In traditional relay control loops, when using relay and contactor , the number of contacts needs to be considered. For example, commonly used relays generally have 2 or 4 normally open/normal closed contacts. If it is not enough, the contactor can be added with auxiliary contacts, and the relay can expand the number of contacts in parallel. How to expand the number of contacts through relays. Friends who don’t know how to expand can go and take a look. So in the PLCh program? Input, output, auxiliary relay M, are there any restrictions on the number of use of these devices?
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Gu Mingsi means that these are all devices, which are different from the hardware in our relay control loop. The contacts of these devices can be reused many times without the need for complex program structures to reduce the number of contacts used. As shown in the figure below, I0.2 and I0.3 use
in multiple networks. But it should be noted that output coils with the same number should not be used multiple times in the program, otherwise there will be a problem of double coils, because the PLC is executed in a cyclic scanning order. Double coils may cause malfunctions and should be avoided as much as possible. After this, I will write a special article on the problem of double coils and solutions
