Fault diagnosis device

Abstract

To provide a fault diagnosis device capable of diagnosing a fault of a temperature sensor in an inexpensive configuration.SOLUTION: A fault diagnosis device 1 includes: a switch 10 capable of switching to a first state for applying first potential to a temperature sensor 2 and a second state for applying second potential to it; a capacitor 20 for composing an integral circuit with a resistor R that the temperature sensor 2 has; a diagnosis instruction output part 30 for outputting a diagnosis instruction including at least one of a charge instruction for charging the capacitor 20 and a discharge instruction for discharging the capacitor 20 to the switch 10; a normal time range setting part 40 for setting a normal time range; a voltage acquisition part 50 for acquiring a voltage value of voltage in an output terminal 2B; and a determination part 60 for determining whether or not the temperature sensor 2 fails on the basis of a comparison result between a voltage value acquired by the voltage acquisition part 50 and lapse time and a normal time range until the voltage value reaches a predetermined reference value from a first point of time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fault diagnosis device for diagnosing a fault in a temperature sensor. [Background technology]

[0002] Conventionally, in combustion-type heating devices, in order to prevent empty-fire or oil fires, a function is used to detect the temperature of the bottom of a cooking device such as a pot (pan bottom) using a temperature sensor and automatically stop combustion based on the detection result.If such a temperature sensor malfunctions, combustion cannot be stopped when necessary, so technology that can determine whether the temperature sensor is abnormal has been studied.

[0003] Patent Document 1 discloses a combustion-type heating device. This combustion-type heating device is configured with a first temperature detection means that detects the temperature of a small-fire heating portion that heats an object to be heated in a small-fire heating state where the amount of heat is small, a second temperature detection means that detects the temperature of a large-fire heating portion that heats an object to be heated in a large-fire heating state where the amount of heat is large, and a temperature estimation means that estimates the temperature of the object to be heated based on the temperature detection values ​​of the first temperature detection means and the second temperature detection means, and is configured to determine that the temperature detection means that detected the temperature detection value is abnormal if either or both of the temperature detection values ​​of the first temperature detection means and the second temperature detection means remain within a predetermined low-temperature range even after a predetermined time has passed since the start of heating.

[0004] Patent Document 2 discloses a non-contact temperature detection device. This non-contact temperature detection device includes a temperature sensor having a sensor element that detects the temperature of an object without contact, an inspection circuit that is connected to the sensor element and inspects the sensor element, a switch element that opens and closes the connection between the inspection circuit and the sensor element, a control device that controls the opening and closing of the switch element, and a temperature detection circuit that detects the temperature of the object based on the output of the sensor element.

[0005] Patent Document 3 discloses a method for detecting an abnormality in a non-contact temperature sensor that can be connected to the input terminal of a temperature regulator, which has an input terminal to which a thermocouple is connected and a disconnection detection circuit that detects disconnection of the thermocouple. This method for detecting an abnormality in a non-contact temperature sensor is characterized by interposing a switch circuit between the non-contact temperature sensor and the input terminal, and controlling the opening and closing of the switch circuit based on whether or not power is being supplied to the non-contact temperature sensor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-189281 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-153726 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-184097 Summary of the Invention [Problem to be solved by the invention]

[0007] The technology described in Patent Document 1 requires a first temperature detection means and a second temperature detection means to determine whether the temperature detection means is abnormal. This requires multiple temperature detection means, which increases costs. Furthermore, the technologies described in Patent Documents 2 and 3 can detect open circuit faults but cannot detect short circuit faults. This may result in failures that cannot be reliably diagnosed (detected).

[0008] Therefore, there is a need for a fault diagnosis device that can diagnose faults in temperature sensors with an inexpensive configuration. [Means for solving the problem]

[0009] The characteristic configuration of the fault diagnosis device according to the present invention is as follows: A fault diagnosis device for diagnosing a fault in a temperature sensor, comprising: a switch that can be switched between a first state in which a predetermined first potential is applied to the temperature sensor and a second state in which a second potential higher than the first potential is applied to the temperature sensor; an output terminal of the temperature sensor; ground a capacitor that is provided between the temperature sensor and the resistor and that constitutes an integrating circuit that is an RC series circuit; a diagnostic instruction output unit that outputs to the switch a diagnostic instruction including at least one of a charge instruction to charge the capacitor that is in a discharged state and a discharge instruction to discharge the capacitor that is in a charged state; a normal time range setting unit that sets a normal time range centered on a second time point when a time has elapsed since the first time point when the diagnosis instruction was received until the potential of the output terminal reaches a reference value that is a predetermined potential between the first potential and the second potential; a voltage acquisition unit that acquires a voltage value of the voltage at the output terminal; a determination unit that determines whether the temperature sensor is faulty based on the voltage value acquired by the voltage acquisition unit, the elapsed time from the first time point until the voltage value reaches the reference value, and a comparison result with the normal time range; Equipped with 、 The determination unit can successively diagnose the temperature sensor based on the charging of the capacitor and the discharging of the capacitor using the current flowing through the resistor included in the temperature sensor. The point is that

