Current source for testing

Abstract

The utility model discloses a current source used for testing. The current source comprises a signal amplification module, a filtering module, a power amplification module, a voltage sampling module, a relay driving module, an FPGA module, a DA module, an AD module and an upper computer. The upper computer is connected with the FPGA module through a serial port, the relay driving module is respectively connected with the FPGA module, the power amplification module and the voltage sampling module, the signal amplification module, the filtering module, the power amplification module and the voltage sampling module are sequentially connected, the signal amplification module is simultaneously connected with the DA module, and the voltage sampling module is simultaneously connected with the AD module; the test product as a load is connected with a power amplifier of the power amplifier module to form a constant current source circuit, so that stable test current is generated on the test product. The current source can output stable test current with a large frequency range and different waveforms, can meet various standard test conditions, and is convenient for performing current release test on various power distribution products.

Description

Technical Field

[0001] The utility model belongs to the technical field of power systems, and in particular relates to a current source for testing. Background Art

[0002] The current source is a wide-spectrum, high-precision constant-current power supply with the advantages of fast response speed, high constant current accuracy, long-term stable operation, and suitability for various load properties (resistive, inductive, capacitive), etc. It is mainly used to detect thermal relays, molded case circuit breakers, small circuit breakers, and production occasions that require setting rated current, operating current, short-circuit protection current, etc.

[0003] During the design phase, power distribution products need to be tested using a current source to measure, calibrate or evaluate their performance. Different power distribution products have different standard test conditions and therefore different test requirements. Therefore, the current source used for testing is required to be able to output a large frequency range, different waveforms and stable test current to meet the testing requirements of different power distribution products and increase the scope of application of the test current source.

[0004] After investigation, it is found that the existing current source can test a small frequency range, has low current accuracy, and has few waveform types, which cannot meet the test of some special equipment. Therefore, in view of these problems, the utility model designs a current source for testing. Utility Model Content

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the utility model is to provide a current source for testing.

[0006] The technical solution adopted by the utility model to solve the technical problem is:

[0007] A current source for testing, comprising a signal amplification module, a filtering module, a voltage sampling module, a relay driving module, an FPGA module, a DA module, an AD module, a host computer and a power amplifier module; the host computer is connected to the FPGA module via a serial port, the relay driving module is respectively connected to the FPGA module, the power amplifier module and the voltage sampling module, the signal amplification module, the filtering module, the power amplifier module and the voltage sampling module are connected in sequence, the signal amplification module is simultaneously connected to the DA module, and the voltage sampling module is simultaneously connected to the AD module;

[0008] The power amplifier module includes a power amplifier, resistors No. 7 to No. 10, relays No. 1 to No. 3, diodes No. 1 to No. 3 and LED lamps No. 1 to No. 3; wherein the positive input end of the power amplifier is connected to the filter module, one end of resistor No. 7 is connected to the negative input end of the power amplifier, and the other end is connected to the second input end of relay No. 1, the first input end of relay No. 1 is connected to the output end of the power amplifier, the four output ends of relay No. 1 are respectively connected to the two input ends of relay No. 2 and the two input ends of relay No. 3, the first control end of relay No. 1 is connected to one end of resistor No. 8, the other end of resistor No. 8 is connected to the conduction end of LED lamp No. 1, and the cut-off end of LED lamp No. 1 is connected to the second control end of relay No. 1; the cut-off end of diode No. 1 is connected to the first control end of relay No. 1, and the conduction end is connected to the second control end of relay No. 1; the four output ends of relay No. 2 are respectively connected to the A phase, B phase, One end of phase C and phase N, one end of resistor No. 9 is connected to the first control end of relay No. 2, and the other end is connected to the conduction end of LED lamp No. 2, and the cut-off end of LED lamp No. 2 is connected to the second control end of relay No. 2; the cut-off end of diode No. 2 is connected to the first control end of relay No. 2, and the conduction end is connected to the second control end of relay No. 2; the four output ends of relay No. 3 are respectively connected to the other ends of phase A, phase B, phase C and phase N of the test product; one end of resistor No. 10 is connected to the first control end of relay No. 3, and the other end is connected to the conduction end of LED lamp No. 3, and the cut-off end of LED lamp No. 3 is connected to the second control end of relay No. 3; the cut-off end of diode No. 3 is connected to the first control end of relay No. 3, and the conduction end is connected to the second control end of relay No. 3; the second input end of relay No. 1 is connected to the voltage sampling module; one end of the test product is connected to the output end of the power amplifier, and the other end is connected to the inverting input end of the power amplifier through resistor No. 7 to form a constant current source circuit.

