A wide-range weak current detection method, device and insulation resistance testing equipment

Abstract

The application relates to the technical field of electronic measurement, and provides a wide-range weak current detection method and device and an insulation resistance test equipment, which comprises the following steps: switching a measurement circuit to the highest gain gear and acquiring a background error parameter in a reference state without connecting a to-be-detected object; acquiring a current sampling value in a measurement state; determining a current change index based on the continuously acquired current sampling value, and dynamically adjusting the gain gear of the measurement circuit according to the current sampling value and the current change index; and compensating the current sampling value according to the background error parameter and a gain parameter corresponding to the current gain gear to obtain an actual current value. The application realizes high-precision real-time measurement and safety protection of fA-level tiny current, and improves the response rate under wide-range measurement.

Description

Technical Field

[0001] This application relates to the field of electronic measurement, and in particular to a wide-range weak current detection method, device, and insulation resistance testing equipment. Background Technology

[0002] In precision electronic measurement fields such as high-voltage ion migration testing and semiconductor device leakage current detection, it is often necessary to detect weak currents over a wide range for the object under test. Existing technologies typically use transimpedance amplifiers to convert weak currents into voltage signals, which are then sampled by an analog-to-digital converter and filtered by software algorithms to obtain the measured values. However, this traditional approach is limited by the inherent noise and offset characteristics of operational amplifiers and other semiconductor devices when dealing with extremely low input currents in the pA or even fA range. It lacks effective hardware-level compensation mechanisms, resulting in insufficient accuracy of the measurement data. Furthermore, when the input current changes drastically over a wide range (such as during ion migration breakdown), the range switching logic, which relies solely on linear sampling, exhibits significant response delays, easily leading to data discontinuity or distortion. In addition, existing circuits often lack rapid hardware protection mechanisms for abnormal leakage conditions, making it difficult to block overcurrent surges within microseconds, thus affecting the safety and reliability of the testing equipment. Summary of the Invention

[0003] This application provides a wide-range weak current detection method, device, and insulation resistance testing equipment, which solves the technical problems of low measurement accuracy, large dynamic response delay, and lack of effective hardware protection in the existing wide-range weak current detection.

[0004] To achieve the above objectives, this application adopts the following technical solution: Firstly, a wide-range weak current detection method is provided, including: In the baseline state where the object under test is not connected, the measurement circuit is switched to the highest gain setting, and the background error parameters of the measurement circuit are obtained. When the object under test is connected to the measurement state, the current sampling value of the object under test is obtained through the measurement circuit; The current change index is determined based on the continuously acquired current sampling values, and the gain level of the measurement circuit is dynamically adjusted according to the current sampling values ​​and the current change index so that the gain of the measurement circuit matches the input current level of the object under test. The current sample value is compensated based on the background error parameter and the gain parameter corresponding to the current gain level to obtain the actual current value.

[0005] Based on the above technical solution, in the wide-range weak current detection method provided in this application, the inherent background error parameter of the measurement circuit is obtained and recorded in advance under the reference state, and the sampled value is subtracted and compensated in real time using this parameter during actual measurement, thereby eliminating the influence of the non-ideal characteristics of the device itself on the measurement of weak signals. At the same time, the rate of change of the current sampled value is introduced as one of the trigger dimensions for gain level adjustment, so that the system can respond to the level switching in advance or quickly when the current undergoes a drastic transient change, avoiding the lag effect caused by a single threshold judgment, thereby realizing high-precision, low-delay continuous detection of weak current under wide range.

[0006] In conjunction with the first aspect above, in one possible implementation, obtaining the background error parameter of the measurement circuit includes: In the reference state, the measurement circuit is switched to the highest gain setting; Read the output value of the measurement circuit at the highest gain setting, and determine the offset current of the measurement circuit based on the output value.

[0007] By setting the measurement circuit to the highest gain setting with the highest sensitivity to obtain the baseline error, it is possible to expose and capture small error components such as offset voltage and bias current inside the circuit to the greatest extent, ensuring the completeness and accuracy of subsequent compensation parameters and preventing compensation failure caused by errors being masked at low gain settings.

[0008] In conjunction with the first aspect above, in one possible implementation, compensation is made for the current sample value based on the background error parameter and the gain parameter corresponding to the current gain level, including: Obtain the feedback resistor value corresponding to the current gain level; The offset voltage error at the current gain setting is determined by the product of the offset current and the feedback resistor value. The equivalent offset current at the current gain level is determined based on the offset voltage error and the transimpedance gain corresponding to the current gain level. The actual current value is obtained by performing a difference calculation between the current sample value and the equivalent offset current.

[0009] This implementation method clarifies that the physical nature of the background error is the offset current, and directly eliminates this fixed deviation through algebraic subtraction. It restores the true current value flowing through the object under test from the mathematical model, effectively solving the measurement zero-point drift problem dominated by the op-amp input bias current under high gain conditions.

[0010] In conjunction with the first aspect above, in one possible implementation, determining the current change index includes: The current sampling value is continuously acquired according to a preset sampling period; The current change index is determined based on the difference between the current sample value obtained at the current sampling time and the previous sampling time, or the current change rate is determined based on the time interval between the difference and the adjacent sampling time. When the current change index or the current change rate exceeds a first preset threshold, the measurement circuit is triggered to adjust the gain level.

[0011] In conjunction with the first aspect above, in one possible implementation, the adjustment of the gain level includes: When the current change index or the current change rate exceeds the first preset threshold, or the current sample value exceeds the second preset threshold, the gain level of the measurement circuit is reduced. When the current sample value is lower than the lower limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is increased. When the current sample value is higher than the upper limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is reduced.

