Thermo calibration question

As long as it's right at boiling don't worry to much about it reading ambient incorrectly....a thermometer is it's most accurate at the middle of its range...and realistically..we don't cook at 90° anyway...mine sometimes read around 150° sitting out in the sun..

how are you gonna get a temp higher than 212?

How about off your heat source. Water will boil at 212º but the burner on stove will get a lot hotter.

Gator

You can use oil and a candy thermometer.

why?

boil water, make sure it's close to 212, call it a day.

(anyway, how do you know if your candy thermometer is accurate?)
hahahaha

Are you saying to use oil and a candy thermometer to verify the calibration of your Egg thermometer? As in heating the oil up to 250°, then verifying (or calibrating) your Egg thermometer to read 250°?

How do you check the candy thermometer first, in boiling water?

Yes, if you want to check the BGE thermo at higher temps, that's the way I'd do it. I suppose you could check the candy thermo beforehand, but it's probably close enough for doing the BGE. If you really want to dial your instrumentation in, you can get a lab thermometer or even a calibrated RTD probe to establish your references.

those types of thermometers are linear, and if they aren't, then they are sprung and it's time to get a new one.

like a bathroom scale... the operating part of the thermometer is intended to be linear. it deforms "x" at a temp, and "2x" at twice that temp. i'm guessing it's a simple torsion spring with a bimetallic strip at the tip. very, very, very difficult to screw that up unless it loses elasticity from being held at some crazy temps for a long time.

if it doesn't, it isn't 'calibratable' even with two point calibration.

guys are trying to turn a two-dollar dome thermometer into a geiger counter.

you can't calibrate it at two points anyway. boil water, see check the temp, turn the screw to make it rwad 212. if you then stuck it in 350 degree oil and decided you needed to dial back ten degrees, well, you just undid the 212 calibration. time to toss the thing anyway, because it is designed to read 350 at 350, just as it should read 212 at 212.

i need to retreat to my original point, that it makes no difference to adjust for altitude for our purposes. i know the engineers are wigging out, but unless we are in a submersible or on top of everest, it's not a big deal. i could hand you three dome thermometers. each one purposefully calibrated differently: one at 212, one at 221 PLUS fiuve degrees, and one at 212 MINUS 5 degrees. if you picked any one at random without knowing which it was, i don't believe you'd notice any difference in any of your cooks. not one that you could attribute to the dome temp anyway.

if the candy thermometer is "probably close enough", then what is the purpose of dialing the dome thermo to 211.88 instead of 212 just to take into account my altitude?

we're cooking over a natural fire with hot spots and cold spots, and with ten or more years experience cooking on gassers that say nothing more than "low-med-hi". hahaha

i can cook without a dome thermo for crying out loud. please guys, don't tell me i gotta start sending the thermo to a lab.

sounds like you don't even do the thing you are proposing yourself. i.e. calibrating the dome thermo at higher temps?

You really can't, but what you can do is do a best-fit type adjustment that gives you the least amount of error in the range you use the most. It might be off 20* at 200 and off 20* at 400, but right on at 300. That's better than being right on at 200 and off 40 or 50 degrees at 400.

those types of thermometers are linear, and if they aren't, then they are sprung and it's time to get a new one.

Exactly right. But if you simply calibrate to a single point - 212* - you'll never know if the unit has sprung as the needle will dutifully return to that reading when dunked in boiling water.

Your description of adjust, dunk, adjust, dunk is spot-on, too. I've calibrated enough instruments in my time to know that's essentially how a lot of them are done: You "walk" the settings into a best-case scenario. Since our dome thermos only have one adjustment, we're stuck with turning that until the units are good enough to use over the range we use them. If they're still 80 degrees off at 200 and 400 when spot-on at, say, 300*, then it's time to replace them.

Linearity and slope are two different things. A thermometer might be perfectly linear, but have the wrong slope. If so, and the error in slope isn't terribly bad, the unit may still be made serviceable by centering the point at which it crosses the ideal temperature curve to the middle point of where you cook.

For example, if the thermometer is linear but displays an error of 30* over a 200* rise in temperature, you can have the point at which the gauge temperature is equal to the actual temperature at 100*, but it will be 30* off at 300 and likely 45* off at 400. Or...you can put the gauge/actual crossover at, say, 300* where it will only be off 15* at 200 and 400 and just right at 300.