third optical coupler output unit 221, one end of the third optical coupler output unit 221 is connected to the output end of the second comparison circuit 220, and the other end is grounded; the sequence judgment circuit 300 receives the optical signal of the second optical coupler output unit 211 and the optical signal of the third optical coupler output unit 221, and converts them into electrical signals and outputs them to the alarm circuit 400.

[0039] Figure 3In the embodiment, taking the first comparison circuit 210 as an example, the first comparison circuit 210 includes a first constant current unit 214 and a second constant current unit 215, the input end of the first constant current unit 214 is connected to the power supply circuit 500, and the power supply circuit 500 provides a +12V voltage, and the input end of the second constant current unit 215 is connected to the power supply circuit 500, and the power supply circuit 500 provides a -12V voltage; the first constant current unit 214 includes: resistors R21, R22, an adjustable resistor R23, and N-type transistors N21 and N22; one end of the resistor R21 is connected to the control end of the transistor N21, and the other end of R21 is connected to the input end of N21, and the input end of N21 is connected to the power supply circuit 500; the control end of N21 is connected to the input end of N22, the output end of N21 is connected to the control end of N22, R22 is connected to the output end of N21, and the output end of N22 is connected to one end of R23; the second constant current unit 215 includes: resistors R24, R25, an adjustable resistor R26, P-type transistors P21, P22, the first constant current unit 214 and the second constant current unit 215 have the same circuit architecture, the connection method of the resistor is consistent with the transistor, and the resistor R25 of the second constant current unit 215 is connected to the resistor R22 of the first constant current unit 214, and the adjustable resistor R26 of the second constant current unit 215 is connected to the adjustable resistor R23 of the first constant current unit 214.

[0040] The first comparison circuit 210 also includes a first comparator 212 and a second comparator 213. The negative electrode access segment of the first comparator 212 and the positive electrode access segment of the second comparator 213 are respectively connected to the positive electrode test access segment of the constant current circuit 100. The output end of N22 is connected to the positive electrode access end of the first comparator 212, and the output end of P22 is connected to the negative electrode access end of the second comparator 213. Two capacitors C21 and C22 are also arranged in series between the output end of N22 and the output end of P22.

[0041] The output end of the first comparator 212 is connected in series with resistors R27 and R28 and then output to LED21, and the output end of the second comparator 213 is connected in series with resistors R29 and R30 and then output to the second optocoupler output unit 211. The adjustable resistor R41 is connected to the test end test A, and the adjustable resistor R41 and the resistor R42 are connected in series to Vcc2. The adjustable resistor is used to adjust the set voltage. The second comparison circuit 220 has the same circuit architecture as the first comparison circuit 210, except that the third optocoupler output unit 221 in the second comparison circuit 220 outputs to the third optocoupler access circuit 330. When the device collects the chip forward test value, the first comparison circuit 210 compares with: outputting a high level within the range, outputting a low level outside the range, and removing the driving sequence judgment circuit 300. When the device collects the chip reverse test value, the second comparison circuit 220 compares with: outputting a high level within the range, outputting a low level outside the range, and removing the driving sequence judgment circuit 300.

[0042] like Figure 4 , is a circuit diagram of another comparison circuit 200, the comparison circuit 200 also includes a third comparison circuit 230 and a fourth comparison circuit 240, and the third comparison circuit 230 and the fourth comparison circuit 240 have the same circuit architecture as the first comparison circuit 210. The third comparison circuit 230 and the fourth comparison circuit 240 are reserved circuits, and when the sensor 20 is installed on different skeleton devices, different parameters may also need to be detected, which can be detected directly on the circuit.

[0043] like Figure 5 , is a schematic diagram of a sequence determination circuit 300, the sequence determination circuit 300 comprising: a first optical coupling access circuit 310, a second optical coupling access circuit 320, a third optical coupling access circuit 330, and a first switch circuit 340, a second switch circuit 350 and a third switch circuit 360 connected in series;

[0044] The first optical coupling access circuit 310 receives the optical signal of the first optical coupling output unit 130 and converts it into an electrical signal input value in the first switch circuit 340; the second optical coupling access circuit 320 receives the optical signal of the second optical coupling output unit 211 and converts it into an electrical signal input value in the second switch circuit 350; the third optical coupling access circuit 330 receives the optical signal of the third optical coupling output unit 221 and converts it into an electrical signal input value in the third switch circuit 360;

[0045] The input end of the first switch is connected to the power supply circuit 500, the output end of the first switch circuit 340 is connected to the input end of the second switch circuit 350, and the output end of the second switch circuit 350 is connected to the input end of the third switch circuit 360.

