Multi-channel resistance test circuit

Abstract

The utility model discloses a kind of multi-channel resistance test circuit, including card slot base plate and at least one multi-channel board card, each multi-channel board card is connected with a group of measured sample, and multiple groups of photoelectric isolation elements are set in each multi-channel board card, photoelectric isolation element is used to control the on-off state of the current path and voltage path of measured sample, the primary side of photoelectric isolation element is driven by triode, the secondary side is connected in series in measurement loop, when external control signal triggers triode conduction, the primary side of photoelectric isolation element can be driven to emit light, the secondary side is conducted to complete the current path and voltage path connection of measured sample. Realize the efficient, stable operation of multi-channel resistance test, applicable to a variety of application scenarios, and use optocoupler as the test switching between measured sample, fast, no noise and arc generation.

Description

Technical Field

[0001] This utility model relates to the field of electronic measurement technology, and in particular to a multi-channel resistance testing circuit. Background Technology

[0002] In the resistor industry, most laboratories use a single-channel testing method for resistance value and temperature drift testing. At the beginning of the test, the samples are connected with wires and placed entirely in a constant temperature chamber, leaving multiple test leads outside. The temperature and time settings of the constant temperature chamber are used as indicators for switching between sample measurements. The connections between each sample and the instrument are manually plugged and unplugged in turn to measure the resistance between different samples. This method is tedious for the laboratory operator, prone to incorrect wire connections, and the connectors can be damaged due to frequent plugging and unplugging. Utility Model Content

[0003] The purpose of this invention is to provide a multi-channel resistance testing circuit that can automatically switch between resistance value and temperature drift testing processes. The specific technical solution is as follows: A multi-channel resistance testing circuit includes a card slot substrate and at least one multi-channel board. Each multi-channel board is connected to a group of test samples. Each multi-channel board contains multiple sets of opto-isolators. The opto-isolators are used to control the on / off state of the current path and voltage path of the test sample. The primary side of the opto-isolator is driven by a transistor, and the secondary side is connected in series in the measurement circuit. When an external control signal triggers the transistor to conduct, it can drive the primary side of the opto-isolator to emit light and the secondary side to conduct, thereby completing the connection of the current path and voltage path of the test sample.

[0004] Furthermore, a multi-channel board switching circuit is provided. The switching circuit includes opto-isolating elements. The current path and voltage path of each group of test samples are controlled by two groups of opto-isolating elements, and the opto-isolating elements are linear optocouplers.

[0005] Furthermore, the secondary side of the linear optocoupler is directly connected in series in the measurement circuit, and the input and output sides of the linear optocoupler are completely electrically isolated to block noise and surge interference.

[0006] Furthermore, the multi-channel board also includes input interfaces and output interfaces. The input interfaces interface with the card slot substrate to transmit power supply, measurement signals and external control signals, while the output interfaces correspond to the four-wire measurement paths of the two sets of test samples.

[0007] Furthermore, the multi-channel board also includes a reference source circuit and a control circuit. The reference source circuit uses a precision voltage reference chip to generate a standard voltage source through a resistor divider network, which is then provided to the control circuit as a reference voltage.

[0008] Furthermore, the multi-channel board also includes an input indicator circuit, which contains multiple DIP switches and multiple diodes. By shorting the input port to the ground terminal, the channel indicator status is controlled and a trigger signal is generated. The anode of the diode is connected to the corresponding input port, and the cathode is grounded through a pull-down resistor. When the input port is not shorted to the ground terminal, the diode lights up and outputs a high level. When the input port is shorted to the ground terminal, the diode turns off and outputs a low level as a trigger signal.

[0009] Furthermore, the control circuit includes a comparator for comparing the trigger signal generated by the input indication circuit with a reference voltage and outputting a drive signal to control the switching circuit. The inverting input of the comparator receives the trigger signal, and the non-inverting input is connected to the reference voltage. When the trigger signal is low, the comparator outputs a high-level drive signal to turn on the transistor and drive the opto-isolator. When the trigger signal is high, the comparator outputs a low-level drive signal to turn off the corresponding channel.

