Thermometer calibration

Anyone else really distrust their thermometer?

Here's an easy way to gauge (I know precision is what we seek, but lets get serious shall we? ) the reasonable accuracy of your thermometer.

I read this info off of a "How not to kill your baby" pamplet - you know what I mean.

Household hot water is (In toronto at least, I imagine it's pretty typical) ~60C.

I have an analog thermometer that tells me it's 50C. It will soon be run through my new corona mill out of spite Seriously though, I have a radio shack digi therm and it read right out at 59.7C

That one is a keeper.

Anyone have any input? Anyone want to flame me for poor scientific method :rockin: ?

Just a little test if you have some concern about not hitting your temps right...

My Local homebrew store sells calibration thermometers. Seems like I paid about $6. It's fragile but I only used it to test the accuracy of my digital unit then wrote down what the indicated readings actually are. I also used it to calibrate the thermometer in my Hot Liquid Tank to the most frequently used temp.

IMHO it was money well spend.

Yes, look for something called a lab thermometer (same thing as a calibration thermometer). They are usually alcohol thermometers that are accurate to within a degree.

The other option is to use a glass of ice water and a pot of boiling water to calibrate your thermometer. Since you are a Foreigner we can use those easy metric numbers: thermometer should read 0 in the ice water (ice cubes made from distilled or RO water is best), and 100 in the boiling water (may need to adjust for elevation).

Just be sure to check that your thermometer is safe at this range of temp (e.g., most glass alcohol lab thermometers will burst at 100 degrees C).

I have a dial and a digi that I use on my brews and every so often I will put them both in a glass of water...if they both read the same...I call that calibrated. I think the odds of them both being exactly the same amount of would be pretty low.

Most of the mechanical dial type thermometers (like those that come with turkey fryers) have a nut on the back of the dial where the probe attaches. You can use a wrench on the nut to adjust the calibration. I did an ice bath (let it sit for a couple minutes) and adjusted it to 32 F and then tested it in boiling water boiling water.

If you have a digital thermometer for checking your temperature, like the one that goes under your tongue, you could test it (assuming you are healthy) on yourself 98.6*. Then prepare a bowl of luke warm water, and use it to calibrate your brewing thermometer.

No, you can't use your tap hot water as a gauge. I can adjust my hot water temp across a wide range. I currently have it set to 135F but can change it to 110 or 145 anytime I want.

I know you can also take other liquids with known boiling points to calibrate at a temp closer to your desired range such as mash temps. For example, Bromine boils at about 59C or 138F at sea level. Not sure if it's safe or not. Pure Isopropyl alcohol boils at 82C.

You could also calibrate your thermo to 72C by boiling water on top of Mt Everest.

Wow, lots of interest.

I wasn't claiming that this is an excellent way to do it, just a little fun test

It is of course based on the same theory as most of the other posts, which is a known temp against which to compare.

so, IF (note big IF) I know the temp of my hottest possible tap water, why worry about it?

I understand the desire for precision, but I'm happy + or - 2 to 3 C

http://www.professionalequipment.co...h-nist-certificate-4039/digital-thermometers/

Problem solved.
Comes with a NIST cert. Samples 1/sec and displays in .1° F increments.

olllllo said:

Samples 1/sec and displays in .1° F increments.

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Very cool! But hey, my all-grain equip is coming along nicely. Sometimes you just need to be a cheap ass, you know

Foreigner said:

Very cool! But hey, my all-grain equip is coming along nicely. Sometimes you just need to be a cheap ass, you know

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Yep.

I'm just being a cheap ass about my time.

olllllo said:

http://www.professionalequipment.com/traceable-mini-thermometer-with-nist-certificate-4039/digital-thermometers/

Problem solved.
Comes with a NIST cert. Samples 1/sec and displays in .1° F increments.

Click to expand...

Yep, that's the one I use. As for calibration, the best method is using ice water. I use this method all the time to calibrate thermistors for the microprocessors in our industrial chillers. Due to the latent heat of fusion, the temperature, regardless of altitude, will remain at exactly 32˚F until all of the ice has melted. Once no ice remains, the temp will rise (sensible heat).

yeah, what Johnsma22 said.

As a professional metrologist (among other things), I'd like to throw one more vote toward the ice and water mix as the easiest, but still accurate, 1-point thermometer calibration technique. Many of the digital temp controllers I work with are calibrated this way.

One tip: agitation and stirring improve the results, especially since certain types of temp probes can produce small amounts of heat themselves.

MrFebtober said:

One tip: agitation and stirring improve the results, especially since certain types of temp probes can produce small amounts of heat themselves.

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I couldn't agree with you more. I should have mentioned that. It takes a little time for the ice/water to stabilize at 32˚F and stirring/agitating will insure that you are not sampling any warmer or cooler spots.

Agree with the ice/water technique but would suggest for those who worry about such things, having a two point calibration is more accurate, in case there a systematic error in the thermometer. Boiling water with altitude compensation is the easiest way to go, and freezing and boiling nicely bracket all of the temperatures we are interested.

Bobby_M said:

You could also calibrate your thermo to 72C by boiling water on top of Mt Everest.

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If I happened to be on Everest I probably would. Imagine the shipping costs on getting a professional thermometer up there

:cross:

If you are worried about that degree of accuracy, you got way too much time on your hands, .... cause I don't think the yeast can tell... but I'm a noob and could be wrong???

jowens said:

If you are worried about that degree of accuracy, you got way too much time on your hands, .... cause I don't think the yeast can tell... but I'm a noob and could be wrong???

