A welding current monitor calibration device and method

Abstract

The invention discloses a welding current monitor calibration device and method, the device comprises a VFD keyboard, a program-controlled standard signal source, an AC / DC voltage power amplifier module, a DC current power amplifier module, a BTL AC current power amplifier module, an air-core coil, an AC / DC current current transformer and a welding current monitor; the output end of the VFD keyboard is connected to the program-controlled standard signal source, the output end of the program-controlled standard signal source is connected to the signal input end of the AC / DC voltage power amplifier module, the output end of the AC / DC voltage power amplifier module is connected to the welding current monitor; the output end of the AC / DC voltage power amplifier module is also connected to its own feedback input end. The invention can quickly output standard analog signals such as welding voltage, welding current, welding duration, etc., and improve the efficiency of welding current monitor calibration.

Description

Technical Field

[0001] The invention relates to a welding current monitor, and in particular to a welding current monitor calibration device and method. Background Art

[0002] Welding process technology has been widely used in all walks of life in industrial production. The control of the main welding parameters of current, voltage and time is very important to the welding process and welding quality. In order to ensure manufacturing quality, welding current monitors have appeared on the market one after another, and welding current monitors have been widely used in welding monitoring work in the industrial field, safeguarding the accurate application of welding technology in industrial manufacturing.

[0003] Therefore, the accuracy of the welding current monitor and the effectiveness of the monitoring indicators are the prerequisites for effectively ensuring the quality of the welding process; but there is currently no accurate integrated welding current monitor standard device on the market; in particular, there is no effective means for regular calibration of the detection and calibration of the peak number. The existing methods for detecting the peak number and time are often to short-circuit the load coil through a manual short-circuit switch after a certain current is passed to make it lose current and achieve a short-term output current signal. However, this method cannot effectively and accurately output the current signal frequency, and therefore cannot accurately determine whether the welding flow monitor peak number detection is correct.

[0004] The welding flow monitor is mainly based on the Rogowski coil. In order to obtain a large ampere-turn ratio output, it is necessary to wind multiple turns of hollow coils for detection to achieve a large ampere-turn ratio output effect with a small current. Because the characteristic of hollow coils is that the AC and DC impedances are different, the more turns the greater the difference, so AC and DC cannot be completed on one device. As the number of turns increases, the AC impedance increases, and a higher AC output voltage is required to obtain the designed current value. The existing power amplifier can no longer meet the use requirements.

[0005] In the past, due to sampling technology reasons, mutual inductance sampling could not achieve the same results for AC and DC, so two sets of sampling circuits needed to be manufactured. Therefore, the current calibration of welding flow monitors can only calibrate current and voltage, and AC and DC need to be detected using two sets of devices respectively, while the number of welding peaks and time cannot be accurately detected and calibrated. Calibrating a welding flow monitor often requires multiple processes and multiple times of detection and calibration, so it takes a long time to calibrate, and the calibration efficiency is low. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a welding current monitor calibration device and method, which can quickly output standard model signals such as welding voltage, welding current, welding duration, etc., to improve the efficiency of welding current monitor calibration work.

[0007] The object of the present invention is achieved by the following technical solutions: a welding current monitor calibration device, comprising a VFD keyboard, a program-controlled standard signal source, an AC / DC voltage power amplifier module, a DC current power amplifier module, a BTL AC current power amplifier module, an air-core coil, an AC / DC current current transformer and a welding current monitor;

[0008] The output end of the VFD keyboard is connected to the program-controlled standard signal source, the output end of the program-controlled standard signal source is connected to the signal input end of the AC / DC voltage power amplifier module, the output end of the AC / DC voltage power amplifier module is connected to the welding current monitor; the output end of the AC / DC voltage power amplifier module is also connected to its own feedback input end;

[0009] The signal input end of the DC current power amplifier module is connected to the output end of the program-controlled standard signal source through a switch K1, and the output end of the DC current power amplifier module is connected to the air-core coil through a switch K3;

[0010] The signal input end of the BTL AC current power amplifier module is connected to the output end of the program-controlled standard signal source through the switch K2, and the output end of the BTL AC current power amplifier module is connected to the air-core coil through the switch K4;

[0011] The AC / DC current transformer is used to detect the air-core coil, and the output end of the AC / DC current transformer is connected to the feedback signal input end of the DC current power amplifier module and the BTL AC current power amplifier module through the switching switch K5.