[0009] Furthermore, the voltage sampling module includes power resistors No. 1 to No. 4, relay No. 4, relay No. 5, resistors No. 11 to No. 17, diode No. 4, diode No. 5, LED lamp No. 4, LED lamp No. 5, instrument amplifier and capacitors No. 4 to No. 6; wherein, one end of power resistor No. 1 is connected to the second input end of relay No. 1 of the power amplifier module, and the other end is connected to one end of power resistor No. 4; one end of power resistor No. 2 is connected to one end of power resistor No. 1, and the other end is connected to the first input end of relay No. 4, and the second input end of relay No. 4 is connected to the other end of power resistor No. 1; one end of resistor No. 11 is connected to the first control end of relay No. 4, and the other end is connected to the conduction end of LED lamp No. 4, and the cut-off end of LED lamp No. 4 is connected to the second control end of relay No. 4; the cut-off end of diode No. 4 is connected to the first control end of relay No. 4, and the conduction end is connected to the second control end of relay No. 4; one end of power resistor No. 3 is connected to one end of power resistor No. 1, and the other end is connected to the first input end of relay No. 5, and the second input end of relay No. 5 is connected to the other end of power resistor No. 1 One end; one end of resistor No. 12 is connected to the first control end of relay No. 5, and the other end is connected to the conduction end of LED lamp No. 5, and the cut-off end of LED lamp No. 5 is connected to the second control end of relay No. 5; the cut-off end of diode No. 5 is connected to the first control end of relay No. 5, and the conduction end is connected to the second control end of relay No. 5; one end of capacitor No. 4 is connected to one end of power resistor No. 4, and the other end is grounded; one end of capacitor No. 5 is connected to the other end of power resistor No. 4 and grounded, and the other end is grounded; one end of resistor No. 13 is connected to one end of power resistor No. 4, and the other end is connected to the positive input end of instrument amplifier; one end of resistor No. 14 is connected to the other end of power resistor No. 4, and the other end is connected to the inverting input end of instrument amplifier; one end of resistor No. 15 is connected to the first gain control end of instrument amplifier, and the other end is connected to the second gain control end of instrument amplifier; one end of resistor No. 16 is connected to the output end of instrument amplifier, and the other end is connected to the reference voltage end of instrument amplifier and grounded; one end of resistor No. 17 is connected to the output end of instrument amplifier, and the other end is connected to one end of capacitor No. 6 and AD module at the same time, and the other end of capacitor No. 6 is grounded.

[0010] Furthermore, when relay No. 4 and relay No. 5 are both disconnected and power resistor No. 1 is connected to the circuit, the current is at level 1; when relay No. 4 is disconnected and relay No. 5 is closed, power resistor No. 1 and power resistor No. 3 are connected to the circuit in parallel, the current is at level 2; when relay No. 4 is closed and relay No. 5 is disconnected, power resistor No. 1 and power resistor No. 2 are connected to the circuit in parallel, the current is at level 3; when relay No. 4 and relay No. 5 are both closed, power resistor No. 1, power resistor No. 2 and power resistor No. 3 are connected to the circuit in parallel, the current is at level 4.

[0011] Furthermore, the signal amplification module includes an operational amplifier No. 1, a resistor No. 1, a resistor No. 2, a resistor No. 3 and a capacitor No. 1; one end of the resistor No. 1 is connected to the DA module, and the other end is connected to the inverting input terminal of the operational amplifier No. 1; one end of the capacitor No. 1 and one end of the resistor No. 2 are simultaneously connected to the inverting input terminal of the operational amplifier No. 1, the other end of the capacitor No. 1 is grounded, the other end of the resistor No. 2 is connected to the output terminal of the operational amplifier No. 1, and the output terminal of the operational amplifier No. 1 is simultaneously connected to the filtering module; one end of the resistor No. 3 is connected to the non-inverting input terminal of the operational amplifier No. 1, and the other end is grounded.

