Detection method, detection device, detection system

Abstract

A detection method, a detection device, and a detection system are provided. The method for detecting a failure of a thermistor (TH) includes: a step (S101) of applying a load to the thermistor (TH) over time; steps (S102, S104) of measuring a physical property value of the thermistor (TH) at least during a first time and a second time during which the load is applied to the thermistor (TH); and a step (S108) of detecting a failure of the thermistor (TH) based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor (TH) measured at the second time.

Description

Technical Field

[0001] The present disclosure relates to a technology for detecting a failure of a thermistor. Background Art

[0002] Various techniques for detecting thermistor failures have been proposed. For example, Japanese Patent Application Laid-Open No. 2000-171309 describes a technique in which a first thermistor and a second thermistor having different temperature output characteristics are housed in a single package, the voltage values of the two thermistors are measured, and the possibility of a thermistor failure is determined using the measured voltage and a predetermined temperature map.

[0003] In the technology described in Patent Document 1, it is determined whether a temperature value TA corresponding to a voltage value VA of a first thermistor and a temperature value TB corresponding to a voltage value VB of a second thermistor are substantially equal. If the determination is negative, abnormality processing is performed. Summary of the Invention

[0004] Conventional technology, such as that described in Patent Document 1, uses the resistance value of a thermistor under a specific test environment to determine if it is good. Specifically, if the thermistor's resistance value is normal when current is applied, it is considered good. Therefore, when determining whether a thermistor, which is operating normally but has a momentary abnormal resistance value, is good, conventional tests sometimes fail to detect it as defective.

[0005] An object of the present disclosure is to provide a detection method that can easily detect a thermistor as being defective even if the thermistor has an abnormal resistance value instantaneously.

[0006] The method for detecting a failure of a thermistor disclosed herein includes: applying a load to the thermistor over time; measuring a physical property value of the thermistor at least at a first time and a second time during which the load is applied to the thermistor; and detecting a failure of the thermistor based on first data representing the physical property value of the thermistor measured at the first time and second data representing the physical property value of the thermistor measured at the second time.

[0007] A detection device for detecting a failure of a thermistor includes: a load unit that applies a load to the thermistor over time; a measurement unit that measures a physical property value of the thermistor at least during a first time and a second time during which the load is applied to the thermistor; and a detection unit that detects a failure of the thermistor based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time.

[0008] A detection system for detecting a failure of a thermistor includes: a loading unit that applies a load to the thermistor over time; a measuring unit that measures a physical property value of the thermistor at least during a first time and a second time during which the load is applied to the thermistor; and a detecting unit that detects a failure of the thermistor based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time.

[0009] The foregoing and other objects, features, aspects and advantages of the disclosure will become more apparent from the following detailed description of the disclosure when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a diagram schematically showing an example of the configuration of a detection device in the first embodiment.

[0011] Figure 2 It is a graph showing the transition of the resistance value of the thermistor.

[0012] Figure 3 It is a graph showing the transition of the resistance value of the thermistor.

[0013] Figure 4 It is a graph showing the transition of the resistance value of the thermistor.

[0014] Figure 5 This is a flowchart showing an example of processing executed when the detection device in the first embodiment detects a failure of the thermistor to be detected.

[0015] Figure 6 It is a graph showing changes in the resistance value and moving average value of the thermistor.

[0016] Figure 7 It is a graph showing changes in the resistance value and moving average value of the thermistor.

[0017] Figure 8 This is a diagram showing an example in which the amount of change in resistance value rapidly increases in a normally operating thermistor.

[0018] Figure 9 It shows Figure 8 A graph showing a moving average of the amount of change in resistance value per predetermined time.

[0019] Figure 10 This is a graph showing the amount of change in resistance value when the moving average value is not calculated.

[0020] Figure 11 This is a diagram schematically showing an example of the configuration of a detection device for detecting a failure of a thermistor according to the second embodiment.

[0021] Figure 12 It is a graph showing changes in the resistance value and moving average value of the thermistor.

[0022] Figure 13 It is a graph showing changes in the resistance value and moving average value of the thermistor. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, identical or corresponding parts are denoted by identical reference numerals, and their description will not be repeated.

[0024] [Implementation Method 1]

[0025] Figure 1 1 is a diagram schematically showing an example of the structure of the detection device 100 in the first embodiment. The detection device 100 is a device for detecting a defect in the thermistor TH to be detected. The defect in the thermistor TH refers to, for example, a poor contact in the internal circuit of the thermistor TH. Figure 1 , a state where the thermistor TH is connected to the detection device 100 is shown.

[0026] The thermistor TH is a negative temperature coefficient (NTC) thermistor, which utilizes the phenomenon that its resistance value increases as the temperature of the thermistor TH decreases. The resistance value of the thermistor TH varies within the temperature range of -35°C to 65°C. When the temperature of the thermistor TH is -35°C, the resistance value of the thermistor TH is 800 kΩ. When the temperature of the thermistor TH is 65°C, the resistance value of the thermistor TH is 6.85 kΩ. In one embodiment, the thermistor TH can also be a positive temperature coefficient (PTC) thermistor.

[0027] The detection device 100 includes a measuring unit 10, a control unit 20, and a cooling unit 30. The detection device 100 does not need to be an integrated device. In other words, it can be configured as a detection system in which the measuring unit 10, the control unit 20, and the cooling unit 30 are independently provided and connected via a wired or wireless network.