[0012] A welding current monitor calibration method comprises the following steps:

[0013] S1. After the user sets the voltage, current, phase, cycle or time parameters to be output and measured through the VFD keyboard and confirms, the VFD keyboard transmits the user-set parameters to the program-controlled standard voltage source;

[0014] S2. The program-controlled standard signal source generates two-phase standard voltage and current signals according to user settings.

[0015] S3. The voltage signal is sent to the PID regulation circuit of the AC / DC voltage power amplifier circuit; the PID regulation circuit performs proportional, integral and differential processing on the standard signal and the standard voltage feedback signal and then transmits them to the AC / DC voltage power amplifier; the power amplifier sends the standard voltage signal after amplifying the weak signal to the welding current monitor, and the welding current monitor displays the relevant voltage information.

[0016] S4. The DC current signal is sent to the PID regulation circuit of the DC current power amplifier circuit; the PID regulation circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the DC current power amplifier; the power amplifier sends the standard current signal after amplifying the weak signal to the hollow coil, and the welding current monitor obtains the DC current signal through the Rogowski coil for numerical display.

[0017] S5. The AC current signal is sent to the PID regulating circuit of the AC current power amplifier circuit; the PID regulating circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the BTL AC current power amplifier module. The level conversion circuit in the BTL AC current power amplifier module first amplifies the signal in the positive direction and converts it into a negative signal with opposite phase and equal absolute value of amplitude; specifically, the level conversion circuit samples the output of the operational amplifier and the output of the power amplifier respectively through the signal detection circuit; and the automatic AGC control circuit ensures that the two signals can still offset the load influence after being loaded, and ensures that the amplitudes of the two signals are equal and the phases are opposite; then the two signals with equal amplitude and opposite positive and negative directions are respectively sent to the positive and reverse power amplifier and the negative power amplifier for power amplification, and then the current signal and voltage after the forward power amplification are synchronously sent to the high end of the hollow coil, and the current signal and voltage after the reverse power amplification are synchronously sent to the low end of the hollow coil, and the welding current monitor obtains the set output AC current signal through the Rogowski coil monitoring and displays the value.

[0018] S6. Record the measured voltage amplitude, current amplitude and cycle number of the welding current monitor, compare them with the parameters set by the user through the VFD keyboard, and complete the calibration of the welding current monitor.

[0019] The beneficial effects of the present invention are: (1) The present invention can quickly and accurately calibrate the welding current monitor's voltage, current, number of peaks, time and other parameters. The integrated design of the AC / DC power amplifier and the introduction of the standard power source technology can quickly and accurately measure the main detection parameters of the welding current monitor, thereby improving the efficiency of the calibration work; and the measurement technical parameters can be effectively traced and calibrated.

[0020] (2) The present invention adopts a digital signal source control application, which can accurately output the number of cycles of the sinusoidal signal, ensuring the calibration of the peak number and time of the welding current monitor.

[0021] (3) The present invention adopts BTL (bridge connection) power amplifier application technology to solve the problem of low voltage power supply and high voltage output. Since the positive and negative half cycles are amplified at the same time, the positive and negative power supplies are output at the same time. Compared with the previous power amplifier that only uses positive power supply or negative power supply at the same time, the power utilization efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the device principle of the present invention;

[0023] Figure 2 This is a schematic diagram of the principle of a program-controlled standard signal source;

[0024] Figure 3 It is a schematic diagram of the principle of the AC / DC voltage power amplifier module;

[0025] Figure 4 It is the principle diagram of BTL AC current power amplifier module;

[0026] Figure 5 This is a schematic diagram of the principle of the level conversion circuit. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0028] like Figure 1 As shown, a welding current monitor calibration device includes a VFD keyboard, a programmable standard signal source, an AC / DC voltage power amplifier module, a DC current power amplifier module, a BTL AC current power amplifier module, an air-core coil, an AC / DC current current transformer and a welding current monitor;

[0029] The output end of the VFD keyboard is connected to the program-controlled standard signal source, the output end of the program-controlled standard signal source is connected to the signal input end of the AC / DC voltage power amplifier module, the output end of the AC / DC voltage power amplifier module is connected to the welding current monitor; the output end of the AC / DC voltage power amplifier module is also connected to its own feedback input end;

