Grounding impedance test circuit and grounding impedance test system

Abstract

This application relates to the field of control for safety testing instruments, and discloses a grounding impedance testing circuit and a grounding impedance testing system. The grounding impedance testing circuit includes: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port; the suppression module is used to suppress the AC test voltage between the first port and the second port; the detection module is used to detect the circuit state between the first port and the second port, and control the working state of the detection module based on the working state of the switching module and the circuit state detection result; the delay module is used to determine whether to provide a time delay to the switching module based on the working state of the detection module; the switching module is used to detect whether the delay module provides a time delay, and control the working state of the switching module based on the delay detection result; the output module is used to control the output state of the third port based on the working state of the switching module.

Description

Technical Field

[0001] This application relates to the field of control of safety testing instruments, and in particular to a grounding impedance testing circuit and a grounding impedance testing system. Background Technology

[0002] Currently, electrical equipment manufacturing production lines typically include a "safety inspection" station, which naturally includes grounding impedance parameter testing. The general process is as follows: When entering the grounding impedance testing phase, an audible and / or visual signal prompts the operator to directly contact and connect the "current probe" to the relevant test point of the equipment under test. Then, the operator presses the "TEST (or START)" button on the front panel of the safety tester to initiate the grounding impedance test. The safety tester outputs an AC test current source I1 with an open-circuit voltage not exceeding 8V at 50Hz / 60Hz through the "CURRENT" port. This current is applied to the relevant test point of the equipment under test through the "current probe," passes through the tested "grounding impedance," and returns to the "RETURN" port of the safety tester, forming a large current of several to tens of amperes. Simultaneously, the safety tester monitors and analyzes the AC voltage drop between the "CURRENT" and "RETURN" ports to determine whether the grounding impedance of the equipment under test exceeds the safety limit.

[0003] To eliminate the need for the operator to press the "TEST button" on the front panel to start the machine, Figure 1 A commonly used solution is presented. This solution includes an "EXTECH 7440 Grounding Impedance Test Current Probe Automatic Start System," comprising: a current probe grounding detection circuit, an FX1S series PLC controller, an RS-232 serial port, a PC computer, an IEEE-488 serial port, and a DC power supply. Its function is to send the electrical connection status of the "current probe" to the GPIBINTERFACE interface of the safety tester to automatically start the grounding impedance test. Its working principle is as follows: When the current probe contacts and connects to the device under test, the "current probe grounding detection circuit" outputs a logic H level. The "FX1S series PLC controller" is connected to the "PC computer" through the "RS-232 serial port". After a time delay of T, the "PC computer" is connected to the GPIB INTERFACE interface of the "EXTECH 7440 safety dielectric analyzer" through the "IEEE-488 serial port". The test power switch SW1 is closed, and the AC test current source I1 is output to the CURRENT port, and then returns to the RETURN port through the device under test. After that, by analyzing the AC voltage drop between the CURRENT port and the RETURN port, it can be determined whether the grounding impedance of the device under test is higher than the safety limit.

[0004] Although the functions of the aforementioned automatic start system are simple, none of the control links can be omitted, and it requires the use of high-cost circuit modules such as PC computers and PLC controllers. As a result, the defects of the aforementioned automatic start system, such as large size, high cost, long control links, and poor reliability, are obvious. Summary of the Invention

[0005] The purpose of this application is to provide a grounding impedance test circuit and a grounding impedance test system, which can simplify the grounding impedance test circuit, significantly reduce the size of the equipment, reduce the cost of the grounding impedance test circuit, and improve the reliability of the grounding impedance test circuit.

[0006] To address the aforementioned technical problems, embodiments of this application provide a grounding impedance testing circuit, comprising: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port; the suppression module is used to suppress the AC test voltage between the first port and the second port; the detection module is used to detect the circuit state between the first port and the second port, and control the operating state of the detection module based on the operating state of the switching module and the circuit state detection result; the delay module is used to determine whether to provide a time delay to the switching module based on the operating state of the detection module; the switching module is used to detect whether the delay module provides the time delay, and control the operating state of the switching module based on the delay detection result; the output module is used to control the output state of the third port based on the operating state of the switching module.

[0007] An embodiment of this application also provides a grounding impedance test circuit system, the system comprising: a safety dielectric analyzer module, a device under test connected to the safety dielectric analyzer module, and the aforementioned grounding impedance test circuit; the safety dielectric analyzer module is used to test the grounding impedance of the device under test based on the grounding impedance test circuit.