[0028] The measuring unit 10 measures the resistance value of the thermistor TH. The measuring unit 10 is electrically connected to the thermistor TH. The measuring unit 10 indirectly measures the resistance value by applying a constant voltage to the thermistor TH and measuring the current value. In other words, the measuring unit 10 measures the value of the current flowing through the thermistor TH.

[0029] The control unit 20 includes a CPU (Central Processing Unit) 21, a RAM (Random Access Memory) 22, and a ROM (Read Only Memory) 23. The CPU 21 executes a program for controlling the operation of the detection device 100.

[0030] The RAM 22 stores application programs and referenced data executed by the CPU 21. In one embodiment, the RAM 22 is composed of an SRAM (Static Random Access Memory) or a DRAM (Dynamic Random Access Memory).

[0031] The ROM 23 stores programs such as an OS (Operating System) executed by the CPU 21. In one embodiment, the ROM 23 is composed of an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), or a flash memory.

[0032] In other embodiments, the control unit 20 may also be composed of circuit elements such as at least one embedded CPU, at least one ASIC (Application Specific Integrated Circuit), or at least one FPGA (Field Programmable Gate Array). Furthermore, in other embodiments, the control unit 20 may also be composed of a combination of two or more circuit elements.

[0033] The cooling unit 30 cools the thermistor TH connected to the measuring unit 10. The cooling unit 30 can cool the thermistor TH using a chemical reaction, or it can be an evaporator of a refrigeration cycle device. Hereinafter, the process of cooling the thermistor TH by the cooling unit 30 is referred to as simply the cooling process.

[0034] <Transition of the Resistance Value of the Thermistor TH>

[0035] Figure 2 1 is a graph showing changes in the resistance value of the thermistor TH1. The thermistor TH1 is a thermistor operating normally. Figure 3 1 is a graph showing the change in the resistance value of thermistor TH2. Thermistor TH2 is a thermistor that has a defect in which the internal circuit momentarily becomes open. Figure 41 is a graph showing the change in the resistance value of thermistor TH3. Thermistor TH3 is a thermistor that has a defect in which the internal circuit is momentarily short-circuited.

[0036] Below, use Figures 2 to 4 , the transition of the resistance value of the thermistor TH as the detection target when it is cooled is described, divided into a case where the thermistor TH as the detection target is normal and a case where it is faulty. Figures 2 to 4 The vertical axis represents the resistance value of the thermistor TH serving as the detection object. Figures 2 to 4 The horizontal axis of represents the time elapsed from the start of the resistance value measurement. The measuring unit 10 measures the resistance value for 40 seconds.

[0037] Figures 2 to 4 The figures show the measurement results for a case where the cooling process started 12 seconds after the start of resistance measurement and ended 3 seconds later, or 15 seconds after the start of resistance measurement. As described above, thermistors TH1 through TH3 used as test targets are NTC thermistors with negative temperature coefficients, whose resistance increases as the temperature decreases.

[0038] Reference Figure 2 , indicating that the thermistor TH1 is operating normally. Figure 2 In the example shown, the resistance of thermistor TH1 begins to rise 12 seconds after the resistance measurement begins. In other words, cooling unit 30 begins cooling thermistor TH1 12 seconds after the start of the cooling process. The resistance of thermistor TH1 before the start of the cooling process is 30 kΩ.

[0039] After that, the cooling process for thermistor TH1 was terminated after 15 seconds. As a result of the cessation of cooling, the temperature of thermistor TH1 gradually rose. As the temperature of thermistor TH1 rose, the resistance of thermistor TH1 gradually decreased. The resistance of thermistor TH1 rose to approximately 280 kΩ in 3 seconds after the cooling process began. On the other hand, the resistance of thermistor TH1 did not drop to 30 kΩ even after 40 seconds had passed since the cooling process ceased. In other words, the increase in the resistance of thermistor TH1 was more rapid than the decrease.

[0040] like Figure 2 As shown, when thermistor TH1 is operating normally, the resistance value of thermistor TH1 increases while thermistor TH1 is being cooled, and then gradually decreases after the cooling process stops. Thus, the resistance value of thermistor TH1 operating normally changes as shown by curve RL1.

[0041] exist Figure 3In the example, the internal circuit of thermistor TH2 is instantaneously open. Figure 3 The curve RL2 shown is Figure 2 The curve RL1 shown is different.

[0042] exist Figure 3 In the example, 12 seconds after the start of the measurement, that is, shortly after the cooling process began, the resistance value of thermistor TH2 suddenly increased, indicating that thermistor TH2 was open. For example, a poorly connected portion of the internal circuit of thermistor TH2 may be affected by the cooling process and open instantly. In this case, the curve RL2 depicting the resistance value of thermistor TH2 is as shown in FIG. Figure 3 After that, the resistance value of thermistor TH2 returns to a normal value after a period P1.

[0043] exist Figure 3 In the thermistor TH2, it does not operate normally for a moment during the period P1, resulting in malfunction. In addition, the period during which the resistance value of the thermistor TH2 becomes abnormal is only during the period P1. Figure 3 In order to facilitate understanding of the description, the period P1 is shown as being approximately 1 second, but the period P1 is an extremely short period shorter than 1 second.

