Eight-channel high-precision megger

Abstract

The invention discloses an eight-channel high-precision megger, which relates to the technical field of precision measurement and comprises eight technical paths including contact detection, rapid charging, integral amplification, signal sampling, rapid discharging, software operation, result output and calibration and compensation, so that contact detection is executed on a capacitor to be detected; the circuit is switched on and off through precise time control of the FPGA on the optocoupler MOS tube; based on the high static stability principle of a chemical battery, it is ensured that the voltage ripple stability of a power supply is lower than 1 microvolt, and oblique lines output by to-be-detected micro-current signals are screened out; the IO of the ARM outputs an analog acquisition completion signal Index through an optocoupler to inform external interaction equipment; and during software operation, the ARM end starts hardware floating point acceleration to filter sampled data and fit a slope by a least square method, and finally the internal resistance is obtained. According to the invention, stable, high-efficiency, high-precision, high-safety, adjustable and low-cost internal resistance measurement is realized, and the influence on the environment is reduced.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of precision measurement, and in particular to an eight-channel high-precision high resistance meter. Background Art

[0002] Ultra-high resistance resistance measuring instrument is a kind of instrument used to measure ultra-high resistance components (10 12 The high-resistance meter market is currently highly monopolized, with Japanese HIOKI, American ESI, and Keithley accounting for over 85% of the global high-end market share. Currently, no universities or companies in China have developed ultra-high-resistance resistance measuring instruments that can rival those of Japanese or European and American manufacturers. This has resulted in China being stuck in a "bottleneck" situation in high-end application areas such as power battery tab insulation testing and quantum device tunneling current detection, severely restricting the development and growth of related industries in my country. At the level of scientific and technological development, among the 35 bottleneck technologies announced by the Ministry of Industry and Information Technology, breakthroughs are urgently needed in the high-end resistance and capacitance industry. This invention focuses on the development of core technologies for high-resistance meters. By overcoming key technical challenges such as high-precision measurement and advanced circuit design, it aims to fill a technological gap in this field domestically and elevate my country's technological capabilities in the development and manufacture of high-end testing instruments. The technical experience and innovative achievements accumulated during this development process will serve as a reference for other related research projects in Shenzhen and across China, promoting the interdisciplinary integration of metrology, electronics, and computer science, and ultimately driving overall scientific and technological progress.

[0003] Currently, most high-resistance meters only support Windows platform applications, limiting their use across diverse work environments and devices. In the future, to adapt to diverse software ecosystems and device requirements, instruments will develop towards cross-platform, multi-OS compatibility, with the potential to operate under multiple ecosystems, including Linux, Mac OS, Hongmeng, and Android. This will not only allow different user groups to choose the appropriate operating system based on their habits and work needs, but also facilitate integration with a wider range of devices, promoting data sharing and system collaboration, enhancing the instrument's versatility and convenience, and promoting its application and promotion in a wider range of fields.

[0004] Traditional resistance meters have the following technical problems:

[0005] 1. Fewer measurement channels leads to lower efficiency: Because traditional resistance measurement relies on the relationship between current and voltage, multiple channels require multiple precision sampling resistors, making the manufacturing process complex and costly, and achieving multi-channel consistency is difficult. The lack of channels means that multiple DUTs require additional instruments or channel switching, which undoubtedly increases cost and measurement time.

[0006] 2. Non-contact detection function: Since the traditional principle of measuring resistance is based on the relationship between current and voltage, when encountering ultra-high resistance, the current in the circuit is very small, and the traditional DC volt-ammeter method is no longer applicable. Moreover, the circuit capacitance effect cannot be ignored in the case of ultra-high resistance, resulting in the traditional method being unable to accurately detect whether the product is in good contact. Therefore, most DC resistance meters do not have this function.

[0007] 3. Poor stability and reliability of resistance measurement: Traditional high resistance meters or resistance meters rely on their own or external power supply. If the stability and reliability of the external power supply are poor, they are easily affected by power fluctuations or failures, causing equipment failure or damage. Therefore, the ripple requirements for the external or internal power supply are extremely high, and the cost is high.