[0008] In this embodiment, the grounding impedance test circuit includes: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port. The suppression module is used to suppress the AC test voltage between the first port and the second port. The detection module is used to detect the circuit state between the first port and the second port, and control the working state of the detection module according to the working state of the switching module and the circuit state detection result. The delay module is used to determine whether to provide a time delay to the switching module according to the working state of the detection module. The switching module is used to detect whether the delay module provides a time delay, and control the working state of the switching module according to the delay detection result. The output module is used to control the output state of the third port according to the working state of the switching module. This application realizes all the electrical functions of the existing automatic start system for grounding impedance testing, which consists of a current probe grounding detection circuit, an FX1S series PLC controller, an RS-232 serial port, a PC computer, an IEEE-488 serial port, and a DC power supply, through five hardware circuit modules. This simplifies the grounding impedance test circuit and reduces its cost. At the same time, since no computer or software is required, the equipment size can be significantly reduced and the reliability of the grounding impedance test circuit can be improved. Attached Figure Description

[0009] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative descriptions do not constitute a limitation on the embodiments.

[0010] Figure 1 This is a schematic diagram of the structure of a grounding impedance testing system provided by existing technology;

[0011] Figure 2 This is a schematic diagram of the grounding impedance test circuit provided in the embodiments of this application. Figure 1 ;

[0012] Figure 3 This is a schematic diagram of the grounding impedance test circuit provided in the embodiments of this application. Figure 2 ;

[0013] Figure 4 This is a schematic diagram of the grounding impedance testing system provided in the embodiments of this application;

[0014] Figure 5 yes Figure 4 The diagram shows the waveform of the current probe in the grounding impedance test system. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this application to help readers better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for the convenience of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0016] The embodiments of this application relate to a grounding impedance testing circuit, which can be applied to any grounding impedance testing system, such as... Figure 2 As shown, it specifically includes: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port.

[0017] In one example implementation, the suppression module is connected to the first port and the second port respectively to suppress the AC test voltage between the first port and the second port; wherein the first port is port IN and the second port is port GND, and the first port and the second port can be regarded as input ports (IN-GND).

[0018] In one example implementation, the detection module is connected to the suppression module to detect the circuit state between the first port and the second port, and controls the operating state of the detection module based on the operating state of the switching module and the circuit state detection results. The circuit state between the first port and the second port includes three states: open circuit, short circuit, and AC test voltage applied. When the circuit state between the first port and the second port is open circuit, the suppression module provides a bias current to the detection module, and controls the operating state of the detection module to be in the on state based on the bias current provided by the suppression module. When the circuit state between the first port and the second port is short circuit, the operating state of the detection module is controlled to be in the off state. When the circuit state between the first port and the second port is AC test voltage applied, the operating state of the detection module is controlled to be in the off state. When the operating state of the detection module is in the off state, the operating state of the switching module is in the on state, and the switching module provides positive feedback to the detection module (i.e., applies a bias voltage). If the applied bias voltage is greater than a threshold, the operating state of the detection module can remain in the off state. The threshold can be set by the user according to the test requirements.

[0019] In one example implementation, the delay module is connected to both the detection module and the second port, and is used to determine whether to provide a time delay to the switching module based on the operating state of the detection module. The operating state of the detection module includes two states: off state and on state. When the operating state of the detection module is on state, the delay module does not need to provide a time delay. When the operating state of the detection module is off state, the delay module needs to provide a time delay of T seconds. During the above T seconds, whether the connection between the first port and the second port is open or closed will not affect the operating state of the switching module, that is, this application has the function of resisting input terminal contact jitter.

[0020] In one example implementation, the switching module is connected to the delay module to detect whether the delay module provides a time delay and to control the working state of the switching module based on the delay detection result. When it is detected that the delay module provides a time delay of T seconds to the switching module, the switching module is controlled to be in the off state for the time delay of T seconds, and after the time delay of T seconds, the switching module is controlled to be in the on state. When it is detected that the delay module does not provide a time delay of T seconds to the switching module, the switching module is controlled to be in the on state.

