JP7285145B2 - Voltage detector - Google Patents

Description

The present invention includes an AD converter that converts a voltage value into a digital value for detection, and a plurality of analog input ports. By switching the analog input port connected to the AD converter, the voltage value of the analog input port can be The present invention relates to a voltage value detection device for detection.

Nowadays, computers are installed in various devices, and it is possible to execute complicated control using computers. The computer acquires various kinds of information when executing control, and executes control while reflecting the content of the information. In addition, the information acquired by the computer includes digital value information such as switch settings and data output from other computers, and analog value information such as voltage values output from various sensors. exists. For example, in the computer of a water heater that generates hot water by burning fuel gas, the setting contents of various switches and the hot water temperature set by the user are acquired as digital value information, and water is supplied to the water heater. The temperature and the temperature of hot water discharged from the water heater are acquired as analog value information.

Here, since the computer cannot directly handle analog values, it is necessary to convert the analog values to digital values in order to obtain the analog values. In the case of a water heater, it is necessary to convert the voltage value output from the temperature sensor into a digital value, and a so-called AD converter is used for this purpose. Conversion from an analog value to a digital value is called AD conversion. Also, the number of pieces of information to be AD-converted is not limited to one. For example, water heaters are equipped with multiple temperature sensors, such as a temperature sensor for detecting the temperature of the water supply (hereinafter referred to as the water supply temperature sensor) and a temperature sensor for detecting the temperature of the discharged hot water (hereinafter referred to as the temperature sensor). ing. In such a case, if an AD converter is mounted for each analog value to be AD-converted (that is, for each temperature sensor), it will be necessary to mount many AD converters. Therefore, a plurality of analog input ports are provided, and analog values to be AD-converted are input to the analog input ports. In general, one AD converter can AD-convert a plurality of analog values by switching analog input ports connected to the AD converter. Furthermore, AD conversion takes a certain amount of time, so if the voltage value changes during AD conversion, a correct digital value cannot be obtained. Therefore, a correct digital value can be obtained by providing a capacitor upstream of the AD converter so that the voltage value is held during the AD conversion (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2001-244813

However, if a single AD converter can detect multiple voltage values by switching between multiple analog input ports, an incorrect voltage value will be detected if a failure such as poor contact or disconnection occurs at the analog input port. There was a problem that it would be done. The reason for this is that, for example, if a certain analog input port fails, even if the analog input port is switched to, the voltage value of the switched analog input port is not transmitted to the capacitor on the upstream side of the AD converter. Therefore, the capacitor retains the voltage value of the analog input port before switching, and as a result of the AD conversion of that voltage value, the voltage value of the analog input port before switching becomes This is because it is detected as the voltage value of the port.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems of the prior art. An object of the present invention is to provide a voltage value detection device that does not detect an erroneous voltage value even when an analog input port fails.

In order to solve the above-described problems, the voltage value detection device of the present invention employs the following configuration. i.e.
A voltage value detector for converting a voltage value into a digital value for detection and a plurality of analog input ports, wherein the voltage value of the analog input port is switched by switching the analog input port connected to the voltage value detector. In a voltage value detection device that detects
The voltage value detector has a voltage value holding capacitor that holds the voltage value of the analog input port by storing charge from the connected analog input port, and the voltage value held by the voltage value holding capacitor. is detected as the voltage value of the analog input port,
a specific port preselected from among the plurality of analog input ports;
a target port selected from the plurality of analog input ports excluding the specific port;
reference state generating means for generating a reference state in which a predetermined reference voltage is input to the specific port and the specific port is connected to the voltage value detector;
detection state generation means for generating a detection state for detecting the voltage value input to the target port by connecting the target port to the voltage value detector;
When the voltage difference between the reference voltage detected by the voltage value detector in the reference state and the detected voltage detected by the voltage value detector in the detection state is equal to or greater than a predetermined threshold voltage, a port fault diagnosis means for diagnosing that the target port is not faulty ;
A voltage at a connection point between a detection resistor and a sensor connected in series with the detection resistor is input to the target port, and an upstream of a detection unit to which the detection resistor and the sensor are connected in series. A power supply is connected to the side, and the downstream side of the detection unit is grounded,
resistance value switching means for switching the resistance value of the detection resistor,
The port failure diagnosis means includes:
When the voltage difference between the reference voltage and the detection voltage is smaller than the threshold voltage, the re-detection voltage detected by the voltage value detector is acquired again while the resistance value of the detection resistor is switched. do,
if the voltage difference between the redetected voltage and the reference voltage is equal to or greater than the threshold voltage, diagnosing that the target port is not malfunctioning;
If the voltage difference between the redetected voltage and the reference voltage is smaller than the threshold voltage, the target port is diagnosed as faulty.
It is characterized by

In the voltage value detection device of the present invention, the reference voltage is detected by connecting the specific port to which the reference voltage is input among the plurality of analog input ports to the voltage value detector. Also, the voltage value of the target port is detected by selecting the target port from among the plurality of analog input ports, excluding the specific port, and connecting the target port to the voltage value detector. Also, the following voltages are input to the target port. A detection resistor is connected in series with the sensor, a power supply is connected to the upstream side of the sensor and the detection resistor, the downstream side of the sensor and the detection resistor is grounded, and the voltage at the connection point between the sensor and the detection resistor is into the target port. Also, the resistance value of the detection resistor is made switchable. When the voltage difference between the reference voltage detected by connecting the specific port and the voltage value detected by connecting the target port is equal to or greater than a predetermined threshold voltage, it is determined that the target port is not malfunctioning. . Furthermore, when the voltage difference between the detected voltage obtained by connecting the target port to the voltage value detector and the reference voltage is smaller than the threshold voltage, the voltage value is detected by switching the resistance value of the detection resistor. A detector is used to detect the re-detected voltage and compare the re-detected voltage with the reference voltage. As a result, if the voltage difference between the re-detected voltage and the reference voltage is equal to or greater than the threshold voltage, the target port is diagnosed as not malfunctioning. Diagnose that there is

The voltage value detected by the voltage value detector is held in a voltage value holding capacitor, and when the target port is connected to the voltage value detector, the voltage value of the voltage value holding capacitor changes to the voltage value of the target port. At this time, if the voltage value of the voltage value holding capacitor is higher than the voltage value of the target port, the voltage of the voltage value holding capacitor will be discharged via the target port, and the voltage value of the voltage value holding capacitor will be discharged. If the value is lower than the voltage value of the target port, the voltage value holding capacitor is charged via the target port. However, if the target port fails, it will be difficult to discharge or charge the voltage via the target port, so the voltage value of the voltage value holding capacitor will not change or the amount of change will be small. . Therefore, if the voltage difference between the reference voltage detected by connecting the specific port and the voltage value detected by connecting the target port is greater than or equal to the threshold voltage, the voltage of the voltage value holding capacitor will be applied to the target port. Therefore, it can be determined that the target port is not out of order. In addition, by switching the resistance value of the detection resistor, the voltage value at the connection point between the detection resistor and the sensor changes, so the voltage value input to the target port also switches. Therefore, even if the voltage value of the target port approaches the reference voltage and the voltage difference from the reference voltage becomes smaller than the threshold voltage, the failure of the target port can be detected by switching the resistance value of the detection resistor. can be diagnosed.