[0012] In conjunction with the first aspect described above, in one possible implementation, the method further includes: The input current of the object under test is monitored in real time by means of a hardware comparison circuit that is independent of the digital processing unit used to perform gain level adjustment; When the input current exceeds the preset leakage threshold, a protection trigger signal is output, and the protection state is maintained through a self-locking circuit to cut off the power supply to the measurement channel of the measurement circuit and output an alarm signal.

[0013] This implementation utilizes pure hardware comparison and a self-locking loop to achieve nanosecond-level response and state maintenance for abnormal overcurrents. Compared to software polling detection, it completely eliminates the safety hazards caused by processor interrupt latency and code execution time, providing reliable physical-level protection for precision measurement front-ends.

[0014] In conjunction with the first aspect above, in one possible implementation, real-time monitoring of the input current of the object under test includes: The voltage difference across the sampling resistor connected in series in the measurement circuit is amplified by an instrumentation amplifier to obtain the amplified signal; The amplified signal is divided to obtain a divided signal; The voltage divider signal is compared with a preset reference voltage; When the voltage divider signal exceeds the preset reference voltage, a flip-level signal is output, and the flip-level signal is input to the comparator through a feedback loop to form a self-locking structure.

[0015] This implementation specifies the signal conditioning and self-locking topology of the hardware protection circuit. It extracts weak overcurrent signals through the high common-mode rejection ratio of the instrumentation amplifier and uses the positive feedback loop of the comparator to achieve irreversible locking of the fault state, ensuring that the measurement channel is always in a safe disconnected state before the anomaly is cleared, thus preventing secondary damage.

[0016] In conjunction with the first aspect above, in one possible implementation, the measurement circuit includes a current-to-voltage conversion operational amplifier and multiple feedback branches connected in parallel; Each of the aforementioned feedback branches includes a gain resistor and a solid-state relay switch connected in series with the gain resistor; By controlling the on / off state of different solid-state relay switches, the corresponding feedback branch is connected to the feedback loop of the current-to-voltage conversion operational amplifier to achieve the switching of the gain level.

[0017] Secondly, a wide-range weak current detection device is provided, comprising: A measurement circuit is used to convert the weak current of the object under test into a current sample value; The background error acquisition module is used to switch the measurement circuit to the highest gain level and acquire the background error parameters when the reference state of the object under test is not connected. A gain level control module is used to determine the current change index based on continuously acquired current sampling values, and to control the measurement circuit to adjust the gain level according to the current sampling values ​​and the current change index. The compensation calculation module is used to compensate the current sample value according to the background error parameter and the gain parameter corresponding to the current gain level to obtain the actual current value; The hardware protection module is used to monitor the input current of the object under test independently of the gain level control module, and to trigger self-locking protection when the input current exceeds a preset leakage threshold to cut off the power supply to the measurement channel of the measurement circuit.

[0018] Thirdly, this application provides an insulation resistance testing device, comprising: A high-voltage power supply is used to apply a high-voltage test voltage to the object under test. The wide-range weak current detection device described in the above scheme is used to detect the input current generated by the object under test under the high voltage test voltage, adjust the gain level and compensate the background error of the input current, and output the actual current value. The control unit is used to determine the insulation resistance of the object under test based on the actual current value.

[0019] This application provides a wide-range weak current detection method, device, and insulation resistance testing equipment, which has the following beneficial effects: 1. This application eliminates the influence of non-ideal characteristics of core components such as operational amplifiers on measurement results by obtaining the background error parameters (such as offset current) at the highest gain level and performing real-time subtraction compensation. Combined with a low leakage current solid-state relay switching network, it achieves weak current measurement with fA-level resolution and ±0.3% FS accuracy, significantly improving the test reliability of parameters such as insulation resistance.

[0020] 2. This application innovatively introduces the rate of change of current sampling value as the trigger condition for range switching, which, together with the amplitude threshold, constitutes a dual criterion, enabling the system to identify and follow transient and drastic signals such as ion migration and breakdown. Compared with the traditional single threshold scheme, it significantly shortens the range switching response time and avoids data fragmentation and distortion.

[0021] 3. The leakage protection mechanism built through hardware comparators and self-locking feedback loops enables real-time monitoring and channel shutdown of abnormal overcurrents, independent of software. This effectively prevents the risk of damage to the measurement circuit due to sample failure during high-voltage testing, and enhances the robustness and service life of the equipment. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a wide-range weak current detection circuit according to an embodiment of this application; Figure 2 This is a flowchart of a wide-range weak current detection method according to an embodiment of this application. Detailed Implementation

[0023] In the description of this application, unless otherwise stated, " / " means "or," for example, A / B can mean A or B. The "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Furthermore, "at least one" means one or more, and "multiple" means two or more. The terms "first," "second," etc., do not limit the quantity or order of execution, and "first," "second," etc., do not necessarily imply differences.

[0024] It should be noted that, in this application, the terms "exemplary" or "for example" are used to indicate that something is being described as an example, illustration, or illustration. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0025] In the following embodiments, the object under test can be insulating material for high-voltage insulation testing, electronic devices, or other objects requiring detection of weak leakage current. The measurement circuit converts the weak current generated by the object under test into a voltage signal that is easy for the analog-to-digital converter to acquire, and uses software control logic to achieve wide-range dynamic range switching and background error compensation.

[0026] Example 1 like Figure 2 As shown in the figure, this application provides a wide-range weak current detection method. This method solves the problems of low measurement accuracy and large dynamic response delay of weak current under wide range through hardware and software coordinated control logic. The detection method mainly includes the following steps: In step S100, under the reference state where the object under test is not connected, the measurement circuit is switched to the highest gain level, and the baseline error parameters of the measurement circuit are obtained.