[0030] The signal input end of the DC current power amplifier module is connected to the output end of the program-controlled standard signal source through a switch K1, and the output end of the DC current power amplifier module is connected to the air-core coil through a switch K3;

[0031] The signal input end of the BTL AC current power amplifier module is connected to the output end of the program-controlled standard signal source through the switch K2, and the output end of the BTL AC current power amplifier module is connected to the air-core coil through the switch K4;

[0032] The AC / DC current transformer is used to detect the air-core coil, and the output end of the AC / DC current transformer is connected to the feedback signal input end of the DC current power amplifier module and the BTL AC current power amplifier module through the switching switch K5.

[0033] In the embodiment of the present application, the VFD keyboard is used to provide a human-computer interaction channel, and the set parameters are quickly input through the numeric keyboard and automatically transmitted to the program-controlled standard voltage source, which solves the backward operation mode of manually adjusting the voltage regulator; the welding current monitor is connected to a Rogowski coil. The switching switch K5 is a single-pole double-throw switch, the moving end of the switching switch K5 is connected to the output end of the AC and DC current current transformer, the first moving end of the switching switch K5 is connected to the feedback signal input end of the DC current power amplifier module, and the second moving end of the switching switch K5 is connected to the feedback signal input end of the BTL AC current power amplifier module.

[0034] like Figure 2 As shown, the program-controlled standard signal source includes an ARM microcontroller, a CPLD chip, a first DAC module, a second DAC module and a crystal oscillator; the output end of the crystal oscillator is respectively connected to the ARM microcontroller and the CPLD chip, and is used to provide a clock reference for the ARM microcontroller and the CPLD chip; the input end of the ARM microcontroller is connected to the VFD keyboard, and the output end of the ARM microcontroller is respectively connected to the first DAC module and the second DAC module through the CPLD chip, the output end of the first DAC module is connected to the AC / DC voltage power amplifier module, and the output end of the second DAC module is respectively connected to the switch K1 and the switch K2.

[0035] The programmable standard signal source is used to generate a 50Hz low-distortion periodic sine signal or a DC pulse square wave signal, and a high-precision crystal oscillator with temperature compensation is used to ensure time accuracy; the second DAC module is used for DA conversion of voltage signals, and the second DAC module is used for DA conversion of current signals.

[0036] like Figure 3 As shown, the AC / DC voltage power amplifier module includes a first PID regulating circuit and an AC / DC voltage power amplifier. The signal input end of the first PID regulating circuit is connected to a program-controlled standard signal source, the output end of the first PID regulating circuit is connected to the AC / DC voltage power amplifier, the output end of the AC / DC voltage power amplifier is connected to the welding current monitor, and the output end of the AC / DC voltage power amplifier is also connected to the feedback input end of the first PID regulating circuit. The module is used to amplify the power of the AC periodic voltage signal or DC pulse voltage signal sent by the standard signal source, and then send the power-amplified voltage signal and current synchronously to the welding current monitor to provide a voltage reference signal. The voltage output signal is fed back to the PID input end through a precision resistor to be compared with the standard voltage signal and automatically corrected.

[0037] In an embodiment of the present application, the DC current power amplifier module includes a second PID regulation circuit and a DC current power amplifier, the input end of the second PID regulation circuit is connected to the program-controlled signal source through a switch K1, and the feedback input end of the second PID regulation circuit is connected to the first moving end of the switching switch K5; the output end of the second PID regulation circuit is connected to the DC current power amplifier, and the output end of the DC current power amplifier includes an IH end and an OV end;

[0038] The switch K3 includes two sub-switches that are opened and closed synchronously, wherein the IH terminal is connected to the first end of the air-core coil through the first sub-switch of the switch K3, and the OV terminal is connected to the second end of the air-core coil through the second sub-switch of the switch K3.

[0039] The DC current power amplifier module is used to amplify the DC pulse current signal sent by the standard signal source, and then send the power-amplified current signal and voltage to the air-core coil synchronously. The welding current monitor obtains the DC current signal through the Rogowski coil for numerical display. The current output signal flowing through the air-core coil is sampled and fed back by the precision AC / DC current transformer and sent to the PID input terminal for comparison with the standard current signal, and automatic correction is performed.