Further, as described above, in the voltage value detection device of the present invention that detects the voltage value by inputting the voltage at the connection point between the sensor and the detection resistor to the target port, the reference voltage is set within the following voltage range. It is good to do. First, as a sensor, a resistance temperature detector whose resistance value changes according to temperature is adopted. Set minimum and maximum possible temperatures. If the voltage value of the sensor output at the highest temperature is lower than the voltage value of the sensor output at the lowest temperature, the sensor output at the highest temperature is detected before and after switching the resistance value of the detection resistor. , and the higher voltage value plus the threshold voltage is set as the lower limit voltage value of the voltage range in which the reference voltage can be set. On the other hand, if the voltage value of the sensor output at the highest temperature is higher than the voltage value of the sensor output at the lowest temperature, the sensor output at the lowest temperature before and after switching the resistance value of the detection resistor The voltage value obtained by adding the threshold voltage to the higher voltage value detected is set as the lower limit voltage value of the voltage range in which the reference voltage can be set. Also, the upper limit voltage value of the voltage range in which the reference voltage can be set is set to the following voltage value. First, if the voltage value of the sensor output at the highest temperature is lower than the voltage value of the sensor output at the lowest temperature, detect the sensor output at the lowest temperature before and after switching the resistance value of the detection resistor. , the voltage value obtained by subtracting the threshold voltage from the lower voltage value is set as the upper limit voltage value of the settable voltage range. On the other hand, if the voltage value of the sensor output at the highest temperature is higher than the voltage value of the sensor output at the lowest temperature, the sensor output at the highest temperature before and after switching the resistance value of the detection resistor A voltage value obtained by subtracting the threshold voltage from the lower voltage value detected may be used as the upper limit voltage value of the voltage range in which the reference voltage can be set.

If the voltage range in which the reference voltage can be set is set to the voltage range determined by the lower limit voltage value and the upper limit voltage value, either the voltage value of the sensor output before or after switching the resistance value can be used as the reference voltage. becomes larger than the threshold voltage. Therefore, regardless of the temperature to be detected, it is possible to diagnose whether or not the target port has a failure.

Also, the voltage value detection device of the present invention can be grasped in the following manner. i.e.
A voltage value detector for converting a voltage value into a digital value for detection and a plurality of analog input ports, wherein the voltage value of the analog input port is switched by switching the analog input port connected to the voltage value detector. In a voltage value detection device that detects
The voltage value detector has a voltage value holding capacitor that holds the voltage value of the analog input port by storing charge from the connected analog input port, and the voltage value held by the voltage value holding capacitor. is detected as the voltage value of the analog input port,
The voltage at the connection point between the detection resistor and the sensor connected in series with the detection resistor is input to the analog input port, and the detection unit in which the detection resistor and the sensor are connected in series. A power supply is connected to the upstream side, and the downstream side of the detection unit is grounded,
resistance value switching means for switching the resistance value of the detection resistor;
a target port selected from among the plurality of analog input ports;
By connecting the target port to the voltage value detector before and after switching the resistance value of the detection resistor, a detection state for detecting the voltage value input to the target port is generated before and after switching the resistance value. detection state generation means for causing
Based on the voltage difference between the detection voltage of the target port detected before switching the resistance value of the detection resistor and the detection voltage of the target port detected after switching the resistance value of the detection resistor, the target and a port failure diagnostic means for diagnosing the presence or absence of a port failure,
The port failure diagnosis means includes:
diagnosing that the target port is not malfunctioning if the voltage difference between the detected voltages is equal to or greater than a predetermined value;
It can also be grasped as a voltage value detection device characterized by diagnosing that the target port is faulty when the voltage difference between the detected voltages is smaller than a predetermined value.

In the voltage value detection device of the present invention in this aspect as well, if the target port fails, it becomes difficult to discharge or charge the voltage through the target port. Even if the voltage value is detected before switching and after switching the resistance value, the voltage value does not change or the amount of change becomes small. Therefore, if the voltage difference between the voltage values detected before and after switching the detection resistor is equal to or greater than a predetermined value, it can be determined that the target port is not malfunctioning. can be determined to be faulty. As a result, it is possible to avoid detecting an erroneous voltage value due to a failure of the analog input port.

1 is an explanatory diagram showing a rough structure of a voltage value detection system 1 including a voltage value detection device 10 of this embodiment; FIG. FIG. 4 is an explanatory diagram of the reason why the voltage value detection device 10 of the present embodiment switches detection resistors; FIG. 4 is an explanatory diagram showing an outline of an operation of detecting voltage values of a plurality of analog input ports by a general voltage value detection device; FIG. 3 is an explanatory diagram showing an overview of the operation of diagnosing whether analog input ports InP1 to InP3 are faulty by the voltage value detection device 10 of the embodiment; FIG. 4 is an explanatory diagram showing the operation of detecting a voltage value by the voltage value detection device 10 of the embodiment when the analog input port is not malfunctioning; FIG. 4 is an explanatory diagram showing the operation of diagnosing a failure by the voltage value detection device 10 of the present embodiment when an analog input port is out of order; FIG. 4 is an explanatory diagram of a settable range of a reference voltage Vcr; FIG. 4 is an explanatory diagram of a method for simply setting a reference voltage Vcr; FIG. 9 is an explanatory diagram of another aspect of simply setting the reference voltage Vcr; FIG. 5 is an explanatory diagram of another aspect of the voltage value detection device 10 of the present embodiment that switches detection resistors connected in parallel. FIG. 11 is an explanatory diagram showing an overview of the operation of diagnosing whether or not analog input ports InP1 to InP3 are faulty by the voltage value detection device 10 of the modification;

FIG. 1 is an explanatory diagram showing a rough structure of a voltage value detection system 1 including a voltage value detection device 10 of this embodiment. The voltage value detection system 1 includes a voltage value detection device 10 for detecting a voltage value, a sensor that outputs a voltage value to be detected, a power supply PWR that supplies power to the sensor, and the like. . In the example shown in FIG. 1, a resistance temperature detector (a so-called thermistor) whose resistance value changes with temperature is used as a sensor, and three voltage values output from three thermistors Th1, Th2, and Th3 are used as sensors. detectable.

As is well known, a thermistor is a sensor that detects temperature by using the property that the resistance value changes with temperature. , and resistors called detection resistors are connected in series. In the example shown in FIG. 1, a detection resistor Rs1 is connected in series upstream of the thermistor Th1, a detection resistor Rs2 is connected upstream of the thermistor Th2, and a detection resistor Rs3 is connected upstream of the thermistor Th3. connected in series. Furthermore, a bypass resistor Rb1 is connected in series to the upstream side of the detection resistor Rs1, and the upstream side of the bypass resistor Rb1 is connected to the power supply PWR. Similarly, for the detection resistor Rs2 and the detection resistor Rs3, a bypass resistor Rb2 is connected to the upstream side of the detection resistor Rs2, and a bypass resistor Rb3 is connected to the upstream side of the detection resistor Rs3. The upstream side of resistor Rb3 is connected to power supply PWR.

Furthermore, a bypass switch SWb1 is connected in parallel with the bypass resistor Rb1, and the bypass resistor Rb1 can be bypassed by turning on the bypass switch SWb1. Similarly, a bypass switch SWb2 and a bypass switch SWb3 are connected in parallel to the bypass resistor Rb2 and the bypass resistor Rb3. By turning on the bypass switch SWb2, the bypass resistor Rb2 is bypassed and the bypass switch SWb3 is turned on. This makes it possible to bypass the bypass resistor Rb3. The downstream sides of the thermistors Th1, TH2, and Th3 are grounded.

