Semiconductor sensor fault detection protection circuit and method

Abstract

The invention relates to the technical field of gas detection, in particular to a semiconductor sensor fault detection protection circuit and method.The circuit comprises a processor, a sensor, a control and collection module and a power module, and the control and collection module comprises a heating electrode collection end, a heating electrode control end and an internal semiconductor collection end; the heating electrode acquisition end is electrically connected with the processor and used for transmitting real-time heating voltage of the heating electrode to the processor, the internal semiconductor acquisition end is electrically connected with the processor and used for transmitting real-time detection voltage of the internal semiconductor to the processor, and the heating electrode control end is connected with the processor and used for controlling whether the heating electrode works or not. The processor is used for judging the circuit state of the heating electrode according to the real-time heating voltage in the non-working state and judging the circuit state of the internal semiconductor according to the real-time detection voltage at different temperatures, the situation that fault diagnosis is easily interfered by factors such as temperature and gas concentration when a single threshold value is used for fault diagnosis is avoided, and therefore the accuracy of fault diagnosis is improved.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and specifically to a fault detection and protection circuit and method for semiconductor sensors. Background Technology

[0002] Most existing gas detectors use semiconductor sensors to detect gas concentrations in the environment. Semiconductor devices only have high sensitivity and accuracy at suitable temperatures. Therefore, current semiconductor gas sensors are equipped with heating electrodes to heat the internal semiconductor devices, ensuring they are always kept at their optimal operating temperature and thus guaranteeing the sensor's detection accuracy. With long-term use, the circuitry within the sensor will age to varying degrees, leading to faults such as short circuits or open circuits. Therefore, it is necessary to monitor the sensor's operating status in real time.

[0003] Current technologies for detecting the operating status of sensors mostly rely on measuring the voltage of the semiconductor device and using this voltage to determine the cause of sensor malfunction. However, the operating status of the heating electrode has a significant impact on the voltage of the semiconductor device, and traditional detection methods that rely on a single threshold often suffer from false positives or false negatives. Summary of the Invention

[0004] To address the technical problems of false positives and false negatives in single threshold detection methods, this application provides a semiconductor sensor fault detection and protection circuit and method, wherein the circuit includes: a processor, a sensor, a control and acquisition module, and a power supply module; The power module is used to supply power; The sensor includes a heating electrode and an internal semiconductor; The control and acquisition module includes a heating electrode acquisition terminal, a heating electrode control terminal, and an internal semiconductor acquisition terminal; The heating electrode acquisition terminal is electrically connected to the processor and is used to transmit the real-time heating voltage of the heating electrode to the processor. The internal semiconductor acquisition terminal is electrically connected to the processor and is used to transmit the real-time detection voltage of the internal semiconductor to the processor. The heating electrode control terminal is connected to the processor and is used to control whether the heating electrode is working. The processor is used to determine the circuit state of the heating electrode based on the real-time heating voltage under different operating states of the heating electrode, and to determine the circuit state of the internal semiconductor based on the real-time detection voltage under different operating states of the heating electrode.

[0005] Furthermore, the control and acquisition module also includes a short-circuit self-locking circuit, which is used to automatically ground the short-circuit current when the heating electrode is short-circuited.

[0006] Specifically, in some embodiments, the short-circuit self-locking circuit includes: The fourth resistor has one end electrically connected to pin 1 of the sensor and the other end grounded. The first transistor has its base connected to the power module via a third resistor, its collector electrically connected to pin 1 of the sensor, and its emitter grounded. The base of the second transistor is electrically connected to pin 1 of the sensor via the sixth and seventh resistors. The base is also electrically connected to the heating electrode control terminal via the seventh resistor. The collector is electrically connected to the base of the first transistor, and the emitter is grounded. The second resistor has one end electrically connected to pin 1 of the sensor and the other end electrically connected to the heating electrode acquisition terminal.

[0007] The fault detection method provided by this invention includes the following steps: At the start of the heating cycle, the real-time heating voltage of the heating electrode and the real-time detection voltage of the internal semiconductor are acquired and denoted as the first heating voltage and the first detection voltage, respectively. At the end of the heating cycle, the real-time heating voltage of the heating electrode and the real-time detection voltage of the internal semiconductor are acquired again and denoted as the second heating voltage and the second detection voltage, respectively. Calculate the absolute difference between the first heating voltage and the second heating voltage. If the absolute difference is greater than the heating voltage fluctuation threshold, then the circuit of the heating electrode is normal. Calculate the absolute difference between the first detection voltage and the second detection voltage. If the absolute difference is greater than the detection voltage fluctuation threshold, then the circuit of the internal semiconductor is normal.

