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Old October 3rd, 2012, 11:19 AM   #1
naegely
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PV Standard Screen Control

I have a SLC 5/04 and PV1000 Standard

In the PV, these tags are defined:

Screen Status Tag = N7:44
Screen Control Tag = N7:43

In the PLC, when one particular alarm occurs, a value of 34 is moved to N7:43, via a one shot. This displays screen 34 as expected.

There is then a rung with the condition that when N7:44 = N7:43, CLR N7:43. The idea is obviously to return screen control to the HMI once the desired screen is displayed. This seems like it should work, but what is observed intermittently is:

Alarm occurs, PV displays screen 34, but PLC retains screen control and operator calls maintenance. I go online and see that N7:43 = 34 and N7:44 = 0.

Does anyone have any idea how / why the status tag can have a value of 0 when the screen being displayed is screen # 34?

Thanks for any help,

Rob
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Old October 3rd, 2012, 12:23 PM   #2
Mickey
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Maybe the PLC program is also clearing N7:44, take a close look at it's program.

Or post it here and maybe someone can spot something. Zip the program (.RSP file) first then post.
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Old October 3rd, 2012, 12:33 PM   #3
naegely
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Thanks for the reply Mickey. That is a good point, I should have mentioned that the only occurence of N7:44 in the program is in the EQU comparison with N7:43.

I wish I could post the program, but unfortunately I'm not permitted to by company policy.

I also should have mentioned that the identical set up and program is running on ~40 machines, and the issue has only been seen on one, and only in the last several days. I've verified no changes have been made to the program. Really strange one, thanks for responding.

Rob
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Old October 3rd, 2012, 01:16 PM   #4
Paul351W
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I have noticed in the past that if there are multiple rungs making changes to the screen control address, it can randomly flicker. I try to set up my screen control such that only one rung that modifies the screen address can be true at one time and that usually fixes the problem.

However, in our setups the PLC always has control of the screen, not the panelview.
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Old October 3rd, 2012, 02:25 PM   #5
naegely
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Thanks Paul,

We actually have just the one rung changing the screen control tag value
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