JPS62255874A - Checking system for analog output signal - Google Patents

Abstract

PURPOSE:To execute a check of an analog signal outputting circuit at high speed by providing a converting circuit having the same constitution as that of the analog signal outputting circuit, and comparing an output from the converting circuit with an output from the analog signal outputting circuit. CONSTITUTION:Parallel signals 23A, 23B,... from a microprocessor 20 are changed to pulse outputs 1A, 1B,... whose pulse width has been modulated by pulse width modulating circuits 21A, 21B,..., and in order to execute a check of voltage or current signals 5A, 5B,... by a pulse width/voltage or current converting circuit 22, the signal 23N is sent successively to the circuit 21N, and whether it is large or small is compared by comparators 6A, 6B,.... Its result is inputted to a processor 20 as outputs 7A, 7B,... of the comparators 6A, 6B,..., and by the magnitude relation of the signals 5A, 5B,... and a comparing signal 11, a check of an outputting circuit can be executed. Also, by setting a time constant of a filter 9 of a generating circuit of the signal 11 to a small value, the check can be executed at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a check method suitable for checking an analog output signal circuit of a distributed process control device.

[Conventional technology]

The conventional analog signal output check is, for example,
As shown in Japanese Patent No. 8-159103, this is performed using an A/D converter. That is, as shown in FIG. 4, the output is taken into the microprocessor via a multiplexer 31 and an A/D converter 32.

[Problem that the invention seeks to solve]

However, the conventional method has the disadvantage that the circuit configuration is complicated and the cost is high because it uses expensive circuit elements such as an A/D converter.

7. An object of the present invention is to provide a simple and low-cost analog signal output checking method using a circuit and a comparator that are almost the same as an analog signal output circuit, without using an expensive A/D converter. be.

[Means for solving problems]

The present invention generally needs to be able to easily and quickly check the analog signal output circuit of a controller using a microprocessor, which has multiple output channels such as 8 channels.

Focusing on the fact that the accuracy of the check is not so necessary,
The repetition frequency of the comparison signal output circuit has been increased and the filter time constant has been reduced to enable high-speed checking.

〔Example〕

Examples of the present invention will be described below.

A block diagram of an embodiment of the invention is shown in FIG.

FIG. 2 shows the internal configuration of the pulse width/voltage or current varying circuit 22.

Parallel signal 23A, 2 from microprocessor 20
3B, . . . are pulse width modulation circuits 21A.

21B, . . . are changed into pulse width modulated pulse outputs IA, IB, .
In order to check..., the pulse width modulation circuit 21
Comparator 6, which sequentially sends output signal 23N to
Compare the size using A, 6B, and so on. The results are taken into the microprocessor 20 through the outputs A, 7B, etc. of the comparators 6A, 6B, and output signals 5A, 5.
The output circuit can be checked based on the magnitude relationship between B and the comparison signal 11.

In Figure 2, pulse outputs LA, IB... are amplifier 2A,
2B... makes it a constant wave high value, and low pass filter 3
A, 3B..., buffers 4A, 4B... are converted into voltages.

Now, it is necessary to check the analog output signal while the microprocessor is doing various work, and it is desirable to check it in a short time.For this reason, the comparison signal 11
By reducing the time constant of filter 9 of the generation circuit, signal 1
If the settling time of 1 is made small, the analog output signal 5
It can be changed to A, 5B...

Here, the output signals 5A, 5B, etc. can be checked in a short time.

Figure 3 shows this situation. The wave height of the two analog outputs is kept constant, and after passing through a low-pass filter, it is converted into an output signal that includes pulsations, as shown in 5A in Figure 2. . The comparison signal 11 with a small filter time constant is
Although it contains pulsations larger than 5A, the output data from the microcomputer does not have a 1 time constant, so the tube widens faster. In other words, the settling time of the comparison signal is shortened, and the time for checking can be shortened.

〔Effect of the invention〕

As explained above, according to the present invention, by adding only the output circuit and comparator with the same configuration,
You can check output easily and quickly.

Furthermore, according to the present invention, if the time constant of the low-pass filter is reduced, it is necessary to increase the repetition frequency of the input pulse, which causes problems such as the rise characteristics of the amplifier, but such accuracy is not required simply for checking. Exactly the same parts can be used.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a diagram showing the waveform of an output signal, and FIG. 4 is a block diagram of one of the conventional examples. LA, IB...Pulse width modulation signal, 3A, 3B...
Low-pass filter, 2A, 2B...Amplifier, 4A. Early 2 Diagram bottom

Claims (1)

[Scope of Claims] 1. The constant peak value is achieved by providing a conversion circuit having the same configuration as the above conversion circuit in a circuit that converts a pulse width modulated periodic pulse train into an analog voltage or analog current signal via a low-pass filter, An analog output signal checking method characterized in that the output from the conversion circuit is compared with the output from the conversion circuit to diagnose the conversion circuit. 2. In the item described in claim 1, the above 2.
An analog output signal checking method characterized in that, among the low-pass filters of the two conversion circuits, the time constant of the low-pass filter of the latter conversion circuit is made smaller than the time constant of the low-pass filter of the former conversion circuit.