[0027] The reference state refers to the no-load state where the input terminal of the measurement circuit is open or not connected to any object under test (DUT). In this case, the input current should theoretically be zero.

[0028] It should be noted that the highest gain setting is chosen as the calibration benchmark because the highest gain setting corresponds to the system's maximum transimpedance amplification. At this point, the inherent errors of the operational amplifier, such as offset current, bias current, and circuit board leakage current, have the most significant impact on the output results, and the signal-to-noise ratio is at its lowest point.

[0029] Under reference conditions, the measurement circuit should theoretically output a zero value. However, due to the non-ideal characteristics of semiconductor devices such as the input bias current of the operational amplifier, offset voltage, and leakage current of the circuit board, there will be a non-zero inherent deviation value at the actual output.

[0030] This embodiment actively acquires this baseline error parameter before the measurement begins and stores it as a system-level calibration benchmark in the processor or register. By performing this step before each test or periodically, zero-point drift caused by factors such as changes in ambient temperature and device aging can be effectively eliminated, providing a reliable dynamic reference benchmark for accurate measurement across the entire measurement range. This avoids the shortcomings of traditional solutions that use fixed factory calibration values ​​that cannot adapt to real-time operating conditions.

[0031] Step S200: In the measurement state of the object under test, the current sampling value of the object under test is obtained through the measurement circuit.

[0032] The measurement state refers to the working stage in which the object under test has been correctly connected to the measurement circuit and the high-voltage power supply has applied the test voltage according to the preset test conditions.

[0033] It should be noted that when the object under test is connected to the measurement circuit, the measurement circuit converts the weak current flowing through the object under test into a voltage signal, and then quantizes it into a digital current sample value through an analog-to-digital converter.

[0034] This sampled value represents the total current amplitude flowing through the object under test at the current moment. It includes both the actual leakage current or conduction current of the object under test and the system background error obtained in step S100. In wide-range testing scenarios, the dynamic range of this current sampled value may span several orders of magnitude, such as from the pA level to the nA level, so subsequent steps are required to adaptively process it.

[0035] Step S300: Determine the current change index based on the continuously acquired current sampling values, and dynamically adjust the gain level of the measurement circuit according to the current sampling values ​​and the current change index, so that the gain of the measurement circuit matches the input current level of the object under test.

[0036] It should be noted that in scenarios such as high-voltage ion migration testing, the current under test often exhibits exponential and drastic changes. For example, at the moment of power-on or insulation breakdown, the current may span several orders of magnitude within microseconds.

[0037] If the system relies solely on the absolute amplitude of the current sample value to determine whether to switch ranges, it often experiences response lag during sudden current changes due to sampling delays and processing time, leading to distorted measurement data or even front-end saturation. Therefore, this embodiment introduces a current change index, which reflects the trend or rate of change of current over time (such as differential, derivative, etc.).

[0038] By combining the "current change index" that characterizes transient trends with the "current sample value" that characterizes steady-state magnitude, a two-dimensional gain decision mechanism is constructed: when a sharp change in current is detected, even if the absolute value has not exceeded the limit, the downgrading protection can be triggered in advance; while in steady-state measurement, the amplitude is finely optimized to ensure resolution.

[0039] This dynamic adjustment mechanism enables the gain of the measurement circuit to follow the magnitude change of the input current in real time, ensuring a high signal-to-noise ratio for small signals and preventing overload saturation for large signals, thus achieving seamless tracking measurement over a wide range.

[0040] Step S400: Based on the background error parameter and the gain parameter corresponding to the current gain level, the current sampling value is compensated to obtain the actual current value.

[0041] It should be noted that the baseline error parameter obtained in step S100 is measured at the highest gain level. However, in actual measurement, the gain level dynamically switches according to the input current magnitude. Different levels correspond to different feedback resistors, and the offset voltage error generated by the same offset current varies at different levels. Therefore, a fixed baseline error value cannot be simply subtracted from the current sampled value. Instead, the baseline error parameter must be equivalently converted based on the gain parameters corresponding to the current gain level (such as feedback resistor value, transimpedance gain, etc.) to calculate the true error at the current level, and then the current sampled value is compensated in real time.

[0042] This compensation mechanism ensures that, regardless of the gain setting, the final output current value can eliminate the influence of inherent system errors, thus maintaining consistently high measurement accuracy across the entire range.

[0043] This embodiment constructs a complete closed-loop system for wide-range weak current detection. It solves the signal-to-noise ratio bottleneck under weak signals by compensating for the background error, and solves the response speed bottleneck under wide dynamic range by introducing dynamic slicing in the rate of change dimension, thus significantly improving the overall performance of precision current detection.

[0044] Example 2 Based on Example 1, this example further refines the specific implementation method for obtaining the background error parameters and the compensation calculation logic.

[0045] As one implementation method, obtaining the baseline error parameters of the measurement circuit includes: In the reference state, switch the measurement circuit to the highest gain setting; Read the output value of the measurement circuit at the highest gain setting, and determine the offset current of the measurement circuit based on the output value.

[0046] It should be noted that the reference state mentioned in step S100 is a prerequisite for obtaining the background error, while selecting the highest gain level is a key means to ensure the accuracy of error parameter acquisition.

[0047] In a transimpedance amplifier circuit, the highest gain level corresponds to the largest feedback resistance value. At this point, the transimpedance amplification factor of the system is the largest, and the sensitivity to the input signal is the highest. However, at the same time, the inherent errors of the operational amplifier itself, such as input offset current, input bias current, and parasitic leakage current of the circuit board, also produce the most significant voltage deviation at the output terminal, meaning the system is at the lowest point of signal-to-noise ratio.