[0010] For example, if the temperature sensor has a short circuit, the resistance value of the resistor in the temperature sensor decreases relative to its normal value (the value in a normal state), whereas if the temperature sensor has an open circuit, the resistance value of the resistor in the temperature sensor increases relative to its normal value (the value in a normal state). Therefore, as in the above-described characteristic configuration, an integrating circuit is formed using the resistor and capacitor in the temperature sensor, and whether the temperature sensor has failed can be determined by determining whether the time (elapsed time) until the voltage value of the output terminal of the temperature sensor, which corresponds to the potential of one terminal of the capacitor, reaches a predetermined reference value falls within a normal time range. Since the failure diagnosis is performed using the resistor and capacitor in the temperature sensor in this way, a simple configuration can be achieved. Therefore, it is possible to diagnose a temperature sensor failure with an inexpensive configuration.

[0011] Preferably, the determination unit is capable of determining whether the temperature sensor has a wire breakage fault or a short circuit fault in response to one of the diagnostic instructions.

[0012] For example, if the time (elapsed time) until the voltage value of the output terminal of the temperature sensor, which corresponds to the potential of one terminal of the capacitor, reaches a predetermined reference value in response to one diagnostic instruction is shorter than the lower limit of the normal time range, it can be determined that the resistor of the temperature sensor has a short-circuit failure, and if it is longer than the upper limit of the normal time range (i.e., the voltage value of the output terminal does not reach the reference value by the time the upper limit of the normal time range is reached), it can be determined that the resistor of the temperature sensor has an open circuit failure. Therefore, it is possible to determine whether the temperature sensor has an open circuit failure or a short circuit failure with one diagnostic instruction.

[0013] Further, when the diagnostic instruction is the charging instruction, It is preferable that the judgment unit judges that the temperature sensor has an open circuit failure if the voltage value does not exceed the reference value even when the time from the first time point exceeds the normal time range, or if the voltage value exceeds the reference value after exceeding the normal time range.

[0014] With this configuration, if the diagnostic command includes at least a charging command, it becomes possible to quantitatively determine whether the temperature sensor is disconnected.

[0015] Further, when the diagnostic instruction is the charging instruction, Preferably, the determination unit determines that the temperature sensor has a short-circuit failure if the voltage value exceeds the reference value before the elapsed time reaches the normal time range.

[0016] With this configuration, if the diagnostic instruction includes at least a charging instruction, it becomes possible to quantitatively determine whether the temperature sensor is short-circuited.

[0017] Furthermore, when the diagnostic instruction is the discharge instruction, It is preferable that the judgment unit judges that the temperature sensor has an open circuit failure if the voltage value has been below the reference value before the discharge instruction was given, or if the voltage value was above the reference value at the time the discharge instruction was given and the voltage value fell below the reference value after the elapsed time reached the normal time range.

[0018] With this configuration, if the diagnostic instruction includes at least a discharge instruction, it becomes possible to quantitatively determine whether the temperature sensor is in a disconnected state.

[0019] Furthermore, when the diagnostic instruction is the discharge instruction, It is preferable that the judgment unit judges that the temperature sensor has a short-circuit failure if the voltage value exceeds the reference value at the time the discharge instruction is issued and the voltage value falls below the reference value before the elapsed time reaches the normal time range.

[0020] With this configuration, if the diagnostic instruction includes at least a discharge instruction, it becomes possible to quantitatively determine whether the temperature sensor is short-circuited.

[0021] The temperature sensor may be a thermopile.

[0022] Even if the temperature sensor is a thermopile, it is possible to appropriately determine whether the thermopile has been broken or short-circuited.

[0023] The temperature sensor may also monitor the temperature of an object to be heated by the cooking appliance.

[0024] With this configuration, it is possible to detect a malfunction of the temperature sensor that monitors the temperature of the object to be heated in the cooking appliance, and to prevent erroneous detection of the temperature of the object to be heated.

[0025] Preferably, the diagnostic instruction output unit outputs the diagnostic instruction when the cooking appliance is turned on.

[0026] With this configuration, it is possible to detect a malfunction of the temperature sensor that monitors the temperature of the object to be heated by the cooking appliance each time the appliance is ignited. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a block diagram illustrating a configuration of a fault diagnosis device. [Figure 2] 10A and 10B are diagrams illustrating a diagnostic instruction and a voltage waveform at an output terminal. [Figure 3] 10A and 10B are explanatory diagrams of determinations made by a determination unit regarding a charging instruction. [Figure 4] 10A and 10B are explanatory diagrams of determinations made by a determination unit regarding a discharge instruction. [Figure 5] FIG. 2 is a diagram showing a circuit configuration of a fault diagnosis device. [Figure 6] FIG. 10 is a diagram illustrating an example of a determination made by the fault diagnosis device. DETAILED DESCRIPTION OF THE INVENTION

[0028] The fault diagnosis device according to the present invention is capable of diagnosing a fault in a temperature sensor. The fault diagnosis device 1 of this embodiment will be described below.

