Power heating system

[gkoper]

I have connected two DS1820 digital thermosensors to my RPi running FHEM. The thermistors are connected to in- and output of the heater. By taking the difference between these two temperatures and multiplying by the heat capacity (assuming a more or less constant flow rate) I can determine the delivered power. Who can tell me how to make a plot of the temperature difference and eventually multiply this with a constant? There are some remarks here and there on the web but these are too cryptic for me: I would like to see a set of instructions that tells me how to do it.

Thanks in advance!

[Starkstrombastler]

My suggestion is to add a user reading in one of your devices:

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attr yourDevice userReading Power{(ReadingsVal("yourDevice","temperature",0)-ReadingsVal("yourDevice2","temperature",0)*factor}
where factor is to be replaced by a number.
Let the reading log to a log-Device.

[Prof. Dr. Peter Henning]

Just as a side remark: These are not "Thermistors".

Regards

pah