[0012] Furthermore, the filtering module includes operational amplifier No. 2, resistor No. 4, resistor No. 5, resistor No. 6, capacitor No. 2 and capacitor No. 3; one end of resistor No. 4 is connected to the signal amplification module, and the other end is connected to the inverting input terminal of operational amplifier No. 2; one end of resistor No. 5 is connected to the non-inverting input terminal of operational amplifier No. 2, and the other end is grounded; one end of capacitor No. 2 and one end of resistor No. 6 are simultaneously connected to the inverting input terminal of operational amplifier No. 2, the other end of capacitor No. 2 is connected to the non-inverting input terminal of operational amplifier No. 2, and the other end of resistor No. 6 is connected to the output terminal of operational amplifier No. 2; one end of capacitor No. 3 is connected to the inverting input terminal of operational amplifier No. 2, and the other end is connected to the output terminal of operational amplifier No. 2, and the output terminal of operational amplifier No. 2 is simultaneously connected to the power amplifier module.

[0013] Compared with the prior art, the beneficial effects of the utility model are:

[0014] The utility model connects the test product as a load to the power amplifier module to form a constant current source circuit, so that a stable test current is generated on the test product. The current source uses devices with large gain-bandwidth product, high slew rate and high power in circuit design, which can achieve the purpose of outputting a large frequency range, high precision and stable current. The current source uses FPGA as the main controller of the current source. By controlling the output signal of the DA module, the current source can output high-precision, stable and multiple waveform currents, ensure the stability of the test, meet a variety of standard test conditions, and facilitate current delivery tests on various power distribution products, broadening the scope of use of the test current source. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the overall structure diagram of the utility model;

[0016] Figure 2 It is a connection diagram of the main components of the utility model;

[0017] Figure numerals, 1-signal amplification module; 2-filtering module; 3-power amplifier module; 4-voltage sampling module; 5-relay drive module; 6-FPGA module; 7-DA module; 8-AD module; 9-host computer; 10-test product. DETAILED DESCRIPTION

[0018] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solution of the utility model in detail, and are not intended to limit the protection scope of the present application.

[0019] The utility model is a current source for testing (referred to as current source, see Figure 1-2 ), the current source includes a control part, a signal processing part and a host computer 9; the control part includes an FPGA module 6, a DA module 7 and an AD module 8, the signal processing part includes a signal amplification module 1, a filter module 2, a power amplifier module 3, a voltage sampling module 4 and a relay drive module 5, the DA module 7 and the AD module 8 are both connected to the FPGA module 6, the FPGA module 6 is also connected to the host computer 9 through a serial port, the relay drive module 5 is respectively connected to the FPGA module 6, the power amplifier module 3 and the voltage sampling module 4, the signal amplification module 1, the filter module 2, the power amplifier module 3, and the voltage sampling module 4 are connected in sequence, the signal amplification module 1 is also connected to the DA module 7, the voltage sampling module 4 is also connected to the AD module 8, the test product 10 is connected to the power amplifier module 3 as a load to form a constant current source circuit.

[0020] The host computer 9 transmits test information to the FPGA module 6 through the serial port. The FPGA module 6 processes the test information to enable the DA module 7 to output a test signal of a specific frequency and waveform. The test signal is amplified by the signal amplification module 1 and then filtered by the filtering module 2. The filtered test signal enters the power amplifier module 3 and generates a constant test current on the test product 10. The voltage sampling module 4 samples and amplifies the voltage across the No. 4 power resistor (sampling resistor), and then converts the sampled voltage from an analog signal to a digital signal through the AD module 8. The FPGA module 6 processes the digital signal and outputs a control signal; the relay drive module 5 drives the relay in the circuit to open and close according to the control signal of the FPGA module 6, and switches the test phase selection of the test product 10 and the current gear.

[0021] The signal amplification module 1 includes an operational amplifier No. 1, a resistor No. 1, a resistor No. 2, a resistor No. 3 and a capacitor No. 1; one end of the resistor No. 1 is connected to the DA module 7, and the other end is connected to the inverting input end of the operational amplifier No. 1, and the output signal of the DA module 7 enters the operational amplifier No. 1 through the resistor No. 1; one end of the capacitor No. 1 and one end of the resistor No. 2 are simultaneously connected to the inverting input end of the operational amplifier No. 1, the other end of the capacitor No. 1 is grounded, the other end of the resistor No. 2 is connected to the output end of the operational amplifier No. 1, and the output end of the operational amplifier No. 1 is simultaneously connected to one end of the resistor No. 4 of the filtering module 2; one end of the resistor No. 3 is connected to the non-inverting input end of the operational amplifier No. 1, and the other end is grounded.

