Has anyone experienced strange behaviour of SFC logic? By strange, I mean that logic written on P1 part of the step does not always execute.
It is 800xA SV 5.1 FP4 rev D with batch management. Abnormal function is observed on SFC logic on custom unit control module.
Any pointers would be highly appreciated.
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No. my experience is that SFC in AC800M is VERY reliable ( unlike some other PLC systems I've worked on ).
It is much more likely that if you are using "one shot" logic ( ie variables that are true for only one scan ) then you could have introduced some error because of Code Sorting. If you have not paid attention to Code Loop errors and just thrown "no-sort" at every error, then you can find that code is not executing in the expected order. This can lead to some very unexpected and un desirable effects. This could potentially be mis-interpreted as the P1 action not executing - but the real error is the control module code is not responding because it is not seeing the P1 order.
Post your suspect code.
Thank you for your inputs.
Batch recipe procedures starts phase execution. “Initialiser” flag is set at the start of the phase. When this flag is set, Unit control module opens or closes the valves as required by the process. When valves are oriented in the desired position, Unit control module resets this flag. Following reset of the flag, phase execution progresses further. We have trouble that the flag does not reset in P1 step in the unit SFC logic (refer screenshot). It eventually results in phase execution standing at same step without progressing forward as transition condition in phase is looking for “Initialiser:=False”.
One of the thing that we are considering is to reset the flag in the N part of the step instead of P1. I believe it should work. Our system is almost 6 years old and we never had trouble because of execution error on SFC. Could it be other factors causing such errors? Scan time for example.