[0044] exist Figure 4 In the example of the internal circuit of thermistor TH3 being short-circuited instantaneously, Figure 4 The curve RL3 shown is Figure 2 The curve RL1 shown is different.

[0045] exist Figure 4 Similarly, the cooling process is completed 15 seconds after the start of the resistance value measurement. Figure 4 As shown in FIG. 1 , the resistance value of thermistor TH3 decreases gradually after 15 seconds from the start of measurement. However, around 23 seconds from the start of measurement, the resistance value of thermistor TH3 momentarily short-circuits, and then returns to a normal resistance value.

[0046] therefore, Figure 4 The thermistor TH3 in the circuit does not operate normally for a moment during the period P2, resulting in malfunction. In other words, the period during which the resistance value of the thermistor TH3 becomes abnormal is only during the period P2. Figure 4 In order to facilitate understanding of the description, the period P2 is shown as being approximately 1 second, but the period P2 is an extremely short period shorter than 1 second.

[0047] Above, if used Figure 3 as well as Figure 4As explained above, if thermistor TH has a potential failure, the internal circuit may become open or short-circuited momentarily when a load such as cooling is applied to the thermistor TH over time. Failure of the thermistor TH that occurs momentarily when such a load is applied cannot be detected by simply measuring the resistance value of the thermistor TH without applying a load.

[0048] In the detection method of the first embodiment, a method of detecting a potential failure of the thermistor TH by focusing on the characteristics of the thermistor TH will be described.

[0049] <Detection Process>

[0050] Figure 5 This is a flowchart showing an example of processing executed when the detection device 100 in the first embodiment detects a failure of the thermistor TH to be detected. Figure 5 As shown in the flowchart, detection Figure 3 as well as Figure 4 The resistance value of thermistor TH shown is abnormal. Figure 5 The flowchart shown in FIG. 1 is executed by the control unit 20 of the detection device 100. Figure 5 The flow chart shown is referred to as the detection method.

[0051] First, the control unit 20 causes the cooling unit 30 to start a cooling process to cool the thermistor TH (step S101). After starting the cooling process, the cooling unit 30 continues the cooling process for a cooling end time tr. The cooling end time tr is, for example, 3 seconds, 5 seconds, or 10 seconds.

[0052] The control unit 20 causes the measuring unit 10 to measure the resistance value of the thermistor TH (step S102 ). In step S102 , the measuring unit 10 transmits the measured resistance value of the thermistor TH to the control unit 20 as data.

[0053] Next, the control unit 20 determines whether a predetermined time t has elapsed since the measurement unit 10 measured the resistance value (step S103 ). Figure 5 In the process in the flowchart shown, the process returns from step S106 or step S112 to step S103. That is, the control unit 20 repeatedly executes the process starting from step S103 until a predetermined condition is satisfied.

[0054] Hereinafter, in the process repeatedly executed from step S103 onward, the first process executed will be referred to as "the first round of processing," the second process executed will be referred to as "the second round of processing," and the third process executed will be referred to as "the third round of processing." Specifically, when the process returns to step S103, the control unit 20 increments a counter indicating the number of the current round of processing.

[0055] In the detection device 100, the predetermined time t is a period indicating the interval between resistance measurements and is a predetermined period. Specifically, until a predetermined condition is satisfied, the control unit 20 causes the measurement unit 10 to measure the resistance of the thermistor TH to be detected each time the predetermined time t elapses.

[0056] If the control unit 20 determines that the predetermined time t has not elapsed after the process in step S102 (No in step S103), the process remains in step S103. While the first round of processing remains in step S103, the temperature of the thermistor TH continues to decrease due to the cooling process.

[0057] After the cooling process starts, the temperature of the thermistor TH continues to change, so the resistance value of the thermistor TH after the predetermined time t also changes. The cooling process in the first embodiment corresponds to the "load" in the present disclosure.

[0058] If the control unit 20 determines that the predetermined time t has elapsed after the processing in step S102 ("YES" in step S103), it causes the measurement unit 10 to measure the resistance value of the thermistor TH again (step S104). In step S104, the measurement unit 10 transmits the measured resistance value of the thermistor TH as data to the control unit 20. As described above, the resistance value of the thermistor TH changes over time. Therefore, the resistance value data received by the control unit 20 in step S102 represents the resistance value before the change, while the data in step S104 during the first round of processing represents the resistance value after the change.

[0059] The data indicating the resistance value before the change corresponds to the "first data" in the present disclosure, and the data indicating the resistance value after the change corresponds to the "second data" in the present disclosure.

[0060] The control unit 20 calculates the amount of change in the resistance value using the first and second data (step S105). Specifically, the control unit 20 calculates the amount of change in the resistance value per predetermined time period t. The control unit 20 stores the calculated amount of change as data in at least one of the RAM and ROM. The amount of change is the difference between the resistance value before the change and the resistance value after the change.

[0061] The time when the resistance value before the change is measured corresponds to the "first time" in this disclosure. The time when the resistance value after the change is measured corresponds to the "second time" in this disclosure. The resistance value of the thermistor TH corresponds to the "physical property value of the thermistor" in this disclosure.

