[SOLVED] How to compare values from 4 temperature sensors?

SilverNodashi · 2017-01-28T10:19:39.412Z

Hi,

Is it possible somehow to compare the differences between 4 temperature sensors, on emoncms.org?

My sensors log data every minute,and I would like to see the differences between the values. I.e. “25.9 - 24.2 = 1.7”

I know I can export the data and compare in excel, but live visual dissference display would be nice.
If this is possible?

Robert.Wall · 2017-01-28T13:05:14.841Z

Look at the input page, under Setup. There you will find various mathematical operators. So you will do something like:

In input 1:
Log to feed (this is raw Temp 1)

Input 2
Log to feed (This is Temp 1 - Temp 2)

In input 2:
Log to feed (This is raw Temp 2)

SilverNodashi · 2017-01-29T13:36:00.260Z

Hi,

Thanx, I’m not sure if I did it right, or if it just doesn’t work as expected.
I have two feeds: “Outside” and “Garage”.
My feeds are setup as follows:

For Garage: “Log to feed Node:1:Outside VS Garage”

For Outside: “Log to feed Node:1:Outside VS Garage”
and “- input Node:1:Garage”

Then when I view the graph in “Data viewer”, I select “Garage”, “Outside” and “Garage VS Outside”. The results are quite strange, to say least. Please see the attached screenshots.
I was expecting a line running in the middle of the other two lines, but it shows sporadic information.

Both the “Garage” and “Output” temp sensor readings are read with the same pythons script, run from crontab every minute.

pb66 · 2017-01-29T13:49:26.558Z

You cannot log both temperatures to the same feed, try this

For Garage:
Log to feed “Node:1:Garage”

For Outside:
Log to feed “Node:1:Outside”

feed “Node:1:Garage”
Log to feed “Node:1:Outside VS Garage”

SilverNodashi · 2017-01-29T14:06:12.032Z

Thanx pb66. I changed the channels and will see what it does. For some odd reason, I can’t upload the screenshots now. The “Uploading 0%” status on the bottom just runs infinitely.

pb66 · 2017-01-29T14:10:00.267Z

SilverNodashi:

I can’t upload the screenshots now.

I have bumped your user status up a notch so there should be less restriction, just in case that was the cause.

SilverNodashi · 2017-01-29T19:05:52.121Z

Thanx Paul.

The differential graphs are now working as expected

emon-graphs.jpg1366×768 101 KB

Only problem now, is that the values goes below 0 degrees Celsius, which is probably kinda expected since the hot and cold values “change places” when it cools down at night. That’s fine for now, cause then I can see in winter if my new thermal insulation makes the place warmer

pb66 · 2017-01-29T19:45:44.951Z

If you want an absolute value you can try extending the processing to something like

For Outside:

Log to feed “Node:1:Outside”

feed “Node:1:Garage”
Log to feed “Node:1:Outside VS Garage”
AllowNeg
scale x “-2”

feed “Node:1:Outside VS Garage”
log to feed “Node:1:Outside VS Garage ABS”

or to save having a semi-redundant feed just to hold the value before making it absolute, something like

Log to feed “Node:1:Outside”

feed “Node:1:Garage”
AllowNeg
scale x “-2”

feed “Node:1:Outside”

feed “Node:1 Garage”
log to feed “Node:1:Outside VS Garage ABS”

might do it!

It would be much easier on self hosted emoncms as there are conditional processes that are not available on emoncms.org.

SilverNodashi · 2017-01-29T20:07:05.324Z

Thanx for the tip. I still need to install a locally hosted emoncms