Write to a tag where a String has Tag Name

Hi everyone,

I am wondering if the following is possible:

I have several Logix 5000 tags of the following format:
TagPre_#_End

where only the # changes.

I am wanting to use a single FTView HMI screen to write to this tag based on the # the user enters.

So if a user enters 1004, I want to write to TagPre_1004_End in the PLC. Then if they change to say, 4056 I want to write to TagPre_4056_End.

Is this possible to do either in FTView or in PLC code?
I can't seem to figure out how to do this.

Your best bet is to create a String Tag Array.

StringData[Index]

Your HMI can directly access any tag in that array by manipulating the Index value.

The pre-defined STRING data-type allows for 82 characters. If you only need 30, for example, you can create your own STRING30 data-type, limiting the string length to 30. For large string arrays, which you are inferring you are using, this will save a considerable amount of memory.

I thought about this however, this didn't help me write to the actual tag which is a DINT, not a string.

jmveerkamp said:

I thought about this however, this didn't help me write to the actual tag which is a DINT, not a string.

Click to expand...

Then create a DINT array just the same as DABA explained, when you enter data on the terminal what you are entering is the index then based on the index you can change data on the tag.

I think your best bet is to change from having the identifying number be part of the tag name to making an array tag.

Then your HMI numeric entry object can write to a tag that's an index value, and your logic can write whatever value you want into that array element.

TagPre[Index] is easy to manipulate in ladder logic, while TagPre_Number_End is not.

I couldn't figure out a way to kludge this with placeholders in FactoryTalk View.

Ken Roach said:

I think your best bet is to change from having the identifying number be part of the tag name to making an array tag.

Click to expand...

This is what I've found too. I was hoping to avoid this. But I think for future projects it'll be okay. Just frustrating for current projects...

I thought about aliasing an array tag to the actual tag, but the actual tag is a pretty large UDT, so making a large array of already large UDTs seems wasteful to me memory-wise since PLCs don't seem to have lots of memory.

Thanks for the feedback everyone!

jmveerkamp said:

This is what I've found too. I was hoping to avoid this. But I think for future projects it'll be okay. Just frustrating for current projects...

I thought about aliasing an array tag to the actual tag, but the actual tag is a pretty large UDT, so making a large array of already large UDTs seems wasteful to me memory-wise since PLCs don't seem to have lots of memory.

Thanks for the feedback everyone!

Click to expand...

You cannot do this - an alias tag cannot have "structure", it can only be a "stepping-stone" to refer to another location in the tag database. When the alias tag is created, you do not define its data-type, it inherits this from the tag or tag-element it is an alias for.