JPH0243812A - Fault detector for a/d converter - Google Patents

Abstract

PURPOSE:To surely detect a fault if an A/D conversion data reaches nearly a constant value by providing a difference detection circuit receiving the A/D conversion data, and detecting whether or not a difference with the A/D conversion data received precedingly is smaller than the fault decision value. CONSTITUTION:The difference detection circuit 15 receives the A/D conversion data from the A/D converter 1, and obtains a difference with the preceding received data to detect whether or not the difference is smaller than the fault decision value. When the difference is smaller than the fault decision value, the difference detecting circuit 15 sends a fault signal to a fault decision circuit 16, and sends the addition signal to a counter 3. When the state is consecutive for a prescribed period, the counter 3 sends an overflow signal to the fault decision circuit 15, which receives the overflow signal and a fault signal is outputted as the final fault decision signal. Thus, is the A/D converter 1 is faulty and even if the A/D conversion data is nearly a prescribed value, the fault is surely detected.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a failure detection device for an A/D converter.

(Prior Art) For example, an electric carpet is provided with a temperature sensor to perform temperature control, and an analog temperature detection signal from the temperature sensor is converted into a digital signal and sent to a microcomputer. For this reason, an A/D (analog/digital) converter is used to perform the digital conversion. By the way, in the A/D converter used in this way, A
Anomalies are being detected in the /D-converted data.

FIG. 4 is a configuration diagram of such an abnormality detection device, and FIG. 5 is a flowchart of abnormality detection of the same device. The A/D converter 1 manually inputs an analog temperature detection signal a from a temperature sensor and converts it into an 8-bit signal D according to its level.

~D7 A/D conversion data, that is, digital temperature detection data, is converted and sent to the upper and lower limit cut circuit 2. This upper/lower limit cut circuit 2 has a tolerance range consisting of an upper limit value and a lower limit value set in advance, and upon receiving digital temperature detection data from the A/D converter 1, checks whether this digital temperature detection data is within the tolerance range. Steps s1 and s2
Judgment shall be made. As a result of this judgment, if the digital temperature detection data is within the allowable range, the upper and lower limit cut circuit 2 sends a reset signal to the counter 3 in step S3. However, if the digital temperature detection data is outside the allowable range, the upper/lower limit cut circuit 2 moves to step S4 and sends an addition signal to the counter 3 and also sends an abnormality signal to the abnormality determination circuit 4. Then,
If this state continues and the count value of the counter 3 overflows, an overflow signal is sent to the abnormality determination circuit 4 in step S5. In this way, the abnormality determination circuit 4 outputs a final abnormality determination signal. Note that 5 is an oscillator that oscillates a signal with a constant period to the counter 3.

However, in the abnormality detection device as described above, the detection is determined to be abnormal when the digital temperature detection data continues to be outside the predetermined range for a predetermined period of time, so if the A/D converter 1 fails and the digital temperature detection If the data shows a substantially constant value within a predetermined range, it cannot be detected as a failure of the A/D converter 1 at all.

(Problem to be solved by the invention) As described above, when the A/D converter fails and the A/D conversion data becomes a nearly constant value, it is not possible to detect the failure of the A/D converter. .

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a failure detection device for an A/D converter that can reliably detect a failure even when A/D conversion data becomes a substantially constant value.

The present invention includes a difference detection circuit that receives A/D converted data from an A/D converter, calculates a difference from previously received A/D converted data, and detects whether this difference is smaller than an abnormality determination value; A to achieve the above object by providing a failure determination means that determines that the A/D converter has failed when the difference is detected by the difference detection circuit to be smaller than the abnormality determination value and this state continues for a predetermined period of time. /D converter failure detection device.

(Function) By providing such a means, the difference detection circuit detects whether the difference with the previously received A/D conversion data is smaller than the abnormality judgment value, and detects whether the difference with the previously received A/D conversion data is smaller than the abnormality judgment value for a predetermined period of time. In this case, the failure determination means determines that the A/D converter has failed.

(Example) Hereinafter, a case will be described in which an example of the present invention is applied to an A/D converter used in an electric carpet. In addition,
Components that are the same as those in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 1 is an overall configuration diagram of a failure detection device for an A/D converter. In the figure, 10 is an electric carpet main body,
A heater 11 is disposed in the electric carpet main body 10, and a temperature sensor 12 is also attached to the heater 10. The heater 11 is connected to an AC power source 13, and the temperature sensor 12 is connected in series to the AC power source 13 via resistors R1 and R2. On the other hand, 14 is an operational amplifier, the "+" side input terminal of this operational amplifier 14 is connected to the connection point of a series circuit consisting of a resistor R3 and a capacitor C, and the "-" side input terminal is connected to each diode. The connection points of the series circuit consisting of dl and d2 are connected. Then, these diodes d1. The connection point of d2 is connected to the connection point of each resistor R1 and R2 through a diode d3.

On the other hand, the A/D converter 1 is connected to the output terminal of the operational amplifier 14 via a resistor R4.

This A/D converter 1 converts the analog hot water temperature detection signal from the operational amplifier 14 into 8-bit digital temperature detection data, and has an output terminal.