[0021] In one example implementation, the output module is connected to the switching module, the third port, and the second port, respectively, and is used to control the output state of the third port according to the operating state of the switching module. The output state of the third port is related to the operating state of the switching module. When the operating state of the switching module is off, the output state of the third port is controlled to be high impedance. When the operating state of the switching module is on, the output state of the third port is controlled to be low impedance. Here, the third port is port OUT, and the third port and the second port can be regarded as output ports (OUT-GND).

[0022] In this embodiment, the grounding impedance test circuit includes: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port. The suppression module is used to suppress the AC test voltage between the first port and the second port. The detection module is used to detect the circuit state between the first port and the second port, and control the working state of the detection module according to the working state of the switching module and the circuit state detection result. The delay module is used to determine whether to provide a time delay to the switching module according to the working state of the detection module. The switching module is used to detect whether the delay module provides a time delay, and control the working state of the switching module according to the delay detection result. The output module is used to control the output state of the third port according to the working state of the switching module. This application realizes all the electrical functions of the existing automatic start system for grounding impedance testing, which consists of a current probe grounding detection circuit, an FX1S series PLC controller, an RS-232 serial port, a PC computer, an IEEE-488 serial port, and a DC power supply, through five hardware circuit modules. It can simplify the grounding impedance test circuit, significantly reduce the size of the equipment, and reduce the cost of the grounding impedance test circuit. At the same time, since no computer or software is required, the reliability of the grounding impedance test circuit can be improved.

[0023] The embodiments of this application relate to a grounding impedance testing circuit, which can be applied to any grounding impedance testing system, such as... Figure 3 As shown, it specifically includes: a first port IN, a second port GND, a suppression module containing a fourth resistor R4, a fifth resistor R5 and a first capacitor C1, a detection module containing a second transistor Q2, a delay module containing a second resistor R2 and a second capacitor C2, a switching module containing a first transistor Q1, an output module containing a first resistor R1 and a third resistor R3, and a third port OUT.

[0024] In one example implementation, the grounding impedance test circuit can be divided into 7 networks: Network n1: Port 1 of the first resistor R1, Port 1 of the second resistor R2, and Port 1 of the fourth resistor R4 are connected to the third port OUT; Network n2: Port 2 of the third resistor R3, Port 2 of the first capacitor C1, and Port 2 of the second capacitor C2 are connected to the second port GND; Network n3: Port 2 of the fourth resistor R4 and Port 1 of the fifth resistor R5 are connected to the first port IN; Network n4: Port 2 of the first resistor R1 is connected to the collector C of the first transistor Q1; Network n5: Port E of the second transistor Q2 and Port 1 of the third resistor R3 are connected to the emitter E of the first transistor Q1; Network n6: Port C of the second transistor Q2, Port 2 of the second resistor R2, and Port 1 of the second capacitor C2 are connected to the base B of the first transistor Q1; Network n7: Port 2 of the fifth resistor R5 and Port 1 of the first capacitor C1 are connected to the base B of the second transistor Q2.

[0025] In one example implementation, the fifth resistor R5 and the first capacitor C1 form a resistor-capacitor voltage divider, which functions to suppress the AC test voltage at the input port. When the AC test voltage is applied between the first port IN and the second port GND, the AC voltage amplitude across the first capacitor C1 can be effectively suppressed because the capacitive reactance of the first capacitor C1 is very small.

[0026] In one example implementation, the second transistor Q2 can be considered as an input state switch, functioning to detect the on / off state of the first port IN and the second port GND. When the first port IN and the second port GND are in an open circuit state, the base bias current provided by the fourth resistor R4 and the fifth resistor R5 in series keeps the second transistor Q2 in a saturated conduction state. When the first port IN and the second port GND are in a short circuit state, the second transistor Q2 is in a cutoff state. When an AC test voltage is applied between the first port IN and the second port GND, the second transistor Q2 is cut off. When the second transistor Q2 is in a cutoff state, the first transistor Q1 is in a conduction state, and the first transistor Q1 provides positive feedback to the second transistor Q2 (i.e., applies a bias voltage). If the applied bias voltage is greater than a threshold, the second transistor Q2 can remain in a cutoff state. The threshold can be set according to the test requirements.

[0027] In one example implementation, the function of the second resistor R2 and the second capacitor C2 is to provide a time delay of T seconds. When the second transistor Q2 is in the off state, the second resistor R2 and the second capacitor C2 provide a time delay of T seconds. During the T-second delay, the first transistor Q1 is in the off state. After the T-second time delay ends, the first transistor Q1 is turned on again. During the above-mentioned T-second period, whether the input port (IN-GND) is open or closed does not affect the off state of the first transistor Q1, that is, this circuit has the function of resisting input terminal contact jitter.

