Temperature reading jumping around + or - 5 ; thermocouple on large stickburner

I have a fairly new HM 4.2.4 with thermocouple I bought as a kit from the store. It works fine except that the pit temperature stays on the move. If I set it at 250 it will get there but then bounce around every second - sometimes a little below that temp and sometimes a little high. I followed the instructions to calibrate the thermocouple and that went fine. In fact, when I place the probe in water on the stove and turn on the heat I get a nice even rise in temperature to boiling and then it holds steady. This tells me that the probe and HM are working ok. I asked a friend that works with thermodynamics and he suggested that what I am seeing is the real temperature changes occurring in my pit at the probe due to the nature of the air currents. The system does work but I am concerned that it is perhaps overreacting to small changes.

Is this really a concern or does the PID settings take this type of fluctuation into account when controlling the fan?

If it is a concern is there a way to change how the HM averages the temp readings so that it is not so jumpy - OR - can I shield the probe out of the air current so that it is still accurate but less susceptible to fluctuations?

Thanks!

Alan

First question is are you seeing noise on your pit probe? Noise would be indicated on more recent firmware versions by a little squiggly line in yellow or red to indicate the noise level on the probes. Sometimes a GFI outlet or a poor ground will cause noise that makes the probes go up and down, did you try enabling the A/C Input Line Noise Filter in the HM config? If you have noise issues you can try another power supply or another power source (outlet).

If it's not noise and the TC is accurately reading the temp, and the temps is going to continue to fluctuate due to the grill design... In that case you might look for a TC that has more mass, something bulky is slower to react to changes and something like a needle is real fast. Or you could put the TC you have into a thermal well, basically a shroud around the probe that protects it from the moving air around it so it reads a more average temperature.

That said, if the temps are really fluctuating that much I might look at sealing things off better, and also make sure you are not forcing too much cold air through the pit with the blower, which can cause a lot of temperature fluctuations. Rig your HM blower output to make the most effective use of he air flow in stoking the fire, don't let the forced air flow of the blower bypass the fire and go straight into the pit...

Thanks for the quick reply Ralph!

No noise is showing in the graph. The power supply was designed for a laptop and has a good clean power output but I will check out that a/c line filter setting just in case.

I like the thermal well idea. That was kinda what I was thinking but didn't know what it was called.

thanks!

OK, after looking closer it was noise. The little squiggly line was there I just didn't notice it. After flashing the newest package to add the ac line filter and turning it on I am now stable. After reading an older thread (that I missed earlier) I realized power was the most likely issue as I am plugged into a GFIC outside.

Thanks again Ralph!

Alan

Awesome, glad it worked out! The new A/C line software filter Bryan added is great for these types of issues. Even if someone doesn't have a noise issue (now), if you move to another outlet or another venue you may suddenly have a noise issue... the first thing you should do is flip on that filter and hopefully you can forget about it and start cooking rather than messing with power supplies, extension cords, ground wires etc!