Therefore, when the power supply PWR generates the power supply voltage Vcc with the bypass switch SWb1 turned on, the power supply voltage Vcc is transmitted from the connection point between the detection resistor Rs1 and the thermistor Th1. A voltage value V1H divided by the resistance value is output as a sensor voltage of the thermistor Th1. When the bypass switch SWb1 is turned off, the bypass resistor Rb1 is added to the detection resistor Rs1, so that the resistance value of the detection resistor Rs1 is increased by the resistance value of the bypass resistor Rb1. . As a result, the sensor voltage of the thermistor Th1 drops to a voltage value V1L obtained by dividing the power supply voltage Vcc by the resistance value obtained by adding the bypass resistance Rb1 to the detection resistor Rs1 and the resistance value of the thermistor Th1.

Similarly, for the thermistor Th2 and the thermistor Th3, when the bypass switches SWb2 and SWb3 are turned on, a voltage value V2H is output from the connection point between the detection resistor Rs2 and the thermistor Th2, and the detection resistor Rs3 and the thermistor are connected. A voltage value V3H is output from the connection point with Th3. The voltage value V2H at this time is a voltage value obtained by dividing the power supply voltage Vcc by the resistance values of the detection resistor Rs2 and the thermistor Th2. It becomes the voltage value divided by the value. When the bypass switches SWb2 and SWb3 are turned off, the resistance value of the detection resistor Rs2 increases as if by the resistance value of the bypass resistor Rb2, and the resistance value of the detection resistor Rs3 increases as if by the resistance value of the bypass resistor Rb3. It will be in a state like Therefore, the sensor output of the thermistor Th2 drops from the voltage value V2H to the voltage value V2L, and the sensor output of the thermistor Th3 drops from the voltage value V3H to the voltage value V3L. The voltage value V2L at this time is a voltage value obtained by dividing the power supply voltage Vcc by the resistance value obtained by adding the bypass resistance Rb2 to the detection resistor Rs2 and the resistance value of the thermistor Th2. The voltage value V3L is a voltage value obtained by dividing the power supply voltage Vcc by the resistance value obtained by adding the bypass resistance Rb3 to the detection resistor Rs3 and the resistance value of the thermistor Th3.

In this embodiment, the detection resistors Rs1 to Rs3 and the bypass resistors Rb1 to Rb3 are connected upstream of the thermistors Th1 to Th3. Rs3 and bypass resistors Rb1 to Rb3 may be connected. In this case, by turning on the bypass switches SWb1 to SWb3 connected in parallel to the bypass resistors Rb1 to Rb3, the sensor outputs of the thermistors Th1 to Th3 are switched to high voltage values. Further, in this embodiment, a detection section D1 is formed by the thermistor Th1, the detection resistor Rs1, and the bypass resistor Rb1. Similarly, the thermistor Th2, the detection resistor Rs2, and the bypass resistor Rb2 form a detection section D2, and the thermistor Th3, the detection resistor Rs3, and the bypass resistor Rb3 form a detection section D3.

The voltage value detection device 10 also includes a control unit 11 that controls the overall operation, a voltage value detector 12 that AD-converts a voltage value into a digital value for detection, and a plurality of analog voltage value inputs. Analog input ports InP0 to InP3 and a selector 13 for switching analog input ports connected to the voltage value detector 12 are mounted. In FIG. 1, the voltage value detection device 10 has four analog input ports InP0 to InP3 because the three voltage values output from thermistors Th1 to Th3 are to be detected. However, it is sufficient that the number of analog input ports is one or more than the number of voltage values to be detected, and the number is not necessarily limited to four.

As shown in FIG. 1, a reference voltage Vcr is input to the analog input port InP0 among the four analog input ports InP0 to InP3. The reference voltage Vcr is generated by dividing the power supply voltage Vcc generated by the power supply PWR with the resistors Rd1 and Rd2. Further, the sensor output of the thermistor Th1 (that is, the voltage value V1L or the voltage value V1H) is input to the analog input port InP1. Similarly, the sensor output of the thermistor Th2 (ie, voltage value V2L or voltage value V2H) is input to the analog input port InP2, and the sensor output of the thermistor Th3 (ie, voltage value V3L) is input to the analog input port InP3. Or voltage value V3H) is input. In addition, capacitors Cn1 to Cn3 of small capacity (several tens of μF or less) are connected to the lines through which the sensor outputs from thermistors Th1 to Th3 are input to the analog input ports InP1 to InP3.

Further, the selector 13 is equipped with switches SW0 to SW3 corresponding in number to the number of analog input ports (four in FIG. 1). Any one of the input ports InP0 to InP3 can be connected to the voltage value detector 12. FIG. For example, if the switch SW0 is turned ON and the other switches SW1 to SW3 are turned OFF, the analog input port InP0 is connected to the voltage value detector 12. FIG. When the switch SW1 is turned ON and the other switches SW0, SW2 and SW3 are turned OFF, the analog input port InP1 is connected to the voltage value detector 12. FIG. Similarly, if the switch SW2 is turned on and the other switches SW0, SW1, and SW3 are turned off, the analog input port InP2 is connected to the voltage value detector 12, the switch SW3 is turned on, and the other switches SW0 to SW2 are turned off. If it is turned off, the analog input port InP3 is connected to the voltage value detector 12 .

Further, inside the voltage value detector 12, there are an AD converter ADC for AD-converting the voltage values of the analog input ports InP0 to InP3 connected by the selector 13, and a capacitor for holding the voltage input to the AD converter ADC. Cs are provided. This capacitor Cs is for holding the voltage value so that it does not change significantly while the AD converter ADC AD-converts the voltage value of the analog input ports InP0 to InP3 connected by the selector 13. . Incidentally, this capacitor Cs corresponds to the "voltage value holding capacitor" in the present invention. Also, although not shown, a switch is provided between the capacitor Cs and the selector 13. By turning off the switch while the AD converter ADC is AD-converting the voltage value, The voltage value does not change.

Further, as shown in FIG. 1, the voltage value detection device 10 is provided with an output terminal OPb, and the control section 11 outputs a switching signal for switching ON/OFF states of the bypass switches SWb1 to SWb3 to the output terminal. output via OPb. In the example shown in FIG. 1, a switching signal is output from one output terminal OPb to the bypass switches SWb1 to SWb3, so that the ON/OFF states of the bypass switches SWb1 to SWb3 are switched at the same time. there is However, by providing an output terminal OPb for each of the bypass switches SWb1 to SWb3, the ON/OFF states of the bypass switches SWb1 to SWb3 may be switched individually.

As described above, when the ON/OFF states of the bypass switches SWb1 to SWb3 are switched, it is as if the resistance values of the detection resistors Rs1 to Rs3 have changed, and the sensor outputs of the thermistors Th1 to Th3 change. The reason for doing this is to increase the detectable range of the sensor as well as increase the resolution. In this embodiment, the thermistors Th1 to Th3 are used as the sensors, so that the detectable temperature range is increased and the resolution of the temperature to be detected is increased. This is possible for the following reasons.

FIG. 2 is an explanatory diagram of the reason why the voltage value detection device 10 of this embodiment switches the ON/OFF states of the bypass switches SWb1 to SWb3. FIG. 2 shows voltage values output from thermistors Th1 to Th3 with respect to temperature. The solid lines shown in the figure represent how the voltage values output from the thermistors Th1 to Th3 change with temperature changes when the bypass switches SWb1 to SWb3 are OFF. The dashed lines shown in the drawing represent voltage values output from thermistors Th1 to Th3 when the bypass switches SWb1 to SWb3 are ON. The thermistors Th1 to Th3 of this embodiment use a type thermistor whose resistance value decreases as the temperature increases. good.

