JP7822210B2 - Fault diagnosis device - Google Patents

Description

The present invention relates to a fault diagnosis device that diagnoses faults in temperature sensors.

Conventionally, combustion-type heating devices have used a function to detect the temperature of the bottom of a cooking device such as a pot using a temperature sensor and automatically stop combustion based on the detection results to prevent empty-fire and oil fires. If such a temperature sensor malfunctions, combustion cannot be stopped when necessary, so technology that can determine whether a temperature sensor is malfunctioning has been investigated.

Patent Document 1 discloses a combustion-type heating device. This combustion-type heating device is equipped with a first temperature detection means that detects the temperature of the small-fire heating portion that heats the heated object in a small-fire heating state where the amount of heat is small; a second temperature detection means that detects the temperature of the large-fire heating portion that heats the heated object in a large-fire heating state where the amount of heat is large; and a temperature estimation means that estimates the temperature of the heated object based on the temperature detection values of the first temperature detection means and the second temperature detection means. 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 elapsed since the start of heating, the temperature detection means that detected the temperature detection value is determined to be abnormal.

Patent Document 2 discloses a non-contact temperature detection device. This non-contact temperature detection device includes a temperature sensor with a sensor element that detects the temperature of an object without contact, an inspection circuit connected to the sensor element and inspecting 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.

Patent Document 3 discloses a method for detecting abnormalities 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 disconnections in the thermocouple. This method for detecting abnormalities in a non-contact temperature sensor involves 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.

JP 2012-189281 A Japanese Patent Application Laid-Open No. 2001-153726 Japanese Patent Application Laid-Open No. 2006-184097

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 are capable of detecting open circuit faults, but are unable to detect short circuit faults. As a result, it may not be possible to reliably diagnose (detect) faults.

Therefore, there is a need for a fault diagnosis device that is inexpensive and can diagnose temperature sensor faults.

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;
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 judgment unit is capable of continuously diagnosing the temperature sensor based on the charging of the capacitor and diagnosing the temperature sensor based on the discharging of the capacitor using the current flowing through the resistor of the temperature sensor .

For example, if the temperature sensor has a short circuit, the resistance value of the temperature sensor's resistor will decrease relative to its normal value (the value in a normal state), and if the temperature sensor has an open circuit, the resistance value of the temperature sensor's resistor will increase relative to its normal value (the value in a normal state). Therefore, as in the characteristic configuration described above, an integrating circuit is formed using the temperature sensor's resistor and capacitor, and whether the temperature sensor has failed can be determined by whether the time (elapsed time) until the voltage value of the temperature sensor's output terminal, which corresponds to the potential at one terminal of the capacitor, reaches a predetermined reference value falls within the normal time range. In this way, fault diagnosis is performed using the temperature sensor's resistor and capacitor, allowing for a simple configuration. Therefore, it is possible to diagnose temperature sensor faults with an inexpensive configuration.

It is also preferable that the determination unit be able to determine whether the temperature sensor has an open circuit fault or a short circuit fault in response to a single diagnostic instruction.

For example, if the time (elapsed time) until the voltage value of the temperature sensor's output terminal, which corresponds to the potential of one terminal of the capacitor, reaches a predetermined reference value in response to a single diagnostic instruction is shorter than the lower limit of the normal time range, it can be determined that the temperature sensor's resistor has a short-circuit failure; 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 temperature sensor's resistor has an open circuit failure. Therefore, with a single diagnostic instruction, it is possible to determine whether the temperature sensor has an open circuit failure or a short-circuit failure.

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 point in time exceeds the normal time range, or if the voltage value exceeds the reference value after exceeding the normal time range.

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

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.

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

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.

With this configuration, if the diagnostic command includes at least a discharge command, it becomes possible to quantitatively determine whether the temperature sensor is broken.

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.

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.

The temperature sensor may also be a thermopile.

Even if the temperature sensor is a thermopile, it is possible to properly determine whether the thermopile has an open circuit or short circuit.

