JPH04364431A - Abnormally detecting device for temperature sensor - Google Patents

Abstract

PURPOSE:To detect abnormality even if a temperature sensor is short-circuited to an intermediate potential in an abnormality detecting device for a temperature sensor by comparing the terminal voltage of the temperature sensor with a specified reference value. CONSTITUTION:A transistor switch 11 is arranged between a thermistor 5 and the ground GD. The opened and closed state of the switch is controlled with a microcomputer 13. When the terminal voltage VIN under the state wherein the switch is opened is not equal to the power supply voltage VCC, it is judged that the sensor is short-circuited to the part at the intermediate potential.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor abnormality detection device for detecting an abnormality in a temperature sensor by comparing the terminal voltage of the temperature sensor with a predetermined reference value.

0002

2. Description of the Related Art Conventionally, when detecting an abnormality in a temperature sensor using a thermistor, it has been determined whether the temperature sensor is disconnected or not based on whether the output from the temperature sensor exceeds predetermined upper and lower limits. It was detected whether the grounding condition was caused by a short circuit.

0003

[Problems to be Solved by the Invention] However, another possible abnormality in the temperature sensor is a short circuit with an adjacent device, and an intermediate potential may be output. Conventional abnormality detection devices have a problem in that they cannot detect such short circuits with intermediate potential points.

[0004] Therefore, the present invention was completed with the object of providing an abnormality detection device for a temperature sensor that can detect an abnormality even when the temperature sensor is short-circuited to a point having an intermediate potential.

[0005]

[Means and Operations for Solving the Problems] In order to achieve the above object, the temperature sensor abnormality detection device of the present invention detects the abnormality of the temperature sensor by comparing the terminal voltage of the temperature sensor with a predetermined reference value. In the abnormality detection device for a temperature sensor that detects the temperature sensor, there is a forced disconnection means that forcibly disconnects the circuit including the temperature sensor, and if a terminal voltage matching the disconnection state cannot be obtained when the forced disconnection means is activated. The present invention is characterized by comprising an abnormality determining means for determining that the temperature sensor is abnormal.

For example, if a resistor is connected in series between the power supply voltage and the ground, and a thermistor is connected downstream, and the terminal voltage is detected between the resistor and the thermistor, the thermistor and the ground are connected in series. When a disconnection state is forcibly established between the two terminals, the terminal voltage should be equal to the power supply voltage under normal conditions. At this time, if the terminal voltage is not equal to the power supply voltage, it can be determined that the temperature sensor is shorted to a point having an intermediate potential. Conversely, if the circuit upstream of the detection terminal is forcibly disconnected, the terminal voltage should be equal to ground if it is normal, but it may appear as if it is shorted to a point with an intermediate potential. In some cases, it is possible to detect an abnormality in the temperature sensor by utilizing the fact that it is not equal to ground.

[0007] The same arrangement can be made even if the thermistor and resistor are arranged in reverse.

[0008]

[Embodiment] Next, an embodiment to which the present invention is applied will be described. As shown in FIG. 1, the temperature sensor abnormality detection device 1 of the embodiment includes a voltage dividing resistor 3 placed in series on the upstream side and a thermistor 5 placed on the downstream side between the power supply voltage Vcc and the ground GD. An A/D converter 9 is connected between the voltage dividing resistor 3 and thermistor 5 via a resistor 7, and a switch 11 made of a transistor is arranged between the thermistor 5 and ground GD. It is equipped with a microcomputer 13 that executes various calculations based on the terminal voltage VIN inputted from the /D converter 9 and also executes opening/closing control of the switch 11. The microcomputer 13 is also connected to an abnormality detection lamp 15, which lights up when it detects any abnormality such as a short-circuit to ground, an open circuit, or a short-circuit to an intermediate potential.

The microcomputer 13 executes temperature sensor abnormality detection processing according to the procedure shown in FIG. In this process, first, it is determined whether the inspection timing for detecting a short circuit with an intermediate potential has arrived (S1). If it is not the inspection timing, the switch 11 is short-circuited, that is, the base voltage continues to be supplied to the transistor (S2), and the terminal voltage VIN at this time is input (S3). And the terminal voltage V
It is determined whether IN is between the upper limit value Vmax and the lower limit value Vmin (S4). Vmin <VI
If N<Vmax, the short/open detection flag fER1 is set to "0" (S5). On the other hand, if the terminal voltage VIN is not within the upper and lower limits, the short/open detection flag fER1 is set to "1" (S6)
.

[0010] Furthermore, when it is determined that the inspection timing has come in the process of S1, the switch 11 is opened, that is, the base voltage to the transistor is cut off (S7), and the terminal voltage VIN at this time is Input (S8). Then, the terminal voltage VIN is the power supply voltage VCC
It is determined whether it is equal to (S9). If the terminal voltage VIN is not equal to the power supply voltage VCC, the intermediate potential short detection flag fER2 is set to "1" (S10), otherwise it is set to "0" (S11).

[0011] After that, the detection flags fER1 and fER2
If either one of them is set to "1" (S
12, S13) and turns on the abnormality detection lamp 15 (S14
), the fail-safe value set for fail-safe use in the event of sensor abnormality is employed as the temperature detection value (S15).

On the other hand, both detection flags fER1 and fE
If both R2 are set to "0" (S12,
S13), the abnormality detection lamp 15 is turned off (S16), and a value based on the terminal voltage VIN detected while the switch 11 is short-circuited is adopted as the temperature detection value (S17).
).

As described above, according to this embodiment, the ground G
In addition to short-circuits and opens with D, it is also possible to detect short-circuit conditions with intermediate potential points of adjacent equipment, etc., thereby further improving the reliability of the temperature detection value. Although one embodiment of the present invention has been described above, the present invention is not limited thereto, and various embodiments can be adopted without departing from the gist of the present invention.

For example, the switch 11 may be interposed between the detection terminal and the power supply voltage VCC. In that case, when the switch is open, the terminal voltage VIN is connected to the ground GD.
It is sufficient to detect an abnormality based on whether or not the values are equal to each other. Note that the ground GD is normally shared with other peripheral devices, so if the configuration is such that the ground side is forcibly opened as in the example, operations such as abnormality detection of various devices can be performed at the same time. The advantage is that it can be done.

On the other hand, if the voltage dividing resistor 3 and the voltage detection terminal are configured to be open, there is an advantage that there is no waste when individual abnormality detection is required.

[0016]

As described above, according to the abnormality detection device for a temperature sensor of the present invention, a short circuit with an intermediate potential point can be detected, and the reliability of the detected value of the temperature sensor can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an abnormality detection device for a temperature sensor according to an embodiment.

FIG. 2 is a flowchart of the temperature sensor abnormality detection process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Temperature sensor abnormality detection device, 3... Voltage dividing resistor, 5... Thermistor, 9... A/D converter, 11... Switch, 13... Microcomputer, 15... ...Anomaly detection lamp, GD...Ground,
VCC...Power supply voltage.

Claims (1)

[Claims] Claim 1: In a temperature sensor abnormality detection device that detects an abnormality in a temperature sensor by comparing the terminal voltage of the temperature sensor with a predetermined reference value, a forced disconnection that forcibly brings a circuit including the temperature sensor into a disconnection state. 1. An abnormality detection device for a temperature sensor, characterized in that it is equipped with a means for determining a temperature sensor and an abnormality determining means for determining that the temperature sensor is abnormal if a terminal voltage matching a disconnection state cannot be obtained when the forced disconnection means is activated.