[0008] The technical effects and advantages of this invention are as follows: This invention determines the circuit state of the heating electrode by observing the voltage changes of the heating electrode under different operating conditions, and determines the circuit state of the internal semiconductor by observing the voltage changes of the internal semiconductor at different temperatures. This achieves dynamic analysis of the circuit state, avoiding the interference of factors such as temperature and gas concentration that are easily affected by single threshold values ​​in fault diagnosis, thereby improving the accuracy of fault diagnosis. Simultaneously, a short-circuit self-locking circuit is set at the hardware level to achieve a rapid response in the event of a short circuit. In the event of a short circuit, the short-circuit current can be quickly grounded, achieving dual protection through both software and hardware, thus improving circuit safety. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the overall circuit structure of the present invention.

[0010] Figure 2 This is the electrical schematic diagram of the short-circuit self-locking circuit of the present invention.

[0011] Figure 3 This is a flowchart illustrating the process by which the processor of the present invention determines the state of the heating electrode circuit.

[0012] Figure 4This is a flowchart illustrating the process by which the processor of the present invention determines the state of its internal semiconductor circuits. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] refer to Figure 1 The present invention provides a semiconductor sensor fault detection and protection circuit, comprising: a processor, a sensor, a control and acquisition module, a power supply module, a human-machine interaction module, and a wireless module.

[0015] The power module is used to provide electrical energy to the entire circuit.

[0016] The sensor includes a heating electrode and an internal semiconductor. The heating electrode is used to heat the internal semiconductor. Its periodic heating and cooling keep the internal semiconductor operating at the optimal temperature, ensuring the detection accuracy and sensitivity of the internal semiconductor for the target gas.

[0017] The control and acquisition module includes a heating electrode acquisition terminal A, a heating electrode control terminal E, and an internal semiconductor acquisition terminal C. The heating electrode control terminal E is connected to the processor, which can control the on / off state of the heating electrode through the heating electrode control terminal E, thereby controlling the temperature of the internal semiconductor. The heating electrode acquisition terminal A is electrically connected to the processor and is used to transmit the real-time heating voltage Vh1 of the heating electrode to the processor. The internal semiconductor acquisition terminal C is electrically connected to the processor and is used to transmit the real-time detection voltage Vc1 of the internal semiconductor to the processor.

[0018] The processor determines the circuit status of the heating electrode based on the real-time heating voltage Vh1 and the working cycle of the heating electrode transmitted by the control and acquisition module, and determines the circuit status of the internal semiconductor based on the real-time detection voltage Vc1 and the working cycle of the heating electrode. The processor then uploads the information to the human-machine interaction module via the wireless module to prompt the user to perform timely maintenance.

[0019] The resistance of the internal semiconductor is related not only to the concentration of the target gas in the environment, but also to its temperature. Therefore, the circuit status can be determined by real-time detection voltage at different temperatures, thus avoiding inaccurate judgment results caused by the influence of other interference factors on a single threshold.

[0020] Furthermore, the control and acquisition module also includes a short-circuit self-locking circuit, which automatically grounds the short-circuit current when the heating electrode is short-circuited, enabling rapid response and protection against short circuits from a hardware perspective.

[0021] Specifically, Figure 2 A specific implementation of a short-circuit self-locking circuit is shown, including: The fourth resistor R4 is electrically connected at one end to pin 1 of sensor P1, and the other end is grounded. The first transistor Q1 has its base connected to the power module through the third resistor R3, its collector electrically connected to pin 1 of the sensor P1, and its emitter grounded. The base of the second transistor Q2 is electrically connected to pin 1 of sensor P1 through the sixth resistor R6 and the seventh resistor R7, and is electrically connected to the heating electrode control terminal E through the seventh resistor R7. The collector is electrically connected to the base of the first transistor Q1, and the emitter is grounded. The second resistor has one end electrically connected to pin 1 of sensor P1 and the other end electrically connected to the heating electrode acquisition terminal A.