[0048] The output value acquired in this state can amplify and characterize the system's noise floor level. By reading this output value and combining it with the known highest-gain feedback resistor, the overall offset current, including operational amplifier offset and environmental leakage current, can be deduced. Using the offset current in this state as a reference value for the noise floor parameter provides an error reference for subsequent compensation across the entire range, avoiding the problem of inaccurate calibration due to the error signal being overwhelmed at low-gain settings.

[0049] Furthermore, to ensure the consistency of measurement results at different gain levels, this application proposes a dynamic mapping compensation algorithm; as one implementation method, the current sampling value is compensated based on the background error parameter and the gain parameter corresponding to the current gain level, including: Obtain the feedback resistor value corresponding to the current gain level; The offset voltage error at the current gain setting is determined by the product of the offset current and the feedback resistance value. The equivalent offset current at the current gain level is determined based on the offset voltage error and the transimpedance gain corresponding to the current gain level. The actual current value is obtained by performing a difference calculation between the sampled current value and the equivalent offset current.

[0050] It should be noted that this compensation process establishes a physical mapping chain from the "reference offset current" to the "current gear equivalent error", which solves the problem of error transmission coefficient changes when switching between multiple gears.

[0051] Although the input offset current of an operational amplifier can be considered a relatively constant current source at a certain temperature, the offset voltage error generated by the same offset current flowing through different feedback resistors will be different at different gain levels due to the change in the feedback resistor value.

[0052] If the fixed voltage error value or fixed current value measured at the highest gain setting is directly used to subtract and compensate for all settings, it will inevitably lead to overcompensation or undercompensation at non-highest gain settings.

[0053] For example, assuming that during the reference calibration phase in step S100, the system measures an output offset voltage of 100μV at the highest gain setting (e.g., a feedback resistor of 10GΩ), the system's baseline offset current Ios is calculated to be 10fA.

[0054] When the system enters the measurement state and automatically switches to a certain low gain range (for example, the feedback resistor is switched to 100MΩ, and the transimpedance gain is reduced accordingly), the compensation calculation module first obtains the feedback resistor value of 100MΩ for the current range; then, it multiplies the reference offset current of 10fA with the current feedback resistor value of 100MΩ to calculate the actual offset voltage error caused by the offset current at the current range as 1nV. Subsequently, the offset voltage error of 1nV is divided by the transimpedance gain of the current range (i.e., 100MΩ), and the equivalent offset current under the current range is recalculated to be 10fA (Note: Although the value here has not changed, it has been verified by complete physical quantity reconstruction). Finally, subtracting the equivalent offset current from the current current sample value yields the actual current value after eliminating system errors.

[0055] Example 3 Based on Example 1, this example further describes the specific implementation method of determining the current change index based on continuously acquired current sampling values, and dynamically adjusting the gain level of the measurement circuit according to the current sampling values ​​and the current change index.

[0056] As one implementation method, determining the current change index includes: Current sampling values ​​are continuously acquired according to a preset sampling period; The current change index is determined based on the difference between the current sampled value obtained at the current sampling time and the previous sampling time, or the current change rate is determined based on the time interval between the difference and the adjacent sampling time. When the current change index or current change rate exceeds the first preset threshold, the measurement circuit is triggered to adjust the gain level.

[0057] It should be noted that this step introduces the signal differential characteristics as the trigger condition for gear adjustment, aiming to solve the response lag problem caused by the exponential change in the current signal during high-voltage ion migration testing.

[0058] In traditional linear sampling judgment logic, the system often needs to wait for the absolute value of the current to exceed the upper limit of the range before starting the range switching. However, when faced with the instantaneous surge current at the moment of power-on or the rapid change when insulation breaks down, this pure amplitude judgment has an inherent sampling and processing delay, which can easily lead to the saturation of the front-end operational amplifier or the overflow of the ADC reading, resulting in the loss of critical transient data.

[0059] This embodiment calculates the difference between adjacent sampling points (i.e.) ) or the ratio of the difference to time (i.e. It can detect changes in current trends in advance.

[0060] For example, when a sudden increase in the rate of change of current is detected and exceeds a first preset threshold, even if the current absolute value of the current has not yet reached the full scale of the current range, the system can predict the impending overload risk and trigger a downscale operation in advance. This adds a proactive correction step to the system, significantly improving its ability to capture transient processes and ensuring the integrity and continuity of wide-range measurement data.

[0061] Furthermore, in order to balance the system's rapid response capability with the stability of steady-state measurement, this application constructs a multi-dimensional dynamic gain adjustment strategy that includes rate of change triggering, single over-limit triggering, and continuous counting triggering.

[0062] As one implementation method, adjusting the gain level includes: When the current change index or current change rate exceeds the first preset threshold, or the current sample value exceeds the second preset threshold, the gain level of the measurement circuit is reduced. When the current sample value is lower than the lower limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is increased by one level. If the current sample value is higher than the upper limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is reduced by one level.

[0063] It should be noted that three different triggering mechanisms have been integrated to form a dynamic response defense system.

[0064] Firstly, regarding downsizing protection, a dual insurance mechanism of rate-of-change triggering and amplitude triggering is adopted. The rate-of-change triggering is used to deal with extremely rapid change scenarios, achieving rapid downsizing at the millisecond or even microsecond level; while the amplitude triggering (i.e., the current sample value exceeds the second preset threshold) serves as a fallback protection to deal with slow-changing overload situations where the rate of change has not reached the threshold but the absolute value has exceeded the safe range, preventing the overcurrent risk from being missed due to improper selection of the rate of change calculation window.