[0040] like Figure 4As shown, the BTL AC current power amplifier module is used to first perform forward and reverse transformation on the AC periodic signal sent by the standard signal source, and the obtained signals with the same amplitude and opposite phase are respectively sent to the forward and reverse power amplifiers for power amplification, and then the current signal and voltage after forward power amplification are synchronously sent to the high end of the hollow coil, and the current signal and voltage after reverse power amplification are synchronously sent to the low end of the hollow coil, and the welding current monitor obtains the AC current signal through the Rogowski coil for numerical display. This circuit forms a BTL (bridge) power amplifier drive circuit, which achieves the effect of low voltage power supply and high voltage output, solving the problem that the existing power amplifier can no longer meet the high voltage output. The current output signal flowing through the air-core coil is sent to the PID input end through the precision AC / DC current transformer sampling feedback signal for comparison with the standard current signal and automatic correction; in the embodiment of the present application, the BTL AC current power amplifier module includes a third PID adjustment circuit, a level conversion circuit, a forward power amplifier, a reverse power amplifier, an iH port and an iL port, and the level conversion circuit includes a forward conversion circuit and a reverse conversion circuit; the input end of the third PID adjustment circuit is connected to the programmable standard signal source through the switch K2, and the feedback input end of the third PID adjustment circuit is connected to the second moving end of the switching switch K5; the output end of the third PID adjustment circuit is respectively connected to the forward conversion circuit and the reverse conversion circuit, the output end of the forward conversion circuit is connected to the iH port through the forward power amplifier, and the output end of the reverse conversion circuit is connected to the iL port through the reverse power amplifier;

[0041] like Figure 5 As shown, the level conversion circuit is composed of input resistors R1~R5, operational amplifier, detection circuit, automatic gain control AGC circuit, etc., which are transmitted to the conversion circuit for forward and reverse conversion. The conversion circuit samples the outputs of the forward conversion operational amplifier and the reverse conversion operational amplifier, as well as the forward power amplifier output and the reverse power amplifier output respectively through the signal detection circuit; through the comparison amplifier circuit, the automatic AGC control circuit performs feedback compensation to ensure that the two signals can still offset the load influence after being loaded, and ensure that the two signals have equal amplitudes and opposite phases; the obtained signals with the same amplitude and opposite phases are respectively sent to the forward and reverse power amplifiers for power amplification. This circuit is the key to ensuring the balanced output of the BTL circuit.

[0042] The switch K4 includes two synchronously turned on and off sub-switches, the iH port is connected to the first end of the air-core coil through one of the sub-switches, and the iL port is connected to the second end of the air-core coil through the other sub-switch.

[0043] In the embodiments of the present application, the latest current sampling technology AC and DC current transformers are adopted, and AC and DC sampling can be realized with a set of current transformers, which solves the problem of multiple AC and DC processes requiring multiple separate detection and calibration, thereby improving work efficiency and reducing manufacturing costs; it also solves the problem of temperature drift introduced by resistor heating leading to changes in electrical parameters during previous resistor sampling.

[0044] The multi-turn air-core coil technology is used to achieve a high ampere-turn ratio output effect with a small current. According to the ampere-turn calculation formula I*N, the larger the N, the smaller the I can be for the same ampere-turn requirement. The smaller the current, the less stringent the working requirements of the power amplifier, which can greatly improve the safety and stability of the system.

[0045] A welding current monitor calibration method comprises the following steps:

[0046] S1. After the user sets the voltage, current, phase, cycle or time parameters to be output and measured through the VFD keyboard and confirms, the VFD keyboard transmits the user-set parameters to the program-controlled standard voltage source;

[0047] S2. The program-controlled standard signal source generates two-phase standard voltage and current signals according to user settings.

[0048] S3. The voltage signal is sent to the PID regulation circuit of the AC / DC voltage power amplifier circuit; the PID regulation circuit performs proportional, integral and differential processing on the standard signal and the standard voltage feedback signal and then transmits them to the AC / DC voltage power amplifier; the power amplifier sends the standard voltage signal after amplifying the weak signal to the welding current monitor, and the welding current monitor displays the relevant voltage information.

[0049] S4. The DC current signal is sent to the PID regulation circuit of the DC current power amplifier circuit; the PID regulation circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the DC current power amplifier; the power amplifier sends the standard current signal after amplifying the weak signal to the hollow coil, and the welding current monitor obtains the DC current signal through the Rogowski coil for numerical display.

