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!