[0010] Furthermore, the card slot substrate includes a power management unit, a signal distribution unit, and an external interface unit. The power management unit provides DC power to the system, and the signal distribution unit transmits external control signals to each multi-channel card.

[0011] Furthermore, the power management unit includes a filter configuration option, which allows users to select whether to connect a filter capacitor by adjusting a jumper.

[0012] Furthermore, it includes multiple multi-channel boards, which are connected in parallel to the card slot substrate.

[0013] The multi-channel resistance testing circuit of this invention has the following advantages: Through precise control and modular design of opto-isolation components, efficient and stable operation of multi-channel resistance testing is achieved, suitable for various application scenarios, including temperature drift testing, aging tests, teaching experiments, and small-batch production sampling inspections. It also uses optocouplers for test switching between measured samples, offering high speed, no noise or arc generation. It can be used with PLCs, PCs, microcontrollers, and other controllers to achieve automatic switching of the measured object during the testing process, eliminating the need for manual plugging and unplugging of test leads. The split design allows for expansion of the number of boards according to the actual number of measured objects. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of the interface terminal of the board for the multi-channel resistance testing circuit of this utility model.

[0015] Figure 2 This is the output circuit diagram of the multi-channel resistance testing circuit board of this utility model.

[0016] Figure 3This is a circuit diagram of the four-channel switching circuit of the multi-channel resistance testing circuit board of this utility model.

[0017] Figure 4 This is a circuit diagram of the reference source circuit of the board for the multi-channel resistance testing circuit of this utility model.

[0018] Figure 5 This is a circuit diagram of the input indicator circuit of the board for the multi-channel resistance testing circuit of this utility model.

[0019] Figure 6 This is a circuit diagram of the control circuit of the board for the multi-channel resistance testing circuit of this utility model.

[0020] Figure 7 This is a circuit diagram of the output terminal of the card slot substrate of the multi-channel resistance testing circuit of this utility model.

[0021] Figure 8 This is a diagram of the external power supply and filtering circuit of the card slot substrate of the multi-channel resistance testing circuit of this utility model.

[0022] Figure 9 This is a circuit diagram showing the external signal input and power supply configuration in the card slot substrate of the multi-channel resistance testing circuit of this utility model.

[0023] Figure 10 This is a schematic diagram of the card plate in the multi-channel resistance testing circuit of this utility model.

[0024] Figure 11 This is a schematic diagram of the card slot substrate in the multi-channel resistance testing circuit of this utility model. Detailed Implementation

[0025] To better understand the purpose, structure, and function of this utility model, the multi-channel resistance testing circuit of this utility model will be described in detail below with reference to the accompanying drawings.

[0026] This invention provides a multi-channel resistance testing circuit. Its core structure includes a card slot substrate and at least one multi-channel board, with multiple multi-channel boards connected in parallel to the card slot substrate. The card slot substrate consists of a power management unit, a signal distribution unit, and an external interface unit. The power management unit provides ±12V DC power to the system, the signal distribution unit transmits external control signals to each multi-channel board, and the external interface unit interfaces with a host computer or controller and supports hot-swapping. Each multi-channel board includes an input interface, an output interface, a switching circuit, and a reference source circuit. The input interface interfaces with the card slot substrate interface to transmit power supply, measurement signals, and external control signals. The output interface corresponds to the four-wire measurement path for two sets of test samples. Each multi-channel board is equipped with two interfaces, supporting independent measurement of four sets of test samples. The switching circuit is the core component; the current path and voltage path of each set of test samples are controlled by two sets of opto-isolated components. The primary side of the opto-isolator is driven by a transistor, while the secondary side is connected in series in the measurement circuit. When an external control signal triggers a certain path, the corresponding transistor conducts, providing a driving current to the opto-isolator, causing its primary side to emit light and its secondary side to conduct, thus connecting the current and voltage paths of the sample under test. A linear optocoupler is used as the opto-isolator, with a linear relationship between its input and output to meet the requirements of low-impedance measurement. The reference source circuit provides a stable reference voltage for the switching circuit. A precision voltage reference chip, combined with a resistor divider network, generates a 2.5V reference voltage. The reference source circuit and the control circuit share a power supply, but noise is isolated through an independent voltage divider network to ensure the stability of the reference voltage.

