Thermocouple and wildly swinging tempratures


 
D

DaveyR

New member
I am hoping that someone can give me some ideas on what to look at.

I just recently finished the electronics part of my HM build. I have done the thermocouple on the cat 5 cable using the thermocouple amplifier from adafruit and it seemed to calibrate just fine. I am still waiting to complete my mount then i will be adding in a roto damper to control the temps but currently i am just using it to monitor what is happening on my system.

Last night i started a brisket cook and it all seemed to be going fine then about 10 hours in to the cook the temps just dropped and then went really unstable. I am running it on a Komodo Kamado so the temps just dont move like the graph shows. It can take an a couple of hours to achieve the drops that the graph is saying happened in 5 - 10 minutes. Also it seems to indicate that the temp swings are just all over the place and it seems really strange to me as the dome temp (Analog thermometer is just rock solid).

It is a rainy windy day here and it is a bit cool but i would not have been expecting this kind of swings as the fresh air gap is about 2mm and the top is about 1/4 of a turn so very little air movement. On the graphs the 2 really big drops one at 08:30 and one about 9:15 was me opening the lid and checking on the amount of coal and drip pans so they make sense but the other swings just seem strange.




Thanks for any thoughts

Davey
 
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You said you have an external TC amp and it was rainy? Did the amp board get wet, maybe that was the cause of the problem? I have run my TC from an external amp for a long while now (using the HM TC circuit), only one time did I have this problem, wait, twice.... Once I had the external TC amp out in the open and it got rained on, the second time I had a loose wire and when the roto damper moved it would rattle it around, both times the graph was real flaky like what you posted. Are you using a proper TC junction to connect the TC to the amp?
 
Hi Ralph.

Yes i have a correct TC socket for it. It was housed in the same box as the HM at the moment until i can get the case / mounting made so it was inside a waterproof box. I had noticed that something like this had happened in the past and it was a number of hours in to a cook. Next time i run a brisket or another L&S cook i will add in a 2nd probe on the pit and i will then be able to compare.

Thanks for the ideas i will check all my connections.
 
Hi Davey,
I have a similar setup and had some shaggy looking thermocouple readings as well. I had some issues with one end of my thermocouple connection where the fiberglass insulation was kind of flaky and I think one of my TC leads was getting on the shield or shorting to the other.

To keep that from happening again, I trimmed back the braid a ways, and made sure I had some good insulation around the TC wires, set everything in the connector and then put a nice dab of white silicone caulk around the braid and insulation and the TC leads to keep things in place as I tested the temp reading using a soldering iron as a heat source for the TC.

Be sure to use some space between the soldering iron and the TC to keep it from overheating. The one I use has seen 2000 F and I think that is why I had the insulation issue to start with. (I was doing some gassification experiments)
 
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