[0022] When the heating electrode is short-circuited, the short-circuit current passes through the sixth resistor R6 and the seventh resistor R7, making the base of the second transistor Q2 high. The second transistor Q2 conducts, grounding the base of the first transistor Q1 and turning it low. The first transistor Q1 is then cut off, allowing the short-circuit current of the heating electrode to pass through the fourth resistor R4 and ground. This achieves short-circuit protection for the heating electrode acquisition terminal A and other electrical components in the hardware.

[0023] When the heating electrode is working normally, the processor sends a low level to the second transistor Q2 through the heating electrode control terminal E. The second transistor Q2 is turned off, and the power module turns on the base of the first transistor Q1 with a high level, so that the heating electrode pin 1 is grounded through the first transistor Q1, the heating electrode voltage increases, and the heating operation begins.

[0024] When the heating electrode needs to stop working, the processor sends a high level to the second transistor Q2 through the heating electrode control terminal E. The second transistor Q2 turns on, the power module is grounded through the third resistor R3, the base of the first transistor Q1 becomes low, the first transistor Q1 is cut off, the heating electrode is grounded through the fourth resistor R4, the fourth resistor R4 shares most of the voltage in the circuit, so that the voltage and current of the heating electrode are reduced, thereby stopping the heating electrode from working.

[0025] The aforementioned short-circuit self-locking circuit not only provides fast-response short-circuit protection in hardware, but its heating electrode control terminal E can also be controlled by a processor. In the event of a short-circuit fault, the heating electrode circuit can be shut off through a program, thus forming a double insurance of software and hardware. This further improves the safety and reliability of the entire circuit. Moreover, the circuit is simple and low-cost, making it a promising candidate for widespread application in household combustible gas detectors.

[0026] Further, in order to better control the temperatures of the heating electrode and the internal semiconductor, a temperature sensor, such as a thermistor, is further included in the circuit of the present invention to measure the temperature of the internal semiconductor and control the operation of the heating electrode according to the temperature of the semiconductor.

[0027] Specifically, referring to Figure 3 , the processor determines the circuit state of the internal semiconductor through the following steps: S1. After the system is powered on, obtain the lower limit value Vca and the upper limit value Vcb of the detection voltage of the internal semiconductor; S2. The heating electrode is periodically powered on, the sensor starts to work, and periodically obtains the real-time voltage Vh1 of the heating electrode and the real-time detection voltage Vc1 of the internal semiconductor; S3. Judge the circuit state of the internal semiconductor according to the real-time detection voltage and the working state of the heating electrode, including: When the real-time detection voltage Vc1 is less than the first threshold (i.e., Vc1≈0 V), the internal semiconductor is open-circuited. When Vca<Vc1<Vcb, the circuit of the internal semiconductor is normal. When the real-time detection voltage Vc1>Vcb, mark Vc1 as the first detection voltage Vcd. At this time, the temperature of the internal semiconductor is the first temperature. Let the heating electrode stop heating. After a time T0 (cooling cycle), obtain the real-time detection voltage Vc1 again. At this time, the temperature of the internal semiconductor is the second temperature. Record Vc1 as the second detection voltage Vcf. If |Vcd-Vcf|<Vc_th (detection voltage fluctuation threshold), the internal semiconductor is short-circuited.

[0028] The resistance value of the internal semiconductor is not only related to the concentration of the target gas in the environment, but also related to the temperature of the internal semiconductor itself. When the circuit state of the internal semiconductor is normal, changing the temperature of the internal semiconductor will cause corresponding changes in its resistance and the voltage drop generated by it. Therefore, the circuit state can be judged according to the real-time detection voltages before and after the temperature change. When the circuit of the internal semiconductor is short-circuited or open-circuited, the real-time detection voltage remains unchanged regardless of how its temperature changes.

[0029] Similarly, the circuit state of the internal semiconductor can also be judged through the following steps: S31. At the beginning of the heating cycle T1 (the temperature of the internal semiconductor is the second temperature), collect the real-time detection voltage Vc1 of the internal semiconductor, record it as the first detection voltage Vcd. At the end of the heating cycle T1 (the temperature of the internal semiconductor is the first temperature), collect the real-time detection voltage Vc1 of the internal semiconductor, record it as the second detection voltage Vcf. If |Vcd-Vcf|>Vc_th (detection voltage fluctuation threshold), the internal semiconductor is normal.