[0062] The control unit 20 determines whether or not more than four pieces of data on the amount of change calculated in step S105 have been stored (step S106). If it is determined that more than four pieces of data on the amount of change have not been stored ("No" in step S106), the control unit 20 returns the process to step S103. At this point, the control unit 20 deems that the first round of processing is complete and the second round of processing has begun, and increments the counter. After a predetermined time t has elapsed, the control unit 20 causes the measuring unit 10 to measure the resistance value again (step S104). The control unit 20 uses the data on the resistance value in step S104 in the first round of processing as the data before the change, and uses the data on the resistance value in step S104 in the second round of processing as the data after the change, and calculates the amount of change in the resistance value (step S105). Thereafter, the control unit 20 returns the process from step S106 to step S103 and starts the third round of processing. In this way, the control unit 20 repeats the process until more than four pieces of data on the amount of change have been stored.

[0063] When the control unit 20 determines that four or more pieces of change data are stored (YES in step S106 ), the control unit 20 calculates a moving average based on the four pieces of resistance value change data (step S107 ).

[0064] The moving average value is calculated using the moving average method. The moving average method smoothes time-series data by dividing the sum of a certain range of varying data by the number of data items. By smoothing time-series data, the detection device 100 can prevent erroneous detections of thermistor TH, even though it is normal. Details regarding moving averages will be described later. The control unit 20 calculates the moving average value based on four data items representing the amount of change in resistance value at each predetermined time interval t. The number of data items used to calculate the moving average value may also be other than four.

[0065] The control unit 20 determines whether the calculated moving average value of the change in resistance value is greater than a reference value (step S108 ).

[0066] The reference value is a predetermined value used to determine that the thermistor TH is defective when the calculated moving average of the amount of change exceeds the reference value. The reference value represents the absolute value of the amount of change. In other words, when the calculated amount of change exceeds the reference value, it indicates that the resistance value of the thermistor TH has increased or decreased rapidly. If the control unit 20 determines that the resistance value of the thermistor TH has changed rapidly based on the moving average of the amount of change per predetermined time period t, it determines that the thermistor TH is defective.

[0067] If the control unit 20 determines that the moving average of the amount of change in the resistance value per predetermined time t is less than the reference value ("No" in step S108), the control unit 20 determines whether the cooling end time tr has passed since the start of the cooling process (step S110). If the control unit 20 determines that the cooling end time tr has passed ("Yes" in step S110), the control unit 20 stops the cooling process started in step S101 (step S111) and proceeds to step S112.

[0068] When the control unit 20 determines that the cooling end time tr has not elapsed (NO in step S110 ), the control unit 20 proceeds to step S112 without stopping the cooling process started in step S101 .

[0069] The control unit 20 determines whether the detection end time td has elapsed since the start of the cooling process (step S112). The detection end time td is the maximum time that the detection process is performed on the thermistor TH to be detected after the start of the cooling process. The detection end time td is predetermined, for example, 30 seconds from the start of measurement by the measurement unit 10. The detection end time td may be a time other than 30 seconds, for example, 40 seconds.

[0070] If the control unit 20 determines that the detection end time td has passed since the start of the cooling process ("YES" in step S108), the process ends. In other words, if the control unit 20 does not detect a failure in the thermistor TH until the detection end time td has passed, the control unit 20 determines that the thermistor TH to be detected is not defective.

[0071] If the control unit 20 determines that the detection end time td has not passed (No in step S112), the process returns to step S103. Thereafter, the control unit 20 determines whether a predetermined time t has passed since the measurement unit 10 last measured the resistance value (step S103).

[0072] When the control unit 20 determines that the predetermined time t has elapsed (YES in step S103 ), it causes the measurement unit 10 to measure the resistance value of the thermistor TH again (step S104 ).

[0073] Next, the control unit 20 calculates the amount of change in the resistance value of thermistor TH from the resistance value before the predetermined time t to the resistance value after the predetermined time t (step S105). The control unit 20 calculates the moving average of the calculated amount of change in the resistance value (step S107) and determines whether it is greater than a reference value (step S108).

[0074] In this manner, the control unit 20 repeatedly executes the process from step S103 until a failure of the thermistor TH is detected or the detection end time td has elapsed. Specifically, the control unit 20 causes the measurement unit 10 to measure the resistance value of the thermistor TH at every predetermined time t and calculates the change in resistance value from the last measurement.

[0075] In the detection method executed by detection device 100, after thermistor TH begins cooling, the resistance value of thermistor TH is continuously measured at predetermined intervals t. If the calculated moving average value shows a change greater than a reference value, control unit 20 determines that the resistance value of thermistor TH is abnormal and detects a failure of thermistor TH.

[0076] In addition, Figure 5 In the flowchart shown, the moving average of the resistance change is compared with the reference value to calculate the thermistor failure. However, the moving average can be omitted. In other words, the control unit 20 can also calculate the thermistor failure by comparing the resistance change itself with the reference value.

[0077] Figure 5 The step S101 in corresponds to the “step of providing a load” in the present disclosure. Figure 5 Steps S102 and S104 in the embodiment correspond to the “step of measuring the physical property values of the thermistor” in the present disclosure. Figure 5 Step S108 in the process corresponds to the "step of detecting a defect" in the present disclosure. The control unit 20 in step S108 functions as the "detection unit" in the present disclosure.

