Scale item directly in items file

Setup, Configuration and Use Items & Sitemaps
1

Hello,

I’m trying to scale a value of an item in my sitemap. This can be done using a rule which works fine.
However I was hoping that somehow it would be possible to scale the value directly in the items file.
This is the basic item:

Number nCpuLoad_1_minute "Load (1 min)" <none> (gSystem) { channel="systeminfo:computer:raspi:cpu#load1" }

Now I would like to add another item that has the value of the basic item multiplied by 100:

Number nCpuLoad_1_minute_scaled "Load (1 min) scaled" <none>          (gSystem)

Is there a way to scale the value of nCpuLoad_1_minute_scaled directly in the items file?

Thanks for looking into this.

  • Platform information:
    • Hardware: Raspberry Pi 3
    • OS: Buster
    • Java Runtime Environment: Zulu 1.8.0_302
    • openHAB version: 2.5.12
2

You can add a transformation to show the value of the Item scaled. You probably need to use the JS transformation which means you’ll have to put it in a separate .js file. The Scale transformation doesn’t do what you are after here.

You could modify the value coming from the channel by applying a profile. But here again you’d need to use the transform profile with a JS transformation which puts the actual multiplication in another file.

So the short answer is no, you can’t do it wholly within the .items file. You’ll either need a JS transformation or you’ll need a rule.

NOTE: OH 2.5 does not have the the same set of profiles as are available in OH 3. Make sure you look at the OH 2.5 version of the docs.

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3

I wrote recently for my own use very basic scale profile (which works also with quantities): ScaleProfile, maybe some day similar thing will come into openHAB core without pulling gain/offset profile from modbus binding? :wink:

Anyhow, above can be easily ported to OH 2.5 where APIs are pretty much the same.

Best,
Łukasz

4

If it really is just that, leave your Item alone altogether.
Add another sitemap widget to include your for-display transformation.

Text item=nCpuLoad_1_minute label="scaled [JS(mutiply100.js):%s]"

Bu if you scale to a real Item you also get persistence. charting etc. available.

Not documented, but noteworthy here; the transform profile will not work with Number type Items in OH2.

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