PLC outputs updating

kallileo

Lifetime Supporting Member
Join Date
Jun 2008
Location
Thessaloniki, Macedonia, Hellas
Posts
353
Typically the PLC cycle consists of Input scan -> Program Run -> Update outputs.
In the attached picture (Carel 1tool software) I have 4 pages which contain plc logic programs in specific order.
The PLC is running first the Process 1, then the second page Process 2, then Process 3 and lastly it updates the outputs.

The problem is that it doesn't matter if the status of the outputs should be updated according to the logic in Process 1 or Process 2 it will not change since the page Process 3 is last one in the order and the outputs will be always updated according to the logic in this page.

What could be the solution for this?

Plc scanning.jpg
 
I understand that you are showing us all the logic on a single page but they actually exist in their own process.


Instead of each 'output bit' have each process update a seperate global bit. For example Process_1 would update 'P1_Output_1', 'P1_Output_2' etc. Process_2 would update 'P2_Output1', 'P2_Output_2' etc.

Then, in the 'Optputs Process' logically OR together the outputs from the other processes. For example 'Output_1' = 'P1_Output_1' OR 'P2_Output_2' OR 'P3_Output_3' before applying the output bit to the actual phwsical outputs.
 

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