Maintenance guy

line true M bit coil not ON

3 posts in this topic


system is Q06UDEH

GX developer 8116W

Large system 2 PLcs with 60K lines of code between them, SFC ladder, 

Issue,      all conditions HIGH, coil not ON or  visa versa  (not all condition ON but coil high) also happen with data comparisons, moves etc.

what i have looked at so far,  

 -batch monitor confirms HIGH/LOW states

- programs all scanned (all 35 of them)

-no MC control ( some CJ and for NEXT seems unrelated)

-force history is clear - not willing to rest CPU as this is a large press and it is running  

-widespread condition throughout the code 

- only monitor one window at a time

Q - is there some monitor setting that I haven't found?

over lapping registers

Have gone online with original backup just to make sure something didn't happen with the read.

No way i'm doing an edit when I cant tell whats going on with this.







Edited by Maintenance guy
wrong information on hardware

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It sounds like coils are being used more than once in a scan. Look for instructions with k4Mxxxx in them (writing bits in blocks of nibbles) or FROM instructions batch writing to bits. They often cause trouble. Or maybe a HMI or other device is manipulating them in some way and it hasn't been documented properly in the code. 

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Thanks Luke i'll try and figure out HMIs and other PLC,  unfortunately no mapping between hardware supplied, might be difficult to get a starting point

I did just find some M0Z0 instructions

thinking this may be a little above my pay grade.....

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