[0027] The following combination Figures 1 to 11 The specific embodiments of this utility model will be described in detail.

[0028] like Figure 1 As shown, the card slot base plate is physically connected to the DB25 male connector of the multi-channel board via a DB25 female connector. Signals from the signal distribution unit of the card slot base plate enter the multi-channel board through the input interface and are finally connected to the device under test (DUT) through the output interface. Specifically, the external ±12V power supply enters the board through the power pin of the DB25, and after being filtered by C7, C10 (+12V), C14, and C15 (-12V), it provides stable power to the internal circuitry. The instrument current / voltage lines enter through the signal pin of the DB25, are conditioned by the R1 resistor network, and are then transmitted to the subsequent signal processing circuitry. The external input IN line enters through the corresponding pin as a control or data signal, participating in the board's logic control or data interaction. The signal processed by the board is output to the card slot base through the DB25 pin, achieving bidirectional communication. The power management unit has a jumper for the filter configuration option, allowing users to adjust the jumper to select whether to connect a filter capacitor to optimize power quality. The signal distribution unit distributes external control signals to each multi-channel board through a multiplexer.

[0029] like Figure 2 As shown, the DB25 female connector of the external interface unit is designed for easy connection with external devices and supports hot-swapping. The input interface connects to the DB25 female connector of the card slot substrate to transmit power supply, measurement signals, and external control signals. The output interface uses a DB9 female connector, with each DB9 female connector corresponding to two sets of four-wire measurement paths for the test sample. Specifically, two DB9 female connectors (DB1 and DB2) are used, each corresponding to the test leads of two samples. The two DB9 connectors support test signal output for a total of four samples. The internal circuitry of the board generates four differential test signals OUT3A / OUT3B / OUT4A / OUT4B, each a differential pair, which are sent to the corresponding pins of DB1 and DB2 respectively. The differential signals are output through pins 2 / 3 and 7 / 8 of DB9. The GND pin and the casing provide grounding and shielding. External samples are connected to DB1 and DB2 through DB9 male connectors. The differential signals are transmitted to the test interface of the sample to drive the sample to complete the test process. Differential transmission can effectively resist interference, and multi-point grounding ensures stability and casing grounding provides shielding, ensuring the integrity of the test signals in complex environments.

[0030] like Figure 3 As shown, the 4-channel switching circuit is divided into 4 independent channels, corresponding to IN1~IN4 signals. Each channel contains four core modules: operational amplifier, transistor, optocoupler, and relay. Ultimately, the relay contacts switch the current and voltage lines to select the test circuit for the sample. When any one of the external signals IN1 to IN4 is received, the operational amplifier drives any one of the corresponding transistors Q1 to Q4. The transistor then drives all the optocouplers in each channel, completing the connection of the current and voltage lines of the corresponding sample, realizing the switching or selection between test samples. Each sample is configured with two sets of optocouplers, used to control the on / off state of the current and voltage lines respectively. For example, the I+ line of sample 1 is conducted by optocoupler U1, and the I− line is conducted by optocoupler U2; the V+ line is conducted by optocoupler U3, and the V− line is conducted by optocoupler U4. The primary side of the optocoupler is driven by NPN transistors (Q1~Q4), and the secondary side is connected in series in the measurement circuit. The optocoupler is a linear optocoupler, with a linear relationship between output and input, matching the requirements of low-impedance measurement. The driving circuit transistors Q1 to Q4 are controlled by the +12V signal output from the comparator. In this configuration, the current line and voltage line are completely isolated, eliminating the influence of lead resistance and meeting milliohm-level measurement accuracy (error <0.1%). In addition, the input and output sides of the optocoupler are completely electrically isolated, blocking noise, surges, and other interference sources, enabling automated testing and selection of multiple samples. Each channel operates independently without affecting others, ensuring the accuracy and safety of the test. Furthermore, the optocoupler serves as a fast, noise-free, and arc-free switching medium between measured samples.

