Thermometer calibration and verification?

[bstacy1974]

I have trust issues. Especially when it comes to thermometers.
I have 4 different devices I use throughout my brewing process. Before brewing last night, I did a calibration check on the 3 digital therms. The 4th is a dial therm that came with my original brew kit and I don't really use it anymore. Granted, none of my thermometers are name brand, expensive devices. I've kinda just dealt with the plus or minus error by writing it on the device and adjusting accordingly.

Two of the digitals read 33F in a crushed ice water bath. The other is a K thermocouple attached to my brew controller. It read ~2F high, so I adjusted it down to 32.0F. I didn't check the dial.

Fast forward to strike water heating.
K thermocouple =173.4F (target strike water temp)
Digital therm 1 = 178F
Digital therm 2 = 176F
Dial therm = 180F

Oh boy. Not helping my trust issues. I pressed on with the mash. After 10 mins, I checked the two digitals in the mash tun. (The thermocouple is mounted in my boil kettle, and I didn't want to take it out again.) Both read 154F, which is exactly the mash temp I was shooting for. If I trusted these readings, I would say my actual temp is 153F as both read +1F high in the ice water bath. But, the strike water temps were so far off, I don't trust either thermometer and have no clue what my actual mash temp was.

I've always used an ice water bath for calibration or verification because it seems to be more stable than calibrating at 212F. I feel that uneven heating or hot and cool spots can form in a boiling pot of water that could effect calibration. I may be completely wrong on this, btw.

That's the background for a simple question, how do you calibrate and verify your thermometers?

 

[day_trippr]

[...]That's the background for a simple question, how do you calibrate and verify your thermometers?

I use a "name brand, expensive device"...

Worth the money for a whole bunch of reasons...

Cheers!

 

[bstacy1974]

Very interested in Thermapen right now.

 

[doug293cz]

Boiling water is actually a more stable reference than a typical ice bath. Water at a good rolling boil continuously mixes, so temp gradients aren't an issue. You do have to worry about an altitude correction for the boiling temp if you are significantly above sea level (http://www.csgnetwork.com/h2oboilcalc.html.) A proper ice bath is a vessel packed with as much crushed ice as fits, then backfilled with water. If you don't have that much ice, then the temp can easily rise above 0°C/32°F.

I also highly recommend a Thermopen.

Brew on

 

[bstacy1974]

Boiling water is actually a more stable reference than a typical ice bath. Water at a good rolling boil continuously mixes, so temp gradients aren't an issue. You do have to worry about an altitude correction for the boiling temp if you are significantly above sea level (http://www.csgnetwork.com/h2oboilcalc.html.) A proper ice bath is a vessel packed with as much crushed ice as fits, then backfilled with water. If you don't have that much ice, then the temp can easily rise above 0°C/32°F.

I also highly recommend a Thermopen.

Brew on

Thanks Doug. I'll have to rethink my calibration procedure. My ice bath is as you describe. My vessel is a stainless insulated thermos to stabilize the temp as much as possible.
I'll try a boiling calibration process to see the difference.
Do you recommend a specific size vessel for this procedure? Small to medium sauce pan?

 

[wilserbrewer]

I have three relatively inexpensive hand held digital thermometers. I tested them with packed and flooded crushed ice in a foam cup and also at boiling and all three were pretty damn close, so I figured I was in clover.

Fast forward a few weeks and my strike water appeared overheated in a very short time....scratched my head and sure enough my $8 Chinese therma pen clone was reading 20 or 30 high.

My take is that most digitalis are pretty accurate, but when they stray they do so drastically.

For the crushed ice test, after adding water, add more crushed ice, as much as you can fit and agitate well while checking temp, takes a bit of effort and manipulation to force it down to the true phase change temp of 32, otherwise you'll get slightly higher ime.

Foam cup better than glass or ceramic coffee mug imo.

I recall getting 32 plus a smudge until I worked it a bit....