[0050] S5. The AC current signal is sent to the PID regulating circuit of the AC current power amplifier circuit; the PID regulating circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the BTL AC current power amplifier module. The level conversion circuit in the BTL AC current power amplifier module first amplifies the signal in the positive direction and converts it into a negative signal with opposite phase and equal absolute value of amplitude; specifically, the level conversion circuit samples the output of the operational amplifier and the output of the power amplifier respectively through the signal detection circuit; and the automatic AGC control circuit ensures that the two signals can still offset the load influence after being loaded, and ensures that the amplitudes of the two signals are equal and the phases are opposite; then the two signals with equal amplitude and opposite positive and negative directions are respectively sent to the positive and reverse power amplifier and the negative power amplifier for power amplification, and then the current signal and voltage after the forward power amplification are synchronously sent to the high end of the hollow coil, and the current signal and voltage after the reverse power amplification are synchronously sent to the low end of the hollow coil, and the welding current monitor obtains the set output AC current signal through the Rogowski coil monitoring and displays the value.

[0051] S6. Record the measured voltage amplitude, current amplitude and cycle number of the welding current monitor, and compare them with the parameters set by the user through the VFD keyboard to complete the calibration of the welding current monitor. The calibration method is as follows:

[0052] Formula 1: Voltage measurement error = ((measured value - set value) ÷ set value) + correction value

[0053] Formula 2: Current measurement error = ((measured value - set value) ÷ set value) + correction value

[0054] Formula 3: Cycle number measurement error = (measured value - set value) ÷ set value

[0055] Measured value: the electrical parameter result actually measured by the welding current monitor.

[0056] Set value: The user sets the electrical parameter value to be output through the VFD keyboard.

[0057] Correction value: The error correction value after system traceability calibration, which is used to compensate for the error information of the calibration device itself. However, this correction value is determined in advance and can be regarded as a known quantity in this application; in some embodiments, the correction value can also be directly ignored.

[0058] The above description shows and describes a preferred embodiment of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. And the changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A welding current monitor calibration device, characterized in that: Including VFD keyboard, program-controlled standard signal source, AC / DC voltage power amplifier module, DC current power amplifier module, BTL AC current power amplifier module, air-core coil, AC / DC current transformer and welding current monitor; The output end of the VFD keyboard is connected to the program-controlled standard signal source, the output end of the program-controlled standard signal source is connected to the signal input end of the AC / DC voltage power amplifier module, the output end of the AC / DC voltage power amplifier module is connected to the welding current monitor; the output end of the AC / DC voltage power amplifier module is also connected to its own feedback input end; The signal input end of the DC current power amplifier module is connected to the output end of the program-controlled standard signal source through a switch K1, and the output end of the DC current power amplifier module is connected to the air-core coil through a switch K3; The signal input end of the BTL AC current power amplifier module is connected to the output end of the program-controlled standard signal source through the switch K2, and the output end of the BTL AC current power amplifier module is connected to the air-core coil through the switch K4; The AC / DC current transformer is used to detect the air-core coil, and the output end of the AC / DC current transformer is connected to the feedback signal input end of the DC current power amplifier module and the BTL AC current power amplifier module through the switching switch K5; The AC / DC voltage power amplifier module includes a first PID regulating circuit and an AC / DC voltage power amplifier, wherein the signal input end of the first PID regulating circuit is connected to a program-controlled standard signal source, the output end of the first PID regulating circuit is connected to the AC / DC voltage power amplifier, the output end of the AC / DC voltage power amplifier is connected to the welding current monitor, and the output end of the AC / DC voltage power amplifier is also connected to the feedback input end of the first PID regulating circuit; The DC current power amplification module includes a second PID regulating circuit and a DC current power amplifier, the input end of the second PID regulating circuit is connected to the program-controlled standard signal source through a switch K1, and the feedback input end of the second PID regulating circuit is connected to the first moving end of the switching switch K5; The output end of the second PID regulating circuit is connected to a DC current power amplifier, wherein the output end of the DC current power amplifier includes an IH end and an OV end; The switch K3 includes two sub-switches that are opened and closed synchronously, wherein the IH terminal is connected to the first end of the air-core coil through the first sub-switch of the switch K3, and the OV terminal is connected to the second end of the air-core coil through the second sub-switch of the switch K3; The BTL AC current power amplifier module includes a third PID regulating circuit, a level conversion circuit, a forward power amplifier, a reverse power amplifier, an iH port and an iL port, wherein the level conversion circuit includes a forward conversion circuit and a reverse conversion circuit; the input end of the third PID regulating circuit is connected to the programmable standard signal source through a switch K2, and the feedback input end of the third PID regulating circuit is connected to the second active end of the switching switch K5; the output end of the third PID regulating circuit is connected to the forward conversion circuit and the reverse conversion circuit respectively, the output end of the forward conversion circuit is connected to the iH port through the forward power amplifier, and the output end of the reverse conversion circuit is connected to the iL port through the reverse power amplifier; The switch K4 includes two synchronously turned on and off sub-switches, the iH port is connected to the first end of the air-core coil through one of the sub-switches, and the iL port is connected to the second end of the air-core coil through the other sub-switch.