[0065] Secondly, a "at least two consecutive" counting judgment mechanism was introduced for upshift optimization and steady-state downshifting. Because weak current signals have low signal-to-noise ratios and are susceptible to instantaneous glitches caused by electromagnetic interference, switching gears immediately based solely on a single sample value being below the lower limit or above the upper limit can easily cause the system to oscillate frequently between two adjacent gears, which not only affects measurement accuracy but also accelerates the aging of switching devices.

[0066] By setting a continuous counting threshold (e.g., triggering only when the condition is met after 3 or 5 consecutive samples), a digital hysteresis comparator is essentially constructed, effectively filtering out random noise interference and ensuring that the switching operation is only performed when the signal has indeed stably entered a new magnitude range.

[0067] For example, during steady-state measurement, if the current decreases slowly, the system will continue to monitor until N consecutive sampling points are all below the lower limit of the current range before confirming that the signal has entered a lower range and increasing the gain, thereby ensuring the smoothness and stability of the measurement process.

[0068] Example 4 Based on the methods described in Examples 1 to 3, in order to further improve the safety of the system under extreme operating conditions, this application also provides a hardware-level security protection mechanism independent of digital control logic.

[0069] As one implementation method, the method further includes: The input current of the object under test is monitored in real time through a hardware comparison circuit that is independent of the digital processing unit used to perform gain level adjustment. When the input current exceeds the preset leakage threshold, a protection trigger signal is output, and the protection state is maintained through a self-locking circuit to cut off the power supply to the measurement channel of the measurement circuit and output an alarm signal.

[0070] It should be noted that in applications such as high-voltage ion migration testing, the object under test may generate transient large currents due to insulation breakdown or accidental short circuit. If overcurrent detection and protection are performed solely by digital processing units (such as MCUs or DSPs), the software polling cycle, interrupt response delay, and program crash risk often prevent the fault identification and shutdown actions from being completed in a short time, which can easily lead to the damage of subsequent precision measurement devices.

[0071] This embodiment achieves nanosecond-level real-time monitoring of input current by constructing a pure analog hardware monitoring link that is completely independent of the digital sampling and gain control path. Even if the digital processing unit is in a crash, reset, or abnormal program state, the hardware comparison circuit can still autonomously determine the overcurrent state and directly drive the actuator to cut off the power supply to the measurement channel, fundamentally eliminating the blind spots and hysteresis of software protection.

[0072] Meanwhile, the self-locking circuit design ensures that the protection state can be forcibly locked after a fault is triggered, until manual intervention and power-off reset, effectively preventing secondary damage caused by automatic retry or repeated switching of the system due to unresolved faults.

[0073] To achieve the aforementioned hardware protection function, this application further provides a specific circuit implementation architecture. As one implementation method, the input current of the object under test is monitored in real time through a hardware comparison circuit, including: The voltage difference across the sampling resistor connected in series in the measurement circuit is amplified by an instrumentation amplifier to obtain the amplified signal; The amplified signal is divided to obtain the divided signal; Compare the voltage divider signal with a preset reference voltage; When the voltage divider signal exceeds the preset reference voltage, a flip-level signal is output, and the flip-level signal is input to the comparator through the feedback loop to form a self-locking structure.

[0074] Combination Figure 1The specific working principle of the hardware protection circuit in area B shown is as follows: First, the sampling resistor R13 is connected in series in the main measurement circuit to convert the input current flowing through the object under test into a voltage signal.

[0075] Since the sampling resistor is typically located on the high-voltage side or withstands a high common-mode voltage, and the weak current detection requires an extremely high signal-to-noise ratio, this embodiment selects instrumentation amplifier U8 as the front-end signal conditioning device, rather than a conventional operational amplifier. Instrumentation amplifier U8 has a common-mode rejection ratio (CMRR), which can effectively suppress common-mode interference on the high-voltage side, accurately extract the weak differential voltage signal across the sampling resistor R13, and amplify it into an amplified signal suitable for subsequent processing.

[0076] Subsequently, the amplified signal is processed by a voltage divider network composed of resistors R20 and R23 to obtain a voltage-divided signal. This voltage divider network not only serves as a level adapter but also flexibly sets the system's preset leakage current threshold by adjusting the resistance ratio of R20 and R23, enabling it to adapt to different test standards or the safety specifications of the object under test.

[0077] The voltage divider signal is sent to the non-inverting input of the first comparator U6A and compared with the preset reference voltage (e.g., 5V reference) at its inverting input.

[0078] Under normal operating conditions, when the voltage divider signal is lower than the reference voltage, U6A outputs a low level; once the input current increases abnormally and causes the voltage divider signal to exceed the reference voltage, the output of U6A immediately flips to a high level.

[0079] The high-level signal is transmitted to the non-inverting input of the second comparator U6B via resistor R17, triggering U6B to output a high-level protection signal OC_UNLOCK.

[0080] The output of U6B forms a positive feedback loop through diodes D3 and D4 and resistor R22, feeding the high-level signal back to its non-inverting input or the preceding node, thus creating a hardware self-locking structure. This means that even if the input current returns to normal or the output of U6A drops, the output of U6B will remain locked at a high level, continuously outputting an alarm signal and controlling the external power management circuit to cut off the power supply to the measurement channel.

[0081] Only after the system is completely powered off and restarted will capacitor C12 discharge, resetting the feedback loop and releasing the protection state. This purely hardware-implemented self-locking mechanism completely eliminates the risk of misjudgment or automatic recovery that may exist in software logic, providing deterministic safety assurance for wide-range weak current detection devices.

[0082] In addition, this hardware protection path is related to Figure 1The MCU / ADC sampling paths shown in area C are physically completely isolated, with the two only interacting at the power supply and control output ends. This ensures that any abnormality in the digital system will not interfere with the normal execution of the hardware protection function, truly achieving a dual-redundancy safety protection system.