[0022] The filtering module 2 includes an operational amplifier No. 2, a resistor No. 4, a resistor No. 5, a resistor No. 6, a capacitor No. 2 and a capacitor No. 3; one end of the resistor No. 4 is connected to the output end of the operational amplifier No. 1 of the signal amplification module 1, and the other end of the resistor No. 4 is connected to the inverting input end of the operational amplifier No. 2, and the output signal of the signal amplification module 1 enters the operational amplifier No. 2 through the resistor No. 4; one end of the resistor No. 5 is connected to the non-inverting input end of the operational amplifier No. 2, and the other end is grounded; one end of the capacitor No. 2 and one end of the resistor No. 6 are simultaneously connected to the inverting input end of the operational amplifier No. 2, the other end of the capacitor No. 2 is connected to the non-inverting input end of the operational amplifier No. 2, and the other end of the resistor No. 6 is connected to the output end of the operational amplifier No. 2; one end of the capacitor No. 3 is connected to the inverting input end of the operational amplifier No. 2, and the other end is connected to the output end of the operational amplifier No. 2, and the output end of the operational amplifier No. 2 is simultaneously connected to the non-inverting input end of the power amplifier of the power amplifier module 3.

[0023] The power amplifier module 3 includes a power amplifier, resistors No. 7 to No. 10, relays No. 1 to No. 3, diodes No. 1 to No. 3, and LED lamps No. 1 to No. 3; the positive input end of the power amplifier is connected to the output end of the operational amplifier No. 2 of the filter module 2, so that the output signal of the filter module 2 enters the power amplifier; one end of the resistor No. 7 is connected to the inverting input end of the power amplifier, and the other end is connected to the second input end of the relay No. 1; the first input end of the relay No. 1 is connected to the output end of the power amplifier, and the four output ends are respectively connected to the two input ends of the relay No. 2 and the two input ends of the relay No. 3; the first control end of the relay No. 1 is connected to one end of the resistor No. 8, and the other end of the resistor No. 8 is connected to the conduction end of the LED lamp No. 1, and the cut-off end of the LED lamp No. 1 is connected to the second control end of the relay No. 1; the cut-off end of the diode No. 1 is connected to the first control end of the relay No. 1, and the conduction end is connected to the second control end of the relay No. 1; the four output ends of the relay No. 2 are respectively connected to one end of the A phase, the B phase, the C phase and the N phase of the test product 10 , one end of resistor No. 9 is connected to the first control end of relay No. 2, and the other end is connected to the conduction end of LED lamp No. 2, and the cut-off end of LED lamp No. 2 is connected to the second control end of relay No. 2; the cut-off end of diode No. 2 is connected to the first control end of relay No. 2, and the conduction end is connected to the second control end of relay No. 2; the four output ends of relay No. 3 are respectively connected to the other ends of phase A, phase B, phase C and phase N of the test product; one end of resistor No. 10 is connected to the first control end of relay No. 3, and the other end is connected to the conduction end of LED lamp No. 3, and the cut-off end of LED lamp No. 3 is connected to the second control end of relay No. 3; the cut-off end of diode No. 3 is connected to the first control end of relay No. 3, and the conduction end is connected to the second control end of relay No. 3; the second input end of relay No. 1 is connected to the power resistor No. 1 of voltage sampling module 4; the test product 10 is connected to the loop of power amplifier module 3 as a load, one end is connected to the output end of the power amplifier, and the other end is connected to the inverting input end of the power amplifier through resistor No. 7, forming a constant current source circuit, so that the test product 10 has a constant current. The test product 10 is connected to four phases A, B, C, and N, and the phase switching is controlled by relay No. 1, relay No. 2, and relay No. 3.

