stack temp thermocouple

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varadhammo

varadhammo

Member
Sep 28, 2014
66
Lexington, VA
I'm almost sure that this info is on here somewhere but I can't find it. I'm starting to put together a temp logging setup. I'd like to put a type K thermocouple in the section of class A double-wall chimney comin out of the Garn. Has someone done this/what do I need/how do I mount it properly & safely? Thanks...
 
varadhammo said:
I'm almost sure that this info is on here somewhere but I can't find it. I'm starting to put together a temp logging setup. I'd like to put a type K thermocouple in the section of class A double-wall chimney comin out of the Garn. Has someone done this/what do I need/how do I mount it properly & safely? Thanks...
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Sorry for the poor pic placement, this is a dual element type k in my class a flue just behind the garn, pic 2 shows the flue temp on the daq. Best results would be to use a ungrounded thermocouple, this came from omega engineering
 
Tom,

Would you mind sharing some details of how you mounted the thermocouple probe? It looks like you have a compression fitting, what's the circular piece around it? I was thinking I would get a probe with a 1/8" npt compression fitting and just drill a hole the size of the probe through both layers of the class a, then drill the 1/8"-27 npt die size through the outer layer and thread the compression fitting in. I can't really see from the pic what you did there, though.
 
What do you think about drilling a hole in the thick metal plate in the front of the Garn that holds that Garn temp sensor and inserting a threaded probe in that hole?
 
The ceramic gray disc was used to electrically isolate the thermocouple from the boiler, it has a compression fitting imbedded to hold the thermocouple. This is probably not necessary as the thermocouple is ungrounded, but it was a extra precaution taken at the time. The thermocouple extends to the center of the flue stream. The flue temp sampled from the front cover is not a accurate representation, it still has the final pass to radiate temp into the water. The front cover location will read about 75 deg higher than the first section of class a flue pipe. Not sure why Dectra settled on that location for other than convenience and liability of perforating the flue pipe, maint concerns. With a turbulator in the last pass reductions of125 deg are common.
 
Another thought, I'm looking to a 1-wire system and it seems difficult to interface a thermocouple. Do you think that if I took an outer surface temperature reading on the flue it would be directly proportional to the actual flue temp? I could do this with a regular ds18b20. Then I could just correct the range, I'm more interested in relative differences than absolute temperatures... Just a thought.
 
Not that it's necessarily relevant, but I put a thermocouple in my TDI Beetle's exhaust. I bought a thermocouple that mounted with a hose clamp. No threading. Worked fine. The 1/2" gap in the double wall would need some adapting. In summary, perhaps there's car related stuff out there that could be adapted.
 
Ok, ordered an ungrounded type K thermocouple with bare leads KMTSS-125U-6 from Omega (http://www.omega.com/pptst/JMTSS.html), compression fitting from Amazon, MAX31850 thermocouple amplifier/adc to 1-wire board (http://www.adafruit.com/product/1727), 1-wire USB adapter DS9490R from hobby-boards.com, some DS18B20 temp sensors from amazon, various wire & connectors. Software will be owfs (http://owfs.org/) and thermd (http://www.klein.com/thermd/) all open source, running on Linux on my tired old netbook... Going to log/graph Garn tank temps, flue temp, system temps. Just for fun. Total for everything about $150. In the mail, will report back...

Our Garn is a horizontal converted to vertical with a tee off the back...going to try mounting the thermocouple on the tee cleanout cap, sticking up. That way I don't have to go through the double-wall, seems easier, cleaner. Only concern is water, what do vertical flue Garn owners do about rain in the chimney during the warm season?? Before we fired the Garn up I dumped several cups of water out of there after some heavy rain...
 
mine is a horizontal like yours, some time back i had type k thermocouples in the outside vertical part,no problems. i dont have a cap on the end of the flue, just open, never have had a rain issue. About once a month i twist off the tee cap and clean the wet flyash, i think the hot fluegas helps evaporate any moisture that finds its way down the vertical flue. Your data logging project sounds interesting, let us know how it works.
 
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