 

[doug293cz]

Thanks Doug. I'll have to rethink my calibration procedure. My ice bath is as you describe. My vessel is a stainless insulated thermos to stabilize the temp as much as possible.
I'll try a boiling calibration process to see the difference.
Do you recommend a specific size vessel for this procedure? Small to medium sauce pan?

Vessel size shouldn't matter much for boiling. Sounds like you did things right for the ice bath.

Brew on

 

[bstacy1974]

Ok, so here's the results so far.

Dig. Therm 1
Ice bath = 33F
Boiling = 213F

Dig. Therm 2
Ice bath = 33F
Boiling = 210F

Old dial therm
Ice bath = 33F
Boiling = 213F

I adjusted the old dial thermometer to get it reading correctly. The digitals can't be adjusted so I'll just continue to note the difference for now.
At one point, Digital thermometer #2 actually started dropping in temp. It dropped to 198F before I adjusted the location of the probe. It bounced back, but never got to 212F. This one will most likely be retired to smoker duty.
Got a little more clean up to do from last nights brew, so I'll check and adjust the thermocouple later.

 

[bstacy1974]

Put my thermocouple in boiling water and it read 209.5F. Adjusted the the controller to get the reading to 212. Looking forward to my next brew day.

 

[RM-MN]

Ok, so here's the results so far.

Dig. Therm 1
Ice bath = 33F
Boiling = 213F

Dig. Therm 2
Ice bath = 33F
Boiling = 210F

Old dial therm
Ice bath = 33F
Boiling = 213F

I adjusted the old dial thermometer to get it reading correctly. The digitals can't be adjusted so I'll just continue to note the difference for now.
At one point, Digital thermometer #2 actually started dropping in temp. It dropped to 198F before I adjusted the location of the probe. It bounced back, but never got to 212F. This one will most likely be retired to smoker duty.
Got a little more clean up to do from last nights brew, so I'll check and adjust the thermocouple later.

It might be better to retire this one to wastecan duty. You can never again trust its reading.

 

[SpeedYellow]

Boiling water is actually a more stable reference than a typical ice bath. Water at a good rolling boil continuously mixes, so temp gradients aren't an issue.

I've found the opposite; I can get a wide variation of temperature at a boil. I'm not sure why, but I've seen a range of 210 to 216+ depending on my process. Perhaps from neglecting to use a pinch of chalk for nucleation sites, or simply using more heat than needed.

So the point is: if you calibrate at boiling, be skeptical of your process. Perhaps add some chalk, change the heat level, make sure your immersion depth is correct, etc. If you see variation, then perhaps discard this method.

 

[jcav]

+ 1 on the Thermapen! Very accurate!

John

 

[RM-MN]

I've found the opposite; I can get a wide variation of temperature at a boil. I'm not sure why, but I've seen a range of 210 to 216+ depending on my process. Perhaps from neglecting to use a pinch of chalk for nucleation sites, or simply using more heat than needed.

So the point is: if you calibrate at boiling, be skeptical of your process. Perhaps add some chalk, change the heat level, make sure your immersion depth is correct, etc. If you see variation, then perhaps discard this method.

Unless you can add pressure water cannot boil at over 212F. If your thermometer is showing 216, it needs to be replaced.

 

[Shwagger]

1 or 2 degrees of variance?!

I'll take that all day. We aren't splitting the atom here folks. KISS

 

[day_trippr]

Classic on sale...

Cheers!

 

[Shwagger]

Fyi

Homebrew Finds page on FB posts deals on equipment all day every day. Seen these go on sale super cheap. I highly recommend checking them out

 

[SouthBayBrewer31]

Just get the Thermapen! Once you have one you'll wonder how you ever brewed without it. It's crazy accurate and fast. Battery lasts years too. As brewers we really need the accuracy in order to maintain consistency.

 

[jturman35]

This is what I use. Now I’m questioning its accuracy. I get 32.5 with ice water test. But perfect 212 at boil.

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