[0083] Example 5 Based on the methods described in Examples 1 to 4, this application further provides a measurement circuit hardware architecture for implementing the above-described wide-range weak current detection method.

[0084] In one implementation, the measurement circuit includes a current-to-voltage conversion operational amplifier and multiple feedback branches connected in parallel; Each feedback branch includes a gain resistor and a solid-state relay switch connected in series with the gain resistor; By controlling the on / off state of different solid-state relay switches, the corresponding feedback branch is connected to the feedback loop of the current-to-voltage conversion operational amplifier to achieve the switching of gain levels.

[0085] like Figure 1 As shown in region A, the measurement circuit is based on a current-to-voltage conversion operational amplifier U4A. Its inverting input receives a weak current signal from input J1 transmitted through input resistor R12 and sampling resistor R13, while the non-inverting input is grounded through grounding resistor R14.

[0086] Three independent feedback branches are connected in parallel between the output terminal and the inverting input terminal of U4A. Each branch consists of a first gain resistor R1 connected in series with a first solid-state relay U1, a second gain resistor R2 connected in series with a second solid-state relay U2, and a third gain resistor R3 connected in series with a third solid-state relay U3.

[0087] The gain resistors R1, R2, and R3 in each branch are precision low-temperature drift resistors with gradient resistance values ​​(e.g., 10MΩ, 100MΩ, 1GΩ, etc.), thus covering a wide range of current measurement needs from nA to fA.

[0088] When the system needs to switch gain levels, the digital processing unit drives the corresponding solid-state relay to turn on through the control signal, while turning off the solid-state relays in other branches, thereby changing the feedback impedance of the transimpedance amplifier and achieving seamless range switching.

[0089] It should be noted that, in this embodiment, the selection of a solid-state relay as the switching device for the feedback network is an inevitable choice based on the special physical constraints of weak current detection.

[0090] In scenarios involving weak current measurements at the pA to fA levels, the leakage current, charge injection effect, and contact stability of the switching device itself directly determine the lower limit of the system's measurement and the signal-to-noise ratio. If a traditional mechanical relay is used, contact oxidation, mechanical jitter, and limited lifespan can lead to unstable contact resistance, and it is prone to failure under frequent switching conditions (such as the dynamic adjustment described in Example 3). If a common CMOS analog switch is used, its turn-off leakage current is typically in the nA level or even higher, and there is a significant charge injection effect, which can completely overwhelm the fA level of the measured signal.

[0091] The solid-state relays U1, U2, and U3 selected in this embodiment have extremely low turn-off leakage current (typical values ​​can be as low as fA) and extremely long switching life, and there is no noise or jitter caused by mechanical contacts.

[0092] To ensure measurement accuracy, the selection of solid-state relays must meet stringent requirements: their turn-off leakage current should be at least two orders of magnitude lower than the system's lowest test current to prevent switch leakage from becoming a new source of error. This provides the physical basis for the fast, low-noise range switching strategy described in Example 3, enabling the system to achieve millisecond-level range adaptation without sacrificing accuracy.

[0093] In a further implementation, to ensure the stability of the transimpedance amplifier over a wide bandwidth and prevent oscillation, phase compensation capacitors are connected in parallel in each feedback branch, namely the first filter capacitor C1, the second filter capacitor C2, and the third filter capacitor C3.

[0094] In weak current detection circuits, these capacitors serve as frequency compensation, and their insulation performance is also crucial. If conventional X7R or Y5V capacitors are used, their dielectric absorption effect and DC leakage current may introduce errors during long-term integration or at high-impedance nodes.

[0095] Therefore, this embodiment specifically selects NPO or C0G ceramic capacitors as phase compensation elements. These capacitors have extremely low dielectric loss and extremely low DC leakage characteristics, which can effectively avoid false current readings caused by capacitor leakage and ensure the accuracy of measurement at high gain levels.

[0096] at the same time, Figure 1 Region A also includes a special short-circuit solid-state relay U7, which is connected between the inverting input of operational amplifier U4A and ground. This device is off during normal measurements, but is briefly turned on when performing the reference calibration steps described in Examples 1 and 2, providing a defined virtual ground potential or discharge loop to the op-amp input.

[0097] Example 6 This application also provides a wide-range weak current detection device, which is applied to the wide-range weak current detection method described in the foregoing embodiments.

[0098] The device includes a measurement circuit, a background error acquisition module, a gain level control module, a compensation calculation module, and a hardware protection module.

[0099] The measurement circuit is used to convert the weak current of the object under test into a current sample value.

[0100] Combination Figure 1 In region A shown, the measurement circuit is the physical front end of signal conditioning. Its core includes a current-to-voltage conversion operational amplifier U4A and a multi-stage feedback network composed of solid-state relays U1-U3 and gain resistors R1-R3.

[0101] The circuit directly receives the weak current signal from the input terminal J1 and converts it into a voltage signal U(IV) suitable for subsequent acquisition through transimpedance amplification.

[0102] The background error acquisition module is used to switch the measurement circuit to the highest gain level and acquire the background error parameters when the object under test is not connected to the reference state.

[0103] The background error acquisition module is typically implemented by a digital processing unit (such as a microcontroller (MCU) or a field-programmable gate array (FPGA)) in conjunction with a storage unit.

[0104] When the system is powered on and initialized or when the user triggers a calibration command, the baseline error acquisition module sends a control signal to the measurement circuit to forcibly close the solid-state relay (e.g., U3) corresponding to the highest gain level, while simultaneously disconnecting other level switches and short-circuit switch U7, so that the system is in the most sensitive no-load test state.