[0029] In this embodiment, the fault diagnosis device 1 diagnoses a fault in a non-contact temperature sensor, which is an example of a temperature sensor 2. Specifically, the non-contact temperature sensor is a thermopile that monitors the temperature of an object to be heated at preset time intervals from when ignition is confirmed in a cooking appliance until the fire is extinguished, and has a resistor R between the input terminal 2A and output terminal 2B of the temperature sensor 2. Therefore, in the following, the temperature sensor 2 will be described as the thermopile 2. Note that the resistor R of the thermopile 2 is a resistor in the equivalent circuit of the thermopile 2, and does not refer only to the resistor actually provided in the thermopile 2.

[0030] Fig. 1 is a block diagram showing a schematic configuration of a fault diagnosis device 1. As shown in Fig. 1, the fault diagnosis device 1 is configured with a switch 10, a capacitor 20, a diagnostic instruction output unit 30, a normal time range setting unit 40, a voltage acquisition unit 50, and a judgment unit 60, and each functional unit is constructed using hardware, software, or both, with a CPU as its core component, in order to perform processing related to the fault diagnosis of the temperature sensor 2. Furthermore, as shown in Fig. 1, the diagnostic instruction output unit 30, the normal time range setting unit 40, the voltage acquisition unit 50, and the judgment unit 60 can be configured using a single microcomputer 3.

[0031] The switch 10 is configured to be switchable between a first state and a second state. The first state is a state in which a predetermined first potential is applied to the thermopile 2. In the example of FIG. 1, the first potential is ground potential. Of course, the first potential may be a potential higher than ground potential. The second state is a state in which a second potential higher than the first potential is applied to the thermopile 2. In the example of FIG. 1, the second potential corresponds to potential V1 higher than ground potential. Therefore, the switch 10 is configured to be able to switch between two different potentials and apply them to the thermopile 2. Of the two potentials, the state in which the lower potential is applied corresponds to the first potential, and the state in which the higher potential is applied corresponds to the second potential. In the example of FIG. 1, the switch 10 is shown as a changeover switch, but it may also be configured as a semiconductor switch using, for example, a transistor, or as a relay.

[0032] The capacitor 20 is connected to the output terminal 2B of the thermopile 2. ground It is provided between the potential. saThe output terminal 2B of the thermopile 2 corresponds to the terminal at which the thermopile 2 outputs the detection result. Therefore, one terminal of the capacitor 20 is connected to the output terminal 2B at which the thermopile 2 outputs the detection result, and the other terminal is connected to ground potential. As described above, the thermopile 2 has a resistor R between the input terminal 2A and the output terminal 2B. Therefore, the resistor R and the capacitor 20 are connected in series between the input terminal 2A of the thermopile 2 and ground potential. In other words, the capacitor 20 forms an integrating circuit consisting of an RC series circuit together with the resistor R of the thermopile 2. An integrating circuit outputs a signal corresponding to the integral value of an input signal, but as this is well known, a detailed description will be omitted.

[0033] The diagnostic instruction output unit 30 outputs a diagnostic instruction to the switch 10. The diagnostic instruction is an instruction to perform a fault diagnosis of the thermopile 2. The fault diagnosis device 1 performs a fault diagnosis of the thermopile 2 in response to this diagnostic instruction. Therefore, if fault diagnosis is to be performed from the time ignition is confirmed in the cooking appliance until the fire is extinguished, the diagnostic instruction may be configured to be output at predetermined time intervals from the time ignition is confirmed in the cooking appliance until the fire is extinguished, and if fault diagnosis is to be performed only when the cooking appliance is ignited, the diagnostic instruction may be configured to be output only after ignition is confirmed in the cooking appliance.

[0034] In this embodiment, the diagnostic instruction includes both a charge instruction to charge the capacitor 20 in a discharged state and a discharge instruction to discharge the capacitor 20 in a charged state. When the switch 10 is in the first state, the potential difference between the two terminals of the capacitor 20 becomes zero. After a sufficient time has passed since this state, the capacitor 20 enters a discharged state. Therefore, in the example of FIG. 1 , the capacitor 20 in a discharged state corresponds to the capacitor 20 after a sufficient time has passed since the switch 10 entered the first state. When the switch 10 is switched to the second state in this state, a potential V1 is applied to one terminal of the capacitor 20 via the resistor R, and a potential difference occurs between the two terminals of the capacitor 20. Therefore, when the switch 10 is switched to the second state while the capacitor 20 is discharged, the capacitor 20 is charged. An instruction to charge the capacitor 20 in such a discharged state corresponds to a charge instruction.

[0035] Furthermore, when switch 10 is in the second state, a potential difference occurs between both terminals of capacitor 20, and after a sufficient amount of time has passed since this state was reached, capacitor 20 enters a charged state. Therefore, in the example of FIG. 1, capacitor 20 in a charged state corresponds to capacitor 20 when a sufficient amount of time has passed since switch 10 entered the second state. When switch 10 is switched to the first state in this state, one terminal of capacitor 20 is connected to ground potential via resistor R, and the charge stored in capacitor 20 moves to ground potential. Therefore, when switch 10 is switched to the first state while capacitor 20 is charged, capacitor 20 is discharged. An instruction to discharge capacitor 20 in such a charged state corresponds to a discharge instruction.

