Author Topic: Thermometer discrepancies  (Read 817 times)

Offline monomer77

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Thermometer discrepancies
« on: September 20, 2010, 06:29:46 PM »
I have two floating thermometers one reads 75 degrees, the other 73 degrees. I have a long metal thermometer with the dial at the end that reads 84 degrees. The clock in the room has a built in temperature reader and it says 76 degrees.

So how on earth does anyone ever hit a proper mash temp? Go by taste? What’s the most reliable type of thermometer to have?

Offline bluesman

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Re: Thermometer discrepancies
« Reply #1 on: September 20, 2010, 06:36:42 PM »
There are two methods that you could use to calibrate thermometers -

Ice Point Method - Fill a container with crushed ice and water. Ensure that the container have enough crushed ice to provide an environment of 32 degrees F, so you may need to add more ice into the container during the process. It will takes about 4 to 5 minutes for the mixture of water to stabilized. Then insert the thermometer which needs to be calibrated into the appropriate immersion depth. Hold the thermometer away from the bottom and sides of the container to avoid error. If your thermometer is not accurate at 32 degrees F, adjust the thermometer accordingly or provide for error correction.

Boiling Point Method - Fill a container with distilled water and heat it up. After the temperature in the water has reached the boiling point, insert the thermometer . Be sure to leave at least a two inch gap between the thermometer sensing element and the bottom and sides of the container to avoid error. If your thermometer is not accurate at 212 degrees F, adjust the thermometer accordingly.



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Offline tygo

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Re: Thermometer discrepancies
« Reply #2 on: September 20, 2010, 06:40:46 PM »
I had the same problem a while back and eventually ended up getting one of these:

http://www.amazon.com/Splash-Proof-Super-Fast-Thermapen-Thermometer-Professional/dp/B0041LOJNS/ref=sr_1_2?ie=UTF8&s=home-garden&qid=1285032707&sr=8-2

Pricey, but effective.  I believe there are also cheaper lab grade NIST certified thermometers that will work well.
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Offline monomer77

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Re: Thermometer discrepancies
« Reply #3 on: September 20, 2010, 06:46:15 PM »
Sincere thanks for the quick reply. With all due respect, I dont think the boiling method works. I'm not trying to be one of those nit-picky knowy it alls. IE "You said zero and I add 1 gram without a problem" (nerd)

I tried it. I had two of them read 212 when put in boling water.

Offline monomer77

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Re: Thermometer discrepancies
« Reply #4 on: September 20, 2010, 06:47:37 PM »
Do non-electrical thermometers ever go bad?

Offline jwaldner

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Re: Thermometer discrepancies
« Reply #5 on: September 20, 2010, 07:27:19 PM »
I'm having the same issue currently with three of my thermomenters. I did the ice methond I pulled off of BYO:  http://www.byo.com/component/resource/article/1995-calibrating-equipment-techniques

I found that it does seem to work with two of my thermometers but a CDN thermometer I have seems only to be accurate at a warmer temps, above 45F. When the other two are reading about 32-33F the CDN thermometer reads 4-5 degrees less. This method seems to work you just have to watch it a bit though and make sure there's no inconsistencies when the temperature ranges change.

Cheers

Offline hokerer

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Re: Thermometer discrepancies
« Reply #6 on: September 20, 2010, 07:39:33 PM »
I think it's better to calibrate your thermometer at the temperature you care most about.  That is, I like to calibrate my thermos around the mash temperature range.  Easiest way I found was to buy a NIST certified lab thermometer and then calibrate the thermos I use to it.  Oh, at mash temp, that is.
Joe

Offline a10t2

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Re: Thermometer discrepancies
« Reply #7 on: September 20, 2010, 07:45:58 PM »
Depending on the type of thermometer, a single-point calibration may not be enough. The discrepancy could vary across the temperature range. Doing a two-point calibration is better, and three is better still.

And yes, an analog thermometer can drift out of calibration, although it's unlikely that it would have anything other than a constant offset.
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Offline BarleynYeast

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Re: Thermometer discrepancies
« Reply #8 on: September 20, 2010, 08:50:46 PM »
I bought one of these glass thermometers with the added thermometer shield to protect it when not in use.  http://morebeer.com/view_product/18677//12_inch_Glass_Thermometer I calibrate all my other thermometers to it at mash temp as hokerer recommends. For 5 dollars you can’t beat it.
Matt

Offline hopfenundmalz

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Re: Thermometer discrepancies
« Reply #9 on: September 21, 2010, 06:20:04 AM »
If you have a good traceable reference thermometer, use that to calibrate the others in the mash temperature range, as that is the most critical temperature we deal with.

You don't freeze the beer (usually), and boiling is what it is (not a constant, only 212F at the standard reference).


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Online Mark G

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Re: Thermometer discrepancies
« Reply #10 on: September 21, 2010, 09:11:11 AM »
I've found that the dial thermometers tend to be accurate only within a certain range, i.e. calibrate it at freezing and it could still be considerably off at mash temps. So I've been using a glass lab thermometer to calibrate my dial thermometers at around 150F.
Mark Gres

Offline denny

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Re: Thermometer discrepancies
« Reply #11 on: September 21, 2010, 09:35:47 AM »
I think it's better to calibrate your thermometer at the temperature you care most about.  That is, I like to calibrate my thermos around the mash temperature range.  Easiest way I found was to buy a NIST certified lab thermometer and then calibrate the thermos I use to it.  Oh, at mash temp, that is.

That's exactly what I do too, and I've been pleased with the results.
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Offline enso

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Re: Thermometer discrepancies
« Reply #12 on: September 21, 2010, 12:52:41 PM »
Frustrating ain't it?  I think we have all dealt with this at some point.  I have 2 of those certified "lab thermometers" and guess what?  They read differently!

As Hopfenundmalz states boiling point is relative.  When you are calibrating you need to find what actual boiling point for where you are is at that time.  It can change.  There are calculators you can find online.  You need to input your elevation and the current barometric pressure to identify the boiling point at the time of adjustment where you are.

Boiling point where I live is usually about 210F.

I have one of those proaccurate calibratable digital thermometers.  I have been pretty happy with it.  After about 1 year the original I had went crazy.  Huge temp fluctuations all over the place.  I contacted the company and they sent me a new one.  The first version I had, had a plastic tip and it had a chip in it.  I think it must have leaked and screwed up the thermistor.  The new one they sent me was solid stainless the for the whole probe.  Works great.
Dave Brush

Offline hopfenundmalz

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Re: Thermometer discrepancies
« Reply #13 on: September 21, 2010, 02:00:37 PM »
Some in Colorado boil at less than 200F.  That would be 6500 ft or a little more.  You want to find a calculator that adjusts for altitude and barometric pressure.

This one will do.
http://www.eggheadforum.com/index.php?option=com_content&task=view&id=60&Itemid=88
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