JPS5975717A - Diagnosing device for ad converter - Google Patents

Abstract

PURPOSE:To detect abnormality and a fault speedily by converting a digital signal obtained by applying the 1st reference voltag to an AD converter into an analog signal, and detecting whether the signal is between the 2nd and the 3rd reference voltages or not through a comparing circuit. CONSTITUTION:A timing circuit 3 generates a switch driving signal 14 shown in a figure (b) to supply a reference voltage V2 for checking to the AD converter 1. When the output signal of the AD converter 1 is inputted to a DA converter 2, the driving signal 14 is ceased and a driving signal 15 is generated as shown in a figure (f) to apply a reference voltage V3 to one input of a comparator 4; when it is ceased, a reference voltage V1 is applied again. Namely, the comparator 4 compares the output signal of the converter 2 with the reference voltages V1 and V3, and then V1 again as shown in a figure (g) during and before and after the generation of the driving signal 15. In this case, V1>V2>V3. If the converter 1 breads down and V3> the output signal of the converter 2>V1, the output signal of the comparator 4 is still at ''L'' or ''H'' and the breakdown is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a diagnostic device for an AD converter that converts an analog signal into a digital signal among process input/output devices connected to a computer.

[Prior art]

A process input/output device has a built-in AD converter that converts analog signals from various process terminals into digital signals and supplies the digital signals to a computer. This AD converter is usually configured to time-divisionally convert a large number of analog signals via a multiplexer. Unfortunately, if one AD converter becomes abnormal or malfunctions for some reason, the entire system may fail.

Historically, repairs to such failures have been carried out exclusively by specialized engineers. However, as direct-direction systems become more sophisticated and complex, it has become extremely difficult for interrogation technicians to find faulty parts, resulting in longer system failure times and lower reliability. I'm there.

[Purpose of the invention]

An object of the present invention is to provide an AD converter diagnostic device that can quickly detect abnormalities or failures in the AD converter, improve maintainability, and improve system reliability. .

[Summary of the invention]

The present invention applies a first reference voltage to an AD converter to be diagnosed, further converts the digital signal obtained at this time into an analog signal, and converts the analog signal into a range of second and third reference voltages. A comparator circuit detects whether it is within or outside the range, and if it is outside the range, a display such as a light emitting diode issues a warning of a failure state.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram showing input and output signals of each part.

To briefly explain the normal AD conversion operation, when an analog signal (voltage signal) is applied to the input signal line 13, the AD converter 1 converts it into a digital signal. Data bus 19 outputs a binary digital signal to data bus 19.
is made up of 20, 1, and 2'' bits, and generally consists of 10 to 12 pits. Note that the AD converter 1 starts the conversion operation in response to the AD conversion start signal J given from the computer side, and when the conversion operation is completed, the AD
Give a conversion completion signal to the computer side. Then, a read signal READ is generated from the computer side, the gate circuit 7 is opened by this signal READ, and the output signal of the AD converter J is sent to the data bus 19.

In this case, a multiplexer is connected to the input of the AD converter 10, and a large number of analog signals are converted into digital signals in a time-division manner.

Next, the diagnostic operation will be explained. This diagnostic operation is carried out by the differential ratio voltage generator 6. Converter to DA', comparator 4. Flip-flop for abnormality detection 5. The timing circuit 3 is used to perform the conversion using the idle time of the normal conversion operation.

Now there is idle time for normal AD conversion operation, as shown in Figure 2 (
Assuming that a diagnostic time T as shown in a) is given, the timing circuit 3 generates a switch drive signal 14 as shown in FIG. A reference voltage V2 for checking is supplied to the input line 13 of the device 1. After this, Figure 2 (C
) is generated from the timing circuit 3 and applied to the AD converter 1. At this point, the AD converter 1 starts converting the reference voltage V2 as shown in FIG. 2(d), and sends out an AD conversion completion signal after a period of time.

The output signal (binary digital signal) of the ADi converter 1 is D
The signal is supplied to the A converter 2, taken in and held by the DA conversion start signal 17 generated from the timing circuit 3 at the timing shown in FIG. 2(e), and then converted into an analog signal.

This analog signal is supplied to the (a) input of the comparator 4.

On the other hand, when the output signal of the AD converter 1 is taken into the DA converter 2, the switch drive signal 14 is stopped, and after that, the switch drive signal 15 with a predetermined width is generated at the timing shown in FIG. 2(f). is generated and the switch 9 is switched. As a result, the reference voltage V1 was initially applied to the (c) input of the comparator 4, but the switch drive signal 1
5 is generated, the reference voltage V3 is applied, and furthermore, when the drive signal 15 is stopped, the reference voltage Vl is applied again.

That is, in the comparator 4, during the generation of the switch drive signal 15 and at timings before and after that, the comparator 4 generates the signal shown in FIG. 2(g).
As shown in , the output signal of the DA converter 2 and the reference voltage V1
Next, the output signal of the DA converter 2 and the reference voltage V3 are compared, and then the output signal of the DA converter 2 and the reference voltage V1 are compared again.

Reference voltages V,, V2. V3 is V 1 > V 2 >
The relationship is set to V3. Therefore, by the comparison operation as described above, the comparator 4 generates a comparison output signal which changes from +1 LII to "H'" to "Ln" as shown in FIG. 2 (11).

This comparison output signal is applied to the trigger input of flip-flop 5. The flip-flop 5 is of a type that takes in and outputs the signal at the D terminal when the trigger input signal changes from "H" to LI+, and the D terminal here is grounded. Therefore, when the trigger input changes from "H" to "L", the Q output changes to I, I+. In this case, the flip-flop 5 receives the set signal 1 generated from the timing circuit 3 at the timing shown in FIG. 2(i).
8 is preset.

Therefore, if the conversion operations of the AD converter 1 and the DA converter 2 are normal, the flip-flop 5 is always in the reset state at the timing when the comparison output signal output from the comparator 4 changes from H''' to ++I, 11. becomes.

However, if a failure occurs in the AD converter 1 and the output signal of the DA converter 2 becomes smaller than the reference voltage v3 or becomes larger than the reference voltage V1, the comparator 4
The comparison output signal remains at "L"t or "HII".Therefore, the flip-flop 5 cannot be reset.

The Q output of this flip-flop 5 is the light emitting diode 12
is supplied to. Therefore, when the flip-flop 5 is no longer reset, the light emitting diode 12 becomes continuously lit, and an alarm is issued.

On the other hand, the Q output of the flip-flop 5 is taken in as an alarm message to the computer side via the gate circuit 7 and the 2''+1 bit signal line of the data bus 19.

Therefore, in this embodiment, by both the alarm message and the lighting of the light emitting diode 12, it is possible to immediately know in which circuit system a failure has occurred.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, failures in AD converters can be immediately known, maintenance is extremely easy, and failure time can be shortened. It has the effect of increasing

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing signals at various parts in the embodiment. DESCRIPTION OF SYMBOLS 1... AD converter, 2... DA converter, 3... Timing circuit, 4... Comparator, 5... Flip-flop, 6... Reference voltage generator, 12... light emitting diode. 1st m t9 ↑ Z decoy

Claims (1)

[Claims] 1. A first voltage generation circuit that applies a first reference voltage to the AD converter to be diagnosed; a DA converter that converts the digital signal output from the AD converter into an analog signal; A second voltage generation circuit that generates a third reference voltage in a time-division manner compares the analog signal value output from the DA converter with the second and third reference voltage values in a time-division manner. and a comparison circuit that generates an alarm when the analog signal value is outside the range of the second and third reference voltages.