As shown by the solid line in FIG. 2, the sensor outputs of the thermistors Th1 to Th3 when the bypass switches SWb1 to SWb3 are OFF vary greatly in voltage value with respect to the change in temperature on the low temperature side. At , the change in voltage value is small. Therefore, temperature changes can be detected with high resolution on the low temperature side, but the detectable temperature resolution is low on the high temperature side. On the other hand, when the bypass switches SWb1 to SWb3 are turned ON, the voltage values of the sensor outputs of the thermistors Th1 to Th3 change greatly with temperature changes on the high temperature side, as indicated by the broken lines in FIG. However, the change in the voltage value is small on the low temperature side. Therefore, in this case, temperature changes can be detected with high resolution on the high temperature side, but the resolution of the detectable temperature on the low temperature side is low.

Therefore, if the temperature is detected on the low temperature side with the bypass switches SWb1 to SWb3 turned off, and if the temperature is detected on the high temperature side with the bypass switches SWb1 to SWb3 turned on, either the low temperature side or the high temperature side will be detected. Temperature can be detected with high resolution even in the temperature range of , and the detectable temperature range can be expanded. Therefore, in the voltage value detection device 10 of the present embodiment, the temperature is detected with the bypass switches SWb1 to SWb3 in the OFF state on the lower temperature side than the preset threshold temperature Tth with respect to the threshold temperature Tth. On the high temperature side of the threshold temperature Tth, the temperature is detected with the bypass switches SWb1 to SWb3 turned on. The sensor output indicated by the solid line in FIG. , indicates that the temperature is detected using the sensor output of the dashed line on the high temperature side.

However, if the temperature is not actually detected, either the low temperature side setting (that is, the bypass switches SWb1 to SWb3 are in the OFF state) or the high temperature side setting (that is, the bypass switches SWb1 to SWb3 are in the ON state). I don't know if I should detect it with Therefore, when detecting the voltage value by switching the detection range (that is, the ON/OFF states of the bypass switches SWb1 to SWb3), the detection is generally performed as follows.

FIG. 3 is an explanatory diagram showing an overview of the operation of detecting voltage values of analog input ports in a voltage value detection device having a plurality of analog input ports. As illustrated, when detecting the voltage value of the analog input port, the analog input port to be detected is selected. As described above with reference to FIG. 1, when selecting the analog input port InP1, the switch SW1 in the selector 13 is turned ON and the other switches SW0, SW2 and SW3 are turned OFF. Also, for example, when selecting the analog input port InP2, the switch SW2 should be turned on, and the other switches SW0, SW1, and SW3 should be turned off.

Subsequently, voltage values before switching the resistance values of the detection resistors Rs1 to Rs3 (that is, before switching the ON/OFF states of the bypass switches SWb1 to SWb3) are detected. As described above, when the ON/OFF states of the bypass switches SWb1 to SWb3 are switched, it is as if the resistance values of the detection resistors Rs1 to Rs3 are switched. Although the bypass switches SWb1 to SWb3 are switched from OFF to ON in this embodiment, the bypass switches SWb1 to SWb3 may be switched from ON to OFF.

In this way, before switching the resistance values of the detection resistors Rs1 to Rs3 (in this case, the bypass switches SWb1 to SWb3 are OFF), if the voltage value of the previously selected analog input port is detected, the detection resistors Rs1 to Rs3 (here, the bypass switches SWb1 to SWb3 are turned ON), the voltage value of the analog input port is detected again. When the voltage values detected before and after switching the resistance value are obtained as described above, it is determined whether the temperature to be detected is on the low temperature side or the high temperature side based on those voltage values. can be judged. For example, focusing on the lower detected voltage value, if the voltage value is higher than a predetermined voltage value, it can be determined that the temperature is on the low temperature side, and if the voltage value is lower than the predetermined voltage value, it can be determined that the temperature is on the high temperature side. As a result, when it is determined to be on the low temperature side, the voltage value detected before switching the resistance value (here, the bypass switches SWb1 to SWb3 are OFF) is selected as the sensor output, and when it is determined to be on the high temperature side, the resistor The voltage value detected after the value switching (in this case, the bypass switches SWb1 to SWb3 are ON) is selected as the sensor output. Thus, when the voltage value input to one analog input port is detected, a new analog input port is selected and the same procedure is performed for that analog input port. This makes it possible to detect voltage values of a plurality of analog input ports.

However, if a failure occurs at the analog input port, the correct voltage value cannot be detected. For example, assume that a failure such as a poor connection or disconnection has occurred at the analog input port InP3. In this case, even if the switch SW3 is turned ON and the other switches SW0 to SW2 are turned OFF in an attempt to detect the voltage value of the analog input port InP3, a connection failure or disconnection occurs at the analog input port InP3. The voltage value V3 of the analog input port InP3 is not transmitted to the voltage value detector 12 . Therefore, the capacitor Cs of the voltage value detector 12 continues to hold the voltage value of the previously connected analog input port, and the AD converter ADC of the voltage value detector 12 converts the voltage value to AD. Convert and detect. In addition, the erroneously detected voltage value is the voltage value of the analog input port other than the analog input port InP3, so the voltage value is not particularly unnatural. It's hard to notice you're there. As a result, there is a problem that control is continued with erroneous detection.

Therefore, in the voltage value detection device 10 of the present embodiment, as shown in FIG. The voltage values of the analog input ports InP1 to InP3 are detected according to the procedure. This makes it possible to easily diagnose whether or not a failure has occurred in the analog input ports InP1 to InP3.

FIG. 4 is an explanatory diagram showing an outline of the operation of diagnosing whether or not the analog input ports InP1 to InP3 are faulty by the voltage value detection device 10 of the present embodiment. Compared with the procedure described above with reference to FIG. 3 (that is, the procedure for not diagnosing a failure), when diagnosing a failure, the operation of detecting the reference voltage Vcr and the voltage value before switching the resistance value are detected. An operation for diagnosing a failure later and an operation for diagnosing a failure after detecting the voltage value after switching the resistance value are added. Each operation constituting the procedure of FIG. 4 will be specifically described below.

FIG. 5 is an explanatory diagram exemplifying a case where the voltage value detection device 10 of this embodiment detects the voltage value when the analog input port is not malfunctioning. In the example shown in FIG. 5, two temperatures, temperature Ta and temperature Tb, shown in FIG. 5A are detected, and FIG. 5(c) shows the case of detecting the temperature Tb.

First, the case of detecting the temperature Ta will be described with reference to FIG. 5(b). FIG. 5(b) shows each of the operations described above with reference to FIG. , port failure diagnosis, detection voltage value selection) are shown to change the voltage value of the capacitor Cs.

As shown in FIG. 5(b), when detecting the voltage value, the reference voltage Vcr is first detected. As described above with reference to FIG. 1, in the voltage value detection device 10 of this embodiment, the reference voltage Vcr is input to the analog input port InP0. When SW1 to SW3 are turned off, the analog input port InP0 is connected to the voltage value detector 12, making it possible to detect the reference voltage. Further, since a capacitor Cs is provided in the voltage value detector 12, when the analog input port InP0 is connected to the voltage value detector 12, the voltage value changes transiently due to the action of the capacitor Cs, and the reference voltage Stable at Vcr. FIG. 5B shows how the voltage value of the capacitor Cs is stabilized at the reference voltage Vcr by performing the "reference voltage detection" operation. After switching the switches SW0 to SW3 in the selector 13, the control unit 11 of the voltage value detection device 10 outputs a trigger signal to the voltage value detector 12 at the timing when the voltage value of the capacitor Cs is stabilized, thereby determining the voltage value. to detect Also, the voltage value detector 12 outputs the detected voltage value to the control unit 11 .

