Scaled Memory Tag

Ignition
1

I am working on a project that will dynamically change from English <=> Metric units.
The values in the PLC will be in Metric but I want to be able to view & edit values in either units.

The best solution I have come up with:
[ul]
[li]Create a two tag folders Metric/ and English/[/li]
[li]Create a tag in each folder pointing to the same OPC tag (e.g. “Metric/temperature” and “English/temperature”) [/li]
[li]Set the scalemode on the tags in the English/ folder to linear and set the scaling factors (e.g. raw 0 - 100, scaled 32-212 for C/F temperatures or raw 0-25.4, scaled 0-1 for in/mm)[/li]
[li]Create a boolean client tag “[Client]Metric” which is true if the units are Metric, false for English[/li]
[li]Create a String type Custom Property on the Root Container called “UnitsPath” with an expression if({[Client]Metric},“Metric”,“English”)[/li]
[li]Create Numeric Text Field and set its Value to an indirect tag “{1}/temperature” and ref1 set to “Root Container.UnitsPath”[/li][/ul]

This works beautifully for OPC tags. I can toggle the “[Client]Metric” tag and my Numeric Text Field changes and is writeable. A little bit of work but no complicated scripting or expressions involved.

Now for my problem:
How do I do this for Memory Tags?
Scaling seems to have no effect on Memory Tags
I can create an expression tag that scales a memory tag but it is not writable to a memory tag (It can write to an OPC tag).

I know I can do this with event scripts but it seems to me there should be a way to do this without having to resort to scripting. (I avoid scripting if possible because the electricians who will maintain the system will be completely lost.)

2

You would need to do the scaling via scripting. Scaling doesn’t work on memory tags like it does OPC items.

3

Thanks for the answer, even if it wasn’t what I was hoping for.
Please add “Scaling of Memory Tags” to the list of suggested new features.

It seems like you could create some kind of memory tag “alias” that could be scaled or add the ability to write to memory tags in the expression tag definition like you can write back to an OPC tag.

4

Add it as a feature request at http://ideas.inductiveautomation.com