A method of detecting a thermal overload protector
By sampling and testing the thermal bending deflection and energizing time of bimetallic strip thermal overload protectors, the process capability index is determined, which solves the problems of high cost and parameter mismatch in existing testing methods and achieves efficient and accurate quality control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DELIXI ELECTRIC
- Filing Date
- 2025-12-31
- Publication Date
- 2026-07-21
AI Technical Summary
Existing testing methods for thermal overload protectors suffer from high full-inspection costs, difficulty in process control, and ineffective quality control due to mismatched distribution of existing testing parameters.
By employing a sampling inspection method, the process capability index is determined by measuring the correlation between the thermal bending deflection of the bimetallic strip and the energizing time, replacing the traditional current multiple and action time parameters, thus achieving quality control.
This reduces the cost of full inspection, improves the effectiveness and accuracy of quality control, and ensures the stability and reliability of product quality.
Smart Images
Figure CN121702578B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of thermal overload technology, and in particular to a detection method for a thermal overload protector. Background Technology
[0002] Thermal overload protectors are devices that prevent electrical equipment from being damaged due to overload or overheating. They are widely used in motors, home appliances, and other fields. They can cut off power when the equipment temperature rises above a threshold and can be manually or automatically reset after the fault is cleared. Among them, bimetallic strip protectors use overload current to heat up the resistive element, causing the bimetallic strip to bend and push the trip.
[0003] Product standards require that the overload tripping current be within the range of overload current multiples between the inability to operate and the necessity to operate. The theoretical tripping current is the minimum current that operates within 2 hours. However, this parameter is difficult to obtain and is uneconomical, so it cannot be used for process control.
[0004] Existing process control methods have obvious shortcomings: the two-step detection and verification method requires the management of multiple parameters, making process control difficult and only allowing for sampling judgment; full inspection would significantly increase the cost of quality control. The fixed current multiple energization detection method uses action time as a single parameter, but this parameter has a skewed distribution, which is not compatible with process capability control measures based on normal distribution, making it difficult to achieve effective quality control. Summary of the Invention
[0005] This application provides a testing method for thermal overload protectors, which avoids the high cost of full inspection and provides a technical solution for effective quality control.
[0006] In a first aspect, this application provides a method for detecting a thermal overload protector, the thermal overload protector comprising a bimetallic strip; the method includes: The thermal overload protector test set is sampled to obtain multiple thermal overload protector samples. Each thermal overload protector sample is tested according to the preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample. Based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the tripping thermal bending deflection corresponding to each thermal overload protector sample is determined. Based on the first thermal bending deflection corresponding to the lower limit current of the operating range, the second thermal bending deflection corresponding to the upper limit current of the operating range, and the tripping thermal bending deflection corresponding to multiple thermal overload protector samples, the process capability index corresponding to the thermal overload protector sample is determined. The process capability of the thermal overload protector is determined based on the process capability index corresponding to the thermal overload protector sample.
[0007] In an optional implementation, before determining the process capability index corresponding to the thermal overload protector sample based on a predetermined first thermal bending deflection, a second thermal bending deflection, and the tripping thermal bending deflection corresponding to the plurality of thermal overload protector samples, the method further includes: The thermal overload protector test set is determined based on the thermal overload protector test set; The thermal overload protector test set was sampled to obtain multiple test devices; A lower limit current and an upper limit current of the operating range are respectively applied to each of the test devices. Within a preset time period, the thermal bending deflection data of the bimetallic sheet are collected by a displacement sensor to obtain the first thermal bending deflection corresponding to the lower limit current of the operating range and the second thermal bending deflection corresponding to the upper limit current of the operating range for each of the test devices. The first thermal bending deflection is determined based on the average value of multiple first thermal bending deflections corresponding to the lower limit current of the operating range of the multiple test devices, and the second thermal bending deflection is determined based on the average value of multiple second thermal bending deflections corresponding to the upper limit current of the operating range of the multiple test devices.
[0008] In one optional implementation, the preset stepped current test parameters include a preheating current and a multi-level gradient current that increases sequentially, and the preheating current and each level of the gradient current correspond to a preset energizing time. The step of testing each thermal overload protector sample according to preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample includes: For each thermal overload protector sample, the preheating current is first applied and the corresponding preset energizing time is maintained. Then, the gradient current of each level is applied sequentially and the corresponding preset energizing time is maintained respectively until the sample triggers the tripping action. The cumulative energization time when the sample triggers the tripping action is recorded, which is the test tripping time corresponding to the sample.
[0009] In one optional implementation, the multi-level gradient current is a sequence of multi-level gradient currents that increases with a preset step value, and the range of the multi-level gradient current includes a current from the lower limit of the operating range to a current not less than 1.1 times the second thermal bending deflection.
[0010] In an optional implementation, before determining the tripping thermal bending deflection corresponding to each thermal overload protector sample based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the method further includes: The multiple test devices are energized according to the preheating current and the sequentially increasing multi-level gradient current, and the corresponding thermal bending deflection is obtained by the displacement sensor at a preset time interval. Based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the correspondence between the thermal bending deflection and the energizing time is determined.
[0011] In one optional implementation, determining the correspondence between the thermal bending deflection and the energizing time based on the acquired plurality of thermal bending deflections and the energizing time corresponding to each thermal bending deflection includes: Based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the initial correspondence between the thermal bending deflection and the energizing time is determined; The data of the preheating current stage of the initial correspondence is fitted using a first preset method, and the data of the multi-level gradient current stage of the initial correspondence between thermal bending deflection and energizing time is fitted using a second preset method to obtain the correspondence between thermal bending deflection and energizing time.
[0012] In one optional implementation, the tripping thermal bending deflection corresponding to each thermal overload protector sample is determined based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, including: In the correspondence between thermal bending deflection and energizing time, the thermal bending deflection value corresponding to the test tripping time for each thermal overload protector sample is queried. The thermal bending deflection value is used as the tripping thermal bending deflection corresponding to the thermal overload protector sample.