In this embodiment, the analog input port InP0 corresponds to the "specific port" of the invention, and the state in which the analog input port InP0 is connected to the voltage value detector 12 corresponds to the "reference state" of the invention. Further, the state in which the analog input port InP0 is connected to the voltage value detector 12 is realized by the control unit 11 switching the switches SW0 to SW3 in the selector 13. Corresponds to "generating means".

Next, an analog input port whose voltage value is to be detected is selected from the analog input ports InP1 to InP3. Selection of the analog input port is performed by switching the switches SW0 to SW3 in the selector 13 as described above. Then, since the selected analog input port is connected to the voltage value detector 12, the voltage value of the capacitor Cs in the voltage value detector 12 changes to the voltage value of the selected analog input port. Here, the temperature to be detected is the temperature Ta, and since it is assumed that the bypass switches SWb1 to SWb3 are initially turned off, the voltage value of the analog input port is the voltage value VaL higher than the reference voltage Vcr. (See FIG. 5(a)). Therefore, as shown in FIG. 5B, the voltage value of the capacitor Cs rises from the reference voltage Vcr to the voltage value VaL and stabilizes. Then, the voltage value is detected by the voltage value detector 12 at the timing when the voltage value of the capacitor Cs is stabilized. The control unit 11 controls the operation of switching the switches SW0 to SW3 to select the analog input port and the operation of the voltage value detector 12 detecting the voltage value at the timing when the voltage value of the capacitor Cs is stabilized. Also, the voltage value detector 12 outputs the detected voltage value to the control unit 11 .

An analog input port selected from the analog input ports InP1 to InP3 corresponds to the "target port" in the present invention, and the state in which the selected analog input port is connected to the voltage value detector 12 is the corresponds to the "detection state" in Further, the state in which the selected analog input port is connected to the voltage value detector 12 is realized by the control unit 11 switching the switches SW0 to SW3 in the selector 13. It also corresponds to "detection state generating means".

Subsequently, the control unit 11 diagnoses whether or not the selected analog input port is faulty. Diagnosis of the presence or absence of failure is performed by calculating a voltage difference dV1 between the reference voltage Vcr obtained from the voltage value detector 12 when the reference voltage is detected and the voltage value VaL detected before switching the resistance value, and comparing this voltage difference dV1 with a predetermined value. is compared with the threshold voltage Vth of . Since the voltage value detector 12 detects the voltage value held by the capacitor Cs as described above, a change in the detected voltage value means that the voltage value of the capacitor Cs has changed. Then, for example, if the voltage value of the capacitor Cs has increased, it means that the capacitor Cs has been charged via the analog input port connected to the voltage value detector 12, and conversely, the voltage value of the capacitor Cs has increased. If so, the voltage on capacitor Cs has been discharged through the analog input port. In either case, it can be considered that the analog input port connected to the voltage value detector 12 does not have a failure such as disconnection or poor connection. Therefore, the voltage difference dV1 between the reference voltage Vcr and the voltage value VaL before the resistance value switching is compared with the threshold voltage Vth. If the voltage difference dV1 is greater than the threshold voltage Vth, the selected analog input port is Determine that there is no failure. In the example shown in FIG. 5B, the voltage difference dV1 is greater than the threshold voltage Vth, so it is determined that the analog input port is not malfunctioning. An appropriate value for the threshold voltage Vth may be set through experience or trial and error.

When it is determined that the analog input port is not malfunctioning, the bypass switches SWb1 to SWb3 are turned ON to switch the resistance value, and then the voltage value after switching is detected. That is, the voltage value detection device 10 of the present embodiment improves the detectable temperature range and the resolution at the time of temperature detection by switching the resistance values connected in series with the thermistors Th1 to Th3. After detecting the voltage value before the resistance value switching, the voltage value after the resistance value switching is also detected. Further, since the temperature to be detected is the temperature Ta here, when the bypass switches SWb1 to SWb3 are switched from OFF to ON, the sensor outputs of the thermistors Th1 to Th3 increase from the voltage value VaL to the voltage value VaH. (See FIG. 5(a)). Therefore, as shown in FIG. 5B, the voltage value of the capacitor Cs also rises from the voltage value VaL to the voltage value VaH and stabilizes. Therefore, the control unit 11 uses the voltage value detector 12 to detect the voltage value VaH at the timing when the voltage value of the capacitor Cs is stabilized. Also, the voltage value detector 12 outputs the detected voltage value VaH to the control unit 11 . As described above with reference to FIG. 1, the control unit 11 outputs switching signals to the bypass switches SWb1 to SWb3 to switch the resistance values. Therefore, the control section 11 of this embodiment also corresponds to the "resistance value switching means" of the present invention.

In this way, when it is determined that the selected analog input port is not malfunctioning and the voltage value VaL before the resistance value switching and the voltage value VaH after the resistance value switching are obtained, the voltage value with the higher resolution (here, , as shown in FIG. 5(a), the voltage value VaL) before switching the resistance value is selected because it is assumed that the temperature Ta is detected. After outputting the selected voltage value to the outside, the above-described series of operations starting from the operation of detecting the reference voltage Vcr are executed again in order to detect the voltage value of the next analog input port.

The case where the temperature to be detected is the temperature Ta shown in FIG. 5A has been described above. In this case, the voltage value VaL detected before the resistance value switching is higher than the reference voltage Vcr by the threshold voltage Vth or more. can decide not to. On the other hand, as in the case of detecting the temperature Tb in FIG. 5A, the voltage difference between the voltage value VbL before the resistance value switching and the reference voltage Vcr may become smaller than the threshold voltage Vth. . In such a case, the voltage value VbH after switching the resistance value is also used to diagnose whether or not the analog input port is faulty. A method of diagnosing whether or not an analog input port is faulty will be described below using the voltage value VbH after switching the resistance value with reference to FIG. 5(c).

FIG. 5(c) shows a state of diagnosing whether or not there is a failure in the analog input port when the temperature to be detected is the temperature Tb in FIG. 5(a). In the case of FIG. 5(c) as well, the reference voltage Vcr is first detected as in the case of FIG. 5(b). Subsequently, by switching the switches SW0 to SW3 in the selector 13, the analog input port is selected. As shown in FIG. 5A, the temperature to be detected is the temperature Tb, and the voltage value VbL detected before the resistance value switching (here, the bypass switches SWb1 to SWb3 are in the OFF state) is higher than the reference voltage Vcr. Therefore, when the analog input port is selected, the voltage value of the capacitor Cs drops from the reference voltage Vcr to the voltage value VbL and stabilizes (see FIG. 5(c)). Therefore, the voltage value VbL is detected using the voltage value detector 12 at the timing when the voltage value of the capacitor Cs is stabilized.

