Frustration with temp reliability. Probe placement or other issues?


 
J

J Halvo

TVWBB Member
Hey folks, been using my HM for several months now, sometimes with great results and other times with frustration.

Yesterday did ribs at ~225f starting at 11am. Everything was going well until ~230pm. At that time the reported pit temp (thermistor prob) reported a climbing temp and meanwhile the meat temp started dropping. My guess here is either pit probe placement or hardware issues. Here is the graph and also the prob placement; (1) designates where the prob was from 11am-1:20pm, then I rotated the whole rack at which time (2) designates the new prob location. NOTE: I didn't probe the meat until ~115pm hence the lack of data.

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Q1: Would outside ambient temp negatively affect the HM's operation or reported temps? It was ~5F outside so the HM was very cold.

Q2: Is it possible that since the prob was near the edge of the heat deflector once I rotated it that it picked up more direct heat vs. what the meat was feeling?

Lastly, once I noticed the issue and ramped the temp back up to 245F it held there reliably for HOURS.

Thanks for any ideas/feedback/etc!


TC vs. Thermistor: I've also used the thermistor along side a thermocouple and they generally report differences of ~10F (TC being higher) despite the probes being next to each other. As such, I tend to avoid using my TC prob and just use thermistor for both pit and meat temps until I learn more about why.
 
I feel your pain. I have experienced control issues like this when I cook as well. Always happens when it is cold and windy or when there is high humidity. My cook this weekend was effected by cold air, not wind. I see you secure you pit probe to the grate. I also see the deflector has 3 areas where the shield let smoke through. Point one looks like the ideal spot for mounting the probe to grill. I have another idea you might try. I know a few of the user suspend their pit probes above the grill and in the flow of heat as it makes it`s way out the exhaust damper. On my Primo grill, I suspend my probe down the damper and get it close, if not at the same spot, as the grill thermometer. I am lucky to have a small hole that is used to secure the damper to the dome so I remove screw and fish pit probe down through that. I have excellent results and very stable control. I still have issues when it`s cold. I do have issues when the humidity is high and that is rare, because in the desert west rain is not a regular event and the humidity is usually no more than 40-60% on cloudy days. Summer it always below 30%. The last issue I have ran into when cooking during cold days is the wind. I made a shield that isolates the damper from wind and that helps a lot.
 
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One thing you'll want to keep your eye out for are the noise indicator icons in the home page UI when you're seeing these issues:


If you see yellow or red squiggles in the corner of a probe's box, then that means its value is unreliable due to electrical noise. It can make the temperatures drift all over the place. I don't know where this comes from and we do everything we can to eliminate it with hardware and software filtering. Still, when I use my HeaterMeter in the kitchen and one of the probes or their metal braid shield touches an appliance, I get noise that can either make the reading erratic or downright unusable. This is why home temperature monitors are almost exclusively battery powered and lab temperature sensors run on very specialized and insanely expensive power supplies.

If you see the noise icon when the probes are getting weird, you can click on the icon to view the secondary graph (must be logged in and requires snapshot firmware from the last week or so). A normal graph should look like the one in the image above, with all the values being within 1-2 units of each other. If they're all over the place, then try separating the probe wires, making sure the don't touch metal, use an extension cord to try other outlets, or try to run on a battery.

I've done some testing on probe placement and how it affects temperatures. The takeaway from that is make sure your probe is never exposed to the direct heat coming around the diffuser (your #2 place there would be bad). The center is ideal but you also need to keep it several inches away from any meat so that the meat's temperature doesn't influence the temps or dripping moisture causing steam to change the temperature either. I like to put the probe up in the dome and and just know that the grill surface temperature is usually a few degrees warmer.

I'd put my money on noise problems over placement though, unless the probe was not shielded from the heat. Also, what are the brand of your TC and thermistor probes out of curiosity? My Dad says he has a Thermoworks Pro-Series probe "go bad" every 6-12 months or so, and I've been using the same probes for years so I'm not sure if there's cause to suspect them.
 
Bryan Mayland said:
I've done some testing on probe placement and how it affects temperatures. The takeaway from that is make sure your probe is never exposed to the direct heat coming around the diffuser (your #2 place there would be bad). The center is ideal but you also need to keep it several inches away from any meat so that the meat's temperature doesn't influence the temps or dripping moisture causing steam to change the temperature either. I like to put the probe up in the dome and and just know that the grill surface temperature is usually a few degrees warmer.

I'd put my money on noise problems over placement though, unless the probe was not shielded from the heat. Also, what are the brand of your TC and thermistor probes out of curiosity? My Dad says he has a Thermoworks Pro-Series probe "go bad" every 6-12 months or so, and I've been using the same probes for years so I'm not sure if there's cause to suspect them.
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I didn't notice any noise icons/warnings and yes, I did read that the firmware was recently updated with it built in now instead of being separate. I'll keep an eye out for that. While my probe is indeed a Thermoworks Pro-Series High Temp Air Probe (from my Smoke RF monitor) but it worked just fine afterwards for several hours.

