Thermistors recycling

Hi guys

Im currently working on a project and using 10k Thermistors for take water temps and one to take a heat temperature of a exhaust/flame

A little background. Im using arduino to control a water heater. It currently controls flame intake fan, fuel pump, glow plug and all is working. It monitors water temp and flame temperature for safe running. Currently using normal ebay 10k Thermistors and all is good. But…

The unit has theses sensors as standard and there working but im not sure of there specs etc. If i hook them up inplace of the current ones i feel like there a little out of range. 10 or so c. And the flame sensor seems low. Maybe there right… is there anything i should consider?

See my current circuit for the 10k Thermistor that im using and working ok. Just dont think the Thermistor would cope long term if i put it where the stock one is located.

Thanks

Check the resistance of the thermistor while cold. Are some of them in ceramic shields?

Paul

The flame sensor is in a metal case. Outside the flame near the exit port in a dead end passage.

Would you say a Thermistor would be ok in there? Its currently outside in the passage of exiting exhaust hitting about 130c. When i hook up original one its very slow reacting but i think that might be because of its location.

I might just have to pop it in there and see if it can cope. I assume the metal body around it would make it less sensitive to temp changes. Temps rapidly change from 17c to 120c in matter of seconds and rapidly go down down after all remainly fuel is burnt off

If it's only function is to tell if the fire is on or off, then it's working fine.

Paul

The flame sensor may be a thermocouple.

herbschwarz:
The flame sensor may be a thermocouple.

If this is the case would circuit be best adjusted or just code? It reads lower than the Thermistor and reacts slower. If thats just heatsoak i dont know. I will remove both sensors today and picture them

Thanks
Paul

A thermistor changes its resistance with respect to temperature.
A thermocouple generates a voltage depending on its temperature.
I think the circuit has to change.

I removed sensors.

Left sensor is water temp. At room temp resistance = 11k ohm and changes on blowing on quickly

Right sensor is flame temp. At room temp resistance = 1k ohm and dont react on blowing on

I assume the flame sensor is pretty much at the bottom of its scale. If i put a lighter on it. It moves quickly

herbschwarz:
A thermistor changes its resistance with respect to temperature.
A thermocouple generates a voltage depending on its temperature.
I think the circuit has to change.

I currently pass 5v to Thermistor and get a voltage back to arduino input