[0078] <Detection method using variation>

[0079] Figure 6 : This is a graph showing the resistance value of thermistor TH4 and the transition of the moving average value. Thermistor TH4 is a normal thermistor with no potential failure. Figure 6 The graph shown is applied in Figure 5 The curve graph obtained by the detection processing described in .

[0080] The horizontal axis represents the time elapsed since the measurement of thermistor TH4 was started by the measurement unit 10. The left vertical axis and the curve RL4 represent the change in the resistance value of thermistor TH4 over time. Referring to the left vertical axis and the curve RL4, the resistance value of thermistor TH4 was read as 30 kΩ from the start of measurement by the measurement unit 10 until 10 seconds had passed.

[0081] The right vertical axis and curve SL1 represent the moving average of the resistance change per predetermined time period t. For example, referring to curve RL4, the resistance of thermistor TH4 increases 10 seconds after the start of the cooling process. Therefore, curve SL1, representing the moving average of the resistance change, also increases after 10 seconds.

[0082] The detection device 100 uses 10 seconds from the start of measuring the thermistor TH4 by the measuring unit 10 as a preparation period, and starts the test after 10 seconds have passed. Figure 5 That is, the cooling unit 30 starts cooling after 10 seconds and stops cooling after 14 seconds. Figure 6 In the example shown, the cooling unit 30 stops the cooling process when 4 seconds have passed after the start of the cooling process.

[0083] The control unit 20 receives the resistance value of the thermistor TH4 from the measuring unit 10 at every predetermined time t. The control unit 20 approximates the curve RL based on the received resistance value. Figure 6 The curve RL shown is obtained by approximately plotting a plurality of resistance values per predetermined time t as a curve.

[0084] The reference value ThL is the amount of change per predetermined time t, and is a reference value for determining whether the thermistor TH4 is defective. Figure 6 In the example shown, the reference value ThL is determined to be a change of 200 kΩ per predetermined time t. Here, the control unit 20 compares the reference value ThL with the moving average of the resistance value decrease. In other words, the control unit 20 does not use the resistance value increase as a comparison target for detecting a failure in the thermistor TH. Specifically, the control unit 20 detects a failure in the thermistor TH if the moving average of the resistance value change is less than -200 kΩ per predetermined time t. Hereinafter, the resistance value decrease change may be referred to as a "negative change," and the resistance value increase change may be referred to as a "positive change."

[0085] As mentioned above, Figure 6The thermistor TH4 to be detected is operating normally. Therefore, the curve SL1 does not fall below the reference value ThL during the entire measurement period. The detection device 100 in the first embodiment determines that the thermistor TH4 is not defective.

[0086] In one embodiment, the control unit 20 may calculate an approximate curve of the curve RL1 as a function. In this case, the control unit 20 calculates the curve SL1 as the derivative of the curve RL1. That is, the curve SL1 represents the change in resistance value in a small time period for each elapsed time, which is the approximate curve of the curve RL1. The reference value ThL is a predetermined differential coefficient.

[0087] Figure 7 : is a graph showing the resistance value and the transition of the moving average value of thermistor TH5. Thermistor TH5 is a defective thermistor in which the internal circuit becomes open momentarily. Figure 7 The graph shown is applied in Figure 5 The curve graph obtained by the detection processing described in .

[0088] exist Figure 7 In, with Figure 6 Similarly, the horizontal axis shows the time elapsed since the measurement of thermistor TH5 was started by the measurement unit 10. The left vertical axis and the curve RL5 show the change in the resistance value of thermistor TH5 over time. The right vertical axis and the curve SL2 show the moving average of the change in the resistance value per predetermined time t.

[0089] like Figure 7 As shown, the curve RL5 shows a resistance value exceeding 800 kΩ in the period P3. That is, in the period P3, the electrical circuit including the thermistor TH5 is in an open state.

[0090] The control unit 20 and Figure 6 Similarly, a curve SL2 representing a moving average value of the amount of change in resistance value is calculated. As the period P3 ends, the resistance value of the thermistor TH5 drops rapidly from the resistance value indicating an open state to a normal value.

[0091] As this rapid decrease occurs, curve SL2, representing the moving average of the resistance change, also rises and falls rapidly. Therefore, during period A1, the moving average of the resistance change represented by curve SL2 falls below the change in reference value ThL. During period A1, the negative change in resistance exceeds reference value ThL by 200 kΩ per predetermined time t.

[0092] Thus, the control unit 20 can detect that the thermistor TH5 that is the target of the detection device 100 is defective during the period A1.

[0093] In addition, in the detection method executed by the detection device 100, the processing may be terminated at a time point when the amount of change in the resistance value represented by the curve SL2 falls below the reference value ThL. Figure 7 , for the purpose of explanation, the curve RL5 and the curve SL2 are shown in the figure when the resistance value is continuously measured by the measuring unit 10 even after the period A1.

[0094] Thus, the detection method executed by the detection device 100 increases the likelihood of detection even during an extremely short period P3, compared to a method that focuses solely on the resistance value without considering the amount of change. Specifically, since the period P3 is shorter than the predetermined time t, if the measurement unit 10 cannot measure the resistance value of thermistor TH5 during the period P3, a failure of thermistor TH5 cannot be detected without considering the amount of change in the resistance value.

