Thermometer accuracy


 
S

Stevo (Steve Y)

TVWBB Member
I've done a couple of searches, and haven't found any topic on this yet, so here goes...

Are you finding that your thermometer accuracy goes downhill during a longer smoke? I've been paying attention to my difficulties retaining good temps in my 22.5 WSM (verified accurate stock therm in the dome)... and think I've discovered that the brown sticky coating on the probe (from the smoke) makes it read anywhere from 25* to 45* low.

I've also stuck an accurate wireless therm in the dome vent, to double-check, and found the same thing happen. Cleaned it off after 13 hours of a Butt smoke, and gained 35* instantly.

So... is there something that I'm not doing right here? Do I need to clean my therm probe in the middle of each session?

Thanks... looking forward to my first Mr. Brown pulled pork!!!
 
Steve, Great topic!
While I'm personally new to Comp BBQ, I've done alot of work with temp measurement in my previous career. Let me toss out a few thoughts...
1) You have to kinds of therms going, BiMetal and and a thermocouple. The stock is a Bimetal that is basically two dissimilar metals sandwiched and coiled.When heated, the coil moves predictably and rotates the needle over the scale. While an OK method, its not as accurate as the thermocouple which is the point where two dissimilar metal wires meet at a weld and produce a measurable voltage which changes predictably with the change in temp.

2) The gunk that coats the probe end is presumably equal in temperature to its surrounding environment, so my guess would be that it becomes a non issue.

3) I have found that the temperatures inside my lids vary significantly from height to height.

So....

A truly fair test would require a setup that allows you to return the probe to the exact same position from where it was removed, AND with an alternate probe always present as a control.

While I haven't myself noticed what you have, I would love to hear your results.

Have fun,
Brett
 
Thanks, Brett. I appreciate the insight. I wasn't even thinking about the technical make-up of the therms.

Since my first smoke, I've been using the Williams-Sonoma wireless digital thermometer (until I get my Maverick for Christmas, and I give hers back), and that's the one that gained 35 degrees after cleaning. Given the 90 degree bend in the probe, I think it gives me great repeatability in location. That's what prompted me to write this topic.

In the past, I'd found that my lid thermometer, although accurate for the first smoke, seemed to 'lag' about 40 degrees behind (in time, as I was coming up to temperature), and 25 degrees low (at holding temp) for a few smokes as compared to the WS digital one.

I'm thinking that the smokey film on the probes actually acts as an insulator, as I'm sure the material is not perfectly thermally conductive.

As I'm not planning on removing my lid therm in the middle of each cook... I guess I'll just figure it into the temps.

Anyone else??? What are your experiences?
 
Steve,
Two more things.....
The stock bimetal thermometer on my WSM22 is not adjustable as I see it. Other higher quality thermometers have a calibration screw on the back.
Before I invest in a days time & meat, I calibrate over a sauce pan of boiling water. Everything should read 212ish as Brooklyn is just above sea level. (as the insurance companies are so fond of reminding us)
 
Just got my homemade WSM controller finished and did a calibrated temperature run here at work this last Saturday. So I know my displayed temps are pretty accurate.

I ran my 18 yesterday with a brisket flat to try out the controller. My probe hangs about an inch below the top grate and towards the middle, definately over the pan (which I run dry).

The temps on the probe were running about 40 degs higher than the stock lid thermo. I couldn't believe it so I put one of my Polders in the same place as the probe and sure enough, they agreed!

That sort of explains why my cook times have been SO fast! I turned down the controller to about 245-250 and the stock thermo was reading 205-210. Of course my cook time went WAY up but I got a killer smoke ring in the meat.

Russ
 
I think it has something to do with placement. I know when I had a short stemmed thermometer, I got much different readings. I haven't see a new wsm (with therm installed), but my guess is that the stem is short. In my opinion, the airflow at the top of the dome and across form the top vent causes the bad reading. I get a lot of gunk on my thermometer and it's never changed temp.
 
Hi fellow smokers! I hate to beat this to death but i'm a newbie and I am a bit concerned about the temp gauge. I keep seeing "Maverick" is that the best one to get? I have the WSM 18 w/ the temperature gauge. Just got it last week. Please let me know. I also thought of compensating the 25degrees or so and calculate it on the outside stock temp. If the stock temp reads 25degrees hotter then I could set it to 175 - 200 to achieve the 225-250 range. Any other ideas?
 
I'd read that there were aftermarket therms that would mount into the hole left by the stock therm. There was something about being careful to cover the alignment hole left by the stock therm.

I'm hoping to get the Mav ET-73 for Christmas, so I can read both the interior and meat temps.

Russ - were your findings that the lid therm was consistently higher, or were there variations in the temperature separation?