[0031] like Figure 4As shown, this reference source circuit generates a standard 2.5V voltage source, which is provided to the subsequent control circuit as a reference voltage. Specifically, a precision voltage reference chip such as the TL431 or similar is used. Operating current is provided to the TL431 through R0, and the TL431's internal bandgap reference source generates a stable 2.5V voltage, which is output from the REF pin as a high-precision reference voltage for subsequent circuits. Voltage stabilization is achieved through the temperature compensation characteristics of the internal bandgap reference. Furthermore, the aforementioned switching circuit and reference source circuit are compactly laid out and separated to avoid interference.

[0032] The primary side of the opto-isolator is driven by a transistor, and the secondary side is connected in series in the measurement circuit. When an external control signal is triggered by shorting to ground, the corresponding LED indicator lights up, simultaneously generating an internal signal. The control comparator circuit uses a comparator to compare the internal signal with a reference voltage. When the internal signal is lower than the reference voltage, the comparator outputs a high-level signal, driving the corresponding transistor to conduct. A precision voltage reference chip is connected to a resistor divider network to generate a 2.5V reference voltage. The design of the resistor divider network ensures the stability and accuracy of the reference voltage.

[0033] Specifically, such as Figure 5 and Figure 6 As shown, the input indicator circuit includes a 4-position DIP switch RN1 and four red LEDs (LED1, LED2, LED3, and LED4). These are used to control the channel indicator and generate the trigger signal RZ1 by shorting the IN port to GND. Each LED's cathode is connected to pull-down resistors RZ1-RZ4, with the other end of the resistor connected to GND. The level of the IN port is the RZ1 signal, which is sent to the input of comparator IC18 in the control circuit. When IN4 is not shorted to GND, the IN4 channel of DIP switch RN1 is closed, IN4 is pulled high by +12V, and the anode voltage of LED4 is greater than the cathode voltage (GND), causing LED4 to light up; simultaneously, IN4 outputs a high level. When IN4 is shorted to GND, an external signal pulls IN4 low to 0V, the anode voltage of LED4 = 0V, and a forward conduction voltage cannot be formed, causing LED4 to turn off; simultaneously, IN4 outputs a low level, which serves as the trigger signal sent to the control circuit.

[0034] The control circuit includes a four-channel comparator IC18, which compares the RZ1 (or RZ2) signal generated by the input indicator circuit with the reference voltage REF and outputs a drive signal DR1 (or DR2) to control the subsequent switching circuit. The comparator's operating logic is explained using the first channel as an example; the other channels are the same and will not be repeated. If the IN- voltage is less than the IN+ voltage, the output is high (+12V); otherwise, the output is low (0V). When RZ1 (or RZ2) is high (IN terminal not shorted to GND), the comparator's inverting input voltage is approximately +12V, which is greater than the REF voltage, resulting in a low output DR1 (or DR2) approximately 0V, and the subsequent switching circuit does not operate. When RZ1 (or RZ2) is low (IN terminal shorted to GND), the comparator's inverting input voltage is approximately 0V, which is less than the REF voltage, resulting in a high output (DR1 (or DR2) approximately +12V), driving the subsequent switching circuit. Thus, the control circuit compares the voltage of the input indicator circuit and converts the level signal RZ1 (or RZ2) into the drive signal DR1 (or DR2), thereby realizing the control logic from level triggering to circuit switching.

[0035] The input indicator circuit described above controls the LED to turn on and off via DIP switch RN1, and simultaneously generates an RZ1 (or RZ2) level signal. A high level closes the switch, and a low level opens the switch. The comparator IC18 in the control circuit compares RZ1 (or RZ2) with REF. If RZ1 (or RZ2) is low, it outputs a high level DR1 (or DR2), driving the corresponding transistor to conduct.