[0030] When the circuit of the internal semiconductor is short-circuited or open-circuited, the temperature change and the change in the concentration of the target gas in the environment will not affect its resistance and voltage. Therefore, judging the circuit state through the above steps can exclude the influence of temperature and the concentration of the target gas, which is more reliable than the traditional single threshold.

[0031] The lower detection voltage limit value Vca and the upper detection voltage limit value Vcb can be obtained through high and low temperature experiments under target gases with different concentrations. First, conduct high and low temperature experiments in a normal environment without the target gas, change the temperature of the internal semiconductor, and measure the minimum voltage value and the maximum voltage value when the circuit state of the internal semiconductor is normal. Then, continuously increase the concentration of the target gas in the test environment and measure the minimum voltage value and the maximum voltage value. Finally, determine the lower detection voltage limit value Vca and the upper detection voltage limit value Vcb based on the minimum voltage value and the maximum voltage value that appear in the experiment.

[0032] Furthermore, in actual applications, it is extremely rare for the real-time detection voltage to exceed the upper limit due to an excessive concentration of the target gas. Generally, an alarm is issued for processing when the concentration of the target gas is greater than the preset alarm threshold. Therefore, the upper detection voltage limit value Vcb is generally set to a preset value lower than the power supply voltage according to experience. For example, when the power supply voltage is 5V, the upper detection voltage limit value Vcb is set to 4.5V, and a short-circuit detection action is triggered when it exceeds the upper limit.

[0033] At the same time, the processor judges the circuit state of the heating electrode according to the real-time heating voltage Vh1 transmitted by the control and acquisition module and the working cycle of the heating electrode. Specifically, refer to Figure 4 , including the following steps: S4. After the system is powered on, obtain the initial heating voltage Vh0 of the heating electrode; S5. The heating electrode is periodically powered on, the sensor starts to work, and periodically obtains the real-time heating voltage Vh1 of the heating electrode; S6. When the real-time heating voltage Vh1 is less than the first threshold (i.e., Vh1≈0 V), the heating electrode is open-circuited. When the real-time heating voltage Vh1 is greater than the second threshold (i.e., Vh1≈5 V), the heating electrode is short-circuited. When the heating electrode is within the heating cycle T1, if the real-time heating voltage Vh1 is within the normal working voltage range (0<Vh1<<Vh0), the heating electrode circuit is normal. When the heating electrode ends the cooling cycle T0, if the absolute difference between the real-time heating voltage and the initial heating voltage Vh0 is less than the first threshold (i.e., Vh1≈Vh0), the heating electrode circuit is normal.

[0034] The normal operating voltage range can be obtained by conducting high and low temperature experiments on multiple batches of sensors. By continuously changing the ambient temperature, the minimum and maximum voltage values ​​of the sensor's heating electrode when it is operating normally are measured at different ambient temperatures. The normal operating voltage range is determined based on the minimum and maximum voltage values ​​obtained from multiple measurements.

[0035] Furthermore, the circuit state of the heating electrode can be determined based on the voltage change before and after the heating electrode is energized, specifically including the following steps: S7. At the beginning of the heating cycle T1, after powering on the heating electrode, the real-time heating voltage Vh1 of the heating electrode is collected and recorded as the first heating voltage Vhc. At the end of the heating cycle T1, when the heating electrode is de-powered, the real-time heating voltage Vh1 of the heating electrode is collected again and recorded as the second heating voltage Vhd. The absolute difference between the first heating voltage Vhc and the second heating voltage Vhd is calculated. If |Vhc-Vhd|>Vh_th (heating voltage fluctuation threshold), then the heating electrode circuit is normal.

[0036] This eliminates the need to wait for the heating electrode to cool down to the system's power-on temperature when judging the circuit status. Consequently, the judgment of the circuit status is not affected by the ambient temperature, improving the accuracy of the detection. This allows the entire fault detection and protection circuit to complete a round of detection more quickly, so as to detect potential circuit faults in a timely manner.

[0037] The heating voltage fluctuation threshold Vh_th and the detection voltage fluctuation threshold Vc_th can be obtained through high and low temperature experiments. Considering that the resistance values ​​and temperature responses of heating electrodes and internal semiconductors produced in different batches may vary, it is necessary to conduct experiments on multiple sets of heating electrodes and internal semiconductors from different batches to obtain voltage change data in order to determine a suitable threshold.