[0028] In one example implementation, the first transistor Q1 functions as an output resistor network switching switch, and the conduction and cutoff of the first transistor Q1 are determined based on the T-second time delay provided by the second resistor R2 and the second capacitor C2.

[0029] In one example implementation, the functions of the first resistor R1 and the third resistor R3 are as follows: when the first transistor Q1 is saturated and conducting, the output port (OUT-GND) is in a low impedance state (R1+R3), where the third resistor R3 also serves as a DC coupling resistor; when the second transistor Q2 is turned off and the first transistor Q1 is saturated and conducting, the voltage drop across the third resistor R3 (Vn5 = 4.91V) provides a reverse bias voltage for the second transistor Q2. At this time, the second transistor Q2 can only be turned on again if the base level of the second transistor Q2 is higher than the above reverse bias voltage. In conjunction with the above-mentioned "fifth resistor R5 and first capacitor C1 form a RC voltage divider" suppression module, the ability of the normal logic function of this circuit to be unaffected by the AC voltage interference of the input port is greatly enhanced.

[0030] In one example implementation, the fourth resistor R4 and the fifth resistor R5 function as base bias resistors for the second transistor Q2, providing base bias current for the second transistor Q2; when the "current probe" is open, the base bias current provided by the fourth resistor R4 and the fifth resistor R5 in series causes the second transistor Q2 to saturate and conduct.

[0031] In one example implementation, this circuit is a 3-port circuit: port IN, port GND, and port OUT. Port IN and port GND constitute the input port (IN-GND), and port OUT and port GND constitute the output port (OUT-GND). The input port has three operating states: open circuit, short circuit, and an AC test voltage not exceeding 8V 50 / 60Hz. The output port has two states: high impedance and low impedance (R1+R3). The states of the input and output ports of this circuit are shown in Table 1.

[0032] Table 1. Status Correspondence Table for Input and Output Ports

[0033] Input port (IN-GND) Output port (OUT-GND) open circuit High resistance Short circuit Low resistance (R1+R3) 8V 50 / 60Hz AC test voltage Low resistance (R1+R3)

[0034] In one example implementation, the grounding impedance test circuit provided in this application has three states: State 1: When the input port (IN-GND) is open, the base bias current provided by the fourth resistor R4 and the fifth resistor R5 in series causes the second transistor Q2 to saturate and conduct, causing the first transistor Q1 to turn off, resulting in a high-impedance state at the output port (OUT-GND); State 2: When the input port (IN-GND) is short-circuited, the voltage across the fifth resistor R5 is zero, and the second transistor Q2 turns off due to the loss of base bias current. The second resistor R2 and the second capacitor C2 provide a time delay of T seconds, and then the first transistor Q1 saturates and conducts again, causing the first resistor R1 and the third resistor R3 in series, resulting in a low-impedance state at the output port (OUT-GND) (R1+R3); State 3: When a voltage not exceeding 8V is applied to the input port (IN-GND)... When the AC test voltage is 50 / 60Hz, the AC capacitive reactance of the first capacitor C1 is very small. The RC voltage divider composed of the fifth resistor R5 and the first capacitor C1 effectively suppresses the AC voltage amplitude across the first capacitor C1. The average value of the above AC test voltage, which is not higher than 8V 50 / 60Hz, is zero, making the DC component of the voltage across the fifth resistor R5 zero. This causes the second transistor Q2 to be cut off and the first transistor Q1 to be saturated and turned on, making the first resistor R1 and the third resistor R3 connected in series, so that the output port (OUT-GND) is in a low-resistance state (R1+R3).

[0035] This embodiment of the application, based on other embodiments, can cover all the electrical functions of the existing comparative technical solutions with only 9 discrete components (2 NPN transistors, 5 resistors and 2 capacitors): power supply acquisition, grounding detection of the current probe, time delay T, resistance to contact jitter of the current probe, closing the test power switch SW1, outputting the AC test current source I1, and automatically starting the test process; its advantages in terms of equipment cost, size, simplicity, reliability and many other aspects are obvious.