[0008] 4. Limited rapid response and control capabilities: Traditional high-impedance meters lack multi-channel functionality. Achieving multi-channel functionality requires cascading multiple instruments and applying an external synchronization signal, which is overly complex. This capability is particularly limited in time-sensitive applications (1mS synchronization). This invention's subsequent solution perfectly addresses this issue.

[0009] In summary, a high resistance meter that improves measurement efficiency and requires simultaneous output measurement of multiple channels is a technical problem that needs to be urgently solved by people in this technical field. Summary of the Invention

[0010] Based on this, the purpose of the present invention is to provide an eight-channel high-precision high resistance meter to solve the technical problems raised in the above background technology.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] An eight-channel, high-precision high-resistance meter, comprising eight technical pathways: contact detection, rapid charging, integral amplification, signal sampling, rapid discharge, software calculation, result output, and calibration and compensation. Contact detection is used to detect contact with the capacitor to be tested. Phase and frequency comparisons are performed with the SPWM signal using a built-in algorithm to ensure good contact.

[0013] The fast charging is equipped with a current limiting unit. The fast charging is used to precisely control the time of the optocoupler MOS tube through the FPGA to make the circuit on and off, so as to charge the capacitor to be detected.

[0014] Integral amplification is used based on the principle of high static stability of chemical batteries to ensure that the power supply voltage ripple stability is less than 1 microvolt. Only ultra-low ripple power can be applied to both ends of the detection capacitor to screen out the oblique line of the micro-current signal output to be detected;

[0015] Signal sampling is used to sample the slope of the integral amplifier output according to a fixed period after ADC analog-to-digital conversion;

[0016] Fast discharge is used to discharge the charge stored in the capacitor to be detected through the current limiting circuit. The ARM IO outputs an analog acquisition completion signal Index through the optocoupler to notify the external interactive device.

[0017] Software operations are used to enable hardware floating-point acceleration on the ARM side when the software is running to filter the sampled data and fit the slope using the least squares method, ultimately obtaining an accurate slope K. Based on this slope K, key calculation formulas are used to calculate the current and the internal resistance of the capacitor to be tested.

[0018] Preferably, in contact detection, FPGA is used to generate a high-frequency SPWM signal, which is then converted into a sinusoidal signal through a bandpass filter. The sinusoidal signal is used to drive a high-frequency transformer through a PA power amplification unit, and then the high-voltage DC and the sinusoidal signal are superimposed into a mixed signal by means of a high-frequency coupling transformer to realize a power line carrier.

[0019] After the mixed signal is applied to the capacitive load to be tested, the DC signal will be isolated at the other end while retaining the high-frequency AC signal. The high-frequency signal then flows through the LC frequency selection circuit. The amplified high-frequency sinusoidal signal is converted into a square wave signal after rectification and detection. The FPGA is then used to implement frequency and phase detection of the signal, thereby realizing the comparison between the output SPWM signal and the converted square wave and contact detection.

[0020] Preferably, the current limiting unit uses a MOSFET and an operational amplifier to form a constant current limiting unit.

[0021] Preferably, the key calculation formula is as follows:

[0022]

[0023] Among them, R x : Indicates the internal resistance of the capacitor to be detected; I x :Indicates the internal resistance R of the capacitor to be detected x Converts and calculates the output current; K: expresses the slope; V in : Represents the high resistance meter input voltage, V out : Indicates the output voltage of the high resistance meter; C 11 : Indicates a known value capacitor. R 14 : Indicates a resistor of known value.

[0024] Preferably, the result output is used to output data obtained by software calculations;

[0025] The results are output in three communication modes: USB, Ethernet, and RS232. An external Handler interface is also configured, and the ARM IO port is used to realize 4 groups of 8-channel signals for exceeding the upper limit, exceeding the lower limit, good products, and poor contact. An additional group of measurement completion signals EOM is configured to cooperate with the automation system integration.

[0026] Preferably, calibration and compensation are used to reduce the detection error of the high resistance meter.

[0027] In summary, the present invention mainly has the following beneficial effects:

[0028] In the present invention, 1. Power line carrier technology is used to superimpose high-voltage direct current on a high-frequency alternating current signal. After the signal flows through the load, a horizontal phase difference is formed, which is then detected using detection technology, solving the problem that microcurrents of capacitive loads cannot be directly detected by direct current. The technical solution for contact detection adopts the idea of "passing AC and blocking DC" for capacitive loads to achieve the contact detection function. Because power line carrier technology is used to compare the output signal with the detection signal, it has a very strong anti-interference ability. Compared with the traditional branch voltammetry method, the characteristics are obvious. In addition, the power consumption of the contact detection circuit implemented by power line carrier is very low, about 1 / 10 of the power consumption of the branch voltammetry method.