Subsequently, the presence or absence of failure of the analog input port is diagnosed by comparing the voltage difference dV1 between the reference voltage Vcr and the voltage value VbL before switching the resistance value with the threshold voltage Vth. As described above with reference to FIG. 5B, if the voltage difference dV1 is greater than the threshold voltage Vth, it can be determined that the analog input port is not faulty. However, if the temperature to be detected is the temperature Tb, the voltage value VbL before the resistance value switching is close to the reference voltage Vcr. It can be smaller than the voltage Vth. Therefore, even when the voltage difference dV1 from the reference voltage Vcr is smaller than the threshold voltage Vth, the voltage value VbL before the resistance value switching is switched while the failure determination is suspended. is detected. As shown in FIG. 5A, the voltage value VbH after switching the resistance value is higher than the reference voltage Vcr. Along with this, as shown in FIG. 5(c), the voltage value of the capacitor Cs also rises to the voltage value VbH and stabilizes. Therefore, when the voltage value is stabilized, the voltage value detector 12 is used to detect the voltage value VbH after the resistance value switching, and the voltage difference dV2 between the reference voltage Vcr and the voltage value VbH after the resistance value switching is calculated. , and the threshold voltage Vth. As a result, when the voltage difference dV2 is greater than the threshold voltage Vth, it indicates that the voltage of the capacitor Cs has been charged or discharged through the selected analog input port. Therefore, in this case, it can be determined that the analog input port is not out of order.

It should be noted that the voltage value VbH after switching the resistance value was detected with the resistance value switched when the voltage difference dV1 between the voltage value VbL before the resistance value switching and the reference voltage Vcr was smaller than the threshold voltage Vth. voltage value. Therefore, in this embodiment, the voltage value VbH after switching the resistance value corresponds to the "re-detection voltage" in the present invention.

In the above description, the case where the selected analog input port is not faulty has been described. On the other hand, if the analog input port is faulty, the occurrence of the fault can be detected as follows. FIG. 6 is an explanatory diagram showing the operation of diagnosing the failure of the voltage value detection device 10 of the present embodiment when the analog input port fails. FIG. 6(a) shows how the voltage value of the capacitor Cs changes when the temperature to be detected is the temperature Ta, and FIG. 6(b) shows the temperature to be detected is the temperature Tb. It shows how the voltage value of the capacitor Cs changes in the case of . In any case, when the reference voltage Vcr is detected, the voltage value of the capacitor Cs has changed to the reference voltage Vcr, and the voltage value detector 12 can correctly detect the reference voltage Vcr.

However, when an analog input port is selected, the voltage value of the selected analog input port will not be transmitted to the voltage value detector 12 if the analog input port has a failure such as disconnection or poor contact. , the voltage value of the capacitor Cs does not change, or even if it changes, the amount of change is a small value. Therefore, even if the temperature to be detected is Ta as shown in FIG. 6A or Tb as shown in FIG. A voltage difference dV1 between the values VaL and VbL and the reference voltage Vcr is smaller than the threshold voltage Vth. Furthermore, even if the resistance value is switched, the voltage value of the selected analog input port is not transmitted to the voltage value detector 12, so the voltage value of the capacitor Cs does not change, or even if it changes, the amount of change is small. Become. Therefore, the voltage difference dV2 between the voltage values VaH and VbH detected after switching the resistance values and the reference voltage Vcr is smaller than the threshold voltage Vth. Therefore, the threshold voltage Vth If it is less than , it can be determined that the selected analog input port is faulty. On the other hand, if either one of the voltage differences dV1 and dV2 is greater than the threshold voltage Vth, it can be determined that the selected analog input port is not malfunctioning.

In the above description, when the reference voltage Vcr is detected, the voltage value before switching the resistance value is detected, and the presence or absence of failure is diagnosed. If it is not a diagnosis result), after switching the resistance value, the voltage value (that is, the voltage value after switching the resistance value) is detected again to diagnose the presence or absence of a failure (FIGS. 4 to 6). checking). However, the reference voltage Vcr may be detected again at any timing after the voltage value before the resistance value switching is detected and before the voltage value after the resistance value switching is detected. Alternatively, the capacitor Cs of the voltage detector 12 may be charged with the reference voltage Vcr without detecting the reference voltage Vcr. This makes it possible to more accurately diagnose the presence or absence of a failure in the analog input port for the following reasons.

First, when detecting the reference voltage Vcr, the capacitor Cs of the voltage value detector 12 is charged to the reference voltage Vcr. After that, the switches SW0 to SW3 in the selector 13 are switched to select the analog input port. If the selected analog input port does not malfunction, the voltage value of the capacitor Cs changes to the voltage value of the analog input port, and the voltage value detector 12 detects the voltage value of the analog input port. has failed, the voltage value of the capacitor Cs remains at the reference voltage Vcr. However, the capacitor Cs may naturally discharge electric charges to the surroundings, or may be naturally charged by electric charges flowing in from the surroundings. The amount of charge that is naturally discharged or charged is only a small amount, but if the capacity of the capacitor Cs is small, the amount of change in the voltage value of the capacitor Cs due to the natural discharge or charge is also large.

As described above, if the voltage value before switching the resistance value does not provide a diagnostic result, it is necessary to detect the voltage value again after switching the resistance value (that is, the voltage value after the resistance value switching). , the time from detection of the reference voltage Vcr to obtaining the diagnosis result becomes long. Therefore, when the voltage value after switching the resistance value is detected, the amount of change in the voltage value due to the natural discharge or charge of the capacitor Cs exceeds the threshold voltage Vth. Since the voltage value after switching the resistance value changes greatly (more than the threshold voltage Vth) with respect to the reference voltage Vcr (in spite of the failure), the analog input port is erroneously diagnosed as not having a failure. It can happen. Therefore, at some timing after the voltage value before the resistance value switching is detected and before the voltage value after the resistance value switching is detected, the reference voltage Vcr is detected again, or at least the voltage value detector 12 The capacitor Cs is charged with the reference voltage Vcr. In this way, it is possible to avoid erroneous diagnosis due to natural discharge or natural charge of the capacitor Cs, so that it is possible to more accurately diagnose the presence or absence of a failure in the analog input port.

It is important to set the reference voltage Vcr to an appropriate value in order to diagnose the presence or absence of a failure in the analog input port by the method described above. A voltage range in which the reference voltage Vcr can be set will be described below. FIG. 7 is an explanatory diagram of the settable range of the reference voltage Vcr. First, as shown in FIG. 7A, focusing on the sensor output with respect to temperature when the bypass switches SWb1 to SWb3 are ON, consider a region where the voltage value differs by the threshold voltage Vth around the sensor output. In FIG. 7(a), this area (hereinafter referred to as an undiagnosable area) is displayed with diagonal lines. When a certain reference voltage Vcr is set, the voltage value output by the sensor and the reference voltage Vcr are in the temperature range (range of temperature Tc to temperature Td in FIG. 7A) in which the reference voltage Vcr passes through the diagnosis impossible region. becomes smaller than the reference voltage Vcr. Therefore, when the temperature to be detected is within this temperature range (range of temperature Tc to temperature Td), this sensor output (here, the sensor output when the bypass switches SWb1 to SWb3 are ON) and the reference It becomes impossible to diagnose whether or not the selected analog input port has a failure based on the voltage difference from the voltage Vcr.

