Have just discovered this forum - extremely informative & stimulates some interesting HA interfacing concepts & ideas.
I had separately been contemplating how to monitor gas hot water heater "status", I have planned - but not as yet implemented this idea.
I wonder if any others have attempted this or similar idea??
Method 1 Thermocouple
- which generates a very small voltage based upon "flame" temperature (an appropriate thermocouple can even be inserted directly into the flame)
This technique is typically used for monitoring the pilot light in gas appliances & when hooked to an appropriate circuit (more below) will generate a voltage that is proportional to flame temp.
Accordingly this has potential uses for monitoring "presence of flame" - some that come to mind :
- monitor pilot light on gas appliances (eg hot water heater, heating furnace)
- monitor status of hot water "heating" (ie when the main gas jets & thus flame is operating in heat mode)
- monitor gas fireplace status ("on/off")
Thermocouple types : there are a number of different thermocouples - the one required (most common) for above applications is "Type K"
(this type of thermocouple has Sensitivity approximately 41 µV/°C.) with temp range up to 1200 °C
A suitable Type K from Digikey could be : BK Precision TP-29-ND (approx $11) - note this is limited to +392F (hence not suitable for insertion into flame)
Thermocouple would need to be positioned in proximity to flame to ensure max temp is well within the max rating of thermocouple.
Thermocouple Amplifier Circuit : to amplify the very small voltage produced by a thermocouple
Analog Devices AD597AR digikey $6
Thus the thermocouple temp will produce a voltage output proportional to temperature, this can be used to
a) close a relay & thus become an input for DS10, 1 wire switch, input to digital IO board input
input to a analog to digital IO board, HVAC 1 wire board
Method 2 Encapsulated Temp Switch
An "encapsulated thermal switch" is used to measure surface temperature - are available in +5C steps & are (claimed) accurate to +/-5C
Digikey has these units (approx $9 each) model 317-10XX-ND in both normally open & normally closed contacts. (select XX according to temp)
They are available in nominal temp steps of +5C from 70C to 150C
Note that max permanent temp of housing is +220C - hence the unit needs to be mounted to a surface with a good differential temp between ambient & the internal heating areas, BUT is always within rated max temp.
Note that the "conducting surface" that brings heat from the flame area needs to not be "too large" - as otherwise it will have a high thermal hysterisis that will slow the response (ie the switch off when flame is extinguished will have a time lag)
The thermal switch method is much simpler, requires no power (its a simple passive switch) or knowledge of electronics - but does require some "mechanical" dexterity & also experimentation to get temperatures in the correct range to trigger the switch. It also has some hysterisis & thus will have a time lag both for "flame on" & "flame off"
The thermal switch can be used directly as an input to DS10, IO board, 1 wire switch, powerflash module, etc.