The temperature sensor may also monitor the temperature of an object being heated by a cooking appliance.

This configuration makes it possible to detect malfunctions in the temperature sensor that monitors the temperature of the heated object in the cooking appliance and prevent erroneous detection of the temperature of the heated object.

Furthermore, it is preferable that the diagnostic instruction output unit outputs the diagnostic instruction when the cooking appliance is ignited.

With this configuration, it is possible to detect a malfunction in the temperature sensor that monitors the temperature of the heated object in the cooking appliance each time the appliance is ignited.

FIG. 1 is a block diagram illustrating a configuration of a fault diagnosis device. 10A and 10B are diagrams illustrating a diagnostic instruction and a voltage waveform at an output terminal. 10A and 10B are explanatory diagrams of determinations made by a determination unit regarding a charging instruction. 10A and 10B are explanatory diagrams of determinations made by a determination unit regarding a discharge instruction. FIG. 2 is a diagram showing a circuit configuration of a fault diagnosis device. FIG. 10 is a diagram illustrating an example of a determination made by the fault diagnosis device.

The fault diagnosis device of the present invention is capable of diagnosing faults in temperature sensors. The fault diagnosis device 1 of this embodiment is described below.

In this embodiment, the fault diagnosis device 1 diagnoses faults in a non-contact temperature sensor, which is an example of a temperature sensor 2. Specifically, a 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, below, the temperature sensor 2 will be described as thermopile 2. Note that resistor R of thermopile 2 is a resistor in the equivalent circuit of thermopile 2, and does not refer only to the resistor actually provided in thermopile 2.

Figure 1 is a block diagram that schematically illustrates the configuration of the fault diagnosis device 1. As shown in Figure 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. 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 Figure 1, the diagnostic instruction output unit 30, normal time range setting unit 40, voltage acquisition unit 50, and judgment unit 60 can be configured using a single microcomputer 3.

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, which is 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 these 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 selector switch, but it may also be configured as a semiconductor switch using, for example, a transistor, or a relay.

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

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 it is extinguished, the diagnostic instruction can be configured to be output at predetermined intervals from the time ignition is confirmed in the cooking appliance until it is extinguished. If fault diagnosis is to be performed only when the cooking appliance is ignited, the diagnostic instruction can be configured to be output only after ignition is confirmed in the cooking appliance.

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, and if a sufficient amount of time has passed since this state was reached, the capacitor 20 will be in a discharged state. Therefore, in the example of Figure 1, the capacitor 20 in a discharged state corresponds to the capacitor 20 when a sufficient amount of time has passed since the switch 10 was in the first state. When the switch 10 is switched to the second state in this state, potential V1 is applied to one terminal of the capacitor 20 via resistor R, creating a potential difference between the two terminals of the capacitor 20. Therefore, when the switch 10 is switched to the second state while the capacitor 20 is in a discharged state, the capacitor 20 will be charged. An instruction to charge the capacitor 20 in such a discharged state corresponds to a charge instruction.

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

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 the resistor R and the capacitor 20, and is equal to or greater than the time required for the capacitor 20 to be fully charged in response to the charge instruction when the thermopile 2 is in a normal state. Therefore, the diagnostic instruction output unit 30 issues a charge instruction to switch the switch 10 to the second state when the capacitor 20 is discharged, and after the time required for the capacitor 20 to be fully charged by the charge instruction has elapsed, outputs a diagnostic instruction to the switch 10 to issue a discharge instruction to switch the switch 10 to the first state when the capacitor 20 is charged.

Figure 2 (A) shows the waveform of such a diagnostic instruction. In the case of the diagnostic instruction in Figure 2 (A), 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.

The normal time range setting unit 40 sets the normal time range centered on 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 and second potentials. 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 Figure 2 (A), 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.

