Mhahn

PLC tag issue

5 posts in this topic

I wonder if anyone can help me.

I didn't write the program but just revising it. I tried to delete some unused tags(not being used anywhere in the PLC) but the PLC won't let me while online, it's telling me that the tag is being used externally. I have RSLogix5000 v 20.4, the only thing on that network is the PLC processor, two kinetix drives and an HMI.

I've a Panelview plus 1000 using Factorytalk View Studio - ME ver.8

My questions are: Can I delete tags that are being used by the HMI from my PLC? How do I find all the tags that are being used in the HMI?

 

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you should not delete the tags being used on HMI because ,for very least,it would create a error message  on HMI.

to find tags used on HMI, generally you have to open HMI application in  Factorytalk View Studio and look under"Tags".However, it could be tricky because the PLC programmer can use direct address of the PLC tags in the HMI so it is not easy to tell if the PLC tags are used on HMI or not .If the tags are not used in logic ,it could be safe to delete  but you have to  absolutely sure they are not used.If the PLC tells you the tags is being used externally ,i'd would check again .Be carefult because the tags could be used by other PLCs or other HMIs over the network.

Unless you have a very good reason to delete them,I usually just leave those tags alone unless if they don't hurt anything but that is just me  :-)

Edited by mikey431

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It's not unusual to make a tag for HMI or other PLC use only. I tend to include them in an array (created from a UDT) but say for example you needed to display degrees F but the PLC scaling was deg C (I can't think of a reason that would be necessary but it fits the scenario) you can do the conversion in the PLC and write it to the HMI tag.

If it says the HMI is using it and it won't let you delete the tag I wouldn't delete it. Also, you can cross reference a tag by right clicking on the tag and selecting cross reference. That will tell you where it's used (don't think it will include the HMI though. 

 

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Thanks guys...

I did a cross reference for these tags and they are not being used anywhere in the PLC. Like I mentioned, this machine is a stand alone machine with not network tie-in to other machines, only a HMI and two kinetix drives.

I just wanted to know if there's a way to generate a list of tags being used in the HMI without going to each screen and each button/display. I tried the HMI Tags - Tags on the explorer trees but nothing shows up.

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You can narrow down how much digging you have to do on the HMI screens by pressing CTRL-A, which selects all items on the screen, then CTRL-R for replace.  You do NOT want to use the replace function, but you can scroll through EVERY tag that is used on that screen at this point, with two caveats:

This will not show you what tags are being read by Parameter Files

Realize that the Alarm Table in the .mer will poll tags separately.

 

 

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