[0029] 2. By developing a charge pump power supply circuit, we can address the power supply noise issue and, in turn, the measurement issues caused by power supply fluctuations. The charge pump power supply circuit solution only provides a weak current to the load during measurement, eliminating the circuit's fluctuations caused by large loads. Furthermore, the discharge capacitor is always connected only to the load to be measured, resulting in minimal ripple. This approach cleverly utilizes multiple capacitors to filter the external power supply, further addressing the power supply ripple issue.

[0030] 3. The micro-current integral amplifier circuit is developed to solve the problem that the traditional Ohm's law is not applicable in micro-current conditions. In the PCB design process, high insulation materials and special PCB processing are used to solve the leakage current problem of traditional PCB boards.

[0031] 4. Developed a hardware processing platform based on FPGA+ARM heterogeneous parallelism to achieve high-speed data transmission and collaborative work between FPGA and ARM. It fully utilizes the time accuracy of FPGA and the computing power of ARM to achieve multi-channel parallel sampling and calculation, achieving a sampling accuracy of 5nS and a measurement cycle accurately controlled within 2ms, solving the problem of long measurement time of traditional high resistance meters.

[0032] 5. The least squares linear fitting principle is used to accurately calculate the slope, and the reverse calibration algorithm is used to accurately calculate the actual capacitance value, which solves the problem of differences in electronic components themselves and achieves multi-channel consistency and accuracy of the instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Detailed implementation principle circuit diagram of the present invention;

[0034] Figure 2 Schematic diagram of the square wave signal DETECT of the present invention;

[0035] Figure 3 Schematic diagram of charging current waveform of the present invention;

[0036] Figure 4 This is a circuit diagram of the ultra-low ripple working principle of the present invention;

[0037] Figure 5 This is a schematic diagram of the IO timing of the present invention;

[0038] Figure 6 Schematic diagram of the timing of Index and EOM of the present invention. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0040] like Figure 1 As shown, the high resistance meter described in the present invention is an 8-channel synchronous ultra-high resistance measuring instrument, which implements 8 technical paths: contact detection, fast charging, integral amplification, analog sampling, fast discharge, software calculation, result output, calibration and compensation;

[0041] Example 1: The contact detection technology solution is as follows:

[0042] FPGA is used to generate a high-frequency SPWM signal, which is then converted into a sinusoidal signal through a bandpass filter. The sinusoidal signal is used to drive a high-frequency transformer through a PA power amplifier unit. The high-voltage DC and sinusoidal signals are then superimposed with the help of a high-frequency coupling transformer to realize a power line carrier. After this mixed signal is applied to the capacitive load to be measured, the DC signal will be isolated at the other end while retaining the high-frequency AC signal. The high-frequency signal then flows through an LC frequency selection circuit. The amplified high-frequency sinusoidal signal is converted into a square wave signal after rectification and detection. The FPGA is then used to realize the frequency and phase detection of the signal, thereby realizing the comparison between the output SPWM signal and the converted square wave. Contact detection is realized through the above principle.

[0043] like Figure 1 Shown: Detailed implementation principle of core implementation

[0044] The FPGA outputs an SPWM signal through the SPWM pin, which is converted into a sinusoidal signal SIN after passing through a low-pass filter composed of R1 and C1. After the driving capability of the sinusoidal signal is enhanced by the U1.1 unit, it is coupled to the transformer T1 through the AC-passing and DC-blocking circuit composed of C2 and R2. The secondary side of T1 is connected to VIN as a high-voltage DC power supply; C3 is the capacitor to be measured, and Rx is the internal resistance of the capacitor to be measured; the internal resistance of the capacitor to be measured, Rx, is detected through the following contact detection steps.