[0036] The embodiments of this application relate to a grounding impedance testing system. The details of the grounding impedance testing system of this embodiment are described below. The following content is merely for ease of understanding and is not essential for implementing this example. Figure 4 This is a schematic diagram of the grounding impedance testing system in this embodiment, including: a safety dielectric analyzer module, a grounding impedance testing circuit, and the device under test.

[0037] In one example implementation, the safety dielectric analyzer module can use the EXTECH 7440 safety dielectric analyzer, and the internal equivalent relationship diagram of the instrument is shown below. Figure 4As shown, the front panel includes: a current output port CURRENT and a current loop port RETURN; the rear panel includes: an input inverter IC1 for the "REMOTE I / O SIGNAL INPUT" interface INPUT-3 port; an equivalent pull-up resistor R6; a +24V DC power supply V1; a test power switch SW1; an AC test current source I1; a current output port CURRENT; and a current loop port RETURN.

[0038] In one example implementation, the grounding impedance test circuit in the grounding impedance test system is any one of the grounding impedance test circuits in the embodiments of this application.

[0039] In one example implementation, the equivalent grounding impedance diagram of the device under test is as follows: Figure 4 As shown, it is connected to the safety dielectric analyzer via a current probe.

[0040] In one example implementation, the electrical principles of this system are as follows: the first port IN of the grounding impedance test circuit is connected to the "CURRENT" port of the EXTECH 7440. The main electrical characteristics of the "CURRENT" port are high impedance when not started and an open-circuit voltage of no more than 8V 50Hz / 60Hz AC test current source I1 when started; the third port OUT of the grounding impedance test circuit is connected to the INPUT-3 port of the remote control input interface of the EXTECH 7440. The main electrical characteristics of the INPUT-3 port are open-circuit voltage (V1) +24V, short-circuit current 2mA, and equivalent pull-up resistance (R6) 12kΩ; the input characteristics of the inverter IC1 in the safety dielectric analyzer are open-circuit (H) level >18.5V and start-up (L) level <17.5V.

[0041] In one example implementation, during a grounding impedance test of a device under test, the measured waveform of the current probe is shown below. Figure 5 As shown, specifically, at time t1: the "current probe" is in contact with and connected to the test point of the "device under test"; the first port IN and the second port GND are short-circuited, and the input port voltage Vin = 0; at time t2: after a delay of 944ms, the AC test current source I1 is applied to the test point of the "device under test", forming an AC test voltage (Vin = I1 * the grounding impedance under test) at the first port IN; at time t3: the network impedance test and analysis are completed, the AC test current source I1 is turned off, and Vin = 0; at time t4: the "current probe" is disconnected from the test point of the "device under test"; at time t5: the input port IN returns to its initial state.

[0042] In one example implementation, the grounding impedance test circuit of the grounding impedance test system has two circuit states. Circuit state one: "Current probe" open circuit: the fourth resistor R4 and the fifth resistor R5 are connected in series to charge the first capacitor C1, the base level Vb2 of the second transistor Q2 rises, the second transistor Q2 is saturated and conducting, and the first transistor Q1 is cut off; the output port is in a high impedance state; at this time, the steady-state levels of networks n1 to n7 are respectively: Vn1 = 23.08V; Vn2 = 0V; Vn3 = 6.61V; Vn4 = 23.08V; Vn5 = 0.39V; Vn6 = 0.42V; Vn7 = 0.80V; the network level Vn1 = 23.08V is equivalent to the "open circuit (H) level" of the inverter IC1 input. Circuit State Two: The "current probe" is in contact with and connected to the device under test: the first port IN and the second port GND are short-circuited, the base level of the second transistor Q2 is Vb2 = 0V, the second transistor Q2 is cut off, the second resistor R2 charges the second capacitor C2, and after a time delay T, the first transistor Q1 is saturated and conducting; the output port (OUT-GND) has a low impedance (R3+R1 = 12.6kΩ); at this time, the steady-state levels of networks n1 to n7 are respectively: Vn1 = 12.17V; Vn2 = 0V; Vn3 = 0V; Vn4 = 5.05V; Vn5 = 4.91V; Vn6 = 5.37V; Vn7 = 0V; the network level Vn1 = 12.17V is equivalent to the "start (L) level" input of IC1; then, the test power switch SW1 is closed, EXTECH... The 7440 outputs an AC test current source I1 with an open-circuit voltage not exceeding 8V through the "CURRENT" port. The safety tester module simultaneously monitors and analyzes the AC voltage drop between the "CURRENT" and "RETURN" ports, which can determine whether the grounding impedance of the device under test is higher than the safety limit. The fifth resistor R5 and the first capacitor C1 form a voltage divider for the AC voltage drop of the "CURRENT" port. Under the conditions of fifth resistor R5 = 180kΩ, first capacitor C1 = 1uF, Vin <= 8V, and f = 50Hz, the base level of the second transistor Q2, Vb2 <= 0.14Vac; also, at this time, Vn5 = 4.91V, the emitter junction of the second transistor Q2 is reverse biased, and the second transistor Q2 is still in a deep cutoff state, that is, the AC test current source I1 will not interfere with the logic state of this circuit; the non-zero level Vn1 in the above two circuit states provides the operating power for this circuit.

