There are a lot of small partners who don't understand what it means between relay interlock control and PLC control, because they have a lot in common. Today, Xiaobian will talk about the connection between them and take a look at it.
If you look at the relay chain control loop and the plc control loop, they work differently.
Figure 1 corresponds to the logical interlocking control loop. If there are n such control loops, then when you operate any of the start or stop control buttons, the corresponding contactor will pick up or open. Here we ignore the time it takes for the contactor to be powered or to be powered off. To be precise, it is controlled in parallel. If described in computer terms, he is always in the process of "interrupting work", that is, any one of your input operations will respond immediately.
For the PLC control loop like Figure 2. If it corresponds to a program like program 1. It works like this: input, input latch, scan the result from top to bottom according to program 1 from left to right, output latch, output. It is driven by the clock signal and is timed serially. That is, input, program operation, output, and repeated iterations. It's just that the serial program scan runs too fast and we don't notice it. Or it is output in a non-stop operation refresh (except for specific interrupt run programs).
The completely different working methods of the above two should be fully understood. Not all input signals can be received by the PLC system. For example, the input with faster frequency, such as the count input. If you enable the normal counter inside the PLC and cannot fully reproduce the input value of the count, you should enable the input interface corresponding to the high-speed counter and the high-speed counter. Of course, for ordinary input signal PLC is fully acceptable. For example, I use the FX2 PLC, the program is about 1K, the start button of the automatic program is the button of the IDEC brand, I will run the program when I click it, and the results of repeated trials are the same. That is to say, although I have pressed the button for a very short time, he has been able to be recognized and accepted by the PLC system. Therefore, we can understand that although the PLC system is controlled by "serial", because the PLC runs at a particularly fast speed, and the CPU system's CPU speed is continuously improved, special signals are required for special PLC interfaces. In addition to the special instructions of some PLCs, the ordinary control program should be no problem, except that you have a big idea or ignore it.
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