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I think everyone is more worried about mash temperature in an all grain batch. Mash temps have to be precise -- a few degrees either way can really change the flavour and character of the finished beer.

FlyGuy said:

I think everyone is more worried about mash temperature in an all grain batch. Mash temps have to be precise -- a few degrees either way can really change the flavour and character of the finished beer.

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Yup - I just want to know that I am reasonably accurate. 10C off = garbage.

I'd have to say that the 32 F and 212 F boiling point measuring test seems almost meaningless. If it's boiling it's boiling that should be plane to see why would anyone need to measure that temp? The same with freezing.

And just because a digital themometer is accurate near boiling or freezing does not mean it's accurate at 152 F or 68 F. At least that's the case with my digital thermometer. But then again I didn't fork over $40 for it either.

abracadabra said:

I'd have to say that the 32 F and 212 F boiling point measuring test seems almost meaningless. If it's boiling it's boiling that should be plane to see why would anyone need to measure that temp? The same with freezing.

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I think you might have missed the intent here -- it was to check to see if a thermometer was accurate or not. The temperature of freezing or boiling water doesn't really vary, so if you thermometer reads 40F for freezing or 190F for boiling, then you know it isn't accurate. Further, some thermometers are adjustable, meaning that they can be calibrated to these temperatures to make them more accurate.

And just because a digital themometer is accurate near boiling or freezing does not mean it's accurate at 152 F or 68 F. At least that's the case with my digital thermometer. But then again I didn't fork over $40 for it either.

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Perhaps, but usually the errors are systematic, meaning that an inaccurate thermometer will consistently read too high or too low. It is odd that your thermometer had a non-systematic error - that is atypical and probably meant that your probe was shot.

I can make myself silly calibrating thermometers. Can take three thermometers at random, calibrate in an ice bath and then put them in boiling water and come up with three different readings. Calibrate in boiling water and then take three different readings in an ice bath. Just picked out the one or two that give the most consistant readings.

Then that is the whole point -- you have just demonstrated that you have some bad thermometers that can't be trusted to be reliable.

You can't assume your hot water temp is anything. It's very adjustable and cools while going through pipes. Using something with a high degree of variability to calibrate something is ridiculous. Spend 5$ on a lab thermometer.

FlyGuy said:

I think you might have missed the intent here -- it was to check to see if a thermometer was accurate or not. The temperature of freezing or boiling water doesn't really vary, so if you thermometer reads 40F for freezing or 190F for boiling, then you know it isn't accurate. Further, some thermometers are adjustable, meaning that they can be calibrated to these temperatures to make them more accurate.


Perhaps, but usually the errors are systematic, meaning that an inaccurate thermometer will consistently read too high or too low. It is odd that your thermometer had a non-systematic error - that is atypical and probably meant that your probe was shot.

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No I don't think I missed the point at all.

I just disagree. I've seen far to many thermometers that were dead on accurate at certain temps and off at others.

And wanted to make the point that it's more important that your thermometer be accurate at the temps you are trying to hit than at the freezing point or boiling point. I understand using freezing or boiling as a reference point but if your thermometer is dead on at boiling and off by 5 degrees in the 150 degree range and you don't know it simply because you assumed it is accurate because it was accurate at extreme ranges than you are just making an assumtion.

Most people know what happens when you assume.

Also most people don't really care if they are off by 5-6 degrees.

I am simply trying to help the ones that want dead on accuracy but don't want to fork over $40 for a thermometer. When a $6 calibration and a $12 digital thermometer can do the same thing.

I post to this forum inorder to help people just getting into the hobby save some money along the way. So I frequently post opinions outside the main stream. Especially if I think it could save someone a $ or 2.

I'll save you $4 right now.
The one I posted is $35.95, not $40.

My hourly rate is more than $18, so I saved a bunch of time.

Also 5-6 degrees matters a bunch in the mash.

I understand what you are going for though. A $6 calibration and a $12 digital thermometer can get the job done... there's no disputing that. And to your point, I would rather know that the thermo is accurate @151 rather than 32 or 212.

Just an FYI, stirring your mash or HLT water can change your reading as much as 10 degrees. You need to eliminate hot and cold spots.

EDIT: Posted about this in the past: https://www.homebrewtalk.com/showthread.php?t=30722

olllllo said:

I'll save you $4 right now.
The one I posted is $35.95, not $40.

My hourly rate is more than $18, so I saved a bunch of time.

Also 5-6 degrees matters a bunch in the mash.

I understand what you are going for though. A $6 calibration and a $12 digital thermometer can get the job done... there's no disputing that. And to your point, I would rather know that the thermo is accurate @151 rather than 32 or 212.

Just an FYI, stirring your mash or HLT water can change your reading as much as 10 degrees. You need to eliminate hot and cold spots.

EDIT: Posted about this in the past: https://www.homebrewtalk.com/showthread.php?t=30722

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I agree completely but I'm inclulding shipping, and or sales tax in my $40 est.

But then again I'm usually not posting for someone like you. You are the guy I'd be asking questions of. Not answering .

abracadabra said:

I agree completely but I'm inclulding shipping, and or sales tax in my $40 est.

But then again I'm usually not posting for someone like you. You are the guy I'd be asking questions of. Not answering .

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Don't confuse post count with actual knowledge. I can fake it with the best of them.

so yes i realize this is an old post but is it safe to assume that if my thermometer reads 38* F in a glass of ice water then it is 6* off? Should the ice water be 32* or should it be warmer than that since ice water is technically not frozen?