[0024] The voltage sampling module 4 includes power resistors No. 1 to No. 4, relay No. 4, relay No. 5, resistors No. 11 to No. 17, diode No. 4, diode No. 5, LED lamp No. 4, LED lamp No. 5, instrument amplifier and capacitors No. 4 to No. 6; one end of the power resistor No. 1 is connected to the second input end of the relay No. 1 of the power amplifier module 3, and the other end of the power resistor No. 1 is connected to one end of the power resistor No. 4; one end of the power resistor No. 2 is connected to one end of the power resistor No. 1, and the other end is connected to the first input end of the relay No. 4, and the second input end of the relay No. 4 is connected to the other end of the power resistor No. 1; one end of the resistor No. 11 is connected to the first control end of the relay No. 4, and the other end is connected to the conduction end of the LED lamp No. 4, and the cut-off end of the LED lamp No. 4 is connected to the second control end of the relay No. 4; the cut-off end of the diode No. 4 is connected to the first control end of the relay No. 4, and the conduction end is connected to the second control end of the relay No. 4; one end of the power resistor No. 3 is connected to one end of the power resistor No. 1, and the other end is connected to the first input end of the relay No. 5, and one end of the second input end of the relay No. 5 is connected to the the other end; one end of resistor No. 12 is connected to the first control end of relay No. 5, and the other end is connected to the conduction end of LED lamp No. 5, and the cut-off end of LED lamp No. 5 is connected to the second control end of relay No. 5; the cut-off end of diode No. 5 is connected to the first control end of relay No. 5, and the conduction end is connected to the second control end of relay No. 5; one end of capacitor No. 4 is connected to one end of power resistor No. 4, and the other end is grounded; one end of capacitor No. 5 is connected to the other end of power resistor No. 4 and grounded, and the other end is grounded; one end of resistor No. 13 is connected to one end of power resistor No. 4, and the other end is connected to the positive input end of instrument amplifier; one end of resistor No. 14 is connected to the other end of power resistor No. 4, and the other end is connected to the inverting input end of instrument amplifier; one end of resistor No. 15 is connected to the first gain control end of instrument amplifier, and the other end is connected to the second gain control end of instrument amplifier; one end of resistor No. 16 is connected to the output end of instrument amplifier, and the other end is connected to the reference voltage end of instrument amplifier and grounded; one end of resistor No. 17 is connected to the output end of instrument amplifier, and the other end is simultaneously connected to one end of capacitor No. 6 and AD module 8, and the other end of capacitor No. 6 is grounded. The No. 4 power resistor is used as a sampling resistor. By controlling the opening and closing of the No. 4 and No. 5 relays, the No. 1, No. 2 and No. 3 power resistors are connected in parallel in pairs or in threes, and the current gear can be divided into four gears, thereby changing the voltage difference across the No. 4 power resistor. The two input ends of the instrument amplifier are respectively connected to the two ends of the No. 4 power resistor to collect, amplify and output the voltage across the No. 4 power resistor. The No. 4 and No. 5 relays are used for gear switching control. The No. 1 power resistor is connected to the circuit in the first gear, the No. 1 power resistor is connected to the circuit in parallel with the No. 3 power resistor in the second gear, the No. 1 power resistor is connected to the circuit in parallel with the No. 2 power resistor in the third gear, and the No. 1 power resistor is connected to the circuit in parallel with the No. 2 power resistor in the fourth gear. The No. 1 power resistor, the No. 2 power resistor and the No. 3 power resistor are connected to the circuit in parallel together in the fourth gear.

[0025] The following examples provide feasible component models, which do not limit the protection scope of this application, and models can also be selected according to actual needs.

[0026] The power amplifier model is APEX's MP38CL, which has the characteristics of high power, high voltage, high current, high slew rate, etc. The slew rate can reach 10V / us. Relays 1, 2, and 3 are all JQX-115F / 024-2ZS4, with double-pole double-throw type and contact voltage of 24V. Relays 4 and 5 are all JQX-115F / 024-1HS3, with single-pole single-throw type and contact voltage of 24V. Power resistors 1, 2, 3, and 4 are all high-power planar non-inductive resistors with power up to 100W. The current source is powered by a separate power module, and the voltage is divided into +24V and ±48V. The +48V voltage is converted to ±24V voltage through the power module URA4824YMD-15WR3, and the +24V voltage is converted to ±5V voltage through the power module URA2405YMD-15WR3.