[0036] In this embodiment, the diagnostic instruction is configured to first issue a charge instruction, and then issue a discharge instruction after a predetermined time has elapsed. The predetermined time is determined by the respective characteristics of resistor R and capacitor 20, and is a time equal to or longer than the time required for capacitor 20 to be sufficiently charged in response to the charge instruction when thermopile 2 is in a normal state. Therefore, diagnostic instruction output unit 30 outputs a diagnostic instruction to switch switch 10 to the second state when capacitor 20 is discharged, and after the time required for capacitor 20 to be sufficiently charged by the charge instruction has elapsed, issues a discharge instruction to switch switch 10 to the first state when capacitor 20 is charged.

[0037] The waveform of such a diagnostic instruction is shown in (A) of Figure 2. In the case of the diagnostic instruction in (A) of Figure 2, the rising edge of the diagnostic instruction that switches from the first state to the second state corresponds to a charge instruction, and the falling edge of the diagnostic instruction that switches from the second state to the first state corresponds to a discharge instruction. Of course, depending on the configuration of switch 10, it is also possible for the falling edge of the diagnostic instruction to be a charge instruction and the rising edge of the diagnostic instruction to be a discharge instruction.

[0038] The normal time range setting unit 40 sets the normal time range around a second time point, which is the time elapsed from the first time point when the diagnostic instruction was issued until the potential of the output terminal 2B of the thermopile 2 reaches a reference value consisting of a predetermined potential between the first potential and the second potential. In this embodiment, the diagnostic instruction includes a charge instruction and a discharge instruction. Therefore, the first time point when the diagnostic instruction was issued refers to the time point when the charge instruction was issued and the time point when the discharge instruction was issued. The time point when the charge instruction was issued is the time point when the diagnostic instruction output unit 30 outputs a charge instruction to the switch 10. The time point when the discharge instruction was issued is the time point when the diagnostic instruction output unit 30 outputs a discharge instruction to the switch 10. In FIG. 2A, the time point when the charge instruction was output and the time point when the discharge instruction was output are shown as first time points.

[0039] The reference value, which is a predetermined potential between the first and second potentials, can be set, for example, at a potential that is 1 / 2 the difference between the first and second potentials, with the second potential as the reference. In Fig. 2B, the reference value is set between the ground potential and the sum of V1 and the internal electromotive force Va of the thermopile 2. Of course, the reference value may be set at a potential that is 1 / 4 the difference between the first and second potentials, with the second potential as the reference, or at a potential that is 3 / 4 the difference between the first and second potentials, with the second potential as the reference. Therefore, if the reference value is set to, for example, half the difference between the first and second potentials, with the second potential as the reference, the time from the first time point when the diagnostic instruction is issued until the potential at output terminal 2B of thermopile 2 reaches the reference value consisting of a predetermined potential between the first and second potentials corresponds to the time from the time point when a charge instruction or a discharge instruction is output until the potential at output terminal 2B of thermopile 2 reaches half the difference between the first and second potentials, with the second potential as the reference, when thermopile 2 is normal. The point at which such time has elapsed from the first time point corresponds to the second time point, and normal time range setting unit 40 sets a normal time range having a predetermined range (width) centered around this second time point.

[0040] The time from the first point in time when the diagnostic instruction is given until the potential of the output terminal 2B of the thermopile 2 reaches a reference value consisting of a predetermined potential between the first potential and the second potential can also be set to a time corresponding to the time constant of the capacitance of the capacitor 20 and the resistance value of the resistor R from the first point in time when the diagnostic instruction is given, as shown in Figure 2(B).

[0041] Here, if the voltage at one terminal of capacitor 20 in the RC series circuit is Vc, the internal electromotive force of thermopile 2 is Va, and the time after charging of capacitor 20 begins is t1, Vc when capacitor 20 is charging is given by the following equation (1).

number

[0042] On the other hand, if the time after the start of discharging of the capacitor 20 is set to t2, Vc when the capacitor 20 is being charged is given by the following equation (2).

number

[0043] If the time constant between the capacitance of capacitor 20 and the resistance value of resistor R is τ, the time constant τ is given by the following equation (3).

number

[0044] The voltage waveforms at output terminal 2B, Vc, when capacitor 20 is charged and discharged are shown in Figure 2(B). As shown in Figure 2(B), the time when a time corresponding to the time constant τ between the capacitance of capacitor 20 and the resistance value of resistor R has elapsed from the first time point when a charge command was issued is shown as a second time point, and the time when a time corresponding to the time constant τ between the capacitance of capacitor 20 and the resistance value of resistor R has elapsed from the first time point when a discharge command was issued is shown as a second time point. Normal time range setting unit 40 sets normal time ranges consisting of predetermined ranges centered on each second time point. Since these normal time ranges are used to determine fault diagnosis of thermopile 2, they should be set according to the time constant τ calculated taking into account variations in resistor R.

[0045] The voltage acquiring unit 50 acquires the voltage value of the voltage at the output terminal 2B. The voltage value of the voltage at the output terminal 2B is the voltage value at the output terminal 2B of the thermopile 2, and corresponds to the above-mentioned Vc. Vc is the voltage value of the voltage at the terminal of the capacitor 20 that is charged via the resistor R. Therefore, the voltage acquiring unit 50 acquires the voltage value of the voltage at the terminal of the capacitor 20 that is charged via the resistor R.

