Allen Bradley Plc4 microtrol -CMR instruction?

Oliver Micka

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Oct 2015
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Hello Everybody. We have a too old plc ( allen bradley plc4 microtrol ) which was a run mode until now, but a one pretty morning this plc cannot going to RUN mode.. soo ok, its lifetime is finished..
I would like replaced this plc to a new brand. I have completly plc program which was wrote on a paper ( yes that is crazy, but is very good helper if you cannot possible doing upload ) .. all on the paper is ok, but i saw a one istruction (for me is unknown) , this instruction is "CMR01" which is begin a rung 3, and the same instruction are used on a rung 18 ( total rung is 26 ).. does anybody know what is this instruction ?
What its mean. ?
Command Master Relay or Command Master Reset..? Reset..?
 
If I had to guess, I'd say it's similar to the "Master Control Relay" (MCR) instruction in the PLC-5 and ControlLogix, or the "Zone Control" (ZCL) instruction in the PLC-2.

These operate a little bit differently but the basic idea is that they force all the rungs between them to FALSE.
 
First let me try to clarify he difference between the MCR and the ZCL instruction
both are used in pairs a conditional MCR or ZCL followed by an unconditional MCR or ZCL
But the MCR and ZCL work differently
The MCR Master Control Relay when the conditional rung is true all rungs between the open and close control are scanned and executed as per logic when the conditional is false all runs between the are not scanned and all the real outputs are set to 0 or off no mater what the logic is.

The ZCL Zone Control Logic when the conditional rung is true all the rungs between the open and closed ZCL are scanned and executed as per logic but when the conditional rung is false the rungs are not scanned or updated but all outputs are left in their last state. if it was on it will remain on

as for your command CMD01 I could not find any reference to that command but the use may tell us something. If I could see the ladder logic I may be able to figure it out. it looks like it may be a label CMD01 would be used as a jump to label look for a command in the output rail CMD01

be careful with label loops in programming they can lockup your system if not used carefully the program could stay in the loop nd not complete the ladder logic
I hope this helps
 

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