[0038] Specifically, the heating voltage fluctuation threshold is obtained through the following steps: S311. Conduct high and low temperature experiments in a high and low temperature test chamber. The heating electrode is continuously energized and de-energized to cool down. Record the first heating voltage Vhc when the heating electrode is energized and the second heating voltage Vhd when the heating electrode is de-energized at different temperatures. Calculate the absolute difference between the first heating voltage Vhc and the second heating voltage Vhd recorded each time to obtain multiple absolute differences. S312. After multiple experiments, the multiple absolute differences basically conform to a normal distribution. Calculate the average value Vh_mean and standard deviation Vh_stan of the multiple absolute differences, and set the heating voltage fluctuation threshold to Vh_mean-n*Vh_stan, where n is 2 or 3.

[0039] For a normal distribution, when n=2, it means that the voltage fluctuation will exceed the heating voltage fluctuation threshold only 95% of the time. When n=3, the voltage fluctuation will exceed the heating voltage fluctuation threshold only 99.7% of the time. For general application scenarios, n=2 is preferred, which can ensure sufficient accuracy and will not cause the sensor to malfunction and false alarm too frequently.

[0040] The steps for obtaining the voltage fluctuation detection threshold are basically the same: S611. The heating electrode continuously performs power-on heating and power-off cooling operations, and records the first detection voltage Vcd and the second detection voltage Vcf of the internal semiconductor at the first temperature and the second temperature multiple times, and calculates the absolute difference between the first detection voltage Vcd and the second detection voltage Vcf recorded each time to obtain multiple absolute differences. S612. Calculate the average value Vc_mean and standard deviation Vc_stan of multiple absolute differences, and set the detection voltage fluctuation threshold to Vc_mean-n*Vc_stan, where n is 2 or 3.

[0041] The heating voltage fluctuation threshold and detection voltage fluctuation threshold obtained through the above steps can cover voltage fluctuations in most cases, ensuring the accuracy of circuit status judgment results.

[0042] The advantages of the circuit provided in this application are that it determines the circuit state of the heating electrode by observing the voltage changes of the heating electrode under different operating conditions, and determines the circuit state of the internal semiconductor by observing the voltage changes of the internal semiconductor at different temperatures. This enables dynamic analysis of the circuit state and avoids the interference from factors such as temperature and gas concentration that are easily affected when using a single threshold for fault diagnosis, thereby improving the accuracy of fault diagnosis. Simultaneously, a short-circuit self-locking circuit is set at the hardware level to achieve a rapid response in the event of a short circuit. In the event of a short circuit, the short-circuit current can be quickly grounded, achieving dual protection through both software and hardware, thus improving the safety of the circuit.

[0043] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A semiconductor sensor fault detection and protection circuit, characterized in that, Includes processor, sensors, control and acquisition modules, and power supply module; The power module is used to supply power; The sensor includes a heating electrode and an internal semiconductor; The control and acquisition module includes a heating electrode acquisition terminal, a heating electrode control terminal, and an internal semiconductor acquisition terminal; The heating electrode acquisition terminal is electrically connected to the processor and is used to transmit the real-time heating voltage of the heating electrode to the processor. The internal semiconductor acquisition terminal is electrically connected to the processor and is used to transmit the real-time detection voltage of the internal semiconductor to the processor. The heating electrode control terminal is connected to the processor and is used to control whether the heating electrode is working. The processor is used to determine the circuit state of the heating electrode based on the real-time heating voltage under different operating states of the heating electrode, and to determine the circuit state of the internal semiconductor based on the real-time detection voltage under different operating states of the heating electrode.

2. The circuit according to claim 1, characterized in that, The control and acquisition module also includes a short-circuit self-locking circuit, which is used to automatically ground the short-circuit current when the heating electrode is short-circuited.

3. The circuit according to claim 2, characterized in that, The short-circuit self-locking circuit includes: The fourth resistor has one end electrically connected to pin 1 of the sensor and the other end grounded. The first transistor has its base connected to the power module via a third resistor, its collector electrically connected to pin 1 of the sensor, and its emitter grounded. The base of the second transistor is electrically connected to pin 1 of the sensor via the sixth and seventh resistors. The base is also electrically connected to the heating electrode control terminal via the seventh resistor. The collector is electrically connected to the base of the first transistor, and the emitter is grounded. The second resistor has one end electrically connected to pin 1 of the sensor and the other end electrically connected to the heating electrode acquisition terminal.