[0105] Subsequently, the module reads the digital value output by the ADC chip U5 at this time, converts it to obtain the offset current value that characterizes the inherent noise level of the system, and stores it in non-volatile memory for subsequent compensation.

[0106] The gain level control module is used to determine the current change index based on continuously acquired current sampling values, and to control the measurement circuit to adjust the gain level according to the current sampling values ​​and the current change index.

[0107] The gain level control module can also be implemented by the digital processing unit executing a preset program. It receives the current sampling data stream from the ADC in real time, calculates the difference or derivative between adjacent sampling points to obtain the current change rate, and monitors the absolute amplitude of the current sampling value.

[0108] When any of the triggering conditions described in Example 3 is detected (such as rate of change exceeding the limit, amplitude exceeding the limit, or continuous count reaching the standard), the module immediately generates the corresponding gear switching command, drives the corresponding solid-state relay in the measurement circuit to switch on and off, thereby changing the transimpedance gain.

[0109] The compensation calculation module is used to compensate the current sampling value based on the background error parameter and the gain parameter corresponding to the current gain level to obtain the actual current value.

[0110] The compensation calculation module runs immediately after each sampling. It retrieves the pre-calibrated background offset current from the memory and, in conjunction with the feedback resistance value of the currently active range, recalculates the equivalent offset current in the current state according to the mapping algorithm described in Example 2, and then subtracts the error component from the original sampled value.

[0111] The hardware protection module is used to monitor the input current of the object under test independently of the gain level control module, and triggers self-locking protection when the input current exceeds the preset leakage threshold to cut off the power supply to the measurement channel of the measurement circuit.

[0112] Combination Figure 1 In area B shown, the hardware protection module has a pure analog signal link that is completely independent of the digital sampling and gain control path. Its front end uses an instrumentation amplifier U8 to directly acquire the voltage difference across the sampling resistor R13, which is then adjusted by the voltage divider network R20 / R23 and sent to the self-locking judgment circuit composed of comparators U6A and U6B.

[0113] Once the input current abnormally exceeds the safety threshold set by the voltage divider ratio, the comparator output flips and is locked to a high level through a positive feedback loop, directly outputting an OC_UNLOCK alarm signal to control the external power management circuit to cut off the power supply to the measurement channel.

[0114] Example 7 This application also provides an insulation resistance testing device, including a high-voltage power supply, a wide-range weak current detection device, and a control unit.

[0115] The high-voltage power supply is used to apply a high-voltage test voltage to the object under test; the wide-range weak current detection device is used to detect the input current generated by the object under test under the high-voltage test voltage, adjust the gain level and compensate for the background error of the input current, and output the actual current value; the control unit is used to determine the insulation resistance of the object under test based on the actual current value.

[0116] It should be noted that this insulation resistance testing equipment is a complete system that materializes the wide-range weak current detection method and device described in the foregoing embodiments and applies them to the field of high-voltage insulation performance evaluation.

[0117] In this system, a high-voltage power supply serves as the excitation source, typically requiring a stable DC voltage of several hundred to several thousand volts to stimulate ion migration or leakage current within the object under test. A wide-range weak current detection device serves as the core measurement front end, connected in series to the low-voltage side of the high-voltage circuit or accessed through a dedicated sampling interface. It is responsible for accurately converting the pA-level or even fA-level weak current flowing through the object under test into a digital quantity. The control unit serves as the data processing and system scheduling center, not only calculating the insulation resistance value in real time based on Ohm's law (R=U / I), but also coordinating the start-up and shutdown of the high-voltage power supply, the calibration and range switching of the detection device, and the execution of safety interlock logic.

[0118] To more clearly demonstrate the application effectiveness of the technical solution of this application in actual industrial testing, the following detailed explanation will be based on a typical harsh working condition: high-voltage ion migration testing.

[0119] In ion migration testing, a DC high voltage of 500V to 1000V is usually applied to the insulating material under test, and the leakage current is continuously monitored over time.

[0120] This process has three significant characteristics: first, there is a large charging current or transient impact at the initial power-on moment; second, the leakage current is extremely low in the steady state stage and decays exponentially over time; and third, when the material suffers insulation degradation or breakdown, the current will change by orders of magnitude in a very short time.

[0121] In response to these characteristics, the insulation resistance testing equipment provided in this embodiment effectively solves the three major pain points of traditional solutions through a software and hardware collaborative mechanism.

[0122] Firstly, regarding safety protection under high-voltage impact, when the device under test experiences a short circuit at the moment of power-on or a catastrophic breakdown during testing, the loop current may instantly surge from the pA level to the mA level or even higher. In this situation, the independent hardware protection module in this application can, without relying on software intervention from the control unit, identify the overcurrent state within nanoseconds using an instrumentation amplifier and a self-locking comparator circuit, and lock the alarm signal OC_UNLOCK, directly cutting off the power supply to the measurement channel.

[0123] This purely hardware-based protection mechanism completely eliminates protection blind spots caused by software polling delays or program anomalies, ensuring that expensive precision measuring devices will not suffer secondary damage in the event of a high-voltage test accident, and significantly improving the long-term operational reliability of the equipment.

[0124] Secondly, in the extraction of weak signals with high signal-to-noise ratio, the leakage current in the steady-state stage of ion migration is often as low as fA, which is easily overwhelmed by operational amplifier offset current and environmental noise.

[0125] This embodiment automatically performs a baseline error calibration at the highest gain setting before each test to obtain the true offset current parameters under the current ambient temperature and device conditions, and then performs real-time dynamic compensation in subsequent measurements by combining the feedback resistance value of the current gain setting.

