Flu top temps

[john26]

As I mentioned in another thread I have K type thermocouple on the top of my flu. The flu is insulated and 36' total from top of stove 6' in the basement and 30' in a masonry chimney. The thermocouple is pinntched on the outside of the liner with the band clamp from the top plate. I just calibrated my pyrometer with a fluke multi meter my temp are between 100 and 150F. I plan on probe at 18" and a stove top thermocouples later along with a manometer. This is on an Ashley AF700 furnace but I thought I would post here since the subject came up and this would apply to any wood burning appliance.

 

[stoveliker]

I'd be concerned with the length of wire decreasing the thermocouple voltage read out. Are you compensating for that?

 

[john26]

Thermocouple wires do not experience voltage drop like power distribution wire due to the low voltage and current associated with temperature measurements and the thermocouple wire is its own source of voltage. I measure temperatures in drying ovens and autoclaves with long wires then test small ovens with shorter wires all with the same test equipment with no changes.

 

[stoveliker]

Ok. That is your experience. Mine is different. Maybe I used smaller gauge.

 

[stoveliker]

Btw, did you think about lighting strikes?

 

[velvetfoot]

Great work! The instrumentation possibilities are endless. Integrating it all, and then controlling the heater like that fellow recently with the RaspberryPi, RC servo motors, etc, is the ultimate. I just wish I had the skills.

 

[john26]

I am using 24ga shielded my experience voltage drop is not a concern but induced electrical noise can affect the accuracy for my use probably not enough to matter but I did use shielded wire (metal braid). As far as lightning strikes go I am not to worried about it. If It happens that will probably be the end of my K type wire and possibly the old pyrometer I would be more concerned with damage to the liner and possibly the furnace, which would be the same with or without the thermocouple. As far as automation I have thought about it but I would drive that with a sensor in my T just before the liner and another on stove top to prevent overfire if that happens maybe next year? The top temp is just for my reference just to check things I temporarily put a thermocouple on the outside of the pipe just above my T before it enters the masonry chimney it was 190F. So 115F seems plausible up 30' and on the outside of the flu. I may consider running inside the flu through a small hole just below the cap.