[0045] 1. Before performing contact detection, Figure 1 U4 and U5 are in the off state and not conducting, K1 is conducting to short-circuit discharge C11;

[0046] 2. At this time, due to the virtual short and virtual disconnection of U1.2, the negative input terminal of the U1.2 op amp is equivalent to the ground point. At this time, the SIN sinusoidal signal is coupled to the capacitor C3 to be measured through T1, and then flows back to the GND node through R14;

[0047] 3. The above circuit will form an AC signal at the node where C4 and C3 are connected. C4, L1, and R6 form an LC frequency selection unit to filter the frequency of the input signal. The signal within the frequency range will be amplified to the appropriate amplitude range by the secondary amplifier circuit composed of U2.1 and U2.2.

[0048] 4. Figure 1 The DAC unit outputs a comparison voltage that forms a comparator circuit with U3.1. The output of U3.1 is then limited by Q1 to 0-3.3V and becomes a square wave signal DETECT. Figure 2 shown.

[0049] 5. After receiving the DETECT signal, the FPGA uses the built-in algorithm to compare the phase and frequency with the SPWM signal to determine whether it is the signal sent by itself. If the frequency and phase are consistent, it is judged that the contact is good, otherwise it is judged that the contact is poor.

[0050] Example 2: Fast charging technology solution:

[0051] After the contact is confirmed to be correct in Example 1, the product under test needs to be charged. Charging requires a current limiting unit. The purpose of current limiting is to prevent the product under test from damaging the detection circuit due to short circuit during the test due to poor quality. Here, the current limiting unit uses a constant current limiting unit composed of a MOSFET and an operational amplifier. The FPGA then precisely controls the timing of the optocoupler MOS tube to turn the circuit on and off to achieve the purpose of charging, thereby allowing the product to quickly enter the leakage current stable zone. The process of performing fast charging is as follows:

[0052] 1. If Figure 1As shown, stop the SPWM signal output, U4 is turned on, U5 is turned off, and K1 is closed. At this time, C3 is connected to the ground through R11. The resistance of R11 is relatively small (about 200 ohms). At this time, the loop current is large, and C3 is quickly charged. The charging current waveform is exponential, as shown in the following figure. Figure 3 shown.

[0053] 2. After t4, capacitor C3 is fully charged, U4 is disconnected, U5 is disconnected, and K1 is closed. At this time, the capacitor is fully charged and enters the leakage current range. The current tends to be stable and the waveform is horizontal. Figure 3 shown.

[0054] Example 3, integral amplification technical solution:

[0055] 1. Power supply design issues and solutions in micro-current detection:

[0056] When testing microcurrent in a noisy circuit environment with a capacitive load, it is necessary to distinguish between leakage current and charge and discharge current caused by voltage fluctuations. Existing components inevitably have capacitive characteristics, and power supply fluctuations can cause the load charge and discharge signals to interfere with the signal to be tested. Traditional circuits and components are difficult to meet the requirements of high-precision power supply.

[0057] Therefore, drawing on the idea of high static stability of chemical batteries, multiple capacitors (at least three, such as A, B, and C) are used in conjunction with a switching circuit; the traditional DC power supply (switching power supply or linear power supply) is processed, and the capacitor charging and discharging are controlled by the switching tube, such as A charging, B on standby, and C discharging. The working time of each capacitor is extremely short (such as 1 millisecond); when A is charging, it is connected to the external power supply. At this time, the ripple is synchronized with the external power supply; when B is on standby, the capacitor is in a self-excited oscillation process and needs to be left still for a period of time to complete self-charging and eventually stabilize; during the discharge period of C, only one capacitor is connected to the product under test, and the charge of the capacitor has stabilized at this time.

[0058] The above method ensures that the power supply voltage ripple stability is less than 1 microvolt, so that an ultra-low ripple power supply can be applied to both ends of the load to be tested to ensure that the micro-current signal to be detected is screened out.

[0059] like Figure 4 As shown in the figure, during charging, the three IO ports of the FPGA output PWM1, PWM2, and PWM3 control the on and off of the three optocoupler MOS tubes according to the timing polling, and the input power supply VP charges the three capacitors C5, C6, and C7 respectively; during discharging, the three IO ports PWM4, PWM5, and PWM6 poll the discharge in turn. The program inside the FPGA cooperates to keep the timing polling continuously, thus realizing the continuous operation of the charge pump, and the output terminal VIN can obtain a highly stable power supply; the specific IO timing is as follows Figure 5 shown.