[0095] On the other hand, by focusing on the amount of change, as detection device 100 does, even if measurement unit 10 cannot measure the resistance value during period P3, it is still possible to detect a return from an open circuit state to a normal state based on the amount of change in the resistance value around period P3. Therefore, compared to a method that focuses solely on the resistance value, the detection method executed by detection device 100 makes it easier to detect as a defective thermistor TH that momentarily reaches an abnormal resistance value.

[0096] Furthermore, in Figure 7 The thermistor TH5 that is the target of the detection device 100 sporadically repeats a sharp rise and fall in resistance value during periods P4, P5, and P6. Thus, during periods P4, P5, and P6, the electrical circuit including the thermistor TH5 does not reach an open circuit state, but Figure 2 The resistance values of thermistor TH1 and thermistor TH5 shown in FIG. 1 are normal and repeatedly increase and decrease sharply.

[0097] In the detection method of the first embodiment, sporadic rapid increases and decreases in resistance value that do not reach the open state and occur during periods A2 , A3 , A4 , A5 , and A6 can also be detected as a failure of the thermistor TH5 .

[0098] Furthermore, in the detection method executed by the detection device 100, the load applied to the thermistor TH5 is cooling, so only the moving average of the negative change is compared with the reference value ThL. In other words, the control unit 20 does not include the moving average of the positive change in the comparison. When the temperature of the thermistor TH5 decreases due to cooling by the cooling unit 30, the change in resistance value becomes more dramatic compared to when the temperature of the thermistor TH5 increases due to the cessation of cooling.

[0099] like Figure 7As shown in FIG. 1 , the resistance value of thermistor TH5 increases rapidly from 12 seconds to 15 seconds. This is because the amount of change in the resistance value of thermistor TH5 in the upward direction is greater than the gradual increase in the temperature of thermistor TH5 due to heat exchange with the air surrounding thermistor TH by natural convection after the cooling process stops.

[0100] Thus, in the detection method executed by the detection device 100 in Embodiment 1, the condition for detecting a failure in thermistor TH5 is whether the calculated amount of change in the resistance value in the negative direction is greater than the reference value ThL. If the calculated amount of change in the resistance value in the positive direction is compared with the reference value ThL, the control unit 20 is likely to mistakenly detect a failure in thermistor TH5 due to a sudden increase in the resistance value caused by the cooling process of the cooling unit 30.

[0101] Therefore, the detection method executed by the detection device 100 uses whether the negative change in resistance value is greater than the reference value ThL as a condition to prevent a sudden increase in resistance value caused by the cooling process of the cooling unit 30 from being erroneously detected as a failure of the thermistor TH5.

[0102] exist Figure 7 , an example of detecting a defect based on the negative change in resistance value when the device is in an open-circuit state is described. In a short-circuit state, the resistance value drops sharply. Therefore, the detection method performed by the detection device 100 can detect even a short-circuit state.

[0103] exist Figure 7 2 shows an example in which the resistance value is measured in the entire period from the start of measurement by the measuring unit 10 to the detection end time td. However, the control unit 20 may stop the process at the time when an abnormality of the thermistor TH5 is detected in the period A1.

[0104] <Smoothing using moving average>

[0105] Figure 8 This is a diagram showing an example in which the amount of change in resistance value rapidly increases in the thermistor TH6 that is operating normally. Figure 8 The vertical axis represents the resistance value of thermistor TH6. Figure 8 The horizontal axis represents the elapsed time since the start of measurement by the measuring unit 10. The following describes the advantages of calculating the moving average value after calculating the amount of change in the resistance value in the detection device 100.

[0106] exist Figure 8 In the example, the thermistor TH6 that is the target of the detection device 100 is a thermistor that operates normally. Figure 3 or Figure 4As shown, the resistance value of the thermistor TH6 measured by the measuring unit 10 is not an abnormal value. In other words, the electrical circuit including the thermistor TH6 is not in an open circuit state or a short circuit state.

[0107] In addition, the resistance value of thermistor TH6 measured by the measuring unit 10 will not be as Figure 7 During this period, it rises and falls sporadically like P4, P5, and P6.

[0108] That is, in Figure 8 In the figure, the change in the resistance value of thermistor TH6 is relatively gradual from the time thermistor TH6 is connected to the measurement unit 10 until 40 seconds have passed. However, as shown in region S1, the shape of curve RL5 may have slight irregularities. Such irregularities shown in region S1 may sometimes appear to be large when focusing on the change over a short period of time.

[0109] Figure 9 It shows Figure 8 The control unit 20 calculates the amount of change in the resistance value for each predetermined time t.

[0110] The control unit 20 then calculates a moving average of the calculated changes per predetermined time period t. This generates a curve SL3 as the transition of the moving average of the changes per predetermined time period t. Calculating the moving average smoothes the curve SL3. In other words, the curve SL3 becomes flat.

[0111] like Figure 8 As shown in FIG. 1 , the thermistor TH6 to be detected is operating normally. Therefore, the moving average of the change per predetermined time t does not exceed the reference value ThL in the negative direction until the detection end time td. Therefore, the control unit 20 determines that the thermistor TH6 is not defective.

