HI
I have seen a program (AB rslogix 500) with 15 subroutines but I have noticed that the same output being repeated on different subroutine. This production machine works fine and no problem with it at all.
My question: Is this acceptable or not and why some programmer repeat the same output within the plc program, any reason behind it
MIKE31

Personally I do not like to use, or see them used multiple times.

That does not mean that it is not acceptable. There are situations, that assuming the rest of the program is written correctly, that you can use the same output multiple times without any problems. The problem is when the output gets called twice in a single program scan, which tells the output to change its state at the wrong time causing damage or something.

One example would be: If your machine has several different "Setups" that the machine would function differntly for each setup. Generally there is a selector switch or selection on a operator interface, to determine the appropriate way the program will function. In this case chances are the program only calls the appropriate subrutine to run, so that the output is only called / looked at once by that situation per program scan.

Even in the example, I will use internal bits, instead of outputs, and then call each output only once, perhaps in a seperate subrutine, that runs all the time.

Output can be used in mulitple places when it is latched & unlatched
energise the output can cause dangerous results due to scan of the PLC