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 Figure 2 (B), the reference value is set between the ground potential and the sum of V1 and the internal electromotive force Va of thermopile 2. Of course, it may also 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, using the second potential as the reference, the time from the first point in time when the diagnostic command is issued until the potential of output terminal 2B of thermopile 2 reaches the reference value, which is a predetermined potential between the first and second potentials, corresponds to the time from the point in time when a charge command or a discharge command is output until the potential of output terminal 2B of thermopile 2 reaches half the difference between the first and second potentials, using the second potential as the reference, when thermopile 2 is normal. The point in time after which this amount of time has elapsed from the first point in time corresponds to the second point in time, and normal time range setting unit 40 sets a normal time range having a predetermined range (width) centered around this second point in time.

The time from the first point in time when the diagnostic command is issued until the potential of output terminal 2B of thermopile 2 reaches a reference value consisting of a predetermined potential between the first and second potentials can also be determined based on the time constant of the capacitance of capacitor 20 and the resistance value of resistor R from the first point in time when the diagnostic command is issued, as shown in Figure 2 (B).

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 during charging of capacitor 20 is given by the following equation (1).

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

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

The voltage waveform at output terminal 2B, Vc, when capacitor 20 is charging and discharging is shown in Figure 2(B). As shown in Figure 2(B), the second point in time is 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 point in time when a charge command was issued, and the second point in time is 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 point in time when a discharge command was issued. The normal time range setting unit 40 sets a normal time range consisting of a predetermined range centered on each second point in time. Since this normal time range is used to determine a fault diagnosis of thermopile 2, it is preferable to set it according to the time constant τ calculated taking into account variability in resistor R.

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

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 point in time until the voltage value reaches the reference value, and the result of comparing 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 Figure 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 terminals when the capacitor 20 is being charged, and when the capacitor 20 is being discharged, it is 36.8% of the potential difference between the 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.

The determination unit 60 compares the elapsed time with the normal time range, and further determines whether 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 detailed explanation is provided below using the diagram.

Figure 3A shows an enlarged view of the charge instruction portion of the diagnostic instruction. Figure 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 point in time when the charge instruction was issued until the reference value is reached is counted. In Figure 3, the elapsed time is indicated by T. Meanwhile, in the example of Figure 3, the normal time range is indicated by the range from t1 to t2. This range is set with a predetermined width, centered on the point at which a time corresponding to the time constant τ has elapsed from the first point in time. Under normal conditions, as shown in Figure 3B, the elapsed time T falls within the normal time range. Therefore, when t1 ≤ T ≤ t2 holds, the determination unit 60 determines that thermopile 2 is not faulty.

If thermopile 2 is open, capacitor 20 cannot be charged even if a diagnostic instruction to charge is issued. In this case, as shown by (i) in Figure 3(C), the voltage value of one terminal of capacitor 20 in a discharging state does not change, so even if the time since the first point in time exceeds the normal time range, the voltage value of one terminal of capacitor 20 will not exceed the reference value. Therefore, when the diagnostic instruction is an instruction to charge, if the voltage value of one terminal of capacitor 20 does not exceed the reference value even if the time since the first point in time exceeds the normal time range, the determination unit 60 determines that thermopile 2 has an open circuit fault.

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 Figure 3C, 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 an instruction to charge, 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.

If thermopile 2 is short-circuited, and a diagnostic instruction to charge is issued, the current charging capacitor 20 will be larger than when thermopile 2 is normal. In this case, as shown in Figure 3 (D), the voltage value of one terminal voltage of capacitor 20 will reach the reference value before the time (elapsed time T) until it reaches the reference value falls within the normal time range. In other words, T < t1 holds. Therefore, when the diagnostic instruction is a charging instruction, if the voltage value of one terminal voltage of capacitor 20 exceeds the reference value before the elapsed time T reaches the normal time range, the determination unit 60 determines that thermopile 2 has a short-circuit fault.