[0013] In one optional implementation, determining the process capability index corresponding to the thermal overload protector sample based on the first thermal bending deflection, the second thermal bending deflection, and the tripping thermal bending deflection corresponding to each thermal overload protector sample includes: The average value of the tripping thermal bending deflection of each thermal overload protector sample is determined based on the tripping thermal bending deflection of each sample. The standard deviation of the thermal overload protector sample is determined based on the average tripping thermal bending deflection of the thermal overload protector sample and the tripping thermal bending deflection corresponding to each thermal overload protector sample. Based on the first thermal bending deflection, the second thermal bending deflection, the mean value of the tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, the process capability index corresponding to the thermal overload protector sample is determined.
[0014] In an optional implementation, based on the first thermal bending deflection, the second thermal bending deflection, the mean tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, the process capability index corresponding to the thermal overload protector sample can be characterized as follows: ; in, This represents the process capability index corresponding to the plurality of thermal overload protector samples, the Indicates the second thermal bending deflection. Indicates the first thermal bending deflection. This represents the standard deviation of the thermal overload protector sample. This represents the minimum value.
[0015] In one optional implementation, determining the process capability of the thermal overload protector based on the process capability index corresponding to the thermal overload protector sample includes: Set multiple sets of process capability index thresholds and corresponding process capability levels; If the process capability index corresponding to the thermal overload protector sample meets the target process capability index threshold, the process capability of the thermal overload protector is determined according to the target process capability level corresponding to the target process capability index threshold.
[0016] This application provides a method for testing a thermal overload protector, the thermal overload protector including a bimetallic strip; the method includes: sampling a set of thermal overload protectors to be tested to obtain multiple thermal overload protector samples; testing each thermal overload protector sample according to preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample; determining the tripping thermal bending deflection corresponding to each thermal overload protector sample based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample; determining the process capability index corresponding to each thermal overload protector sample based on a preset first thermal bending deflection, a second thermal bending deflection, and the tripping thermal bending deflections corresponding to the multiple thermal overload protector samples; and determining the process capability of the thermal overload protector based on the process capability index corresponding to the thermal overload protector sample.
[0017] Based on the above description, existing two-step detection and verification methods require the control of multiple parameters, resulting in high process control difficulty and high full inspection costs. This method, however, avoids the high costs associated with full inspection through sampling inspection. Furthermore, it uses the bimetallic strip's thermal bending deflection as a control parameter, replacing the theoretical tripping current and operating time. This fundamentally anchors the overload tripping trigger condition, eliminating the problems of uneconomical parameter acquisition and mismatched data distribution. By setting the first and second thermal bending deflections corresponding to the upper and lower limits of the operating range current as specification boundaries, and by inferring the tripping thermal bending deflection from the experimental tripping time, the judgment standard becomes more stable and repeatable, avoiding misjudgments / missed judgments caused by the coupling of multiple parameters in the traditional two-step method.
[0018] Existing fixed current multiple energization detection methods use skewed operating time as a single parameter, which is incompatible with process capability control measures based on normal distribution, making it difficult to effectively manage quality. This new method, however, comprehensively considers two key factors: thermal bending deflection and energization time. By determining the first thermal bending deflection, the second thermal bending deflection, and the tripping thermal bending deflection, and further calculating the process capability index, it can more accurately reflect the performance of thermal overload protectors under different current conditions. This overcomes the limitations of a single parameter, makes process capability control measures more aligned with actual conditions, and thus improves the effectiveness of quality control.
[0019] Furthermore, the method provided in this application obtains samples through sampling, first determining the thermal bending deflection of the samples under the lower and upper limits of the operating range current, then obtaining the test tripping time through stepped current parameter testing, thereby determining the tripping thermal bending deflection, and finally calculating the process capability index based on these data to determine the process capability of each thermal overload protector in the test set. Therefore, the embodiments of this application adopt a multi-step, multi-parameter analysis approach, which can more accurately evaluate the process capability of thermal overload protectors, helping to promptly identify potential quality problems and ensure the stability and reliability of product quality. Attached Figure Description
[0020] Figure 1 A flowchart illustrating the steps of a detection method for a thermal overload protector provided in this application embodiment; Figure 2 A schematic diagram of a thermal bending deflection test provided in an embodiment of this application; Figure 3 A thermal bending deflection test curve of 1.05Ir provided for embodiments of this application; Figure 4 A 1.2Ir thermal bending deflection test curve is provided for an embodiment of this application; Figure 5 A step current thermal bending deflection test curve is provided for an embodiment of this application; Figure 6A schematic diagram of the step current thermal bending deflection test provided by the embodiment of the present application and the fitted curve; Figure 7 A schematic diagram of the fitted curve of the step current thermal bending deflection provided by the embodiment of the present application; Figure 8 A schematic diagram of the structure of the bimetal driving mechanism provided by the embodiment of the present application; Figure 9 A schematic diagram of the structure for measuring the bending deflection of the bimetal provided by the embodiment of the present application. Detailed implementation manners
[0021] A thermal overload protector is a protection device used to prevent electrical equipment from being damaged due to overload and overheat. It is widely used in fields such as motors, transformers, household appliances, and industrial electrical equipment, and is used to automatically cut off the circuit when the temperature rise of the equipment exceeds the safety threshold. After the fault is eliminated, it can be reset manually or automatically.
[0022] For a bimetal thermal overload protector, when the circuit is overloaded, the resistance element generates heat, causing the bimetal to bend greatly due to high temperature, thereby pushing the mechanism to trip.
[0023] Relevant product standards usually require the overload current multiples that cannot cause action and the overload current multiples that must cause action. Obviously, for the product to be qualified, the overload tripping current needs to be greater than the overload current multiple that cannot cause action and less than or equal to the overload current multiple that must cause action. In theory, the overload tripping current is the minimum current that causes the product to act within 2 hours. In the actual production control process, it is very difficult and uneconomical to obtain this parameter, so it cannot be used as a technical parameter for process control.