[0046] The first optical coupling access circuit 310 includes resistors R31, R32, R33, a P-type transistor P31, an N-type transistor N31, and a capacitor C31. The input end of N31 is connected to the power supply circuit 500, the output end of N31 is connected to R32, the control end of N31 is connected to the output end of P31, the control end and the input end of P31 are connected through R31, and the input end of P31 is connected to R31 and R32. The capacitor C31 is connected in parallel with the resistor R33, one end is connected to R32, and the other end is connected to the output end of the first switch circuit 340, and the connection between R32 and R33 is also connected to the control end of the first switch circuit 340, and the first switch circuit 340 here includes an MCR switch element.

[0047] The second optocoupler access circuit 320 and the third optocoupler access circuit 330 have the same circuit architecture as the first optocoupler access circuit 310. The second optocoupler access circuit 320 includes resistors R34, R35, R36, a P-type transistor P32, an N-type transistor N32, and a capacitor C32. The third optocoupler access circuit 330 includes resistors R37, R38, R39, a P-type transistor P33, an N-type transistor N33, and a capacitor C33. The connection sequence of the components of the second optocoupler access circuit 320 and the third optocoupler access circuit 330 is as follows: Figure 5 The first switch circuit 340, the second switch circuit 350 and the third switch circuit 360 in the present invention are MCR switch circuits.

[0048] When the constant current circuit 100 works normally, the first optical coupler output unit 130 outputs a signal to the first optical coupler access circuit 310 to trigger the MCR1 device test signal to be normal; the test voltage of the sensor 20 to be tested will be compared with the first comparison circuit 210, and the second optical coupler output unit 211 outputs a signal to the second optical coupler access circuit 320, triggering the MCR2 device to pass the forward test; the first relay 111J1 works to reverse the sensor 20. The test voltage of the sensor 20 to be tested will be compared with the second comparison circuit 220, and the second optical coupler output unit 211 outputs a signal to the second optical coupler access circuit 320, triggering the MCR3 device to pass the reverse test. If all the tests are qualified, it means that the sensor 20 is qualified.

[0049] The alarm circuit 400 includes a constant current indication module 410, a forward-measurement voltage indication module 420 and a reverse-measurement voltage indication module 430, wherein the constant current indication module 410 is connected to the output end of the first switch circuit 340, the forward-measurement voltage indication module 420 is connected to the output end of the second switch circuit 350, and the reverse-measurement voltage indication module 430 is connected to the output end of the third switch circuit 360.

[0050] The resistor R51 is connected in series with the constant current indication module 410 and then connected in parallel with the capacitor C51. The resistor R52 is connected in series with the forward voltage indication module 420 and then connected in parallel with the capacitor C52. The resistor R53 is connected in series with the reverse voltage indication module 430 and then connected in parallel with the capacitor C53. Each step of detection is performed in the order of constant current value, forward voltage value, and reverse voltage value.

[0051] Furthermore, the alarm circuit 400 is also provided with an error-proofing switch K2; the power supply circuit 500 is connected to one end of the error-proofing switch, and the other end of the error-proofing switch is respectively connected to the first optical coupler access circuit 310, the second optical coupler access circuit 320, the third optical coupler access circuit 330, the first switch circuit 340 and the second relay J2, J2 is connected in parallel with the capacitor C54, the C54 capacitor is 1000uf, and the second relay J2 and the capacitor C54 form a delay circuit, the delay is 1s, for example, when the constant current indication module 410 displays normally, after waiting for 1s, if the normal display of the forward voltage indication module 420 is not checked, then no more waiting is done, and the test result is judged to be unqualified. Only after the previous step of the test is qualified will the next step of the test be carried out, otherwise the defective product, the alarm 440 prompts, and the error-proofing circuit is started. The test will be reset after manual intervention. It is necessary to manually press the error-proofing switch for 3 seconds to reset. The alarm circuit 400 includes an alarm 440, and the alarm 440 can be an LED light flashing and a buzzer whistle alarm.

[0052] According to the working principle of the Hall chip, in order to identify the above-mentioned various adverse conditions, it is necessary to first determine the constant current resistance of the Hall chip, and then measure and determine the forward and reverse virtual resistances of the Hall chip. Under normal circumstances, the forward and reverse virtual resistances differ greatly. The working process of the screening device 10 is as follows: the sensor 20 is processed. When the skeleton component with the sensor 20 that has been formed and spot-welded and riveted is connected to the positive test access terminal 100a and the negative test access terminal 100b, a constant current source (the current is within the chip safety value) using a constant current circuit 100 is used to measure the Hall chip, and a preliminary judgment is made based on the voltage on the Hall chip whether it is within the range. If it is not within the range, the buzzer alarms; when the constant current source determines that it is qualified, the forward and reverse virtual resistances of the skeleton component are measured; first, the forward virtual resistance is tested. Since the resistance is affected by temperature, the qualified range of the forward virtual resistance here is manually adjustable. When the virtual resistance is within the set range, the forward qualified light is on, otherwise the light is off and the buzzer alarms; when the forward test is qualified, the external foot switch 110 is manually stepped on to perform a reverse virtual resistance test. The qualified range of the reverse resistance is also adjustable. When the virtual resistance is within the set range, the reverse qualified light is on, otherwise the light is off and the buzzer alarms. When the test is qualified, the next skeleton component can be tested directly; when the test fails and the buzzer alarms, it is necessary to manually press and hold the error prevention switch for 3 seconds to turn off the buzzer before continuing the test. Since the entire test process includes a constant current source and forward and reverse virtual resistance, it is possible to identify bad conditions such as open circuit, short circuit, chip circuit damage, etc. of the skeleton component, thereby reducing product scrapping.