4. The circuit according to claim 1, characterized in that, The processor determines the circuit state of the heating electrode through the following steps: After the system is powered on, the initial heating voltage of the heating electrode is obtained; The heating electrode is periodically energized, and the real-time heating voltage of the heating electrode is periodically acquired. When the real-time heating voltage is less than the first threshold, the heating electrode is open-circuited; when the real-time heating voltage is greater than the second threshold, the heating electrode is short-circuited; when the heating electrode is in the heating cycle, if the real-time heating voltage is within the normal operating voltage range, the heating electrode circuit is normal; when the heating electrode is at the end of the cooling cycle, if the absolute difference between the real-time heating voltage and the initial heating voltage is less than the first threshold, the heating electrode circuit is normal.

5. The circuit according to claim 1, characterized in that, The processor determines the circuit state of the heating electrode through the following steps: When the heating electrode is energized, the real-time heating voltage of the heating electrode is obtained and recorded as the first heating voltage; When the heating electrode is de-energized, the real-time heating voltage of the heating electrode is acquired and recorded as the second heating voltage; Calculate the absolute difference between the first heating voltage and the second heating voltage. If the absolute difference is greater than the heating voltage fluctuation threshold, then the circuit of the heating electrode is normal.

6. The circuit according to claim 1, characterized in that, The processor determines the circuit state of the internal semiconductor through the following steps: When the real-time detected voltage is less than the first threshold, the internal semiconductor is open-circuited. When the real-time detected voltage is greater than the lower limit of the detection voltage but less than the upper limit of the detection voltage, the internal semiconductor device is normal. When the real-time detected voltage is greater than the upper limit of the detection voltage, the real-time detected voltage is recorded as the first detection voltage, and the heating electrode is stopped. After a cooling cycle, the real-time detected voltage is obtained again and recorded as the second detection voltage. If the absolute difference between the first detection voltage and the second detection voltage is less than the detection voltage fluctuation threshold, the internal semiconductor is short-circuited.

7. A fault detection method, employing the circuit described in any one of claims 1-3, characterized in that, Includes the following steps: At the start of the heating cycle, the real-time heating voltage of the heating electrode and the real-time detection voltage of the internal semiconductor are acquired and denoted as the first heating voltage and the first detection voltage, respectively. At the end of the heating cycle, the real-time heating voltage of the heating electrode and the real-time detection voltage of the internal semiconductor are acquired again and denoted as the second heating voltage and the second detection voltage, respectively. Calculate the absolute difference between the first heating voltage and the second heating voltage. If the absolute difference is greater than the heating voltage fluctuation threshold, then the circuit of the heating electrode is normal. Calculate the absolute difference between the first detection voltage and the second detection voltage. If the absolute difference is greater than the detection voltage fluctuation threshold, then the circuit of the internal semiconductor is normal.

8. The method according to claim 7, characterized in that, The detection voltage fluctuation threshold is obtained through the following steps: The heating electrode continuously performs power-on heating and power-off cooling operations, and records the first detection voltage and the second detection voltage of the internal semiconductor at the first temperature and the second temperature multiple times, and calculates the absolute difference between the first detection voltage and the second detection voltage recorded each time to obtain multiple absolute differences. Calculate the average value Vc_mean and standard deviation Vc_stan of multiple absolute differences, and set the detection voltage fluctuation threshold to Vc_mean-n*Vc_stan, where n is 2 or 3.

9. The method according to claim 7, characterized in that, The heating voltage fluctuation threshold is obtained through the following steps: The heating electrode continuously performs power-on heating and power-off cooling operations. The first heating voltage when the heating electrode is powered on and the second heating voltage when it is powered off are recorded multiple times at different temperatures. The absolute difference between the first heating voltage and the second heating voltage recorded each time is calculated to obtain multiple absolute differences. Calculate the average of multiple absolute differences, Vh_mean, and the standard deviation, Vh_stan. Set the heating voltage fluctuation threshold to Vh_mean - n * Vh_stan, where n is 2 or 3.

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