Hi nafiseh,

you can not wait inside your PLC code. The PLC has to finish the program cycle per default within 150ms.

Of course, your functionality would be possible to program, but you'll need a different approach. Could you therefore please describe your requirements in details? Should it work like this:

• Positive edge on #start will start the procedure.
• 1st array element will turn to TRUE.
• After 5s the 1st array element turns to FALSE while the 2nd element turns to TRUE.
• Another 5s later, the 2nd element turn FALSE and the 3rd turns TRUE.
• …
• After the last element, the procedure stops and can be started again.

You should also describe additional requirements. Should it be possible to abort the procedure? Should it be possible to change the array length? …

Kind regards
Stefan

Stop thinking like you are programming a PC.  A PLC is a deterministic controller that runs similar to how Arduino and other microcontrollers operate, with a setup routine that's called once at startup, and a "loop" that runs forever.  The "loop" is a combination of all the cyclic OB logic (or just OB1 if that's the only cyclic OB in your PLCs logic).

Paradigm shift in your thinking is required.

Once you understand that the PLC is time-slicing, giving everything a little time, then moving on, things get better.

[NOTE: not recommended, but a simple approach for learning] If you need a 5 sec delay, you can use the system clock memory bits, input with an edge transition into an INC instruction (LAD/FBD) to increment an integer tag.  When it reaches the value of 5 (using a compare instruction), act on whatever needs the 5 second delay, then set the integer tag to 0.

This is not ideal, but for many situations, it is more than adequate since the average delay will be ~5.5 seconds, +/- 0.5 seconds.  Most people accept that as 5 seconds unless they are using a stopwatch and accuracy counts.

Then you come back to the forums and say, customer/professor/manager complained.  Need better accuracy.

That's when a different solution (similar to what others are recommending) is useful.

It all depends on how accurate and repeatable the delay needs to be.  It may also depend on what the delay is driving.

qwazee

Add one more thought..
Do not put a timer inside a loop.. _{unless using an array of timers}