Next, fault diagnosis in response to a discharge command will be explained using diagrams. Figure 4A is an enlarged view of the discharge command portion included in the diagnostic command. Figure 4B shows the voltage waveform at one terminal of capacitor 20 when thermopile 2 is normal, i.e., not faulty. When a discharge command is issued, the elapsed time from the first point in time when the discharge command is issued until the reference value is reached is counted. In Figure 4, the elapsed time is indicated by T. Meanwhile, in the example of Figure 4, the normal time range is indicated by the range from t1 to t2. This range is set with a predetermined width, centered on the point at which a time corresponding to the time constant τ has elapsed since the first point in time. Under normal conditions, as shown in Figure 4B, the elapsed time T falls within the normal time range. Therefore, when t1 ≤ T ≤ t2 holds, the determination unit 60 determines that thermopile 2 is not faulty.

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 by (i) in (C) of Figure 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 point in time when the discharge instruction is issued. Therefore, even if the time since the first point in time exceeds the normal time range, the voltage value of one terminal voltage of capacitor 20 will not fall below the reference value. 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, the determination unit 60 determines that thermopile 2 has an open circuit fault.

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 Figure 4C, 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 the elapsed time T reaches the normal time range, the determination unit 60 determines that thermopile 2 has an open circuit fault.

If thermopile 2 is short-circuited, when a discharge instruction is issued as a diagnostic instruction, the current discharging capacitor 20 will be larger than when thermopile 2 is normal. In this case, as shown in Figure 4 (D), the voltage value of one terminal voltage of capacitor 20 reaches the reference value before the time from the first time point falls within the normal time range. In other words, T<t1 holds. Note that at this time, Vc>reference value holds at the time of the discharge instruction (first time point). Therefore, when the diagnostic instruction is a discharge instruction, if the voltage value of one terminal voltage of capacitor 20 exceeds the reference value when the discharge instruction is issued and the voltage value of one terminal voltage of capacitor 20 falls below the reference value before the elapsed time T reaches the normal time range, the determination unit 60 determines that thermopile 2 has a short-circuit fault.

In this way, the determination unit 60 can determine whether the thermopile 2 has an open circuit fault or a short circuit fault based on a single diagnostic instruction. A single diagnostic instruction is a diagnostic instruction that includes at least one of a discharge instruction and a charge instruction. This allows the determination unit 60 to determine whether the thermopile 2 is normal, has an open circuit fault, or has a short circuit fault, as described above.

Next, the specific circuit configuration and specific judgments of the fault diagnosis device 1 when the fault diagnosis device 1 performs a fault diagnosis on the thermopile 2 of a cooking appliance will be described using Figures 5 and 6. In the example of Figure 5, the diagnostic instruction output unit 30, normal time range setting unit 40, voltage acquisition unit 50, and judgment unit 60 are shown as the microcomputer 3. Furthermore, the switch 10 is composed of a pnp bipolar transistor (hereinafter referred to as "transistor") Q, resistors R1, R2, and R3. Furthermore, V5 is applied to resistor R1, and V6 is applied to the emitter terminal of transistor Q.

First, before fault diagnosis is performed, terminal A of microcontroller 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, as shown in Figure 6(C), 0.16V is input to terminal B.

To diagnose a fault in thermopile 2, microcomputer 3 outputs a diagnostic command, including a charge command. In the example of Figure 5, 0V is output from terminal A as a charge command (see Figure 6 (B)). This turns transistor Q on, 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 = 5V and R3 = 510Ω, the potential of input terminal 2A is 2.52V. Therefore, as shown in Figure 6 (C), 2.52V is input to terminal B.

At this time, the charging circuit consisting of resistor R and capacitor 20 of thermopile 2 transiently changes the potential of terminal C of microcontroller 3 to the aforementioned 2.52V in response to the switching timing of terminal B (or the timing of the microcontroller output voltage switching), as shown in Figure 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 microcontroller 3. From the above operation, the transient change in terminal C exceeds the threshold set between 0.16V and 2.52V, resulting in a delay from the switching timing of terminal B (or the timing of the microcontroller output voltage switching). For example, if thermopile 2 has an open circuit failure, no current flows and the voltage of capacitor 20 does not change, so the voltage of terminal C never exceeds the voltage of terminal B. In other words, the delay time of terminal C is infinite. Furthermore, when thermopile 2 is short-circuited, the resistance value of resistor R becomes 0 Ω, so the potential at terminal C is nearly synchronized with the microcomputer output voltage switching, and the delay time becomes zero.