[0036] like Figures 7 to 9 As shown, CN1 in the card slot substrate serves as an external ±12V power supply port, receiving +12V, GND, and -12V power supplies. Through internal routing, the power is distributed to the corresponding pins of the four DB25 interfaces (DSUB1~DSUB4). The ±12V power supply is connected to the designated pins of the DB25, providing dual DC power to the boards. This unified access to the power, interrupt, and analog signals of the four boards through the four DB25 interfaces avoids the complexity of multiple independent wiring, improving system reliability and maintainability.

[0037] The VCC logic power supply is directly connected to +12V via the configuration of R1 / R2. VCC is then output through pins 1 and 15 of DB25 to provide power to the logic circuit of the board. Each DB25 interface corresponds to one board and supports quick plug-in and plug-out. When adding or replacing a board, you only need to connect to DB25 without additional wiring, which meets the expansion needs of multiple boards working together.

[0038] CN2 is an 18-pin external signal input terminal, containing interrupt signals such as INT1~INT16, INT, and INTE. These signals are precisely distributed to the corresponding interrupt pins of the four DB25 interfaces through internal routing, enabling differentiated control of multiple boards by external interrupt signals.

[0039] The instrument's input current / voltage signals are connected to the corresponding pins of the four DB25 interfaces via internal traces, enabling the transmission of external instrument signals to the board and supporting multi-channel current / voltage measurement and acquisition scenarios. R1 and R2 are used for flexible configuration of the VCC power path. By default, R1 is not connected, and R2 is a jumper, with +12V directly connected to VCC via the jumper, suitable for scenarios where the board's logic power supply is 12V. An extended configuration involves removing the R2 jumper and connecting the R1 resistor, enabling custom logic such as current limiting and voltage division to adapt to different hardware platforms.

[0040] In addition, the power input terminal (CN1) is equipped with filter capacitors (C1~C4) to suppress power supply noise. The analog signal is transmitted through a dedicated pin to reduce interference and ensure signal integrity.

[0041] In actual operation, the signal flow path between the card slot substrate and the multi-channel board is clearly defined. First, the host computer or controller sends an external control signal, which is transmitted to the input interface of the multi-channel board via the signal distribution unit on the card slot substrate. The external control signal triggers each signal connection to a current-limiting resistor and an LED indicator by shorting it to ground. When a signal is triggered, the corresponding LED lights up, simultaneously generating an internal signal. The control comparison circuit uses a comparator to compare the internal signal with a reference voltage. When the internal signal is lower than the reference voltage, the comparator outputs a high-level signal, driving the corresponding transistor to conduct. After the transistor conducts, it provides a driving current to the opto-isolator, causing its primary side to light up and its secondary side to conduct, thus completing the connection of the current and voltage paths of the test sample. The measuring instrument reads the resistance value of the test sample through the connected path. During this process, the conduction impedance of the opto-isolator is highly consistent, maintaining a low level, resulting in minimal signal attenuation during transmission. The influence of the opto-isolator on the measurement circuit in its on and off states is negligible. Furthermore, the design is simple, operation is convenient, the switching speed is significantly faster than mechanical relays, and data acquisition is stable and reliable. In addition, the overall cost is lower than that of multi-board expansion solutions, which greatly improves testing efficiency and reduces maintenance costs during production.

[0042] This invention is applicable to various scenarios, including temperature drift testing of materials such as alloy resistors, wire-wound resistors, and chip resistors; periodic resistance monitoring in long-term stability aging tests; multi-sample comparative testing in teaching experiments and R&D laboratories; and parameter sampling systems in small-batch production processes. In temperature drift testing, the modular design of the multi-channel board supports flexible expansion, allowing for the addition or removal of multiple channels as needed, supporting up to sixteen channels. The modular design also facilitates replacement and maintenance, and the use of standard interfaces results in a lower overall cost compared to traditional relay array solutions. In long-term stability aging tests, the input and output of the opto-isolation element are completely isolated, preventing crosstalk between channels and improving the system's anti-interference capability. The opto-isolation element has no mechanical movement, and its switching time reaches the microsecond level, making it suitable for high-frequency polling tests.