[0024] Currently, the more widely used process control methods include: implementing two-step detection and verification according to the standard regulations: The first step is to apply the overload current multiple that cannot cause action for 2 hours; the second step is that if the first step is qualified, then immediately apply the overload current multiple that must cause action continuously in the hot state. If the product acts within 2 hours, it is determined that the product is qualified. However, this method involves 4 technical parameters, such as the overload current multiple that cannot cause action, the misaction time under the overload current multiple that cannot cause action, the overload current multiple that must cause action, and the action time under the overload current multiple that must cause action. The process control is difficult, and usually only the sampling products can be judged as qualified or not. Therefore, in this method, if it is necessary to ensure the product qualification rate, the best approach is to conduct full inspection. However, this will undoubtedly increase a very large amount of product quality control costs.
[0025] Continuously power on the product at a fixed current multiple higher than the standard requirement until the tripping action occurs. If the product operates within the specified time range, it is qualified. Obviously, the technical parameter for process control is the operating time. Although this method uses a single technical parameter as the judgment basis, in mass-produced products, when continuously powering on each product at a fixed current multiple higher than the standard requirement, the data values of their operating times often show a skewed distribution pattern, that is, they tend to the smaller value of the allowable time range, the tail drags towards the larger value, and the average value is greater than the median, etc. However, currently, the process quality control means of most manufacturing enterprises are based on technical parameters that conform to the normal distribution law to formulate process capability control measures. Therefore, there are still relatively large defects in using the operating time as the process control technical parameter.
[0026] Based on this, the technical concept of the embodiments of the present application is: taking the thermal bending deflection of the bimetallic strip as a quantitative index, replacing the current multiple and operating time parameters that are difficult to control in traditional detection, and realizing the quality determination of batch products of thermal overload protectors through sampling inspection and process capability index analysis.
[0027] Next, the technical solutions shown in the present application will be described in detail through specific embodiments. It should be noted that the following several embodiments can exist independently or be combined with each other. For the same or similar content, it will not be repeated in different embodiments.
[0028] Refer to Figure 1 , in the first aspect, the embodiments of the present application provide a thermal overload protector including a bimetallic strip; the method includes: S100, sample the set of thermal overload protectors to be inspected, obtain multiple thermal overload protector samples, and test each of the thermal overload protector samples according to a preset stepped current parameter to obtain the test tripping time corresponding to each of the thermal overload protector samples; It should be understood that the set of thermal overload protectors to be inspected refers to a set of thermal overload protector products waiting for quality inspection and performance evaluation. These products may come from the same production batch, the same production line, or have similar production processes and raw materials. The purpose of sampling is to select a part of representative thermal overload protectors from the set to be inspected as samples, and through the detection and analysis of these samples, to infer the quality and performance status of the entire set to be inspected, avoiding the high cost and low efficiency problems brought by comprehensively detecting all products.
[0029] The method of sampling the set of thermal overload protectors to be inspected may include: Number all the thermal overload protectors in the set to be inspected, and then use a random number table or a random number generator to randomly select a certain number of products as samples. This method is simple and easy to implement, and the probability of each product being selected is equal, which can ensure the randomness and representativeness of the samples.
[0030] If there are significant hierarchical differences among the thermal overload protectors in the inspection set, such as products of different specifications, from different production periods, or produced by different production teams, the inspection set can be divided into several tiers, and then random sampling can be performed within each tier. This ensures that products from each tier are represented in the samples, improving the representativeness of the samples.
[0031] Samples are drawn from the test set at regular intervals. For example, the test set is arranged in sequence, and then one product is drawn as a sample every certain number of products. This method is suitable when the products in the test set are arranged in an orderly manner and there is no obvious periodic change.
[0032] It should be understood that determining the sampling size requires comprehensive consideration of multiple factors, including the size of the sample set, the product's quality stability requirements, testing costs, and time constraints. Generally, a larger sampling size results in a more representative sample, but also increases testing costs. In this embodiment, a suitable sampling size can be determined based on relevant statistical standards or empirical formulas, and this embodiment does not impose any special limitations on this.
[0033] In this embodiment, the stepped current in the preset stepped current parameters needs to be divided based on the operating current range of the thermal overload protector, and must meet two core requirements: The current gradient should be reasonable, and the step current difference should be set according to the product sensitivity to ensure that the entire operating range is covered, while avoiding data loss due to excessive gradient.
[0034] The current levels should be set in an orderly manner, with the currents set progressively from smallest to largest, to ensure that the test process is consistent with the actual increasing overload current conditions.
[0035] Then, for a single sample, a preheating current is applied first, followed by the first step current in the step current system, while simultaneously activating the time recording device; the contact status of the sample is monitored in real time, and when the contact breaks, i.e., a tripping action occurs, the timing is immediately stopped, and the tripping time under that current level is recorded.
[0036] Optionally, if the current applied at this level fails to trip after 2 hours, the tripping time is recorded as >2 hours, and the system switches to the next current level.
[0037] Repeat the above operation step by step, that is, after completing each level of current test, apply the next level of higher step current, until the sample trips at a certain level of current, or completes the test of all levels of current.
[0038] Perform the same stepped current test procedure on all sampled samples, and record the test tripping time of each sample at the corresponding current level.
[0039] S200, based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, determine the tripping thermal bending deflection corresponding to each thermal overload protector sample.
[0040] It should be understood that the thermal bending deflection of the bimetallic sheet increases monotonically with the extension of the energizing time (under constant current conditions), and the relationship between deflection and time has stable functional characteristics (such as linear relationship and exponential relationship) under the same current level.
[0041] Optionally, a standard sample of the same batch and specification as the sample to be tested is selected. A certain level of stepped current is applied to the standard sample, and the bimetallic sheet thermal bending deflection at different energizing time points is collected in real time (a high-precision deflection measuring instrument, such as a laser displacement sensor, is required). The collected time-deflection data is fitted to obtain the deflection-time function relationship under that current level; the above operation is repeated to complete the calibration of the function relationship under all stepped current levels, forming the deflection-time correspondence across the entire current range.
[0042] In this embodiment of the application, the tripping hot bending deflection is calculated by reverse-engineering the test data for each sampled specimen using the following steps: Extract the corresponding test tripping time of the sample; retrieve the deflection-time function relationship under this current level from the database of the correspondence between thermal bending deflection and energizing time; substitute the test tripping time into the function to calculate the corresponding tripping thermal bending deflection, which is the tripping thermal bending deflection of the sample. The tripping thermal bending deflection of the sample corresponds to the critical deflection state of the bimetallic strip of the sample that drives the tripping mechanism to act.
