Good Method for Checking Thermometer Accuracy/Calibration

[Rokfather]

My Weber gas grill is 6 years old so I decided to check the dome thermometer. I had fried some indan food earlier and the pot of oil was still lying on the stove, so I decided to use the hot oil instead of boiling water to check its accuracy. I used my thermapen as a reference and held both in the oil as it heated up. I used a fish turner to lower the dome thermometer into the oil and hold it there. Up to about 200 degrees, the dome dial was about 30-50 degrees lower than the actual tempurature, but once it got to 300, 400, and 450 it was pretty close, within less than 10 degrees. There were a couple benefits to this method. 1. You don't have to contend with the steam of boiling water, and 2. you get to test at more realistic temperatures at which gas grills are normally operated.

I can't seem to get mine below 300 degrees with all 3 burners going so I stopped trying. I have a Summit Charcoal for low and slow.

[tbob4]

Good advice - thank you

[ItsAllGoneToTheDogs]

The better way is to use ice water No energy required for the test... Having said that, I'm talking temp probes. Do a little digging around here and you'll learn why dome thermometers don't really matter

[fzxdoc]

Good idea to take advantage of some hot oil on the stove to compare thermometer accuracy. It's all about getting to know our cookers, after all.

While the temp of the air at the dome level doesn't really reflect what's going on at grate level, it's always interesting to have a reference. Perhaps that might be your next experiment, comparing the temperature reading of the dome thermometer at its level in the gasser with the temperature at the grate.

I've done this for my Summit Gasser, because I like to use it as an outside oven, especially in the summertime and for foods like bacon that heat up the house. I've recorded the dome temp readings and the corresponding grate temps for various combinations of burner settings. Now that was a fun experiment.

P.S. What was originally cooked in the oil? Samosas, I hope.

Kathryn

[Kascon11]

I also have a summit gasser (4burner) and I have often thought about tracking the delta of dome vs grate temp. However I get overwhelmed by all the variables (4 burners, each with different settings, Grate probe placement, cleanliness of the burners, etc..) Do you do one burner at a time, letting them cool in between? if you have all 4 burners going do you need 4 air probes since they are tracking a specific location? I can get very lost in the details.

[Rokfather]

Yes, it was samosas!

[WillTravelForFood]

We use the dome thermometer as a suggestion, not reality.

We know that when the needle is HERE that the grill is hot, and if the needle is THERE that it's not hot enough.

[WillTravelForFood]

agreed that calibrating/checking your food thermometers regularly (or at least once) is a good idea.

Calibrating against a Thermopen is also a winner.

[rlozinak]

Yea, I dont trust the dome thermonitor but I do trust my fireboard 2.

[fzxdoc]

from Kascon 11: "I also have a summit gasser (4burner) and I have often thought about tracking the delta of dome vs grate temp. However I get overwhelmed by all the variables (4 burners, each with different settings, Grate probe placement, cleanliness of the burners, etc..) Do you do one burner at a time, letting them cool in between? if you have all 4 burners going do you need 4 air probes since they are tracking a specific location? I can get very lost in the details."

Actually, Kascon11, I made the process very simple. I set an oven thermometer in the center of the Summit's grate, because it's where the food goes when I use the the Summit as an oven.

Next I began turning on the outermost burners first, starting with low and progressing to high for later settings (to allow the temp to be increasing, not working with decreasing temps). So for example, I'd put the two outermost burners on Low, let it run for 20 or 30 min, and record the grate thermometer and the dome thermometer readings.

Next I'd increase the settings of those two outermost burners to Medium, wait 20 or 30 min, and record the grate and dome temp readings.

Then the outermost burners were set to High. Ditto.

Next I began with leaving the outermost burners on High and setting the second rightmost burner to low. Ditto.

Then I'd add the second leftmost burner to Low. Ditto.

By that time I had the range that I wanted. Then I could fiddle around with the progression (done on a couple of different days, depending on the temps that I was looking for) until I had the range of oven temps I wanted from around 250° in 25° to 50° increments until it reached 500°

I only actually needed 8 or so settings to get the range I needed for my purposes, and I only use the two outermost burners, never the two center ones.

Remember that the temps are measurements at a point in time, since the gasser's burners do not cycle like oven heating elements do to regulate the temp. I use them to give me a place to start, then I fiddle with the knobs during the cook, depending on the length of the cook.

The nice thing about having the dome thermometer readout is that I can use it to know approximately what the temperature is at the grate, using a simple graph of the two temps plotted against each other.

I don't get fancy with a remote thermometer since I don't use the gasser to cook things that might be super temperature sensitive. Plus with the food centered on the grate, where to place a thermometer with respect to the burners and still get a good "oven" reading becomes a much bigger issue.

I use the Summit as an oven to warm things, to make casseroles, cook beans, and to cook bacon in a batch, mostly. It comes in really handy during power outages when I don't want to burden the generator with an electric oven cook when the gasser can do an OK job.

HTH,
Kathryn

[Kascon11]

fzxdoc, thank you very much. Time to research a good oven thermometer. I also use the summit for bacon and the rotisserie (lamb and chicken) mostly and anytime I don't have time to fire up the PBC. Funny I never thought about it before, but I am always adjusting the dials (just like cooking on a gas stove top. It just come natural when it look too hot turn it down. Once I get a good thermometer I will start the calibration process. Thanks again.

[Bruceski44]

There are two primary error sources in thermometers: offset and gain. Offset is a fixed difference which stays the same across the entire temperature range. Think Y-intercept in the Y=mx+b linear equation (b term is intercept). Gain is the m term and should be equal to 1.0. The only way to calibrate both terms is a 2-point measurement. Use an ice-bath where you stir or shake the bath to get the offset and boilng water to test the gain. Most thermometers only have one correction, and it's not clear which term they're correcting. Remember that the boiling point for water will change with altitude. Where I live at 2700 feet, it's about 206.5 degrees.

i should add more detail for how this works. The x-value is the measured temp, or process variable, and, after adjusting for gain and offset, the y-value is displayed. If there's no gain and offset error, you get y=x, which is a straight line with a slope of 1 or 45 degrees on a cartesian graph. You can use the calibrated gain and offset values to correct the measurement at any point on the line, according to the y=mx+b equation. Linearity is usually pretty well controlled, by design, but that will deviate from a straight line if present.

[Rokfather]

Oops, I should have added some context here. I'm well aware that the dome temp is not a guide for grate level. I have a lot of probes with grate clips from Thermoworks (along with a Smoke unit and a Signals unit), so my thermometer game is pretty solid. I mainly tested the thermometer out of curiosity because I just put in upgraded grates and flavorizer bars and the max reading I used to get was around 500-550. With the new equipment it now pegs the thermometer out of its range of 600 degrees. Also seeing that oil on the stove made a light bulb go off that I could use it to measure at a higher temp than boiling water.