2. A welding current monitor calibration device according to claim 1, characterized in that: The welding current monitor is connected to a Rogowski coil.

3. A welding current monitor calibration device according to claim 1, characterized in that: The switching switch K5 is a single-pole double-throw switch, the moving end of the switching switch K5 is connected to the output end of the AC / DC current transformer, the first moving end of the switching switch K5 is connected to the feedback signal input end of the DC current power amplifier module, and the second moving end of the switching switch K5 is connected to the feedback signal input end of the BTL AC current power amplifier module.

4. A welding current monitor calibration device according to claim 1, characterized in that: The program-controlled standard signal source includes an ARM microcontroller, a CPLD chip, a first DAC module, a second DAC module and a crystal oscillator; the output end of the crystal oscillator is respectively connected to the ARM microcontroller and the CPLD chip, and is used to provide a clock reference for the ARM microcontroller and the CPLD chip; the input end of the ARM microcontroller is connected to a VFD keyboard, the output end of the ARM microcontroller is respectively connected to the first DAC module and the second DAC module through the CPLD chip, the output end of the first DAC module is connected to an AC / DC voltage power amplifier module, and the output end of the second DAC module is respectively connected to a switch K1 and a switch K2.

5. A welding current monitor calibration method, using the device according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. After the user sets the voltage, current, phase, cycle or time parameters to be output and measured through the VFD keyboard and confirms, the VFD keyboard transmits the user-set parameters to the program-controlled standard voltage source; S2. The program-controlled standard signal source generates two-phase standard voltage and current signals according to user settings. S3. The voltage signal is sent to the PID regulation circuit of the AC / DC voltage power amplifier circuit; the PID regulation circuit performs proportional, integral and differential processing on the standard signal and the standard voltage feedback signal and then transmits them to the AC / DC voltage power amplifier; the power amplifier sends the standard voltage signal after amplifying the weak signal to the welding current monitor, and the welding current monitor displays the relevant voltage information; S4. The DC current signal is sent to the PID adjustment circuit of the DC current power amplifier circuit; the PID adjustment circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the DC current power amplifier; the power amplifier sends the standard current signal after weak signal amplification to the air-core coil, and the welding current monitor obtains the DC current signal through the Rogowski coil for numerical display; S5. The AC current signal is sent to the PID regulating circuit of the AC current power amplifier circuit; the PID regulating circuit performs proportional, integral and differential processing on the standard signal and the standard current feedback signal and then transmits them to the BTL AC current power amplifier module. The level conversion circuit in the BTL AC current power amplifier module first amplifies the signal in the positive direction and converts it into a negative signal with an opposite phase and an equal absolute value of amplitude. Then, these two signals with equal amplitude and opposite positive and negative directions are respectively sent to the positive and reverse power amplifier and the negative power amplifier for power amplification. Then, the current signal and voltage after the forward power amplification are synchronously sent to the high end of the hollow coil, and the current signal and voltage after the reverse power amplification are synchronously sent to the low end of the hollow coil. The welding current monitor obtains the set output AC current signal through the Rogowski coil monitoring and displays the value. S6. Record the measured voltage amplitude, current amplitude and cycle number of the welding current monitor, compare them with the parameters set by the user through the VFD keyboard, and complete the calibration of the welding current monitor.

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