[0043] It is worth noting that if a sample does not trip after being energized for 2 hours at a certain current level, the deflection value corresponding to that current level after 2 hours should be retrieved and recorded as the maximum non-tripping deflection. If the tripping deflection of the sample is higher than this value, further analysis should be conducted in conjunction with test data from a higher current level.
[0044] S300, based on the first thermal bending deflection corresponding to the lower limit current of the operating range, the second thermal bending deflection corresponding to the upper limit current of the operating range, and the tripping thermal bending deflection corresponding to the multiple thermal overload protector samples, determine the process capability index corresponding to the thermal overload protector sample.
[0045] In this embodiment of the application, the sample tripping deflection data is correlated with the qualified deflection range by the process capability index, thereby determining the degree to which the production process meets the specification requirements.
[0046] In this embodiment, thermal bending deflection, a physical parameter, is used as the statistical object, and the data distribution is closer to a normal distribution, which solves the problem of index calculation distortion caused by the skewed distribution of action time in traditional methods. By replacing the qualitative judgment of qualified / unqualified with a quantified process capability index, the stability of the production process can be reflected intuitively, providing data support for process optimization.
[0047] S400, determine the process capability of the thermal overload protector based on the process capability index corresponding to the thermal overload protector sample.
[0048] It should be understood that when determining the process capability of a thermal overload protector, since the process capability index is an indicator calculated based on sample data to reflect the overall production process capability status, the process capability index calculated based on the sample cannot be directly applied to each individual in the test set. However, the overall process status reflected by the sample process capability index can be used.
[0049] In this embodiment of the application, the process capability of the thermal overload protector may include: Sufficient process capability indicates that the production process involved in calculating the process capability index based on the samples is relatively stable, and key product characteristics (such as thermal bending deflection) can be well controlled within the specification range. In this case, it can be preliminarily inferred that the process capability of most thermal overload protectors in the test set is also relatively good, but it still needs to be verified through sampling inspection.
[0050] A qualified process capability means that there are some fluctuations in the production process, and the key characteristics of the product may occasionally exceed the specification limits. For the test set, it is necessary to increase the sampling size and more rigorously test the key characteristics of each product in order to accurately assess its process capability.
[0051] Insufficient process capability indicates an unstable production process and a high risk of product key characteristics exceeding specification limits. In this case, the inspection of the sampled products needs to be more comprehensive and detailed, which may require testing every single product or significantly increasing the sampling ratio. At the same time, an immediate investigation and improvement of the production process is necessary.
[0052] Based on the above description, it should be understood that existing two-step detection and verification methods require the control of multiple parameters, resulting in high process control difficulty and high full inspection costs. This method, however, avoids the high costs associated with full inspection through sampling inspection. Furthermore, it uses the bimetallic strip thermal bending deflection as a control parameter, replacing the theoretical tripping current and operating time. This fundamentally anchors the overload tripping trigger condition, eliminating the problems of uneconomical parameter acquisition and mismatched data distribution. By setting the first and second thermal bending deflections corresponding to the upper and lower limits of the operating range current as specification boundaries, and by inferring the tripping thermal bending deflection from the experimental tripping time, the judgment standard becomes more stable and repeatable, avoiding misjudgments / missed judgments caused by the coupling of multiple parameters in the traditional two-step method.
[0053] It should be further understood that the existing fixed current multiple energization detection method uses the skewed operating time as a single parameter, which is incompatible with process capability control measures based on normal distribution, making it difficult to effectively control quality. This method, however, comprehensively considers two key factors: thermal bending deflection and energization time. By determining the first thermal bending deflection, the second thermal bending deflection, and the tripping thermal bending deflection, and further calculating the process capability index, it can more accurately reflect the performance of the thermal overload protector under different current conditions. This overcomes the limitations of a single parameter, makes process capability control measures more aligned with actual conditions, and thus improves the effectiveness of quality control.
[0054] Furthermore, the method provided in this application obtains samples through sampling, first determining the thermal bending deflection of the samples under the lower and upper limits of the operating range current, then obtaining the test tripping time through stepped current parameter testing, thereby determining the tripping thermal bending deflection, and finally calculating the process capability index based on these data to determine the process capability of each thermal overload protector in the test set. Therefore, the embodiments of this application adopt a multi-step, multi-parameter analysis approach, which can more accurately evaluate the process capability of thermal overload protectors, helping to promptly identify potential quality problems and ensure the stability and reliability of product quality.
[0055] In an optional implementation, before determining the process capability index corresponding to the thermal overload protector sample based on a predetermined first thermal bending deflection, a second thermal bending deflection, and the tripping thermal bending deflection corresponding to the plurality of thermal overload protector samples, the method further includes: First, determine the thermal overload protector test set based on the thermal overload protector test set.
[0056] In this embodiment of the application, a test set of thermal overload protectors, which is from the same batch or a different batch and manufactured using the same process, is determined based on the thermal overload protector test set.
[0057] Second, the thermal overload protector test set is sampled to obtain multiple test devices.
[0058] In this embodiment of the application, the test set is randomly sampled to obtain a test device. The test device is typically not a complete product; it only needs to be able to collect stable deflection values corresponding to the second and first deflections under the condition that the upper and lower limit currents of the operating range are energized for a preset duration.
[0059] Third, a lower limit current and an upper limit current of the operating range are respectively applied to each of the test devices, and the thermal bending deflection data of the bimetallic sheet is collected by a displacement sensor within a preset time period to obtain the first thermal bending deflection corresponding to the lower limit current of the operating range and the second thermal bending deflection corresponding to the upper limit current of the operating range for each of the test devices.
[0060] In the embodiments of this application, two types of characteristic currents are applied to each test device, and the tests of the two types of currents must be performed independently; Operating range lower limit current: The overload current multiple that cannot be operated according to the product standard, and the power must be continuously supplied for the preset time.
[0061] Upper limit of operating range current: The overload current multiple that must be activated according to the product standard, and the power must be continuously supplied for the preset time.
