If you’ve had any experience with PLC programming, you’ve probably heard terms like self-locking, interlocking, and mutual locking. These are typical fundamental programming steps in PLC programming that we must master. Below, I will share several of the most classic small programs.
Self-locking requires a normally open contact in parallel with an output coil. When started, the parallel normally open contact maintains the output closure, which is self-locking. The most commonly used start-stop program is self-locking.
Interlocking uses two or more signals to control one output, essentially forming a series contact program. Mutual locking is an extension of interlocking, using an output signal from one program line as the interlocking contact for other program lines to control each other, which is mutual locking. When there are situations where two or more outputs cannot operate simultaneously, mutual locking is needed, such as in forward and reverse control.
A flashing circuit, also known as an oscillating circuit, is a continuous cycle of turning the light on and off. By changing the timer settings, the flashing frequency of the light can be controlled.
Using a timer to achieve a delay before the output closes and a delay before the output opens.
The alternating output circuit is essentially a single button control start-stop function. There are many programming methods for alternating output; here, I will provide just one example.
When controlling one output from multiple locations, connect all normally open contacts in parallel and normally closed contacts in series to achieve multi-point start-stop.
In relay control, momentary operation is achieved using a composite button. The composite button’s function of first breaking then closing can realize momentary operation. Converting from relay control to ladder diagram, just modify it slightly, as shown in the ladder diagram below, to achieve momentary plus continuous operation. When X22 is disconnected, M1 disconnects after Y20, and the normally closed contact of X22 prevents the self-locking path of Y22.
These are the classic programs that must be mastered in PLC learning. Have you learned them all?
Source: Jicheng Training Network, Author: Cai Huixing; reproduction without authorization is prohibited, violators will be prosecuted!
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