Basic doubt in plc

Hi all,

I am new to plc and new to here. I am learning PLC using the free software PSIM from learningpit.com.

I want to clarify how this code works. See the link

https://lh5.googleusercontent.com/-GuYyrvABsPQ/T6555vPQ9nI/AAAAAAAAAxI/zw-3mlkyIMs/s636/doubt.jpg

I have given two separate input to the same counter. I observe that when any of the inputs is high the counter continuously start counting like a timer, that too even when the other input is low. How this happens?

Thanks in advance

Don't use the same counter twice. Instead OR the two inputs into a single counter.

To understand what's going on, you have to think like the PLC thinks and understand that the PLC constantly runs the program, evaluating each rung of the ladder logic in sequence repeatedly. The counter increments its AC value each time the logic controlling changes from false to true.

For the case when I:100 is true and I:103 is false, when the PLC evaluates the first rung, the logic controlling the counter is true and the counter increments by one. In the very next rung the controlling logic is false. As a consequence, the next time the PLC evaluates the first rung, the controlling logic once again transitions from false to true and the AC value increments by one.

Thanks Steve