[0062] Optionally, the thermal bending deflection data can be acquired using a high-precision displacement sensor, such as a laser displacement sensor, which is placed close to the free end of the bimetallic strip for non-contact measurement: when the lower limit current is applied, the stable deflection value at the end of the preset time period is collected and recorded as the single first thermal bending deflection of the test device; when the upper limit current is applied, the stable deflection value at the end of the preset time period is collected and recorded as the single second thermal bending deflection of the test device.
[0063] Fourth, the first thermal bending deflection is determined based on the average value of multiple thermal bending deflections corresponding to the lower limit current of the operating range of multiple test devices, and the second thermal bending deflection is determined based on the average value of multiple thermal bending deflections corresponding to the upper limit current of the operating range of multiple thermal overload protector samples.
[0064] As a concrete example, the first thermal bending deflection LSL, the second thermal bending deflection USL, and the nominal value of thermal bending deflection are determined. It can include: Prepare samples and determine the stable thermal bending deflection of the bimetallic strip at the lower and upper limits of its operating range according to relevant standards. For example, the stable thermal bending deflection LSL at the lower limit of the operating range (1.05Ir) and the stable thermal bending deflection USL at the upper limit of the operating range (1.2Ir), nominal values. .
[0065] The specific testing principle is as follows: Figure 2 As shown, the bimetallic strip exhibits thermal bending deflection y when the resistive element is energized and heats up. τ The bending deflection tester will record data at every moment in real time according to a predetermined program, and its test probe is a laser displacement sensor with high measurement accuracy.
[0066] Taking a certain model of 30A thermal relay as an example, the resistive element is energized with currents of 31.5A and 36A for 1770s respectively, and the relevant test data can be obtained as follows: Figure 3 , Figure 4 The blue curve is shown. To eliminate the influence of instability factors on the test data, the following formula can be used with fine-tuning of the stable thermal bending deflection. A smooth red curve was obtained by fitting the curve with the time constant T, from which we can obtain LSL = 0.9 mm and USL = 1.18 mm. =SL=(LSL+USL) / 2=1.04mm.
[0067] .
[0068] In one optional implementation, the preset stepped current test parameters include a preheating current and a multi-level gradient current that increases sequentially, and the preheating current and each level of the gradient current correspond to a preset energizing time.
[0069] In the embodiments of this application, the preheating current is the rated operating current of the thermal overload protector or a value slightly lower than the lower limit current of the operating range.
[0070] The multi-level gradient current operates with a starting value of less than or equal to the lower limit current and a stopping value of greater than or equal to 1.1 times the second thermal bending deflection. For example, the stopping value could be 1.1 times the second thermal bending deflection, 1.2 times the second thermal bending deflection, or 1.3 times the second thermal bending deflection. The multi-level gradient current is divided into several current levels according to the principle of equal gradient, such as a gradient value of 0.1 times the rated current. The preset energizing time for each gradient current level needs to be set according to the product's sensitivity (usually 2-15 minutes), and the difference between adjacent current levels must be consistent.
[0071] Optionally, the step of testing each of the thermal overload protector samples according to preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample includes: First, for each thermal overload protector sample, the preheating current is applied and maintained for the corresponding preset energizing time. Then, the gradient current of each level is applied sequentially and maintained for the corresponding preset energizing time, until the sample triggers the tripping action.
[0072] In this embodiment of the application, a preheating current is first applied to the sample, and a timing device is started at the same time, and the power is continuously supplied until the preset preheating time is reached.
[0073] After preheating, continuously switch to the first-level gradient current and keep energized for the preset time. If the sample does not trip under this current level, immediately switch to the next higher gradient current and repeat the energizing operation. Monitor the sample contact status in real time, and stop timing immediately when the sample triggers a tripping action.
[0074] It is worth noting that if a sample fails to trip after completing the energization of all gradient current levels, the tripping time of the sample is determined to be outside the test range, and it should be marked as an invalid sample and excluded from subsequent data analysis.
[0075] Then, the cumulative power-on time when the sample triggers the tripping action is recorded, which is the test tripping time corresponding to the sample.
[0076] In this embodiment, the normal operating temperature rise of the protector is simulated by the preheating current stage, and then the overload state is gradually approximated by the gradient current, thus reproducing the entire process of normal operation, overload, and tripping in actual application. This makes the measured tripping time more consistent with the actual working characteristics of the product and greatly reduces test errors.
[0077] Optionally, the multi-level gradient current is a sequence of multi-level gradient currents that increases according to a preset step value, and the range of the multi-level gradient current includes the current from the lower limit of the operating range to the current corresponding to not less than 1.1 times the second thermal bending deflection.
[0078] In the embodiments of this application, the initial value of the multi-level gradient current is less than or equal to the lower limit current of the operating range. That is, the initial value of the multi-level gradient current can be equal to or less than the lower limit current of the operating range, so as to ensure that the gradient current sequence starts to cover the critical starting point of the qualified interval.
[0079] The termination value of the multi-stage gradient current is no less than the current corresponding to 1.1 times the second thermal bending deflection. In other words, the termination value of the multi-stage gradient current can be equal to or greater than the current corresponding to 1.1 times the second thermal bending deflection. The second thermal bending deflection corresponds to the overload current multiple that must trigger the trip. The termination value of the multi-stage gradient current is designed to ensure that the gradient current sequence covers overload conditions exceeding the acceptable range, preventing tripping actions outside the gradient current sequence due to individual sample differences (such as excessive deflection), and ensuring that tripping actions of all sampled samples can be effectively captured.
[0080] In this embodiment, the step value is the difference between two adjacent gradient current levels, and needs to be set according to the product sensitivity and test accuracy requirements. The starting value of the multi-level gradient current is the first level, and the step value is increased step by step according to the preset step value until the termination value of the multi-level gradient current is reached, forming a complete gradient current sequence.
[0081] The gradient current should be applied sequentially after the preheating current stage is completed, and the energizing time of each current level should be kept consistent.