[0046] The determination unit 60 determines whether the thermopile 2 is faulty based on the voltage value acquired by the voltage acquisition unit 50, the elapsed time from the first time point until the voltage value reaches the reference value, and a comparison result with the normal time range. The voltage value acquired by the voltage acquisition unit 50 is the voltage value of the terminal of the capacitor 20 to which the resistor R is connected. In the example of FIG. 2, the reference value is a reference value set based on a time constant. When the capacitor 20 is being charged, the reference value set based on the time constant is 63.2% of the potential difference between the two terminals when the capacitor 20 is being charged, and when the capacitor 20 is being discharged, the reference value is 36.8% of the potential difference between the two terminals when the capacitor 20 is being charged (i.e., a value 63.2% lower than the potential in a fully charged state). Therefore, the elapsed time from the first point in time until the voltage value reaches the reference value corresponds to the time from when charging of capacitor 20 begins until the voltage value of the terminal of capacitor 20 that is charged via resistor R reaches 63.2% of the potential difference between the two terminals when capacitor 20 is charged, and corresponds to the time from when discharging of capacitor 20 begins until the voltage value of the terminal of capacitor 20 that is discharged via resistor R reaches 36.8% of the potential difference between the two terminals when capacitor 20 is discharged, when capacitor 20 is discharged.

[0047] The determination unit 60 compares the elapsed time with the normal time range, and further determines whether or not the thermopile 2 is faulty based on the voltage value of the terminal of the capacitor 20 to which the resistor R is connected. A specific description will be given below with reference to the drawings.

[0048] FIG. 3A is an enlarged view of the charge instruction portion included in the diagnostic instruction. FIG. 3B shows the voltage waveform at one terminal of capacitor 20 when thermopile 2 is normal, i.e., not faulty. When a charge instruction is issued, the elapsed time from the first time point when the charge instruction was issued until the reference value is reached is counted. In FIG. 3, the elapsed time is indicated by T. Meanwhile, in the example of FIG. 3, a normal time range is indicated by the range from t1 to t2. This range is set with a predetermined width, centered on the point when a time corresponding to the time constant τ has elapsed from the first time point. Under normal conditions, as shown in FIG. 3B, the elapsed time T falls within the normal time range. Therefore, when t1≦T≦t2 holds, determination unit 60 determines that thermopile 2 is not faulty.

[0049] If thermopile 2 is broken, capacitor 20 cannot be charged even if a charging instruction is issued as a diagnostic instruction. In this case, as shown by (i) in (C) of FIG. 3, the voltage value of one terminal voltage of capacitor 20 in a discharging state does not change, and therefore the voltage value of one terminal voltage of capacitor 20 does not exceed the reference value even if the time from the first time point exceeds the normal time range. Therefore, when the diagnostic instruction is a charging instruction, if the voltage value of one terminal voltage of capacitor 20 does not exceed the reference value even if the time from the first time point exceeds the normal time range, the determination unit 60 determines that thermopile 2 has a broken fault.

[0050] Furthermore, if thermopile 2 is partially open, when a diagnostic instruction to charge is issued, the time it takes for capacitor 20 to charge will be longer than when thermopile 2 is not partially open. In this case, as shown in (ii) in (C) of FIG. 3, the voltage value of one terminal voltage of capacitor 20 will exceed the reference value after exceeding the normal time range. Therefore, when the diagnostic instruction is a charging instruction, if the voltage value of one terminal voltage of capacitor 20 exceeds the reference value after exceeding the normal time range, the determination unit 60 determines that thermopile 2 has an open circuit fault.

[0051] If the thermopile 2 is short - circuited, when there is a charging instruction as a diagnostic instruction, the current charging the capacitor 20 becomes larger compared to the case where the thermopile 2 is normal. In this case, as shown in (D) of FIG. 3, the voltage value of the voltage at one terminal of the capacitor 20 reaches the reference value before the time (elapsed time T) until the voltage value reaches the reference value reaches the normal time range. That is, T < t1 holds. Therefore, when the diagnostic instruction is a charging instruction, if the voltage value of the voltage at one terminal of the capacitor 20 exceeds the reference value before the elapsed time T reaches the normal time range, the determination unit 60 determines that the thermopile 2 has a short - circuit fault.

[0052] Next, the fault diagnosis in the discharge instruction will be described with reference to the drawings. (A) of FIG. 4 is an enlarged view of the part of the discharge instruction included in the diagnostic instruction. (B) of FIG. 4 shows the voltage waveform at one terminal of the capacitor 20 when the thermopile 2 is normal, that is, when it is not faulty. When there is a discharge instruction, the elapsed time from the first time point when the discharge instruction is given until it reaches the reference value is counted. In FIG. 4, the elapsed time is indicated by T. On the other hand, in the example of FIG. 4, the normal time range is shown as the range from t1 to t2. This range is set to have a predetermined width centered around the time point when the time corresponding to the time constant τ has elapsed from the first time point. When normal, as shown in (B) of FIG. 4, the elapsed time T is included in the normal time range. Therefore, when t1 ≦ T ≦ t2 holds, the determination unit 60 determines that the thermopile 2 is not faulty.