[0043] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing this application, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of this application.

Claims

1. A grounding impedance testing circuit, characterized in that, The circuit includes: a first port, a second port, a suppression module, a detection module, a delay module, a switching module, an output module, and a third port; The suppression module is used to suppress the AC test voltage between the first port and the second port; The detection module is used to detect the circuit status between the first port and the second port, and to control the working status of the detection module according to the working status of the switching module and the circuit status detection result. The delay module is used to determine whether to provide a time delay to the switching module based on the working status of the detection module; The switching module is used to detect whether the delay module provides the time delay, and control the working state of the switching module according to the delay detection result; The output module is used to control the output state of the third port according to the working state of the switching module; The delay module is further configured to provide the time delay to the switching module when the detection module is in a closed state. The suppression module includes a fourth resistor, a fifth resistor, and a first capacitor; the detection module includes a second transistor; the delay module includes a second resistor and a second capacitor; the switching module includes a first transistor; and the output module includes a first resistor and a third resistor.

2. The grounding impedance testing circuit according to claim 1, characterized in that, The detection module is further configured to control the working state of the detection module to be in the conducting state based on the bias current provided by the suppression module when the state detection result is an open circuit state; The detection module is also used to control the working state of the detection module to the cut-off state when the state detection result is a short circuit state; The detection module is further configured to control the operating state of the detection module to the off state when the state detection result indicates that the AC test voltage has been applied.

3. The grounding impedance testing circuit according to claim 2, characterized in that, The detection module is further configured to control the detection module to be in the off state when the detection module is in the off state, the switching module is in the on state, and the bias voltage of the switching module meets a preset condition.

4. The grounding impedance testing circuit according to claim 1, characterized in that, The switching module is also used to control the working state of the switching module to the off state within the time delay when the delay detection result is a time delay. The switching module is further configured to control the switching module to a conducting state when the delay detection result indicates that no time delay is provided.

5. The grounding impedance testing circuit according to claim 1, characterized in that, The output module is also used to control the output state of the third port to be in a high-impedance state when the working state of the switching module is in the off state. The output module is also used to control the output state of the third port to be in a low-impedance state when the working state of the switching module is in the on state.

6. The grounding impedance testing circuit according to claim 1, characterized in that, The suppression module is connected to the first port, the detection module is connected to both the suppression module and the switching module, the delay module is connected to the detection module, the switching module is connected to the delay module, the output module is connected to the switching module, the third port is connected to the suppression module, the delay module, and the output module, and the second port is connected to the suppression module, the delay module, and the output module.

7. The grounding impedance testing circuit according to claim 1, characterized in that, One end of the first resistor, one end of the second resistor, and one end of the fourth resistor are connected to the third port. The other end of the third resistor, the other end of the first capacitor, and the other end of the second capacitor are connected to the second port. The other end of the fourth resistor and one end of the fifth resistor are connected to the first port. The other end of the first resistor is connected to the collector of the first transistor. The emitter of the second transistor and one end of the third resistor are connected to the emitter of the first transistor. The collector of the second transistor, the other end of the second resistor, and one end of the second capacitor are connected to the base of the first transistor. The other end of the fifth resistor and one end of the first capacitor are connected to the base of the second transistor.

8. A grounding impedance testing system, characterized in that, The system includes: a safety dielectric analyzer module, a device under test connected to the safety dielectric analyzer module, and a grounding impedance test circuit according to any one of claims 1-7; The safety dielectric analyzer module is used to test the grounding impedance of the device under test based on the grounding impedance test circuit.

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