[0082] Based on the above description, the embodiments of this application extend the termination value of the multi-level gradient current to the current corresponding to 1.1 times the second thermal bending deflection, or greater than the current corresponding to 1.1 times the second thermal bending deflection, to cover the critical overload conditions outside the qualified range. This ensures that even samples with large deflection and low tripping sensitivity can still trip within the gradient current sequence, guaranteeing that each sample can obtain an effective test tripping time and avoiding the impact of missing data on subsequent process capability assessment.
[0083] In an optional implementation, before determining the tripping thermal bending deflection corresponding to each thermal overload protector sample based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the method further includes: First, the multiple test devices are energized according to the preheating current and the sequentially increasing multi-level gradient current, and the corresponding thermal bending deflection is obtained by the displacement sensor at preset time intervals.
[0084] In this embodiment of the application, multiple test devices can be preheated with a current and kept energized for a preset time according to the same test parameters as the sampled sample. Then, multiple gradient currents are applied in sequence, covering the current corresponding to 1.1 times the second thermal bending deflection USL. Each gradient current is kept for a corresponding preset energization time.
[0085] Afterwards, a non-contact displacement sensor can be used to closely attach to the free end of the bimetallic strip to collect deflection data in real time; data is recorded at preset time intervals (e.g., once every 5 minutes), and the data collection nodes need to cover the entire preheating stage and the entire energizing stage of each gradient current. When a test device triggers a trip, the deflection value at the moment of trip and the cumulative energization time need to be recorded. Repeat the above operation for all test devices to obtain the deflection value at the moment of trip and the cumulative energization time for each test device.
[0086] Then, based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the correspondence between the thermal bending deflection and the energizing time is determined.
[0087] In this embodiment, for each gradient current level, a function is fitted with energizing time as the independent variable and thermal bending deflection as the dependent variable. Then, the fitted functions for all gradient current levels are integrated to form a database of thermal bending deflection-energizing time correspondence across the entire current range, clarifying the quantitative correlation rules between time and deflection under different current intensities.
[0088] Based on the above description, the test devices were selected from the test set, eliminating individual differences caused by variations in the bimetallic strip manufacturing process. The fitted correspondence perfectly matches the product characteristics of the test set. Compared with general models (such as models based on theoretical formulas or other batch data), its conversion error is significantly reduced, ensuring the accuracy of subsequent tripping deflection calculations. The correspondence between thermal bending deflection and energizing time covers the entire range from the lower limit of the operating range current to the current corresponding to 1.1 times the second thermal bending deflection USL. This not only allows for the calculation of deflection when tripping occurs but also the analysis of the deflection variation trend of the bimetallic strip under different overload currents.
[0089] Optionally, determining the correspondence between the thermal bending deflection and the energizing time based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection includes: First, based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the initial correspondence between the thermal bending deflection and the energizing time is determined.
[0090] In this embodiment, all data collected by all test devices during the preheating current stage and the multi-level gradient current stage are integrated and organized into a structured dataset according to the dimensions of current stage, energizing time, and thermal bending deflection. A scatter plot of the data for all stages is obtained with energizing time as the horizontal axis and thermal bending deflection as the vertical axis, forming an initial correspondence between thermal bending deflection and energizing time, providing a data foundation for staged fitting.
[0091] Then, the data of the preheating current stage of the initial correspondence is fitted using a first preset method, and the data of the multi-level gradient current stage of the initial correspondence between thermal bending deflection and energizing time is fitted using a second preset method to obtain the correspondence between thermal bending deflection and energizing time.
[0092] In the embodiments of this application, the preheating current is usually the rated operating current or slightly lower than the lower limit of the operating range current. The temperature rise process of the bimetallic strip is mainly based on the establishment of thermal equilibrium. The deflection increases at a rate that is fast and slows down over time, eventually stabilizing.
[0093] In one example, the stepped current test parameters are as follows: preheating current 1.01Ir for 30 min, 1.03Ir for 5 min, 1.05Ir for 5 min, 1.07Ir for 5 min, 1.09Ir for 5 min, 1.11Ir for 5 min, 1.13Ir for 5 min, 1.15Ir for 5 min, 1.17Ir for 5 min, 1.19Ir for 5 min, 1.21Ir for 5 min, 1.23Ir for 5 min, 1.25Ir for 5 min, 1.27Ir for 5 min, 1.29Ir for 5 min, and 1.31Ir for 5 min. It is recommended that the number of stepped current tests be at least 1.1 USL.
[0094] The samples were continuously tested according to the stepped current test parameters, and the thermal bending deflection-time curve was plotted based on the test data, such as... Figure 5 As shown; Affected by environmental fluctuations and many other unstable factors Figure 6 Curves inevitably contain burrs, therefore they need to be smoothed, such as... Figure 6 , Figure 7As shown. Based on this, the corresponding y can be quickly calculated using a functional relationship at each moment of the stepped current test. τD .
[0095] The initial relationship between thermal bending deflection and energizing time was fitted using a standard function formula. During the preheating current phase of 1.01Ir for 30 minutes, the relationship can be fitted using the standard function formula, as shown below:
[0096] The multi-stage gradient current represents an increasing overload current. The power density borne by the bimetallic strip gradually increases, the temperature rise rate accelerates, and the deflection increases approximately linearly with time. A standard function formula can be used for fitting, as shown in the following equation:
[0097] In the formula: This represents the maximum effective deflection of the bimetallic strip during the (i-1)th step current test. is the time constant for the (i-1)th step current test of the bimetallic strip; The test time for the i-th step current; The steady-state thermal bending deflection of the bimetallic sheet under the i-th step current test. Let be the time constant for the i-th step current test of the bimetallic strip.
[0098] Based on the above description, this application embodiment uses phased differentiated fitting to ensure that the model at each stage highly matches the physical characteristics of the thermal deformation of the bimetallic sheet, significantly reducing the fitting residual. Compared with a single fitting method, this improves the overall accuracy and provides a precise basis for subsequent tripping deflection calculation. Furthermore, phased fitting can accurately describe the deflection stability characteristics under normal operating conditions (preheating stage) and precisely describe the deflection growth characteristics under overload conditions (gradient current stage), achieving quantitative analysis of deflection under all operating conditions: normal operation, overload, and critical tripping.