[0053] If thermopile 2 is open, capacitor 20 cannot be discharged even if a discharge instruction is issued as a diagnostic instruction. In this case, as shown in (i) in (C) of FIG. 4, capacitor 20 is not charged by a charge instruction. Therefore, the voltage value of one terminal voltage of capacitor 20 does not change from before the first time point when the discharge instruction is issued, and therefore the voltage value of one terminal voltage of capacitor 20 does not fall below the reference value even if the time since the first time point exceeds the normal time range. In other words, when a discharge instruction is issued, Vc<reference value. Therefore, when the diagnostic instruction is a discharge instruction, if the voltage value of one terminal voltage of capacitor 20 has been below the reference value since before the discharge instruction is issued, determination unit 60 determines that thermopile 2 has an open circuit fault.

[0054] Furthermore, if thermopile 2 is partially open, when a discharge instruction is issued as a diagnostic instruction, the time it takes for capacitor 20 to discharge will be longer than when thermopile 2 is not partially open. In this case, as shown in (ii) in (C) of FIG. 4, the voltage value of one terminal voltage of capacitor 20 will exceed the normal time range and fall below the reference value. Therefore, when the diagnostic instruction is a discharge instruction, if the voltage value of one terminal voltage of capacitor 20 exceeds the reference value at the time the discharge instruction is issued and the voltage value of one terminal voltage of capacitor 20 falls below the reference value after elapsed time T reaches the normal time range, the determination unit 60 determines that thermopile 2 has an open circuit fault.

[0055] If the thermopile 2 is short-circuited, when there is a discharge instruction as a diagnostic instruction, the current for discharging the capacitor 20 becomes larger than when the thermopile 2 is normal. In this case, as shown in (D) of FIG. 4, the voltage value of one terminal voltage of the capacitor 20 reaches the reference value before the time from the first time point is included in the normal time range. That is, T < t1 holds. At this time, when the discharge instruction is given (the first time point), Vc > reference value holds. Therefore, when the diagnostic instruction is a discharge instruction, the determination unit 60 determines that the thermopile 2 has a short-circuit failure if the voltage value of one terminal voltage of the capacitor 20 exceeds the reference value at the time when the discharge instruction is given and the voltage value of one terminal voltage of the capacitor 20 falls below the reference value before the elapsed time T reaches the normal time range.

[0056] In this way, the determination unit 60 can discriminate whether the thermopile 2 has an open-circuit failure or a short-circuit failure in one diagnostic instruction. One diagnostic instruction is a diagnostic instruction including at least one of a discharge instruction and a charge instruction. Thereby, as described above, it becomes possible for the determination unit 60 to determine whether the thermopile 2 is normal, has an open-circuit failure, or has a short-circuit failure.

[0057] Next, the specific circuit configuration and specific determination of the failure diagnosis device 1 when the failure diagnosis device 1 diagnoses the failure of the thermopile 2 of the cooking appliance will be described using FIGS. 5 and 6. In the example of FIG. 5, the diagnostic instruction output unit 30, the normal time range setting unit 40, the voltage acquisition unit 50, and the determination unit 60 are shown as the microcomputer 3. The switch 10 is composed of a pnp bipolar transistor (hereinafter referred to as "transistor") Q, a resistor R1, a resistor R2, and a resistor R3. Further, V5 is applied to the resistor R1, and V6 is applied to the emitter terminal of the transistor Q.

[0058] First, before fault diagnosis is performed, terminal A of microcomputer 3 outputs a signal with the same potential as V6. For example, if V6 is 5V, then 5V is output from terminal A before the stove is operated, as shown in Figures 6(A) and 6(B). This turns transistor Q off, and a potential obtained by dividing V5 by resistors R1 and R2 is applied to input terminal 2A of thermopile 2. This potential corresponds to the first potential described above. For example, if V5 = 3.3V, R1 = 10kΩ, and R2 = 510Ω, then 0.16V is applied to input terminal 2A. Therefore, 0.16V is input to terminal B, as shown in Figure 6(C).

[0059] To diagnose a fault in thermopile 2, microcomputer 3 outputs a diagnostic command including a charge command. In the example of FIG. 5, 0 V is output from terminal A as a charge command (see FIG. 6(B)). This turns on transistor Q, and the potential of input terminal 2A of thermopile 2 changes to a potential determined by V5, V6, transistor Q, resistors R1, R2, and R3. This potential corresponds to the second potential described above. For example, if V6=5 V and R3=510 Ω, the potential of input terminal 2A becomes 2.52 V. Therefore, as shown in FIG. 6(C), 2.52 V is input to terminal B.