[0126] Finally, in terms of lossless recording of rapidly changing processes, traditional linear sampling schemes often suffer from loss of critical transient data or waveform clipping due to range switching lag when faced with exponentially abrupt signals such as ion migration and breakdown.

[0127] The control unit in this embodiment incorporates multi-dimensional dynamic switching logic based on current change rate, single amplitude over-limit, and continuous counting triggers. This allows the system to identify current surge trends and adaptively adjust the gain level with only three data samples. This millisecond-level rapid response capability ensures that the device can accurately capture the inrush current waveform at the moment of power-on, seamlessly track the slow decay process in the steady-state phase, and completely record the details of the rapid jump at the moment of breakdown. This achieves lossless recording of current signals across a wide dynamic range, significantly improving the integrity and reliability of insulation performance evaluation data.

[0128] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, disclosure, and appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0129] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of this application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from the spirit and scope of this application. Thus, if such modifications and modifications of this application fall within the scope of the claims of this application and their equivalents, this application is also intended to include such modifications and modifications.

Claims

1. A wide-range weak current detection method, characterized in that, include: In the baseline state where the object under test is not connected, the measurement circuit is switched to the highest gain setting, and the background error parameters of the measurement circuit are obtained. When the object under test is connected to the measurement state, the current sampling value of the object under test is obtained through the measurement circuit; The current change index is determined based on the continuously acquired current sampling values, and the gain level of the measurement circuit is dynamically adjusted according to the current sampling values ​​and the current change index so that the gain of the measurement circuit matches the input current level of the object under test. The current sample value is compensated based on the background error parameter and the gain parameter corresponding to the current gain level to obtain the actual current value.

2. The method according to claim 1, characterized in that, The process of obtaining the baseline error parameters of the measurement circuit includes: In the reference state, the measurement circuit is switched to the highest gain setting; Read the output value of the measurement circuit at the highest gain setting, and determine the offset current of the measurement circuit based on the output value.

3. The method according to claim 2, characterized in that, Based on the background error parameter and the gain parameter corresponding to the current gain level, the current sample value is compensated, including: Obtain the feedback resistor value corresponding to the current gain level; The offset voltage error at the current gain setting is determined by the product of the offset current and the feedback resistor value. The equivalent offset current at the current gain level is determined based on the offset voltage error and the transimpedance gain corresponding to the current gain level. The actual current value is obtained by performing a difference calculation between the current sample value and the equivalent offset current.

4. The method according to claim 1, characterized in that, The determination of the current change index includes: The current sampling value is continuously acquired according to a preset sampling period; The current change index is determined based on the difference between the current sample value obtained at the current sampling time and the previous sampling time, or the current change rate is determined based on the time interval between the difference and the adjacent sampling time. When the current change index or the current change rate exceeds a first preset threshold, the measurement circuit is triggered to adjust the gain level.

5. The method according to claim 4, characterized in that, The adjustable gain levels include: When the current change index or the current change rate exceeds the first preset threshold, or the current sample value exceeds the second preset threshold, the gain level of the measurement circuit is reduced. When the current sample value is lower than the lower limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is increased. When the current sample value is higher than the upper limit threshold corresponding to the current gain level at least twice consecutively, the gain level of the measurement circuit is reduced.

6. The method according to claim 1, characterized in that, The method further includes: The input current of the object under test is monitored in real time by means of a hardware comparison circuit that is independent of the digital processing unit used to perform gain level adjustment; When the input current exceeds the preset leakage threshold, a protection trigger signal is output, and the protection state is maintained through a self-locking circuit to cut off the power supply to the measurement channel of the measurement circuit and output an alarm signal.

7. The method according to claim 6, characterized in that, Real-time monitoring of the input current of the object under test includes: The voltage difference across the sampling resistor connected in series in the measurement circuit is amplified by an instrumentation amplifier to obtain the amplified signal; The amplified signal is divided to obtain a divided signal; The voltage divider signal is compared with a preset reference voltage; When the voltage divider signal exceeds the preset reference voltage, a flip-level signal is output, and the flip-level signal is input to the comparator through a feedback loop to form a self-locking structure.

8. The method according to claim 1, characterized in that, The measurement circuit includes a current-to-voltage conversion operational amplifier and multiple feedback branches connected in parallel; Each of the aforementioned feedback branches includes a gain resistor and a solid-state relay switch connected in series with the gain resistor; By controlling the on / off state of different solid-state relay switches, the corresponding feedback branch is connected to the feedback loop of the current-to-voltage conversion operational amplifier to achieve the switching of the gain level.

9. A wide-range weak current detection device, applied to the method described in any one of claims 1-8, characterized in that, include: A measurement circuit is used to convert the weak current of the object under test into a current sample value; The background error acquisition module is used to switch the measurement circuit to the highest gain level and acquire the background error parameters when the reference state of the object under test is not connected. A gain level control module is used to determine the current change index based on continuously acquired current sampling values, and to control the measurement circuit to adjust the gain level according to the current sampling values ​​and the current change index. The compensation calculation module is used to compensate the current sample value according to the background error parameter and the gain parameter corresponding to the current gain level to obtain the actual current value; The hardware protection module is used to monitor the input current of the object under test independently of the gain level control module, and to trigger self-locking protection when the input current exceeds a preset leakage threshold to cut off the power supply to the measurement channel of the measurement circuit.

10. An insulation resistance testing device, characterized in that, include: A high-voltage power supply is used to apply a high-voltage test voltage to the object under test. The wide-range weak current detection device as described in claim 9 is used to detect the input current generated by the object under test under the high voltage test voltage, adjust the gain level and compensate the background error of the input current, and output the actual current value. The control unit is used to determine the insulation resistance of the object under test based on the actual current value.

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