[0099] Optionally, based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the tripping thermal bending deflection corresponding to each thermal overload protector sample is determined, including: In the correspondence between thermal bending deflection and energizing time, the thermal bending deflection value corresponding to the test tripping time of each thermal overload protector sample is queried.
[0100] The thermal bending deflection value is used as the tripping thermal bending deflection corresponding to the thermal overload protector sample.
[0101] In this embodiment, based on the established correspondence between thermal bending deflection and energizing time, which can be a function expression or a data table, the test tripping time of each sample is substituted into the table to obtain the corresponding thermal bending deflection value. For example, if the correspondence is in the form of a data table, the thermal bending deflection value corresponding to the energizing time closest to the test tripping time can be found in the table; if it is a function expression, the test tripping time is directly substituted into the expression to calculate the thermal bending deflection value. The obtained thermal bending deflection value is used as the tripping thermal bending deflection of the corresponding thermal overload protector sample.
[0102] Based on the above description, the stability of the tripping thermal bending deflection during the production process of thermal overload protectors reflects the consistency of the production process and the consistency of product quality. By monitoring the tripping thermal bending deflection of each sample, potential problems in the production process can be identified in a timely manner, such as fluctuations in raw material quality or deviations in production process parameters. This allows for timely adjustments to the production process, ensuring stable product quality. For example, if a batch of samples is found to have generally excessively large or small tripping thermal bending deflections, it may indicate changes in raw material parameters such as the thickness and composition of the bimetallic strip, requiring inspection and adjustment of the raw materials.
[0103] In one optional implementation, determining the process capability index corresponding to the thermal overload protector sample based on the first thermal bending deflection corresponding to the lower limit current of the operating range, the second thermal bending deflection corresponding to the upper limit current of the operating range, and the tripping thermal bending deflection corresponding to each thermal overload protector sample includes: The average value of the tripping thermal bending deflection of each thermal overload protector sample is determined based on the tripping thermal bending deflection corresponding to each thermal overload protector sample.
[0104] The standard deviation of the thermal overload protector samples is determined based on the average tripping thermal bending deflection of the thermal overload protector samples and the tripping thermal bending deflection corresponding to each thermal overload protector sample.
[0105] Based on the first thermal bending deflection, the second thermal bending deflection, the mean value of the tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, the process capability index corresponding to the thermal overload protector sample is determined.
[0106] In the embodiments of this application, the tripping thermal bending deflection and test tripping time corresponding to each thermal overload protector sample are shown in Table 1.
[0107]
[0108] Mean deflection of the sample during thermal bending X, standard deviation σ, and process capability index CPK can be calculated using the following formulas:
[0109] In the formula: The deflection during thermal bending of each sample; This represents the sample size.
[0110]
[0111] The process capability index corresponding to the thermal overload protector sample can be characterized by the first thermal bending deflection, the second thermal bending deflection, the mean value of the tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, as follows: ; in, This represents the process capability index corresponding to the plurality of thermal overload protector samples, the Indicates the second thermal bending deflection. Indicates the first thermal bending deflection. This represents the standard deviation of the thermal overload protector sample. This represents the minimum value.
[0112] In one optional implementation, determining the process capability of the thermal overload protector based on the process capability index corresponding to the thermal overload protector sample includes: Set multiple sets of process capability index thresholds and corresponding process capability levels; If the process capability index corresponding to the thermal overload protector sample meets the target process capability index threshold, the process capability of the thermal overload protector is determined according to the target process capability level corresponding to the target process capability index threshold.
[0113] In the embodiments of this application, the process capability and corresponding processing method can be determined by the principles in Table 2.
[0114] For example, based on the result of CPK=1.047 in Table 1, it can be seen from Table 2 that the process capability is Grade B and needs to be improved to Grade A.
[0115] Table 2
[0116] In this embodiment of the application, by using the pre-set threshold and grade correspondence rules, the set to be inspected is divided into corresponding quality grades, and the judgment results are more instructive. This not only clarifies the batches that can be released directly, but also identifies the risk batches that need to be controlled, thus improving the scientific nature of quality decisions.
[0117] The above content provides a detailed description of the embodiments of this application. The feasibility of selecting hot bending deflection as a process capability control parameter in the embodiments of this application is explained below: For bimetallic strip protective electrical devices, when the circuit is energized, the bimetallic strip generates high temperature under the heating effect of the resistive element, causing it to bend and deflect. :
[0118] In the formula: This refers to the bending deflection of the bimetallic strip after heating. is the coefficient by which the specific bending of the bimetallic strip decreases due to factors such as thermal element winding, stacking, and high temperature; K is the specific bending of the bimetallic strip material. l This refers to the effective length of the bimetallic strip; For the temperature rise of the bimetallic strip; The thickness is the bimetallic strip thickness.
[0119] like Figure 8 As shown, after the bimetallic strip protector is assembled, two important parameters are generated: tripping stroke S and tripping force F.
[0120] For the product to trip under circuit overload, the thermal bending deflection of the bimetallic strip must exceed the tripping stroke S and overcome the resistance of the tripping force P. For example... Figure 9 As shown, the deflection corresponding to the bimetallic strip's thermal bending action that causes the product to just move is denoted as y. τD The bimetallic strip bending deflection corresponding to the tripping stroke S is denoted as y. S The bimetallic strip bending deflection required to generate the tripping force P is denoted as y. F ,So: ; in, ; ; In the formula: denoted as , where is the force-dissipating deflection of the bimetallic strip; F is the actuating force required from a certain bimetallic strip to disengage the actuating mechanism. For single-phase products, F = P; for three-phase products, F = P / 3 can be selected according to the product structure; E is the elastic modulus of the bimetallic strip material; b is the width of the bimetallic strip.
[0121] The required temperature rise for the product to trip is: ; In the formula: Temperature rise due to bimetallic strip operation; This is the multiple of the overload trip current. R is the overload protection setting current; R is the resistance of the bimetallic heating element. This is the heat dissipation coefficient corresponding to the overload current multiple.