[0060] At this time, the potential at terminal C of microcomputer 3 transiently changes to the above-mentioned 2.52V due to the charging circuit of resistor R of thermopile 2 and capacitor 20 in response to the switching timing of terminal B (or the timing of switching the microcomputer output voltage), as shown in FIG. 6(D). Meanwhile, since terminal B is connected to input terminal 2A of thermopile 2 as described above, it changes from 0.16V to 2.52V in synchronization with the output of microcomputer 3. As a result of the above operation, the transient change in terminal C exceeds the threshold set between 0.16V and 2.52V, resulting in a delay time from the switching timing of terminal B (or the timing of switching the microcomputer output voltage). For example, if thermopile 2 has an open circuit fault, no current flows and the voltage of capacitor 20 does not change, so the voltage at terminal C never exceeds the voltage at terminal B. In other words, the delay time at terminal C is infinite. Furthermore, when the thermopile 2 is short-circuited, the resistance value of the resistor R becomes 0Ω, so the potential of the terminal C is almost synchronized with the switching of the microcomputer output voltage, and the delay time becomes zero.

[0061] The microcomputer 3 converts the output change at terminal C into a digital signal, reads it, and measures the time from when the voltage at terminal B switches (or when control of terminal A begins) until the potential at terminal C exceeds a threshold using a built-in timer. It then evaluates whether the measured time is within a specified range. If it is within the range, it determines that there is no fault, and if it is outside the range, it determines that there is a fault.

[0062] Next, after the voltage at terminal C reaches the final voltage, 5V is output from terminal A of microcomputer 3 as a discharge command (see FIG. 6(B)). This switches transistor Q to the off state, and the potential at input terminal 2A of thermopile 2 changes from 2.52V to 0.16V. Therefore, as shown in FIG. 6(C), 0.16V is input to terminal B. At this time, due to the discharge circuit of resistor R and capacitor 20 of thermopile 2, the potential at terminal C changes to the final voltage of 0.16V from the timing at which terminal B is switched (or the timing at which the microcomputer output voltage is switched), as shown in FIG. 6(D).

[0063] From the above operation, in order for the potential of terminal C to exceed the threshold value set between 0.16V and 2.52V, a delay time occurs from the switching timing of terminal B (or the timing of switching the microcomputer output voltage). For example, if thermopile 2 has an open circuit fault, no current flows and the voltage of capacitor 20 does not change, so the potential of terminal C does not fall below the potential of terminal B. In other words, the delay time of terminal C is infinite. Furthermore, if thermopile 2 is short-circuited, the resistance value of resistor R becomes 0Ω, so terminal C is nearly synchronized with the switching of the microcomputer output voltage, and the delay time of terminal C is zero.

[0064] The microcomputer 3 converts the output change at terminal C into a digital signal, reads it, and uses a built-in timer to measure the time from when the voltage at terminal B switches (or when control at terminal A begins) until the potential at terminal C exceeds the threshold. It then evaluates whether the measured time is within a specified range. If it is within the range, it determines that there is no fault, and if it is outside the range, it determines that there is a fault.

[0065] Next, we will explain how to determine the threshold value (reference value) and the fault detection range (normal time range). The fault detection range is set taking into account the variation (upper and lower limit values) in the resistance value of resistor R2 of thermopile 2.

[0066] For example, if the resistance value of the resistor R of the thermopile 2 is 500 kΩ±10%, the threshold is 1.18 V (a potential that is half the difference between the first potential and the second potential), and the delay time when the capacitor 20 is charged is Ton (see (D) of FIG. 6), the range of Ton is as follows: 25ms≦Ton≦32ms. When converted to resistance value, 450kΩ≦R≦550kΩ.

[0067] In other words, it is possible to detect not only complete disconnections or complete short circuits in the thermopile 2, but also faults in which the resistance value of the resistor R in the thermopile 2 changes, which corresponds to a time delay of 25 ms or less or 32 ms or more.

[0068] On the other hand, if the delay time when the capacitor 20 is discharged is Toff (see (D) of FIG. 6), the range of Toff is as follows: 37ms≦Toff≦47ms. When converted to resistance, 450kΩ≦R≦550kΩ.

[0069] In other words, it is possible to detect not only complete disconnections or complete short circuits in thermopile 2, but also faults in which the resistance value of resistor R in thermopile 2 changes, corresponding to a time delay of 37 ms or less or 47 ms or more.

[0070] The capacitance of capacitor 20 must be set so that the time it takes for the threshold to be exceeded is longer than twice the fault detection processing cycle (10 ms) of the microcomputer program. Furthermore, since fault detection of thermopile 2 is performed during initial diagnosis immediately after startup, there is a delay until the steady state (temperature detection) is reached. Therefore, it is advisable to set the capacitance appropriately according to the system requirements.

[0071] In a cooking appliance, for example, if the temperature of the heated object is monitored by a non-contact temperature sensor at 100 ms intervals from when the ignition is turned on and confirmed until the fire is extinguished, it is advisable to complete failure detection of the non-contact temperature sensor within 100 ms after ignition is confirmed (32 ms + 47 ms < 100 ms).

[0072] Other Embodiments (1) In the above embodiment, the diagnostic instruction output unit 30 is described as outputting a diagnostic instruction including a charge instruction and a discharge instruction to the switch 10. However, the diagnostic instruction output unit 30 may be configured to output a diagnostic instruction including only a charge instruction to the switch 10, or may be configured to output a diagnostic instruction including only a discharge instruction to the switch 10.