[0053] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various improvements are made using the method concept and technical solution of the present invention, or they are directly applied to other occasions without improvement, they all fall within the protection scope of the present invention.

Claims

1. A sensor screening device, characterized in that: include: The constant current circuit provides a constant positive and negative voltage for the sensor to be detected; A comparison circuit compares the test voltage on the sensor to be detected with the set voltage and outputs the result to the sequence judgment circuit; A sequence judgment circuit receives the output results of the constant current circuit and the comparison circuit, and outputs the results to the alarm circuit in the order of the input of the output results of the constant current circuit and the comparison circuit; as well as An alarm circuit is used to alarm when the sensor to be tested fails to meet the requirements; A power supply circuit, which provides power to the constant current circuit, the comparison circuit, the sequence judgment circuit and the alarm circuit; Wherein, the constant current circuit includes an external foot switch, and the external foot switch provides a forward or reverse constant voltage when in different states; The constant current circuit is provided with a positive electrode test access terminal and a negative electrode test access terminal; the external foot switch includes a first relay, and the first relay includes: a fixed connection terminal, a first port and a second port; wherein, when the first relay is in a first state, the fixed connection terminal is connected to the first port, and when the first relay is in a second state, the fixed connection terminal is connected to the second port The fixed connection end includes a first sub-fixed connection end and a second sub-fixed connection end, and the first sub-fixed connection end and the second sub-fixed connection end are respectively connected to the input end of the sensor to be detected; the first port includes: a first sub-port and a second sub-port; the first sub-port is connected to the positive test access end, and the second sub-port is connected to the negative test access end; the second port includes a third sub-port and a fourth sub-port; the third sub-port is connected to the positive test access end, and the fourth sub-port is connected to the negative test access end; The screening device further comprises a digital voltmeter and a first switch connected in series; the other end of the digital voltmeter is connected to the positive electrode test access terminal, and the other end of the first switch is connected to the negative electrode test access terminal; The constant current circuit is provided with a first optical coupler output unit, one end of the first optical coupler output unit is connected to the constant current circuit, and the other end is connected to the positive electrode test access terminal; The sequence judgment circuit receives the optical signal of the first optical coupling output unit, converts it into an electrical signal and outputs it to the alarm circuit; The comparison circuit arrangement comprises a first comparison circuit and a second comparison circuit; an input end of the first comparison circuit and an input end of the second comparison circuit are respectively connected to the positive electrode test access end; The first comparison circuit is provided with a second optical coupler output unit, one end of the second optical coupler output unit is connected to the output end of the first comparison circuit, and the other end is grounded; The second comparison circuit is provided with a third optical coupler output unit, one end of the third optical coupler output unit is connected to the output end of the second comparison circuit, and the other end is grounded; The sequence judgment circuit receives the optical signal of the second optical coupling output unit and the optical signal of the third optical coupling output unit, converts them into electrical signals and outputs them to the alarm circuit; The sequence judgment circuit comprises: a first optical coupling access circuit, a second optical coupling access circuit, a third optical coupling access circuit, and a first switch circuit, a second switch circuit and a third switch circuit connected in series; The first optocoupler access circuit receives an optical signal from the first optocoupler output unit and converts it into an electrical signal input to the first switch circuit, the second optocoupler access circuit receives an optical signal from the second optocoupler output unit and converts it into an electrical signal input to the second switch circuit, and the third optocoupler access circuit receives an optical signal from the third optocoupler output unit and converts it into an electrical signal input to the third switch circuit; The alarm circuit includes a constant current indication module, a forward voltage indication module and a reverse voltage indication module, wherein the constant current indication module is connected to the output end of the first switch circuit, the forward voltage indication module is connected to the output end of the second switch circuit, and the reverse voltage indication module is connected to the output end of the third switch circuit; The alarm circuit is also provided with an error-proofing switch, and the power supply circuit is connected to one end of the error-proofing switch.

Images