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Dome Thermometer vs. Probe clipped to Dome Thermometer - Why are they different!?


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Hello all:

 

This is my first post, so please don't haze me to much!  :)  

 

I have read many threads here and elsewhere about the differences between grate temperatures as measured by an electronic probe and the dome temperatures as measured by built in analog thermometers.  I know there can be differences and many (but not all) say the dome temperature is typically higher than the grate and they usually converge over the course of a long slow cook.  I also know that many say it really does not matter that much in terms of results - pick one and run with it!  Fair enough.

 

My questions are somewhat different.....

 

I often use my BBQ Guru Wifi (still works after all these years) for my low and slow cooks in my Kamado Joe Classic.  I have seen that I have been, pretty consistently, experiencing grate readings that are around 25 degrees higher than dome readings.  I have checked, rechecked and calibrated my dome thermometer and that does not seem to be the issue.

 

I generally seek a temperature of around 250 or so.  Given these differences, I have often "split the difference" by setting my controller to around 270.  The controller does a great job, maintaining temperatures that average 270 and usually stays within a +/-  3 degree range.  The dome typically reads around 245.  So, I figure I am getting the "real" (whatever that may mean) temperature somewhere in that range.  And, I have been happy with my results (mostly).  If not satisfied, I blame it on me, not the KJ temperature.

 

This week, I decided to smoke some ribs by clipping the BBQ Guru probe to the dome thermometer stem.  I slid one of those metal clips, designed to hold probes at the grate) onto the thermometer stem and then clipped the probe to that.  To my surprised, the readings still did not match and were consistently different throughout the entire 6 hour cook.  The probe read 270 +/- and the dome stayed in the 240's.  

 

I then rechecked both to see if they were properly calibrated by measuring the temperature of boiling water.  The dome thermometer was at exactly 212 and the probe measured 211.  

 

So.............what gives?  Why am I getting such consistently different readings with these 2 calibrated devices measuring temperatures in the same spot???

 

Ideas?

 

Thanks!

- Mitch

 

 

 

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They are different because the bimetallic thermometer on your dome is very slow to react to temperature changes.  The thermistor based probe on whatever electronic thermometer you are using is very quick to react to changes.  The answer to your next question is:

 

Pick one of them and go with it.  The difference is really insignificant.

 

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12 minutes ago, John Setzler said:

They are different because the bimetallic thermometer on your dome is very slow to react to temperature changes.  The thermistor based probe on whatever electronic thermometer you are using is very quick to react to changes.  The answer to your next question is:

 

Pick one of them and go with it.  The difference is really insignificant.

 

John:

 

Thank you for that.  I get that the bimetallic thermometer is slow t react while the probe reacts fast.  That would explain (at least to me) that the dome would usually lag behind the probe.  And, I would expect the probe to jump around more and the dome thermometer to be more steady.

 

But, help me understand how, over a 6 hour period, the dome would stay steady and the probe would stay steady with both in the same place.  That does not seem to be explained by reaction times since they are both steady and the gap is steady over a long haul.

 

Thanks again,

Mitch

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1 hour ago, Mitchjg said:

John:

 

Thank you for that.  I get that the bimetallic thermometer is slow t react while the probe reacts fast.  That would explain (at least to me) that the dome would usually lag behind the probe.  And, I would expect the probe to jump around more and the dome thermometer to be more steady.

 

But, help me understand how, over a 6 hour period, the dome would stay steady and the probe would stay steady with both in the same place.  That does not seem to be explained by reaction times since they are both steady and the gap is steady over a long haul.

 

Thanks again,

Mitch

 

There is no understanding.  Pick one of them and go with it.  You will run into all kinds of different readings between electronic probes and bimetallic thermometers depending on the weather, humidity, and a host of other factors.  Many before you have pulled their hair out trying to figure out this puzzle.  You will come to a point on your barbecue and grilling hobby at some point were the realization that precision temperatures just don't matter.  Low and slow is 250, give or take 20-30 degrees.  Medium is 350, give or take 20-30 degrees.  High is 450, give or take 20-30 degrees.  Sometimes your probe will match the dome.  Sometimes it won't.  Trust me.  I have been playing with these things for a long time.

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4 hours ago, John Setzler said:

Many before you have pulled their hair out trying to figure out this puzzle. 

Well, my male pattern baldness has already left me with very little hair left to pull out.....:)

 

But, I am by nature and (retired) profession an analyst, so not getting to "why" is frustrating.  I will, however, try to follow your guidance and let it go.

 

In your "Grate Temperature vs. Dome Temperature" thread, you mentioning using the dome temperature as your reference and that you  "use the temperature controller to make my DOME thermometer read at or near my desired temperature."  The context was a preference to clip the probe up near the dome thermometer rather than the grate.  Assuming I did not misinterpret,  I think that makes sense and I believe I was, at least to some degree, setting my controller to 270 in order to get a dome reading in the neighborhood of 250.

 

Thanks for your feedback on this - much appreciated.

 

- Mitch

 

 

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Before I bought a remote-reading food thermometer which would tell me the firebox and the food temperature, I relied on the "lid thermometer" with very good results.  Now, I basically ignore it.

 

(About $35 at Home Depot ... and it's even wireless!)

 

The only thing that really matters here is that you find some grill-temperature reference to work from and understand how it works ... so that you can achieve repeatable results.

 

The most important temperature is always the internal temperature of the meat.  ("Never mind what's going on 'outside' ... what's happening 'inside?'")

 

If you look too hard for "differences" between any two sources of data, you will always find them.  But, they don't actually matter.  Just develop what is for you a repeatable process that doesn't demand too much of your time and attention.  Kamado-style grills actually enable you to do that ... predictably.  You'll never fire up your "Smokey Joe" again. :)

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