On the other hand, as shown in FIG. 7(b), a diagnosis impossible region is also considered in which the voltage value differs by the threshold voltage Vth with respect to the sensor output when the bypass switches SWb1 to SWb3 are OFF. In this non-diagnosable region, there is also a temperature range (range from temperature Te to temperature Tf in FIG. 7B) in which it is not possible to diagnose the presence or absence of a failure in the analog input port. However, the undiagnosable temperature range (temperature Tc to temperature Td) for the sensor output in FIG. 7(a) and the undiagnosable temperature range (temperature Te to temperature Tf) for the sensor output in FIG. 7(b) overlap. If not, the voltage difference between the output of any sensor and the reference voltage Vcr becomes larger than the threshold voltage Vth, so it is possible to diagnose whether or not the analog input port is faulty. Conversely, if the reference voltage Vcr is set so that the two undiagnosable temperature ranges overlap at least in part, the analog input port It becomes impossible to diagnose the presence or absence of failure of

For example, in FIG. 7(c), a region where the non-diagnosable region shown in FIG. 7(a) and the non-diagnosable region shown in FIG. are displayed with If the reference voltage Vcr is set to the voltage value Vcr1 shown in FIG. 7C, the temperature range on the low temperature side (in FIG. Since the voltage Vcr passes through the non-overlapping region, it becomes impossible to diagnose whether or not the analog input port is faulty within this temperature range. Also, when the reference voltage Vcr is set to the voltage value Vcr2 shown in FIG. 7(c), analog It becomes impossible to diagnose whether or not there is a failure in the input port. Therefore, within the voltage range sandwiched between the non-overlapping region on the high temperature side and the non-overlapping region on the low temperature side shown in FIG. Vcr should be set.

However, in the above-described method, in order to appropriately set the reference voltage Vcr, it is necessary to determine the lower limit voltage value VcrL and the upper limit voltage value VcrH by obtaining non-overlapping regions on the low temperature side and the high temperature side. Therefore, simply, the settable voltage range of the reference voltage Vcr may be determined by determining the lower limit voltage value VcrL and the upper limit voltage value VcrH as follows.

FIG. 8 is an explanatory diagram showing a method for simply determining the settable voltage range of the reference voltage Vcr. As described above, the voltage value detection device 10 of this embodiment detects the voltage values output by the thermistors Th1 to Th3 depending on whether the bypass switches SWb1 to SWb3 are in the OFF state or the ON state. Therefore, even at the lowest temperature Tmin in the temperature range measurable by the voltage value detection device 10, the voltage value detected when the bypass switches SWb1 to SWb3 are OFF and the voltage value detected when the bypass switches SWb1 to SWb3 are ON are different. exists. Among these two voltage values, the lower voltage value is selected as the maximum voltage value Vmax. The reason why the lower one of the two voltage values for the minimum temperature Tmin is selected and the reason for making the voltage value selected for the minimum temperature Tmin the maximum voltage value Vmax will be described later. Also, the maximum temperature Tmax in the temperature range measurable by the voltage value detection device 10 has two voltage values, one when the bypass switches SWb1 to SWb3 are OFF and one when the bypass switches SWb1 to SWb3 are ON. Therefore, from among these two voltage values, the higher voltage value is selected this time as the minimum voltage value Vmin.

FIG. 8 shows the highest voltage value Vmax and the lowest voltage value Vmin thus selected. In this embodiment, the voltage values output by the thermistors Th1 to Th3 with respect to temperature have a characteristic that the voltage value decreases as the temperature increases. higher than the voltage value for Correspondingly, for the minimum temperature Tmin, the lower voltage value is selected from among the two voltage values, and this voltage value is set as the maximum voltage value Vmax. Further, for the maximum temperature Tmax, the higher voltage value is selected from the two voltage values, and the selected voltage value is set as the minimum voltage value Vmin. A voltage value higher than the selected minimum voltage value Vmin by the threshold voltage Vth is set as the lower limit voltage value VcrL. Alternatively, a voltage value lower than the maximum voltage value Vmax by the threshold voltage Vth may be set as the upper limit voltage value VcrH. In this way, the settable voltage range of the reference voltage Vcr can be determined by a simpler method than the strict method shown in FIG. 7(c).

In FIG. 8, the voltage values output by the thermistors Th1 to Th3 have a characteristic that the higher the temperature, the lower the voltage value. The reason for such characteristics is that the thermistors Th1 to Th3 having the characteristic that the resistance value decreases as the temperature rises are used, and the detection resistors Rs1 to Rs3 and the detection resistors Rs1 to Rs3 are provided upstream of the thermistors Th1 to Th3. This is because the bypass resistors Rb1 to Rb3 are connected. Therefore, thermistors Th1 to Th3 are changed to thermistors whose resistance value decreases as the temperature rises, or the detection resistors Rs1 to Rs3 and the bypass resistors Rb1 to Rb3 are connected downstream of the thermistors Th1 to Th3. In such a case, the characteristics of the voltage values output by the thermistors Th1 to Th3 are reversed with respect to the temperature. Therefore, a method for simply determining the voltage range in which the reference voltage Vcr can be set in such a case will also be briefly described.

FIG. 9 is an explanatory diagram showing another aspect of simply determining the settable voltage range of the reference voltage Vcr. Compared to the case described above with reference to FIG. 8, the characteristics of the voltage values output by the thermistors Th1 to Th3 are reversed with respect to temperature, and the higher the temperature, the higher the output voltage value. Therefore, in such a case, the higher one of the two voltage values for the lowest temperature Tmin in the measurable temperature range is selected as the lowest voltage value Vmin. Further, the lower voltage value is selected from among the two voltage values for the maximum temperature Tmax in the measurable temperature range and set as the maximum voltage value Vmax. A voltage value higher than the minimum voltage value Vmin by the threshold voltage Vth is determined as the lower limit voltage value VcrL, and a voltage value lower than the maximum voltage value Vmax by the threshold voltage Vth is determined as the upper limit voltage value VcrH. This makes it possible to easily determine the settable voltage range of the reference voltage Vcr even when the voltage value output by the sensor has the characteristics shown in FIG.

In the voltage value detection device 10 of the present embodiment described above, the bypass resistors Rb1 to Rb3 are connected in series with the detection resistors Rs1 to Rs3, and the bypass resistors Rb1 to Rb3 are connected using the bypass switches SWb1 to SWb3. It has been explained that the resistance values of the detection resistors Rs1 to Rs3 are substantially switched by bypassing. However, as shown in FIG. 10, a detection resistor Rsa1 and a detection resistor Rsb1 having different resistance values are connected in parallel, and a switch SWs1 is used to switch the detection resistor connected to the thermistor Th1. , the resistance value of the detection resistor may be switched. Similarly, for the thermistors Th2 and Th3, detection resistors Rsa2 and Rsa3 having different resistance values and detection resistors Rsb2 and Rsb3 are connected in parallel, and switching switches SWs2 and SWs3 are used to switch the thermistors Th2 and Th3. By switching the connected detection resistor, the resistance value of the detection resistor may be switched. Even in this way, the resistance value of the detection resistor can be switched by outputting a switching signal from the output terminal OPb to the switching switches SWs1 to SWs3. As a result, it becomes possible to diagnose whether or not the analog input ports InP1 to InP3 are faulty in the same manner as the voltage value detection device 10 of the present embodiment described above.

Further, the voltage value detection device 10 of the present embodiment described above detects the reference voltage Vcr, the voltage value before the resistance value switching, and the voltage value after the resistance value switching. It has been explained that the presence or absence of a failure in the analog input ports InP0 to InP3 is diagnosed based on the voltage difference from the previous voltage value (and the voltage difference between the reference voltage Vcr and the voltage value after switching the resistance value). However, as shown in FIG. 5(a), there always exists some voltage difference between the voltage value before the resistance value switching and the voltage value after the resistance value switching. Therefore, by comparing the voltage value before the resistance value switching and the voltage value after the resistance value switching, if there is a voltage difference of a predetermined value or more, the voltage value before and after the resistance value switching is correctly detected. If the voltage difference is less than a predetermined value, it may be diagnosed that the analog input port is faulty. The predetermined value used for diagnosis can be set to an appropriate value through trial and error based on experience.