[0060] 2. Signal amplification and sampling circuit design:

[0061] Chip selection: The amplification of tiny currents requires the use of an operational amplifier with extremely small bias current and sufficiently low offset voltage to meet the detection accuracy requirements, achieve the measurement of ultra-high resistance, ensure the detection capability reaches the 10fA (femtoampere) level, and guarantee the accurate detection of 1pA (picoampere) current.

[0062] 3. Adopt integral amplifier circuit design:

[0063] Microcurrents need to be amplified before they can be detected by conventional chips. Traditional amplifier circuits need to convert current into voltage before amplification according to Ohm's law, which requires the use of very large resistors, resulting in circuit losses. Here, an integral method is proposed to integrate the current over time, and the output voltage signal after passing through the integral amplifier circuit will present a slanted line with a fixed slope.

[0064] 4. Selection of integral switch tube:

[0065] As we all know, the integration circuit is composed of three components: an operational amplifier, a bias resistor, and an integration capacitor. The integration capacitor needs to maintain zero charge every time it integrates, so a discharge switch tube is needed here. The introduction of the discharge tube will generate additional leakage current, affecting the bias current. Therefore, a switch tube with a leakage current of femtoampere level (such as a reed switch) needs to be selected here.

[0066] 5. Hardware anti-interference and leakage processing:

[0067] The PCB is made of FR4 fiberglass, with insulators to reduce leakage current. The input signal to be tested requires electromagnetic shielding, and a metal shield can be used to reduce electromagnetic interference in the environment.

[0068] The specific implementation process is as follows Figure 1 As shown, SPWM is turned off, U4 and U5 are disconnected, K1 is disconnected at this time, and the FPGA internal timing is turned on to trigger the ADC function through the PORT port.

[0069] Example 4: Signal sampling:

[0070] The oblique line output by the integral amplification in Example 3 is sampled according to a fixed period through ADC analog-to-digital conversion. Here, FPGA is used for precise time control and timing of 8-channel parallel sampling. The sampled data is cached in the FPGA FIFO queue, and then the ARM chip reads the data in the FPGA FIFO. Figure 6 The t5 time period is shown in FIG.

[0071] Example 5: Rapid discharge:

[0072] After the above series of actions, discharge is performed to discharge the charge stored in the product under test through the current limiting circuit. Discharge is similar to charging in Example 2, but the action is reversed. At this time, the ARM IO can output an analog acquisition completion signal Index through the optocoupler to notify the external interactive device that it can perform additional actions, in order to improve system efficiency and achieve high speed. The specific implementation process is as follows Figure 1 As shown in the figure, SPWM is turned off, U4 is disconnected, K1 is closed, and U5 is closed and maintained. Figure 6 During t6 time, U5 is disconnected afterwards.

[0073] Example 6: Software Calculation

[0074] In the discharge process of the fifth embodiment, the ARM side enables hardware floating-point acceleration to filter the sampled data and fit the slope using the least squares method. The discharge process is executed simultaneously with the ARM software operation, which saves time and improves efficiency. Finally, an accurate slope K is obtained, and the current is calculated from this slope. The specific calculation is shown in the following formulas (1), (2), and (3):

[0075]

[0076] Among them, V in : Indicates input voltage; V out : indicates output voltage; K: indicates slope

[0077] R is finally calculated through formula (1), formula (2), and formula (3) x This is the resistance to be measured that we calculated, which can also be converted into current I x =V in ÷(R x +R 14 ) for output.

[0078] Example 7, result output:

[0079] The results are output in a variety of ways, typically USB, Ethernet, and RS232. ARM internally integrates string protocols as well as ModbusRTU and ModbusTCPIP protocols to achieve industrial communication. In addition, an external Handler interface is configured, using the ARM IO port to achieve four groups of 8-channel signals for over-limit, over-low limit, good quality, and poor contact. An additional set of measurement completion signals, EOM, is configured to cooperate with automation system integration. The timing of Index and EOM is as follows: Figure 6 shown.

[0080] Example 8: Calibration and compensation:

[0081] Examples 1 to 7 are all theoretical steps. In reality, there are many unavoidable factors that affect the performance. For example, it is impossible to find two completely identical capacitors and resistors on the market, and various errors caused by PCB materials and welding processes will inevitably introduce errors.

