adccommunitymod (AutomationDirect) asked a question.
EA9 System Bit?
Created Date: November 24,2015
Created By: EddieM
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Are there any system bits that I can used in my PLC ladder that toggles a discrete bit each time the operator touches the panel? I'd like to be able to update a system task on DO-MORE based on the fact that the Operator made changes to the Touch Panel. Since the TASK I'm referring to has many MATH boxes, it slows the CPU scan time and is only necessary to scan if the Operator updates a recipe, parameter, timer, etc. Thanks in advance! EddieM
Created Date: November 24,2015
Created by: BobO
Not sure there is any way to do what you want without setting a bit from the panel, but to deal with the scan time issue, you can insert some YIELD instructions in the slow task to reduce scan bump.
Created Date: November 24,2015
Created by: Do-more PE
Or you could go with some "Is it different this scan than last scan? " logic then set a bit to do the math.
Created Date: November 24,2015
Created by: EddieM
Is there a specific instruction you are referring to do? How can PLC determine "if something is different from last scan " if it didn't scan last scan?
Created Date: November 24,2015
Created by: plcnut
There is a contact in Do-more called a "Delta contact ". It looks like a normally open contact with a triangle in the middle. Any time the referenced value changes, the contact will close for one PLC scan. You could use this to trigger your task.
Created Date: November 24,2015
Created by: EddieM
Thanks for the Feedback. I did see the DELTA contact. I have never used this instruction. I think this will work but I will have to insert this instruction in each rung with a MATH box that I want to "Pass over ". I was hoping to find a bit triggered by the HMI that will toggle when the Operator touched the panel then execute a task from the DO-MORE main rung. With DELTA, DO-MORE will still need to execute the task each scan but save some scan time as it will not have to take the time to execute the MATH box. I know i'm probably splitting hairs here as DO-MORE scan time is really fast.
Thanks again all who have responded!
EddieM
Created Date: November 24,2015
Created by: ControlsGuy
With most HMI's (don't know if this applies to C-More), you can easily tell what screen you 're on. I 've run the code-block that processes the setpoints as long as I'm on the screen where the setpoints can be set.
The delta is a good idea too, but generally only works on one item at a time, so normally it would take a bunch of them, but....someone on here or Host's forum once suggested doing a CRC of a range of values and doing a delta on that. That would tell you if anything in the register range changed and then you enable the processing routine. I thought that was a really cool idea.
Created Date: November 24,2015
Created by: BobO
If you know when the task needs to run, just run the task once in an event mode. I thought the issue was in automatically knowing that the panel had been interacted with vs having the panel write a trigger to the PLC.
If the task itself is too slow, add yields.
And as mentioned, if you want to simplify detection of changes to control values, cluster the critical values in memory and calc the CRC with CHECKSUM, and then use the CRC value in a delta contact to trigger the event based task.
Created Date: November 24,2015
Created by: ControlsGuy
Yeah, it sounded like he was saying he needed an efficient way to detect setpoint changes or the potential for them having occurred so he didn't do the time-consuming setpoint processing unnecessarily.
Created Date: November 25,2015
Created by: a agnone
would the hand shaking feature work? Anytime a button is pushed on the HMI, I use the handshaking feature to acknowledge the change.
Created Date: November 28,2015
Created by: EddieM
Thanks for all of the feedback. All who responded offered great options. I opted for the suggestion made by ControlsGuy. I set up an event in the EA-9 Panel that would copy the screen number of the current screen that the operator was on. When the operator selected 1 of 10 program pages I set the task to run and recalculate all of the process parameters associated with any changes the operator may have made. This seemed like the easiest option.
Thanks again for all of the help.
Best!
EddieM:)