[0073] (2) In the above embodiment, the judgment unit 60 is described as being capable of determining whether the temperature sensor 2 has an open circuit fault or a short circuit fault in response to a single diagnostic instruction. However, the judgment unit 60 may be configured to not determine whether the temperature sensor 2 has an open circuit fault or a short circuit fault in response to a single diagnostic instruction, but to determine that both are faulty.

[0074] (3) In the above embodiment, the determination unit 60 makes a determination when the diagnostic instruction is a charge instruction and when the diagnostic instruction is a discharge instruction. However, the determination may be made in other ways.

[0075] (4) In the above embodiment, the temperature sensor 2 is described as being a thermopile. However, the thermopile is merely an example, and the temperature sensor 2 may be something other than a thermopile.

[0076] (5) In the above embodiment, the temperature sensor 2 is described as monitoring the temperature of the heated object heated by the cooking appliance. However, the temperature sensor 2 can also be provided in an apparatus or device other than the cooking appliance and configured to monitor the temperature of the object used in the apparatus or device.

[0077] (6) In the above embodiment, the diagnostic instruction output unit 30 is described as outputting a diagnostic instruction when the cooking appliance is turned on. However, the diagnostic instruction output unit 30 can also be configured to continue outputting a diagnostic instruction even after the cooking appliance is turned on.

[0078] (7) In the above embodiment, the delay times (Ton, Toff) are calculated and explained taking into account the variation in the resistance value of the resistor R of the thermopile 2. This is an explanation for ease of understanding, and in practice, the delay times should be calculated taking into account the variation in the other components (resistors, capacitor 20, amplifier, etc.).

[0079] The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0080] The present invention can be used in a failure diagnosis device that diagnoses failures in temperature sensors. [Explanation of symbols]

[0081] 1: Fault diagnosis device 2: Temperature sensor 2A: Input terminal 2B: Output terminal 10: Switch 20: Capacitor 30: Diagnostic instruction output unit 40: Normal time range setting section 50: Voltage acquisition unit 60: Judgment section

Claims

1. A fault diagnosis device for diagnosing a fault in a temperature sensor, comprising: a switch that can be switched between a first state in which a predetermined first potential is applied to the temperature sensor and a second state in which a second potential higher than the first potential is applied to the temperature sensor; a capacitor provided between the output terminal of the temperature sensor and a ground potential, the capacitor constituting an integrating circuit including a resistor of the temperature sensor and an RC series circuit; a diagnostic instruction output unit that outputs to the switch a diagnostic instruction including at least one of a charge instruction to charge the capacitor that is in a discharged state and a discharge instruction to discharge the capacitor that is in a charged state; a normal time range setting unit that sets a normal time range centered on a second time point when a time has elapsed since the first time point when the diagnosis instruction was issued until the potential of the output terminal reaches a reference value that is a predetermined potential between the first potential and the second potential; and a voltage acquisition unit that acquires a voltage value of the voltage at the output terminal; a determination unit that determines whether the temperature sensor is faulty based on the voltage value acquired by the voltage acquisition unit, the elapsed time from the first time point until the voltage value reaches the reference value, and a comparison result with the normal time range; Equipped with The determination unit is a fault diagnosis device that can continuously diagnose the temperature sensor based on charging the capacitor and diagnosing the temperature sensor based on discharging the capacitor using the current flowing through the resistor of the temperature sensor.

2. 2. The fault diagnosis device according to claim 1, wherein the determining unit is capable of determining whether the temperature sensor has an open circuit fault or a short circuit fault in response to one of the diagnostic instructions.

3. When the diagnostic instruction is the charging instruction, 3. The fault diagnosis device according to claim 1, wherein the determination unit determines that the temperature sensor has an open circuit fault if the voltage value does not exceed the reference value even when the time from the first point in time exceeds the normal time range, or if the voltage value exceeds the reference value after the normal time range has been exceeded.

4. When the diagnostic instruction is the charging instruction, 4. The fault diagnosis device according to claim 1, wherein the determination unit determines that the temperature sensor has a short-circuit fault if the voltage value exceeds the reference value before the elapsed time reaches the normal time range.

5. When the diagnostic instruction is the discharge instruction, 5. The fault diagnosis device according to claim 1, wherein the determination unit determines that the temperature sensor has an open circuit fault if the voltage value has been below the reference value before the discharge instruction was given, or if the voltage value was above the reference value at the time the discharge instruction was given and the voltage value has fallen below the reference value after the elapsed time has reached the normal time range.

6. When the diagnostic instruction is the discharge instruction, 6. The fault diagnosis device according to claim 1, wherein the determination unit determines that the temperature sensor has a short-circuit fault if the voltage value exceeds the reference value at the time the discharge instruction is issued and the voltage value falls below the reference value before the elapsed time reaches the normal time range.

7. 7. The fault diagnosis device according to claim 1, wherein the temperature sensor is a thermopile.

8. The fault diagnosis device according to claim 1 , wherein the temperature sensor monitors the temperature of an object to be heated by the cooking appliance.

9. The fault diagnosis device according to claim 8 , wherein the diagnostic instruction output unit outputs the diagnostic instruction when the cooking appliance is turned on.

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