Microcontroller 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 of terminal A begins) until the potential at terminal C exceeds a 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; if it is outside the range, it determines that there is a fault.

Next, after the voltage at terminal C reaches the final voltage, 5V is output from terminal A of microcontroller 3 as a discharge command (see Figure 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 Figure 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 of switching terminal B (or the timing of switching the microcontroller output voltage), as shown in Figure 6 (D).

From the above operation, for the potential at terminal C to exceed the threshold set between 0.16V and 2.52V, a delay time will occur from the timing of switching terminal B (or the timing of switching the microcontroller 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 at terminal C will never fall below the potential at terminal B. In other words, the delay time at terminal C is infinite. Furthermore, if thermopile 2 is short-circuited, the resistance value of resistor R becomes 0Ω, so terminal C will be nearly synchronized with the switching of the microcontroller output voltage, and the delay time at terminal C will be zero.

Microcontroller 3 converts the output change at terminal C into a digital signal and reads it, then 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; if it is outside the range, it determines that there is a fault.

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

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 during charging of the capacitor 20 is Ton (see (D) in FIG. 6), the range of Ton is as follows:
25 ms≦Ton≦32 ms. When converted to a resistance value,
450 kΩ≦R≦550 kΩ.

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 25 ms or less or 32 ms or more.

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

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.

The capacitance of capacitor 20 must be set so that the time it takes to exceed the threshold is longer than twice the fault detection processing cycle (10 ms) of the microcomputer program. Furthermore, since fault detection for 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.

For example, in a cooking appliance, if the temperature of the heated object is monitored every 100 ms using a non-contact temperature sensor after the ignition is confirmed and the ignition is turned off, it is recommended that failure detection of the non-contact temperature sensor be completed within 100 ms after ignition is confirmed (32 ms + 47 ms < 100 ms).

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.

(2) In the above embodiment, the determination unit 60 was described as being able to determine whether the temperature sensor 2 has an open circuit fault or a short circuit fault in response to a single diagnostic instruction. However, the determination unit 60 may also be configured to determine that the temperature sensor 2 has both an open circuit fault and a short circuit fault in response to a single diagnostic instruction.

(3) In the above embodiment, the determination unit 60 makes a determination when the diagnostic instruction is a charge instruction or a discharge instruction, but other methods may also be used to make the determination.

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

(5) In the above embodiment, the temperature sensor 2 was described as monitoring the temperature of the object being 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 items used in these.

(6) In the above embodiment, the diagnostic instruction output unit 30 was 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 diagnostic instructions even after the cooking appliance is turned on.

(7) In the above embodiment, the delay time (Ton, Toff) was calculated and explained taking into account the variation in the resistance value of resistor R of thermopile 2. This is an explanation for ease of understanding, and in practice, it is better to calculate it taking into account the variation in other components (resistors, capacitor 20, amplifier, etc.).

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, provided that no contradictions arise. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments. They can be modified as appropriate within the scope of the purpose of the present invention.

The present invention can be used in a fault diagnosis device that diagnoses faults in temperature sensors.

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 unit 50: Voltage acquisition unit 60: Determination unit

Claims (9)

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 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 result of comparison 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 . The fault diagnosis device described in claim 1, wherein the determination unit is capable of determining whether the temperature sensor has an open circuit fault or a short circuit fault in response to a single diagnostic instruction. 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. 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. 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. 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. A fault diagnosis device according to any one of claims 1 to 6, wherein the temperature sensor is a thermopile. A fault diagnosis device according to any one of claims 1 to 7, wherein the temperature sensor monitors the temperature of an object being heated by a cooking appliance. The fault diagnosis device described in claim 8, wherein the diagnostic instruction output unit outputs the diagnostic instruction when the cooking appliance is ignited.