PLC Counter

The device or application which counts is commonly known as Counter. Counter has two function, either it counts upward or it counts downward. As its properties we divide it in two types…. 

1. Count up counter
2. Count down counter

In Siemens plc when the input to a count up counters goes true the accumulator value will increase by 1 (No matter how long the input is true). If the accumulator value reaches the preset value the counter DN bit will be set. A count down counter will decrease the accumulator value until the preset value is reached.

In PLC we have Counter in application tab. We use it (Counter up or Counter down) as our requirement in program and then write like

“C0  5” where C0 is counter name and 5 is its counting number. We studied before in Siemens PLC blog, Counter instructions in program are as below….

Counter instruction: CTU (For counter up), CTD (For counter down)

Counter number: C0 to C255

Timer Accumulator: - C0, C1……..C255 ……………..To give source or accumulate time Counter used.

In above figure we are operating counter with single input X0 (i0.0) and we took two outputs Y0 (Q0.0) and Y1 (Q0.1). In the case of Y0, it turns on only when X0 is clicked five times means counter turns on after counting five times input by X0. Then counter accumulator C0 turns on.

Where as in the case of Y1 it turns on only when X0 is clicked two times means counter turns on after counting two times input by X0. Then counter accumulator C0 = 2 turns on.

Latch is like a sticky switch when pushed it will turn on but stick in place. It must be pulled to release it and turn it off.

Master control relays (MCR) is an electrical control system which is used to shut down a section of electrical system.

Below figure explains the function of MCR….