[0112] Figure 10 Graph showing the amount of change in resistance value when the moving average value is not calculated. Figure 10 The thermistor of the detection object shown is Figure 9 The detection object is the same as the thermistor TH6. Figure 10 The curve SL4 shown is a graph showing the calculated Figure 9 The curve SL4 is a curve showing the amount of change per predetermined time t before the moving average of the curve SL3 shown. In other words, the curve SL4 is a curve before the moving average of the curve SL3 is calculated. Therefore, the curve SL4 is not smoothed.

[0113] Area S2 indicates Figure 8The amount of change in the resistance value in region S1 is ThL. In region S2, the amount of change in the resistance value is greater than the reference value ThL. That is, without calculating the moving average, the control unit 20 calculates the unevenness represented by region S1 as a sudden change.

[0114] In this way, without calculating the moving average, the control unit 20 will Figure 8 The slight unevenness in the shape of curve RL5 shown in region S1 is interpreted as a sudden change. Consequently, even though thermistor TH6 is operating normally, control unit 20 mistakenly detects it as a failure. Therefore, in Embodiment 1, the moving average method is used to prevent false detection of failures.

[0115] [Implementation Method 2]

[0116] In Embodiment 1, cooling is performed as a method of applying a load to the thermistor TH to be detected. However, the method of applying a load to the thermistor TH is not limited to cooling.

[0117] In the detection device 100A according to the second embodiment, description of the configuration that overlaps with that of the detection device 100 according to the first embodiment will not be repeated.

[0118] Figure 11 This diagram schematically illustrates an example of the configuration of a detection device 100A for detecting a failure of a thermistor TH according to Embodiment 2. The detection device 100A includes a heating unit 30A. The heating unit 30A blows hot air toward the thermistor TH, which is the target of detection. This causes the temperature of the thermistor TH to rise. The heating unit 30A includes, for example, a heater and a blower. In one embodiment, the heating unit 30A may consist solely of a heater. Hereinafter, heating the thermistor TH by the heating unit 30A is referred to as a heating process. The heating process in Embodiment 2 corresponds to the term "load" in this disclosure.

[0119] In the detection method executed by the detection device 100A of the second embodiment, a reference value ThH is predetermined instead of the reference value ThL. The reference value ThH is, for example, a change of 150 kΩ per predetermined time t.

[0120] The control unit 20 compares the moving average value of the amount of change in the positive direction with the reference value ThH, unlike in Embodiment 1. That is, the control unit 20 in Embodiment 2 does not include the moving average value of the amount of change in the negative direction in the comparison target.

[0121] Figure 12 1 is a graph showing changes in the resistance value and moving average value of the thermistor TH7. The thermistor TH7 is a normal thermistor with no potential failure.

[0122] In the second embodiment, the heating unit 30A starts blowing hot air 10 seconds after the measurement unit 10 begins measuring thermistor TH7. The resistance value of thermistor TH7 decreases as the temperature rises. Curve RL6 represents the resistance value of thermistor TH7. Curve SL5 represents the moving average of the change in the resistance value of thermistor TH7.

[0123] like Figure 12 As shown, the resistance value of thermistor TH7 is as follows Figure 3 or Figure 4 The values shown are not outliers.

[0124] Therefore, throughout the entire detection process, the moving average of the change in the resistance value of thermistor TH7, represented by curve SL5, remains within a range of approximately -10 kΩ to 10 kΩ. Therefore, the moving average of the change is no greater than the reference value ThH of 150 kΩ, and the control unit 20 determines that thermistor TH7 is not defective.

[0125] Figure 13 1 is a graph showing changes in the resistance value and moving average value of thermistor TH8. Thermistor TH8 is a thermistor that has a defect in which the internal circuit momentarily becomes open.

[0126] The curve RL7 represents the resistance value of the thermistor TH8. In addition, the curve SL6 represents the moving average value of the change in the resistance value of the thermistor TH8. Figure 13 In the periods P7, P8, and P9, the resistance value of the thermistor TH8 rises rapidly, and the internal circuit of the thermistor TH8 becomes open.

[0127] During periods P7, P8, and P9, the moving average of the positive change in resistance value of thermistor TH8 represented by curve SL6 exceeds reference value ThH. In other words, the moving average of the change in resistance value is equal to or greater than 150 kΩ per predetermined time t.

[0128] Thus, since the moving average value of the amount of change in the resistance value is larger than the reference value ThH, the control unit 20 can detect that the thermistor TH8 is defective.

[0129] Furthermore, in the detection method executed by detection device 100A, the load applied to thermistor TH8 is a heating process, so control unit 20 compares the amount of change in the positive direction with reference value Th. In other words, in the detection method executed by detection device 100A, the condition for detecting a failure in thermistor TH8 is whether the calculated amount of change in the resistance value in the positive direction is greater than reference value ThH.

[0130] Thus, in the detection method executed by the detection device 100A, it is possible to prevent an increase in the resistance value due to the heating process of the heating unit 30A from being erroneously detected as a failure of the thermistor TH.

[0131] The control unit 20 may stop the process when an abnormality is detected for the first time during the period P7, or may stop the process when an abnormality is detected a predetermined number of times. Figure 13 In the example, after the period P9 has elapsed, the control unit 20 stops the measurement by the measurement unit 10 .