[0043] In teaching experiments and R&D laboratories, this invention reduces human interference, standardizes the testing process, ensures strong data traceability, and eliminates manual plugging and unplugging operations. Automatic channel switching via opto-isolating elements reduces operational complexity and interface loss. In small-batch production, this invention improves measurement accuracy by employing a four-wire independent control system for both current and voltage paths, combined with low-impedance opto-isolating elements to reduce the impact of contact resistance and meet high-precision measurement requirements.

[0044] To enable those skilled in the art to fully understand and implement this utility model, the following supplementary explanation of the specific implementation principle of this utility model is provided in conjunction with a specific application scenario.

[0045] In the temperature drift test scenario, multiple test samples are first connected to the output interfaces of a multi-channel board. Each multi-channel board is equipped with two DB9 female connectors, each corresponding to a four-wire measurement path for two sets of test samples, ensuring independent control of the current and voltage paths for each set of samples. The card slot substrate is physically connected to the DB25 male connector of the multi-channel board via a DB25 female connector, completing the transmission of power supply, measurement signals, and external control signals. Based on this, the host computer or controller sends external control signals, which are transmitted to the input interfaces of the multi-channel board via the signal distribution unit on the card slot substrate.

[0046] When an external control signal triggers a specific path by shorting it to ground, the corresponding LED indicator lights up, simultaneously generating an internal signal. The control comparator circuit uses a comparator to compare the internal signal with a 2.5V reference voltage generated by the reference source circuit. Due to the design of the precision voltage reference chip and the resistor divider network, this reference voltage exhibits low temperature drift characteristics, with a temperature coefficient of ±5ppm / °C, enabling it to maintain reference accuracy over a long period. When the internal signal is lower than the reference voltage, the comparator outputs a high-level signal to drive the corresponding transistor to conduct. After the transistor conducts, it provides a driving current to the opto-isolated element, causing its primary side to emit light and its secondary side to conduct, thereby completing the connection of the current and voltage paths of the test sample.

[0047] During this process, the opto-isolator exhibits strong on-resistance consistency, with a linear relationship between its input and output, meeting the requirements for low-impedance measurement. The primary side of the opto-isolator is driven by a transistor, while the secondary side is connected in series in the measurement circuit, ensuring minimal signal attenuation during transmission. Furthermore, the complete isolation between the input and output of the opto-isolator prevents crosstalk between channels, improving the system's anti-interference capability. Because the opto-isolator has no mechanical movement, its switching time reaches the microsecond level, making it suitable for high-frequency polling tests.

[0048] In actual operation, the measuring instrument reads the resistance value of the sample under test through the connected path. The modular design of the multi-channel board supports flexible expansion, allowing for the addition or removal of multiple channels as needed, supporting up to sixteen channels of testing. The modular design also facilitates replacement and maintenance, employs standard industrial interfaces, and has a lower overall cost than traditional relay array solutions. During temperature drift testing, the constant temperature chamber is set to different temperature values, and the card slot substrate automatically switches between different samples under test according to a preset program, achieving automated multi-channel testing. This method not only reduces human error but also significantly improves testing efficiency, reduces the influence of contact resistance, and meets milliohm-level measurement requirements.

[0049] In long-term stability aging tests, the system monitors the resistance of multiple test samples according to a set cycle. The fast response characteristics of the opto-isolator enable the system to switch and measure multiple samples in a short time, ensuring stable and reliable data acquisition. Simultaneously, the reference source circuit isolates noise through an independent voltage divider network, ensuring the stability of the reference voltage and further improving measurement accuracy. The experimental data is highly traceable, facilitating subsequent analysis and comparison.

[0050] In teaching experiments and R&D laboratories, this invention eliminates manual plugging and unplugging operations, reducing operational complexity and interface wear. For example, in multi-sample comparison testing, the card slot substrate automatically switches between different samples according to experimental requirements, avoiding data confusion or misjudgment caused by human wiring errors. Furthermore, the system's standardized testing procedures effectively improve experimental efficiency and reduce maintenance costs.

