PLC logic algebra design method - Database & Sql Blog Articles

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Since the electrical control circuit has a one-to-one correspondence with the logic algebra, the control process of the switching quantity can be represented, analyzed and designed by logic algebra.
The basic design steps are as follows:
1. List logical algebraic expressions according to control requirements.
2. Simplify the logical algebra.
3. Draw a ladder diagram based on the reduced logic algebra expression. Here is a simple example to illustrate.
A motor can only be operated when any one or two of the three buttons are actuated, and in any other case, try to design its ladder diagram.
The motor running condition is controlled by the PC output point 0500, and the three buttons correspond to the PC input addresses A, B, and C, respectively. According to the meaning of the question, if any of the three buttons is activated, the output point 0500 of the PC has an output. The logical algebraic expression is that when there are any two actions in the three buttons, the logical algebraic expression of the output point 0500 is because the two conditions are "or", so the motor running condition should be simplified.

Draw a ladder diagram based on the logical algebraic expression as shown.
The biggest feature of this method is that it can simplify many logical relationships.
Of course, redundant design from the perspective of reliability and security is another problem.