[0027] The working principle and process of the utility model are:

[0028] The host computer 9 transmits the test information to the FPGA module 6, and the FPGA module 6 processes the test information to enable the DA module 7 to output a test signal of a specific frequency and waveform. The test signal is amplified by the signal amplification module 1, and then filtered out by the filtering module 2 to remove the interference components in the signal. The filtered test signal enters the power amplifier module 3. Since the test product 10 is connected to the loop of the power amplifier module 3 as a load, a constant current source circuit is formed, and then a constant test current is generated on the test product 10. The output signal of the power amplifier module 3 enters the voltage sampling module 4. The voltage sampling module 4 collects and amplifies the voltage across the No. 4 power resistor, and then outputs it to the AD module 8. The AD module 8 converts the sampled voltage from an analog signal to a digital signal. The FPGA module 6 processes the digital signal to obtain the current test current, and outputs a control signal according to the current test current. The relay drive module 5 drives the relay in the loop to open and close according to the control signal of the FPGA module 6, and switches the test phase selection of the test product 10 and the current gear.

[0029] Anything not described in the present invention is applicable to the prior art.

Claims

1. A current source for testing, comprising a signal amplification module, a filter module, a voltage sampling module, a relay drive module, an FPGA module, a DA module, an AD module, a power amplifier module and a host computer; the host computer is connected to the FPGA module through a serial port, the relay drive module is respectively connected to the FPGA module, the power amplifier module and the voltage sampling module, the signal amplification module, the filter module, the power amplifier module and the voltage sampling module are connected in sequence, the signal amplification module is simultaneously connected to the DA module, and the voltage sampling module is simultaneously connected to the AD module; characterized in that The power amplifier module includes a power amplifier, resistors No. 7 to No. 10, relays No. 1 to No. 3, diodes No. 1 to No. 3, and LED lamps No. 1 to No. 3; Among them, the positive phase input end of the power amplifier is connected to the filter module, one end of resistor No. 7 is connected to the inverting input end of the power amplifier, and the other end is connected to the second input end of relay No. 1, the first input end of relay No. 1 is connected to the output end of the power amplifier, the four output ends of relay No. 1 are respectively connected to the two input ends of relay No. 2 and the two input ends of relay No. 3, the first control end of relay No. 1 is connected to one end of resistor No. 8, the other end of resistor No. 8 is connected to the conduction end of LED lamp No. 1, and the cut-off end of LED lamp No. 1 is connected to the second control end of relay No. 1; the cut-off end of diode No. 1 is connected to the first control end of relay No. 1, and the conduction end is connected to the second control end of relay No. 1; the four output ends of relay No. 2 are respectively connected to one end of phase A, phase B, phase C and phase N of the test product, one end of resistor No. 9 is connected to the first control end of relay No. 2, and the other end The end is connected to the conduction end of the No. 2 LED lamp, and the cut-off end of the No. 2 LED lamp is connected to the second control end of the No. 2 relay; the cut-off end of the No. 2 diode is connected to the first control end of the No. 2 relay, and the conduction end is connected to the second control end of the No. 2 relay; the four output ends of the No. 3 relay are respectively connected to the other ends of the A phase, B phase, C phase and N phase of the test product; one end of the No. 10 resistor is connected to the first control end of the No. 3 relay, and the other end is connected to the conduction end of the No. 3 LED lamp, and the cut-off end of the No. 3 LED lamp is connected to the second control end of the No. 3 relay; the cut-off end of the No. 3 diode is connected to the first control end of the No. 3 relay, and the conduction end is connected to the second control end of the No. 3 relay; the second input end of the No. 1 relay is connected to the voltage sampling module; one end of the test product is connected to the output end of the power amplifier, and the other end is connected to the inverting input end of the power amplifier through the No. 7 resistor to form a constant current source circuit.

