GEfanuc 9030 Set & Reset coils not working

[mschneider]

So we currently have a CPU 374+ running a sort of feed bin process. We've had the PLC installed since 2008, with really no problems. I am currently running into a problem with our alarming function. Basically we have about 100 normally open one-shots paralleled to a set coil (4092m) and a normally open reset coil (4092m) with one normally open tied to an acknowledge button on an HMI. So, what usually happens is something goes into an alarm, on-shot goes true and sets our set coil (4092m). operator goes to HMI and pushes acknowledge button which then resets (4092m). But now recently it's happening that set coil (4092m) goes true because something is in alarm. Operator pushes acknowledge (4092m) is reset until acknowledge button isn't pressed anymore, then goes back to true. I can watch this happen online and none of my 100 normally opens in parallel are going true again to set the set coil (4092m)again? What is going on? Like I say it has worked great this way for 5 years and now something funny is happening. Any ideas?

 

[Steve Bailey]

My first suggestion would be to check to make sure that none of the addresses assigned to the one-shot coils are being written to anywhere else in the program.

 

[mschneider]

I tried putting a always off normally open in front of the set coil and then trying to reset, but same result.

 

[Steve Bailey]

Also check to make sure the address assigned to the Set and Reset coil instructions isn't being used somewhere else in the program. Be sure to check the "Implicit addresses" box in the search dialog.

 

[Eric Nelson]

Since the bit is off when the HMI button is pressed, I would think whatever is turning it on in NOT between the RESET instruction and the end of the program. Otherwise, it would be on at the end of the scan.

Either something is writing to that bit (ahead of the RESET) within the program, or something external is turning the bit on (HMI or other networked device).

You've pretty much ruled out the one-shots by adding that N.O. contact ahead of the SET.



-Eric

 

[mschneider]

Good point Eric, I do have two other PLC's networked to this PLC via Ethernet. Maybe there is something out in that network that is manipulating my set coil (4092m) unknowingly. I will do a quick search through those two programs and maybe will have to change my 4092m to another address.