[0051] In summary, this invention achieves efficient and stable operation of multi-channel resistance testing through precise control and modular design of opto-isolation components. It is suitable for various application scenarios, including temperature drift testing, aging tests, teaching experiments, and small-batch production sampling inspections. It also utilizes optocouplers for switching between measured samples, offering high speed, no noise, and no arcing. It can be used with PLCs, PCs, microcontrollers, and other controllers to achieve automatic switching of the measured object during the testing process, eliminating the need for manual plugging and unplugging of test leads. The modular design allows for expansion of the number of boards based on the actual number of measured objects.

[0052] The terms “above,” “below,” and “within” as used above include the number itself; the terms “exceeding” and “excluding” do not include the number itself.

[0053] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the substance and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention. The various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe various possible combinations.

[0054] If the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

Claims

1. A multi-channel resistance testing circuit, characterized in that, It includes a card slot substrate and at least one multi-channel board. Each multi-channel board is connected to a group of test samples. Each multi-channel board is equipped with multiple sets of opto-isolators. The opto-isolators are used to control the on / off state of the current path and voltage path of the test sample. The primary side of the opto-isolator is driven by a transistor, and the secondary side is connected in series in the measurement circuit. When an external control signal triggers the transistor to conduct, it can drive the primary side of the opto-isolator to emit light and the secondary side to conduct, so as to complete the connection of the current path and voltage path of the test sample.

2. The multi-channel resistance testing circuit as described in claim 1, characterized in that, The multi-channel board pack switching circuit includes opto-isolation components. The current path and voltage path of each group of test samples are controlled by two groups of opto-isolation components, and the opto-isolation components are linear optocouplers.

3. The multi-channel resistance testing circuit as described in claim 2, characterized in that, The secondary side of the linear optocoupler is directly connected in series in the measurement circuit, and the input and output sides of the linear optocoupler are completely electrically isolated to block noise and surge interference.

4. The multi-channel resistance testing circuit as described in claim 2, characterized in that, The multi-channel board also includes input interfaces and output interfaces. The input interfaces are connected to the interface of the card slot substrate to transmit power supply, measurement signals and external control signals. The output interfaces correspond to the four-wire measurement paths of the two sets of test samples.

5. The multi-channel resistance testing circuit as described in claim 4, characterized in that, The multi-channel board also includes a reference source circuit and a control circuit. The reference source circuit uses a precision voltage reference chip to generate a standard voltage source through a resistor divider network, which is then provided to the control circuit as a reference voltage.

6. The multi-channel resistance testing circuit as described in claim 5, characterized in that, The multi-channel board also includes an input indicator circuit, which contains multiple DIP switches and multiple diodes. By shorting the input port to the ground terminal, the channel indicator status is controlled and a trigger signal is generated. The anode of the diode is connected to the corresponding input port, and the cathode is grounded through a pull-down resistor. When the input port is not shorted to the ground terminal, the diode lights up and outputs a high level. When the input port is shorted to the ground terminal, the diode turns off and outputs a low level as a trigger signal.

7. The multi-channel resistance testing circuit as described in claim 6, characterized in that, The control circuit includes a comparator, which compares the trigger signal generated by the input indicator circuit with a reference voltage and outputs a drive signal to control the switching circuit. The inverting input of the comparator receives the trigger signal, and the non-inverting input is connected to the reference voltage. When the trigger signal is low, the comparator outputs a high-level drive signal to turn on the transistor and drive the opto-isolator. When the trigger signal is high, the comparator outputs a low-level drive signal to turn off the corresponding channel.

8. The multi-channel resistance testing circuit as described in any one of claims 1 to 7, characterized in that, The card slot substrate includes a power management unit, a signal distribution unit, and an external interface unit. The power management unit provides DC power to the system, and the signal distribution unit transmits external control signals to each multi-channel card.

9. The multi-channel resistance testing circuit as described in claim 8, characterized in that, The power management unit has a filter configuration option, which can be adjusted by adjusting the jumper to select whether to connect a filter capacitor.

10. The multi-channel resistance testing circuit as described in any one of claims 1 to 7, characterized in that, It includes multiple multi-channel boards, which are connected in parallel to the card slot substrate.

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