I wanted to add hot water temperature to my raspberry pi powered “Pimometer” but wirelessthings dont make a suitable XRF sensor.
I decided to buy a standard wirelessthings temperature sensor, unsoldered the thermistor and added a flying lead resoldering the thermistor to this, making sure to insulate the legs of the thermistor.
Luckily (or not) our hot water cylinder has no insulation around the immersion heater at the top of the tank, using some thermal paste i attached it to the bare metal and taped it in place with some foil tape. I then added it to my pi and left it to get some readings.
The final step was making sure the readings are relatively accurate, using a thermometer under the hot water i compared the real life temperature to the readings on the pi and to my suprise they are are only a couple of degrees out so definitely accurate enough for what I need.
After seven days of data logging i lagged the hot water cylinder to see if there was any significant improvement in heat retention.
NOTE: When first testing this setup I didn’t use thernal paste, the readings were around 30% out which was nowhere near accurate enough, by adding the thermal paste and angling the bead of the thermistor it has improved this considerably.