[0132] The load applied to the thermistor TH to be detected may not only cause the temperature of the thermistor TH to change, but may also cause vibration to the thermistor TH. Applying vibration corresponds to the "load" in this disclosure. The control unit 20 can detect a failure by determining whether the moving average of the amount of change in resistance value during the period of vibration applied to the thermistor TH is greater than a reference value.

[0133] Summary

[0134] The following summarizes implementation modes 1 and 2.

[0135] The method for detecting a failure of a thermistor in the first and second embodiments includes: applying a load including a cooling process, a heating process, and a vibration to the thermistor over time; measuring a physical property value of the thermistor at least during a first time and a second time during which the load is applied to the thermistor; and detecting a failure of the thermistor based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time.

[0136] Therefore, in the detection method of the present disclosure, by measuring the physical property values of the thermistor at least during the first and second times when the load is applied to the thermistor, even a thermistor with abnormal physical property values for a short period of time can be easily detected as defective.

[0137] Preferably, the step of detecting a failure of the thermistor includes: a step of calculating a change in the physical property value per predetermined time t based on a difference between a physical property value represented by a first data and a physical property value represented by a second data, and a difference between a first time and a second time; and a step of detecting a failure of the thermistor by comparing the change in the physical property value per predetermined time t with a reference value.

[0138] Preferably, the step of detecting a failure of the thermistor includes the step of detecting a failure of the thermistor by comparing a moving average value of a change in a physical property value with a reference value.

[0139] Preferably, in the step of applying a load to the thermistor, the temperature of the thermistor is changed.

[0140] Preferably, the physical property value is the resistance value of a thermistor.

[0141] Preferably, in the step of detecting a failure of the thermistor, when the temperature of the thermistor is lowered in the step of applying the load, a change amount of the resistance value among the changes in the physical property value is compared with a reference value.

[0142] Preferably, in the step of detecting a failure of the thermistor, when the temperature of the thermistor is increased in the step of applying the load, an amount of change in the resistance value among the amounts of change in the physical property value is compared with a reference value.

[0143] Preferably, in the step of applying a load to the thermistor, vibration is applied to the thermistor.

[0144] A detection device 100 for detecting a failure in a thermistor includes: a cooling unit 30 or a heating unit 30A for applying a load to the thermistor over time; a measuring unit 10 for measuring a physical property value of the thermistor during at least a first time and a second time during which the load is applied to the thermistor; and a detection unit for detecting a failure in the thermistor based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time.

[0145] A detection system for detecting a thermistor failure includes: a cooling unit 30 or a heating unit 30A for applying a load to the thermistor over time; a measuring unit 10 for measuring a physical property value of the thermistor at least during a first time and a second time during which the load is applied to the thermistor; and a detection unit for detecting a thermistor failure based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time.

[0146] While the embodiments of the present disclosure have been described, they should be considered in all respects to be illustrative and not restrictive. The scope of the present disclosure is indicated by the claims, and all modifications within the meaning and scope of the claims are intended to be encompassed.

Claims

1. A method for detecting a defective thermistor, comprising: providing a load to the thermistor over time; a step of measuring a physical property value of the thermistor during at least a first time and a second time during a time when the load is applied to the thermistor; as well as a step of detecting a failure of the thermistor based on first data indicating the physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time, The steps of detecting a defect of the thermistor include: a step of calculating a change in the physical property value per unit time based on a difference between the physical property value represented by the first data and the physical property value represented by the second data, and a difference between the first time and the second time; as well as A step of detecting a failure of the thermistor by comparing a moving average value of the amount of change in the physical property value per unit time with a reference value.

2. The detection method according to claim 1, wherein The step of applying the load to the thermistor includes the step of changing the temperature of the thermistor.

3. The detection method according to claim 1 or 2, wherein The physical property value is the resistance value of the thermistor.

4. The detection method according to claim 3, wherein The step of detecting a failure of the thermistor includes comparing an amount of change in the resistance value obtained by lowering the temperature of the thermistor in the step of applying the load with a reference value.

5. The detection method according to claim 3, wherein The step of detecting a failure of the thermistor includes comparing an amount of change in the resistance value obtained by increasing the temperature of the thermistor in the step of applying the load with a reference value.

6. A device for detecting a defective thermistor, comprising: a load unit that applies a load to the thermistor over time; a measuring unit configured to measure a physical property value of the thermistor during at least a first time and a second time during a time when the load is applied to the thermistor; as well as a detection unit that detects a failure of the thermistor based on first data indicating a physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time, The detection unit calculates the change in the physical property value per unit time based on the difference between the physical property value represented by the first data and the physical property value represented by the second data, and the difference between the first time and the second time, and detects a defect in the thermistor by comparing a moving average of the change in the physical property value per unit time with a reference value.

7. A system for detecting a defective thermistor, comprising: a load unit that applies a load to the thermistor over time; a measuring unit configured to measure a physical property value of the thermistor during at least a first time and a second time during which the load is applied to the thermistor; and a detection unit that detects a failure of the thermistor based on first data indicating a physical property value of the thermistor measured at the first time and second data indicating the physical property value of the thermistor measured at the second time, The detection unit calculates the change in the physical property value per unit time based on the difference between the physical property value represented by the first data and the physical property value represented by the second data, and the difference between the first time and the second time, and detects a defect in the thermistor by comparing a moving average of the change in the physical property value per unit time with a reference value.

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