Jerry - the stock therm looks to be about a 2" probe.

I find it interesting that we're having different experiences with the the gunk.
 
Thanks Stevo, I emailed Weber and tasked them with finding out what the deal is.
I guess I can always remove the stock and replace it with a quality lid therm. I dont know if the distance between the lid and top grate is far enough to make a big difference. ???
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alexander:
Thanks Stevo, I emailed Weber and tasked them with finding out what the deal is.
I guess I can always remove the stock and replace it with a quality lid therm. I dont know if the distance between the lid and top grate is far enough to make a big difference. ??? </div></BLOCKQUOTE>
 
here are my thoughts:

1) for constant temping, bimeatal, thermistors, and thermocouples are equally acceptable. all need to be calibrated in boiling water or ice water if accuracy is required, however accuracy isn't really essential. If you need instantaneous temping (like for grilling) then thermocouples are essential.

2) while I was learning the cooking dynamics of the wsm, the key was temping at cooking level and at dome level. Once I got a feel for temp control and temps required to get meat to tender, the dome temp was sufficient. At that point the actual temp is insignificant, as long as you keep your therm and the temping location constant. Learning bbq on the wsm is a trial and error process (luckly even the errors are darn tasty) you can't take someone's temp and time and recreate their perfect bbq, so knowing the exact temp is pretty pointless.

3) certainly play with a couple therms, but eventually pick one to trust, and stick with it until you don't need it anymore. I use really cheap bimetal therms and accept them for what they are, a coarse measurement of cooking temp.

4) mavericks are nice because they have high and low alarms but they certainly aren't the best therms. I burned through two mav probes when griling. I use the thermoworks oven probe therms for constant internals, and have a thermoworks themocouple (mtc) for instantaneous internals, both have been good to me. Stay away from polder, their probes are vulnerable to moisture.
 
I love this topic, but I'm surprised to see so many like the Maverick. I had nothing but problems with their probes, and of the three units I've owned, two died quickly. I like Taylor, but i always use two when checking the temp--one for internal and one for chamber temp.

You prompted me to clean the lid probe on my P&S. My cooks seem awfully fast too over the past year. I've never cleaned it.
icon_smile.gif
Yesterday I bought a 6 buck oven thermo to do spot checks on the Cookshack as that fixed probe is a little harder to calibrate.
 
I found the lid temps to be 30-40 degrees lower than what I was getting just below the top grate. To be fair though, it was a somewhat windy, cool, damp afternoon. So maybe that could have thrown things off a bit.

I'm at Perry this weekend for the Triple Crown Championship so I'll verify my findings in both the 18 and the 22.

Russ
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Russ Sylvester:
I found the lid temps to be 30-40 degrees lower than what I was getting just below the top grate. To be fair though, it was a somewhat windy, cool, damp afternoon. So maybe that could have thrown things off a bit.

I'm at Perry this weekend for the Triple Crown Championship so I'll verify my findings in both the 18 and the 22.

Russ </div></BLOCKQUOTE>

Russ,
Please share what you learn. I am also looking to find a solution for my lid therm. Thanks
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Stevo (Steve Y):
I've really struggled with this dilemma. </div></BLOCKQUOTE>

This is BBQ. There's no struggling in BBQ.

Seriously, go to the local Target and get an oven thermometer. $10 to $15 bucks tops. Stick it through a potato and set it on the top grate. Run the wire under the lid. Trust it and move on to more important things like what rub to use. I guarantee you you'll do fine and I guarantee that spending more money will not yield any better BBQ. Anything else equates to man toys. I've bought a number of them and suspect you're on your way to do the same thing but after a few years of using my wsm, all I use is a cheap $20 thermometer through my top vent with a long stem.
 
here's what Weber had to say. Hope someone finds this useful.
"All grills not just Weber grills are designed with the thermometer being on the outside of the lid the same way a convection oven is. The SMC works a lot like a convection oven the way it circulates the air around the food. The recipes you are seeing in other cook books should reflect the same way our recipes do. They are referring to the temperature of the thermometer that is located on the outside of the lid. So when they say smoke at 225-250 they are going off of the reading they are getting from the external thermometer on the lid the same way you do. They are not going off of an internal reading."
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jerry N.:

This is BBQ. There's no struggling in BBQ.

</div></BLOCKQUOTE>

Jerry - I dig yer style. I'm an engineer, and I have a tendency to over analyze things in an attempt to understand them.

With all of the variability I've seen in my temps, I haven't blown a smoke yet. Brisket, Ribs, Turkey, Butts, and Chickens have all turned out fantastic! I guess the message is don't sweat it, and have another beer... the grub's on it's way.

Thanks for the head slap.

I think I'm going with a cheap therm, and just cook away.
 
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