[0082] The correction of this system is very important. Here we use a resistor with a known standard resistance value, connect it to the interface to be tested, implement the algorithm in ARM, and reversely calculate R in formula (1), formula (2), and formula (3). 14 With the integrating capacitor C 11 , store the calculated value into the ARM Flash and call it out for use in subsequent calculations.

[0083] After completing the above steps, the instrument is close to the market level, but there are still slight differences. At this time, use the standard instrument on the market to measure the above standard resistance and compare the data tested by the 8-channel high resistance meter with it. There will be a fixed offset between the 8 channels. Then store these 8 offsets in the ARM Flash. The subsequent calculation becomes R 实际 =R 14 +R Offset .

[0084] The above embodiments are only for illustrating the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. An eight-channel high-precision high resistance meter, including eight technical paths: contact detection, fast charging, integral amplification, signal sampling, fast discharge, software calculation, result output, and calibration and compensation, characterized in that: The contact detection is used to perform contact detection on the capacitor to be detected; the built-in algorithm is used to compare the phase and frequency with the SPWM signal to ensure good contact; The fast charging is provided with a current limiting unit, and the fast charging is used to precisely control the time of the optocoupler MOS tube through the FPGA to switch the circuit on and off, so as to charge the capacitor to be detected; The integral amplifier is used to ensure that the power supply voltage ripple stability is less than 1 microvolt based on the principle of high static stability of chemical batteries. Only an ultra-low ripple power supply can be applied to both ends of the detection capacitor to screen out the oblique line of the micro-current signal output to be detected; The signal sampling is used to sample the oblique line output by the integral amplifier according to a fixed period after analog-to-digital conversion by ADC; The fast discharge is used to discharge the charge stored in the capacitor to be detected through the current limiting circuit, and the ARM IO outputs an analog acquisition completion signal Index through the optocoupler to notify the external interactive device; During the software operation, the ARM side enables hardware floating-point acceleration to filter the sampled data and fit the slope using the least squares method, ultimately obtaining an accurate slope K. The current is then calculated based on this slope K using key calculation formulas, and the internal resistance of the capacitor to be tested is calculated.

2. The eight-channel high-precision high resistance meter according to claim 1, characterized in that: In the contact detection, FPGA is used to generate a high-frequency SPWM signal, which is then converted into a sinusoidal signal through a bandpass filter. The sinusoidal signal is used to drive a high-frequency transformer through a PA power amplification unit. The high-voltage DC and the sinusoidal signal are then superimposed into a mixed signal by means of a high-frequency coupling transformer to realize a power line carrier. After the mixed signal is applied to the capacitive load to be tested, the DC signal will be isolated at the other end while retaining the high-frequency AC signal. The high-frequency signal then flows through the LC frequency selection circuit. The amplified high-frequency sinusoidal signal is converted into a square wave signal after rectification and detection. The FPGA is then used to implement frequency and phase detection of the signal, thereby realizing the comparison between the output SPWM signal and the converted square wave and contact detection.

3. The eight-channel high-precision high resistance meter according to claim 1, characterized in that: The current limiting unit is composed of a MOSFET and an operational amplifier to form a constant current limiting unit.

4. The eight-channel high-precision high resistance meter according to claim 1, characterized in that: The key calculation formula is as follows: Among them, R x : Indicates the internal resistance of the capacitor to be detected; I x :Indicates the internal resistance R of the capacitor to be detected x Converts and calculates the output current; K: expresses the slope; V in : Represents the high resistance meter input voltage, V out : Indicates the output voltage of the high resistance meter; C 11 : Indicates a known value capacitor. R 14 : Indicates a resistor of known value.

5. The eight-channel high-precision high resistance meter according to claim 1, characterized in that: The result output is used to output the data obtained by the software operation and calculation; The results are output in three communication modes: USB, Ethernet, and RS232. An external Handler interface is also configured, and the ARM IO port is used to realize 4 groups of 8-channel signals for exceeding the upper limit, exceeding the lower limit, good products, and poor contact. An additional group of measurement completion signals EOM is configured to cooperate with the automation system integration.

6. The eight-channel high-precision high resistance meter according to claim 1, characterized in that: The calibration and compensation are used to reduce the detection error of the high resistance meter.

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