My guess here is that probe placement is a major issue for me. Given I rotated the probe location which put it more towards the heat side it probably picked that up vs the heat on the more protected side. I'll have to find a better place to locate it or try to attach to dome thermometer. Also seemed that 225F was harder to maintain than closer to 250F.

OK, at least I have a few things to try.

Any thoughts on why TC temp would vary so widely (approx 10F) from thermistor despite being located side-by-side (not shown in this graph, but noticed in several other cooks)?
 
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I have noticed that I get about a year on the Thermoworks probes with the alligator clips. They work great and then I start to gets jump and spikes, noise, and then I change it out to my spare non alligator clip probe. That one I just drop down through the small opening in the top damper to where I want to sample the temp and then close the damper down tight so I have a small opening. I have dissected the probes with clips and found the probe saturated with oils, grease from cooking. I suspect we are getting some shorting across the conductors which is changing the voltage being generated from the junction. I buy a new one and problem is gone till cable gets saturated with cooking goodness. I am getting ready to replace my alligator clip probe. It`s getting noisy. I wish there was a probe out there made with oil and grease proof conductor insulation and with a braided sheath for protection. My backup is the Thermoworks with the 2.5 to 3" probe that comes with the grill clip. This one has had good service and has not displayed any stability issues yet. Another thing that could be happening with the open or exposed junction thermocouple is junction cracking and the crack is filling with grease. This could cause the noise till the junction totally fails and opens up. Even though the junction is secure in the alligator clip, it still is exposed to heat and cooking goodness.
 
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J Halvo said:
Any thoughts on why TC temp would vary so widely (approx 10F) from thermistor despite being located side-by-side (not shown in this graph, but noticed in several other cooks)?
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Not sure about that either. I usually see 2F difference with my TC being lower compared to a Pro-Series. If the difference gets larger the higher the temps go, then you can increase the mv/C in the Thermocouple configuration to help them track more closely. Mine is 4.975 which makes my thermocuple read 0.5% lower than it would by default, but that gives me 212F when boiling water so I feel that more accurate. Note that at 212F, the thermocouple voltage difference between mine and stock is only 0.000020V (20uV) so the values we're measuring here are almost impossibly low and amplified greatly.

If your thermocouple is bare on the end (just the two wires welded together) it can help to put something around them with a little mass when comparing the two probes just to make sure they're in equilibrium together.
 
@Gary @Bryan

My TC has a cap and has only been used two times. Guess I'll have to experiment more once I adjust my other prob placements.

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@Gary, I wonder if you can snip off and re-weld/join the alligator clip end so you don't have to replace the whole thing. Gotta expect just the tip/end of the TC is "bad" and the rest still has plenty of life. Dunno, not an expert here.
 
Yeah I would think you'd get pretty close results with those two probes, unless some hot air is coming around the edge and hitting the thermistor probe more. You could fold a little piece of aluminum foil over the two together just so they're both shielded from any rising air when testing. I'd say try to get some noise readings when they're acting weird to see if that's the issue or we need to be looking somewhere else.
 
I bought the Thermoworks THS-113-041 with the clip mainly because an exposed TC junction is faster to respond and that works well till tip get gummed up and the chemicals start to deteriorate the weld. I do have this probe, Thermoworks TW-113-442 and i am going back to it because it is more durable. It will react slower, but I re-tuned mt Tom Kole ver 2 damper yesterday and when it gets nice again i will re-tune my Adapt-a-Damper. The sealed junction probes do respond slower, but they last a long time. The probe I going back too was in service for about 2 years prior to trying out the clip probes which seem to get a year, before they start to get unstable with my grill. The one thing I do on a sealed probe is clean the surface between cooks to keep it clean of the grilling process goo. More goo on probe, the slower the response and you will see that and might want to start changing parameters because something seemed to change between cooks.

As for snipping the end off and re-welding, I have done that as a test and found out that I also needed to clip out about 6-10" or more of cable. After fusing ends together they did regain their stability, but started acting up after 6 months of use. I am starting to think that leaving the probes out in the weather might be effecting them too. My grill and probes are covered between uses, but moisture can build under grill covers. I did get new ones anyway and they still outperformed the repaired probe, after that i just got new ones when they got unstable.
 
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Brian,
I noticed when i was performing a noise check of a new thermocouple probe, the probe measured 2 degree higher with the noise test firmware versus the latest release firmware. I do have a -1 degree offset with my thermocouple and i see the noise test firmware leaves that at zero which is no big deal. When i loaded latest firmware back it did restore my -1 degree offset. Is this something that needs attention or no big deal. It did not bother me with noise testing, but you never know.
 
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