FIG. 11 is an explanatory diagram showing an outline of the operation of diagnosing the presence or absence of a failure in the analog input ports InP1 to InP3 by the voltage value detection device 10 of the modification described above. Compared with the operation of the present embodiment described above with reference to FIG. 4, there is no need to detect the reference voltage Vcr, so the operation of detecting the reference voltage Vcr is omitted. Further, since the diagnosis cannot be made unless the voltage value after switching the resistance value is known, the operation of diagnosing a port failure before switching the resistance value is omitted. In the operation of diagnosing a port failure after switching the resistance value, the presence or absence of failure of the analog input ports InP1 to InP3 is diagnosed based on the voltage difference between the voltage value before the resistance value switching and the voltage value after the resistance value switching. However, other operations are substantially the same as those of this embodiment.

In the modified example described above, as indicated by the dashed line in FIG. 11, the capacitor Cs of the voltage value detector 12 is charged with the reference voltage Vcr before the voltage value before the resistance value switching is detected. Also good. By doing so, the conditions before diagnosing the presence or absence of a failure in the analog input ports InP1 to InP3 can be matched, so that the diagnosis can be performed accurately. Further, as indicated by the dashed-dotted line in FIG. 11, at any timing from the detection of the voltage value before the resistance value switching to the detection of the voltage value after the resistance value switching (in FIG. 11, the resistance value (before switching), the capacitor Cs may be charged with the reference voltage Vcr. By doing so, it is possible to avoid the possibility of erroneously diagnosing that the analog input ports InP1 to InP3 are not malfunctioning because the voltage value of the capacitor Cs changes due to the influence of natural discharge or charge of the capacitor Cs. It becomes possible.

Although the voltage value detection device 10 of the present embodiment and modifications has been described above, the present invention is not limited to the above embodiments and modifications, and can be implemented in various manners without departing from the gist thereof. is possible.

DESCRIPTION OF SYMBOLS 1... Voltage value detection system, 10... Voltage value detection apparatus, 11... Control part,
12... voltage value detector, 13... selector,
SWb1 to SWb3...Bypass switches, SWs1 to SWs3...Changeover switches,
InP0 to InP3: analog input ports, D1 to D3: detectors,
Vc...reference voltage Vc, Cs...capacitor, dV1, dV2...voltage difference,
ADC... AD converter, SW0 to SW3... switch,
Rb1 to Rb3...Bypass resistors, Th1 to Th3...Thermistors,
Rs1 to Rs3 ... detection resistors, Rsa1 to Rsa3 ... detection resistors,
Rsb1 to Rsb3...detection resistor, PWR...power supply, OPb...output terminal,
Vcc: power supply voltage, Vcr: reference voltage, Vth: threshold voltage.

Claims (3)

A voltage value detector for converting a voltage value into a digital value for detection and a plurality of analog input ports, wherein the voltage value of the analog input port is switched by switching the analog input port connected to the voltage value detector. In a voltage value detection device that detects
The voltage value detector has a voltage value holding capacitor that holds the voltage value of the analog input port by storing charge from the connected analog input port, and the voltage value held by the voltage value holding capacitor. is detected as the voltage value of the analog input port,
a specific port preselected from among the plurality of analog input ports;
a target port selected from the plurality of analog input ports excluding the specific port;
reference state generating means for generating a reference state in which a predetermined reference voltage is input to the specific port and the specific port is connected to the voltage value detector;
detection state generation means for generating a detection state for detecting the voltage value input to the target port by connecting the target port to the voltage value detector;
When the voltage difference between the reference voltage detected by the voltage value detector in the reference state and the detected voltage detected by the voltage value detector in the detection state is equal to or greater than a predetermined threshold voltage, a port fault diagnosis means for diagnosing that the target port is not faulty ;
A voltage at a connection point between a detection resistor and a sensor connected in series with the detection resistor is input to the target port, and an upstream of a detection unit to which the detection resistor and the sensor are connected in series. A power supply is connected to the side, and the downstream side of the detection unit is grounded,
resistance value switching means for switching the resistance value of the detection resistor,
The port failure diagnosis means includes:
When the voltage difference between the reference voltage and the detection voltage is smaller than the threshold voltage, the re-detection voltage detected by the voltage value detector is acquired again while the resistance value of the detection resistor is switched. do,
if the voltage difference between the redetected voltage and the reference voltage is equal to or greater than the threshold voltage, diagnosing that the target port is not malfunctioning;
If the voltage difference between the redetected voltage and the reference voltage is smaller than the threshold voltage, the target port is diagnosed as faulty.
A voltage value detection device characterized by: In the voltage value detection device according to claim 1,
The sensor is a temperature measuring resistor whose resistance value changes with temperature,
a voltage at a connection point between the sensor and the detection resistor is input to the target port as a sensor output of the sensor;
The minimum and maximum detectable temperatures are set in the voltage value detection device,
The lower limit voltage value of the voltage range in which the reference voltage can be set is
When the voltage value of the sensor output at the highest temperature is lower than the voltage value of the sensor output at the lowest temperature, the sensor output at the highest temperature before and after switching the resistance value of the detection resistor is the voltage value obtained by adding the threshold voltage to the higher voltage value when detecting
When the voltage value of the sensor output at the highest temperature is higher than the voltage value of the sensor output at the lowest temperature, the sensor output at the lowest temperature before and after switching the resistance value of the detection resistor is the voltage value obtained by adding the threshold voltage to the higher voltage value when detecting
The upper limit voltage value of the voltage range in which the reference voltage can be set is
When the voltage value of the sensor output at the highest temperature is lower than the voltage value of the sensor output at the lowest temperature, the sensor output at the lowest temperature before and after switching the resistance value of the detection resistor It is a voltage value obtained by subtracting the threshold voltage from the lower voltage value when detecting
When the voltage value of the sensor output at the highest temperature is higher than the voltage value of the sensor output at the lowest temperature, the sensor output at the highest temperature before and after switching the resistance value of the detection resistor is the voltage value obtained by subtracting the threshold voltage from the lower voltage value when detecting
A voltage value detection device characterized by: A voltage value detector for converting a voltage value into a digital value for detection and a plurality of analog input ports, wherein the voltage value of the analog input port is switched by switching the analog input port connected to the voltage value detector. In a voltage value detection device that detects
The voltage value detector has a voltage value holding capacitor that holds the voltage value of the analog input port by storing charge from the connected analog input port, and the voltage value held by the voltage value holding capacitor. is detected as the voltage value of the analog input port,
The voltage at the connection point between the detection resistor and the sensor connected in series with the detection resistor is input to the analog input port, and the detection unit in which the detection resistor and the sensor are connected in series. A power supply is connected to the upstream side, and the downstream side of the detection unit is grounded,
resistance value switching means for switching the resistance value of the detection resistor;
a target port selected from among the plurality of analog input ports;
By connecting the target port to the voltage value detector before and after switching the resistance value of the detection resistor, a detection state for detecting the voltage value input to the target port is generated before and after switching the resistance value. detection state generation means for causing
Based on the voltage difference between the detection voltage of the target port detected before switching the resistance value of the detection resistor and the detection voltage of the target port detected after switching the resistance value of the detection resistor, the target port failure diagnosis means for diagnosing whether or not there is a port failure;
with
The port failure diagnosis means includes:
diagnosing that the target port is not malfunctioning if the voltage difference between the detected voltages is equal to or greater than a predetermined value;
A voltage value detection device, wherein the target port is diagnosed as faulty when the voltage difference between the detected voltages is smaller than a predetermined value.

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