Simple rule math help

Setup, Configuration and Use Beginners
1

Gday,

Could someone point me in the right direction with subtracting a value from a sensor reading.

This is what I have but it does not seem to be working, both items are Number items.

rule "Calibration"
when
		Item Sensor1Temp changed
then
		Sensor1TempCAL = Sensor1Temp - 2
end

Regards,
George

1 Like
2

I think you have to have put:

import java.lang.Math.*

At the top of your rules.

3

You want to calculate with the .state of the item, not the item itself.

4

Thanks guys,
I have put, import java.lang.Math.* at the top of the rules.

watou do you mean to do it this way?

rule "Calibration"
when
		Item Sensor1Temp changed
then
		Sensor1TempCAL=Sensor1Temp.state-2
end

Regards,
George

5

Maybe this would work? Assuming Sensor1TempCAL is an item…

import org.openhab.core.library.types.DecimalType

rule "Calibration"
when
		Item Sensor1Temp changed
then
		Sensor1TempCAL.postUpdate((Sensor1Temp.state as DecimalType) - 2)
end
2 Likes
6

watou,

That did the trick. Thank you!

I think I need to do some work and understand the postupdate command a bit more.

Regards,
George

1 Like
7

Where does the Sensor1Temp item get its value? If it’s a binding that supports transforms (like MQTT, for example), then you could replace the word default in the in-binding string with JS(calibrate.js) and make a file transform/calibrate.js:

(function(temp){
return temp - 2;
})(input)

So you item Sensor1Temp’s value would arrive already adjusted, with no need for a rule and second item. Just a thought – your way obviously works, too, and you may have good reason to do it your way!

8

watou,

Sensor1Tem is coming in from a zwave aeotec multisensor 6. I know there is a calibration method via habmin however when I tried that way it wouldn’t save for temperature or humidity (of course the two I can measure here). For some reason Lux and UV would accept calibration adjustments via habmin but not temp and humidity.
After a few hours of googling it does appear others are having similar challenges with the product. I logged a ticket with the manufacturer to see if they know of a fix.

Not to worry I thought I could just calibrate it within openhab instead.

Does the transform method work with zwave items?

Regards,
George

9

No, so until the vendor can update the firmware to allow temperature calibration, the proxy item/rule approach you are using is the best alternative I’m aware of.

10

Hey, any news on this ?

My Aeotec Multisensor is also off by 2 degrees and the calibration with habmin doesnt work.

Not sure, if its a habmin/zwave-binding error or an aeotec-firmware-bug

11

Hi, I am getting my bar indicators data via Mqtt. Normally, it shows a number like 0.50 high. What kind of js should I do for this? I have never done before. I would be glad if you explain in detail. Thank you…