[0122] Combining the above formula, ; Therefore, the deflection y during hot bending is... τD Proportional to the overload trip current multiple The square of y τD ∝ 2 .
[0123] Given that both the tripping stroke S and the tripping force F are technical parameters that conform to a normal distribution, the thermal bending deflection y, which is a linear combination of these parameters, is... τD These are also technical parameters that conform to the normal distribution law. Therefore, if y is adopted in production... τD This can be addressed as a technical parameter for process capability control.
[0124] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.
Claims
1. A method for detecting a thermal overload protector, characterized in that, The thermal overload protector includes a bimetallic strip; the method includes: The thermal overload protector test set is sampled to obtain multiple thermal overload protector samples, and each thermal overload protector sample is tested according to the preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample. Based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the tripping thermal bending deflection corresponding to each thermal overload protector sample is determined. Based on the first thermal bending deflection corresponding to the lower limit current of the operating range, the second thermal bending deflection corresponding to the upper limit current of the operating range, and the tripping thermal bending deflection corresponding to multiple thermal overload protector samples, the process capability index corresponding to the thermal overload protector sample is determined. The process capability of the thermal overload protector is determined based on the process capability index corresponding to the thermal overload protector sample. The process capability index corresponding to the thermal overload protector sample is determined based on the first thermal bending deflection corresponding to the lower limit current of the operating range, the second thermal bending deflection corresponding to the upper limit current of the operating range, and the tripping thermal bending deflection corresponding to multiple thermal overload protector samples, including: The average value of the tripping thermal bending deflection of each thermal overload protector sample is determined based on the tripping thermal bending deflection of each sample. The standard deviation of the thermal overload protector sample is determined based on the average tripping thermal bending deflection of the thermal overload protector sample and the tripping thermal bending deflection corresponding to each thermal overload protector sample. Based on the first thermal bending deflection, the second thermal bending deflection, the mean value of the tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, the process capability index corresponding to the thermal overload protector sample is determined. The process capability of the thermal overload protector is determined based on the process capability index corresponding to the thermal overload protector sample, including: Set multiple sets of process capability index thresholds and corresponding process capability levels; If the process capability index corresponding to the thermal overload protector sample meets the target process capability index threshold, the process capability of the thermal overload protector is determined according to the target process capability level corresponding to the target process capability index threshold.
2. The detection method according to claim 1, characterized in that: Before determining the process capability index corresponding to the thermal overload protector sample based on the predetermined first thermal bending deflection, second thermal bending deflection, and tripping thermal bending deflection corresponding to the plurality of thermal overload protector samples, the method further includes: The thermal overload protector test set is determined based on the thermal overload protector test set; The thermal overload protector test set was sampled to obtain multiple test devices; A lower limit current and an upper limit current of the operating range are respectively applied to each of the test devices. Within a preset time period, the thermal bending deflection data of the bimetallic sheet are collected by a displacement sensor to obtain the first thermal bending deflection corresponding to the lower limit current of the operating range and the second thermal bending deflection corresponding to the upper limit current of the operating range for each of the test devices. The first thermal bending deflection is determined based on the average value of multiple thermal bending deflections corresponding to the lower limit current of the operating range of the multiple test devices, and the second thermal bending deflection is determined based on the average value of multiple thermal bending deflections corresponding to the upper limit current of the operating range of the multiple test devices.
3. The method according to claim 2, characterized in that, The preset stepped current parameters include a preheating current and a multi-level gradient current that increases sequentially, and the preheating current and each level of the gradient current have a preset energizing time. The step of testing each thermal overload protector sample according to preset stepped current parameters to obtain the test tripping time corresponding to each thermal overload protector sample includes: For each thermal overload protector sample, the preheating current is first applied and the corresponding preset energizing time is maintained. Then, the gradient current of each level is applied sequentially and the corresponding preset energizing time is maintained respectively until the sample triggers the tripping action. The cumulative energization time when the sample triggers the tripping action is recorded, which is the test tripping time corresponding to the sample.
4. The method according to claim 3, characterized in that, The multi-level gradient current is a sequence of multi-level gradient currents that increases with a preset step value, and the range of the multi-level gradient current includes the current from the lower limit of the operating range to the current corresponding to a value not less than 1.1 times the second thermal bending deflection.
5. The method according to claim 3, characterized in that, Before determining the tripping thermal bending deflection corresponding to each thermal overload protector sample based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the method further includes: The multiple test devices are energized according to the preheating current and the sequentially increasing multi-level gradient current, and the corresponding thermal bending deflection is obtained by the displacement sensor at a preset time interval. Based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the correspondence between the thermal bending deflection and the energizing time is determined.
6. The method according to claim 5, characterized in that, The step of determining the correspondence between the thermal bending deflection and the energizing time based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection includes: Based on the acquired multiple thermal bending deflections and the energizing time corresponding to each thermal bending deflection, the initial correspondence between the thermal bending deflection and the energizing time is determined; The data of the preheating current stage of the initial correspondence is fitted using a first preset method, and the data of the multi-level gradient current stage of the initial correspondence between thermal bending deflection and energizing time is fitted using a second preset method to obtain the correspondence between thermal bending deflection and energizing time.
7. The method according to any one of claims 1-6, characterized in that, Based on the correspondence between thermal bending deflection and energizing time, and the test tripping time corresponding to each thermal overload protector sample, the tripping thermal bending deflection corresponding to each thermal overload protector sample is determined as follows: In the correspondence between thermal bending deflection and energizing time, the thermal bending deflection value corresponding to the test tripping time for each thermal overload protector sample is queried. The thermal bending deflection value is used as the tripping thermal bending deflection corresponding to the thermal overload protector sample.
8. The method according to claim 1, characterized in that, Based on the first thermal bending deflection, the second thermal bending deflection, the mean tripping thermal bending deflection of the thermal overload protector sample, and the standard deviation of the thermal overload protector sample, the process capability index corresponding to the thermal overload protector sample is determined as follows: ； in, This represents the process capability index corresponding to multiple thermal overload protector samples. Indicates the second thermal bending deflection. Indicates the first thermal bending deflection. This represents the standard deviation of the thermal overload protector sample. This represents the minimum value.