2. The current source for testing according to claim 1, characterized in that: The voltage sampling module includes power resistors No. 1 to No. 4, relay No. 4, relay No. 5, resistors No. 11 to No. 17, diode No. 4, diode No. 5, LED lamp No. 4, LED lamp No. 5, instrument amplifier and capacitors No. 4 to No. 6; Among them, one end of the power resistor No. 1 is connected to the second input end of the relay No. 1 of the power amplifier module, and the other end is connected to one end of the power resistor No. 4; one end of the power resistor No. 2 is connected to one end of the power resistor No. 1, and the other end is connected to the first input end of the relay No. 4, and the second input end of the relay No. 4 is connected to the other end of the power resistor No. 1; one end of the resistor No. 11 is connected to the first control end of the relay No. 4, and the other end is connected to the conduction end of the LED lamp No. 4, and the cut-off end of the LED lamp No. 4 is connected to the second control end of the relay No. 4; the cut-off end of the diode No. 4 is connected to the first control end of the relay No. 4, and the conduction end is connected to the second control end of the relay No. 4; one end of the power resistor No. 3 is connected to one end of the power resistor No. 1, and the other end is connected to the first input end of the relay No. 5, and one end of the second input end of the relay No. 5 is connected to the other end of the power resistor No. 1; one end of the resistor No. 12 is connected to the first control end of the relay No. 5, and the other end is connected to the conduction end of the LED lamp No. 5, The cut-off end of the D lamp is connected to the second control end of the No. 5 relay; the cut-off end of the No. 5 diode is connected to the first control end of the No. 5 relay, and the conduction end is connected to the second control end of the No. 5 relay; one end of the No. 4 capacitor is connected to one end of the No. 4 power resistor, and the other end is grounded; one end of the No. 5 capacitor is connected to the other end of the No. 4 power resistor and grounded, and the other end is grounded; one end of the No. 13 resistor is connected to one end of the No. 4 power resistor, and the other end is connected to the positive input end of the instrument amplifier; one end of the No. 14 resistor is connected to the other end of the No. 4 power resistor, and the other end is connected to the inverting input end of the instrument amplifier; one end of the No. 15 resistor is connected to the first gain control end of the instrument amplifier, and the other end is connected to the second gain control end of the instrument amplifier; one end of the No. 16 resistor is connected to the output end of the instrument amplifier, and the other end is connected to the reference voltage end of the instrument amplifier and grounded; one end of the No. 17 resistor is connected to the output end of the instrument amplifier, and the other end is connected to one end of the No. 6 capacitor and the AD module at the same time, and the other end of the No. 6 capacitor is grounded.

3. The current source for testing according to claim 2, characterized in that: When relay No. 4 and relay No. 5 are both disconnected and power resistor No. 1 is connected to the circuit, the current is at level 1; when relay No. 4 is disconnected and relay No. 5 is closed, power resistor No. 1 and power resistor No. 3 are connected to the circuit in parallel, the current is at level 2; when relay No. 4 is closed and relay No. 5 is disconnected, power resistor No. 1 and power resistor No. 2 are connected to the circuit in parallel, the current is at level 3; when relay No. 4 and relay No. 5 are both closed, power resistor No. 1, power resistor No. 2 and power resistor No. 3 are connected to the circuit in parallel, the current is at level 4.

4. The current source for testing according to claim 1, characterized in that: The signal amplification module includes an operational amplifier No. 1, a resistor No. 1, a resistor No. 2, a resistor No. 3 and a capacitor No. 1; one end of the resistor No. 1 is connected to the DA module, and the other end is connected to the inverting input end of the operational amplifier No. 1; one end of the capacitor No. 1 and one end of the resistor No. 2 are simultaneously connected to the inverting input end of the operational amplifier No. 1, the other end of the capacitor No. 1 is grounded, the other end of the resistor No. 2 is connected to the output end of the operational amplifier No. 1, and the output end of the operational amplifier No. 1 is simultaneously connected to the filtering module; one end of the resistor No. 3 is connected to the non-inverting input end of the operational amplifier No. 1, and the other end is grounded.

5. The current source for testing according to claim 1 or 4, characterized in that: The filtering module includes operational amplifier No. 2, resistor No. 4, resistor No. 5, resistor No. 6, capacitor No. 2 and capacitor No. 3; one end of resistor No. 4 is connected to the signal amplification module, and the other end of resistor No. 4 is connected to the inverting input end of operational amplifier No. 2; one end of resistor No. 5 is connected to the non-inverting input end of operational amplifier No. 2, and the other end is grounded; one end of capacitor No. 2 and one end of resistor No. 6 are simultaneously connected to the inverting input end of operational amplifier No. 2, the other end of capacitor No. 2 is connected to the non-inverting input end of operational amplifier No. 2, and the other end of resistor No. 6 is connected to the output end of operational amplifier No. 2; one end of capacitor No. 3 is connected to the inverting input end of operational amplifier No. 2, and the other end is connected to the output end of operational amplifier No. 2, and the output end of operational amplifier No. 2 is simultaneously connected to the power amplifier module.

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