~D7 are connected to the difference detection circuit 15 and the upper and lower limit cut circuits 2. Note that the digital temperature signal is sent to the microcomputer, but is omitted here. The difference detection circuit 15 receives the A/D conversion data, that is, the digital temperature detection data, from the A/D converter 1, calculates the difference from the previously received digital temperature detection data, and determines whether this difference is smaller than the abnormality judgment value n. is detected, and if the digital temperature detection data is larger than the abnormality judgment value n, a reset signal is sent to the counter 3, and the digital temperature detection data is larger than the abnormality judgment value n.
If it is smaller than , it has a function of sending an abnormality signal to the abnormality determination circuit 16 .

This abnormality determination circuit 16 has a function of transmitting the abnormal signal as a final abnormality determination signal when receiving an overflow signal from the counter 3 while receiving an abnormal signal from the difference detection circuit 15 or the upper/lower limit cut circuit 2. It is.

Next, the failure detection operation of the apparatus configured as described above will be explained with reference to the failure detection flowchart shown in FIG.

The temperature detection signal output from the operational amplifier 14 is A/D converted by the A/D converter 1 and sent to the upper and lower limit cut circuit 2 and the difference detection circuit 15 as digital temperature detection data. At this time, the upper and lower limit cut circuit 2 performs step el,
At e2, it is determined whether the value of the digital temperature detection data is smaller than the lower limit of a predetermined range or larger than the upper limit as shown in FIG. Based on this judgment, if the value of the digital temperature detection data is within the predetermined range, step e3
Proceed to. In this step S3, the difference detection circuit 16 calculates the difference between the digital temperature data received last time and the digital temperature detection data received this time, and determines whether this difference is smaller than the abnormality determination value n. Based on this judgment, the difference is the abnormality judgment value n
If the difference detection circuit 16 is larger than the A/D converter 1
Assuming that the A/D conversion operation is being performed normally, a reset signal is sent to the counter 3 in step S4.

If the digital temperature detection data is outside the tolerance range set in the upper and lower limit cut circuit 2 for the above operation, the upper and lower limit cut circuit 2 moves to step e5 and sends an addition signal to the counter 3, and also sends an addition signal to the abnormality determination circuit. An abnormality signal is sent to 16. When this state continues and the count value of the counter 3 overflows, an overflow signal is sent to the abnormality determination circuit 16 in step e6.

As a result, the abnormality determination circuit 16 outputs a final abnormality determination signal.

Further, if the difference Δp between the digital 1m degree detection data received this time and the digital temperature detection data received last time is smaller than the abnormality judgment value n as shown in FIG. 3 as determined in step e3, the difference detection circuit 16 sends an abnormal signal to the abnormality determination circuit 17 and sends an addition signal to the counter 3.
Send to. When this state continues for a predetermined period and the count value of the counter 3 overflows, the counter 3 sends an overflow signal to the abnormality determination circuit 16. Thereby, the abnormality determination circuit 16 receives the overflow signal and outputs the abnormality signal as the final abnormality determination signal.

Thus, it can be seen that the value of the digital temperature data output from the A/D converter 1 is almost constant based on this abnormality determination signal, indicating that there is a failure.

In this way, in the above-mentioned embodiment, when the difference between the digital temperature detection data received this time and the previous time is compared with the abnormality judgment value n, the A/D Since it is determined that the converter 1 is malfunctioning, even if the A/D converter 1 malfunctions and its output becomes a substantially constant value, the malfunction of the A/D converter 1 can be reliably detected.

In this case, a failure of the A/D converter 1 can be detected no matter what level the value of the digital temperature detection data becomes substantially constant. Furthermore, since the upper/lower limit cut circuit 2 also detects abnormal A/D conversion, abnormal heating by the heater 12 and failure of the temperature sensor 12 can be detected at the same time.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. For example, in the above embodiment, the case where the present invention is applied to an A/D converter for an electric carpet has been described, but the present invention can also be applied to failure detection of an A/D converter used for an electric kotatsu or other electric equipment.

[Effects of the Invention] As detailed above, according to the present invention, an A/D that can reliably detect a failure even if A/D conversion data becomes a substantially constant value.
A converter failure detection device can be provided.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining one embodiment of a failure detection device for an A/D converter according to the present invention, and FIG.
2 is a block diagram, FIG. 2 is a failure determination flowchart, FIG. 3 is a schematic diagram for explaining failure determination, and FIGS. 4 and 5 are diagrams for explaining the prior art. 1... A/D converter, 2... Upper and lower limit cut circuit, 3
... Counter, 5... Difference detection circuit, 6... Abnormality detection window circuit.

Claims (1)

[Claims] A difference detection circuit that receives A/D conversion data from an A/D converter, calculates the difference from the previously received A/D conversion data, and detects that this difference is smaller than an abnormality determination value; and this difference detection circuit. The A/D converter is characterized by comprising a failure determining means for determining that the A/D converter is malfunctioning when the difference is detected to be smaller than the abnormality determination value and this state continues for a predetermined period. equipment failure detection device.