adccommunitymod (AutomationDirect) asked a question.
Created Date: June 27,2011
Created By: russh
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I am using Stage programming in a DL-260. I set a Stage and the Stage turns on an output coil (simplified, but this is the essence). I reset the Stage and the output turns off. A problem was reported that the system would not start. In looking at the program the Stage is OFF but the output coil is still ON. I can turn the output coil OFF manually and the system is good to go again. How can a Stage be OFF and the output coil remain ON? I have tested this on the DL-06 with the same result. Anyone see this?
Created Date: June 27,2011
Created by: plcnut
is the coil an "out " or a "set "? and is that output used anywhere else in your program?
Created Date: June 27,2011
Created by: russh
Thanks for your reply - the coil is an "OUT " and appears nowhere else in the program.
Created Date: June 27,2011
Created by: bcarlton
If the stage was active when the PLC was cycled off it may not turn off the output. Sense the first scan of the unit and do any appropriate setting/resetting on power up.
Remember that the code within an inactive stage is not being scanned at all. Nothing would be in control of that output.
Created Date: June 27,2011
Created by: plcnut
I don't know, you might try posting at forum.hosteng.com. you may get a quicker reply over there.
Created Date: June 27,2011
Created by: Do-more PE
One possibility is that the coil is in the retentive range of the PLC. If the PLC powers off while the coil is active and the stage is off upon power up, then it will remain active since the stage where it would normally be turned off is not being scanned.
Created Date: June 27,2011
Created by: russh
Thanks for the input - the coil in question is not within the retentive range of the PLC.
I have set up the system to test the coil action when the power to the PLC goes off. Each time on power resumption the Stage and OUTput is OFF. So I still don't know what causes this condition.
I will try bcarlton's idea to sense the first scan and reset on power-up.
Created Date: June 27,2011
Created by: franji1
Check the XRef for the C or Y bit AND its corresponding MAPPED V memory range (e.g. V40400 aka VC0 for C0 thru C17).
Also, it is possible that the Stage could be coming ON for that one scan and immediately transitioning out via JMP that same scan, so the stage appears to be OFF, but the output will be ON. If it did this EVERY scan (i.e. stage is active and JMPs out), then the output would also appear to be ON, but the SG be OFF.
Created Date: June 28,2011
Created by: Glenn
russh, I have had the same issue with c-bits appearing to latch on for several years and it appears to be completely random.
This has been posted before and never seems to be adequately resolved.
I can say that I tried the method proposed by bcarlton and reset all my c-bits on power up and have them turn back on as commanded. This has worked for me.
Created Date: June 28,2011
Created by: russh
Thanks franji1 for your ideas - I have knocked the program back to basics to test the issue - there are no JMP's in the logic. Its a plain issue of the c-coils staying on when the stage is OFF.
Thanks Glenn for your input - we have been using AD PLC's for a few years and have never run into this before. To a certain extent the issue seems to defeat the idea of Stage Programming. But thanks for confirming the work-around.
Thanks bcarlton for the fix. There's always something to learn.
Created Date: June 28,2011
Created by: bcarlton
As a note, I have never seen this problem. But I always use 'first scan ' to set up required initial conditions routinely.