Thermometer Calibration

[Benniee]

Afternoon All,

I use a "spirit" filled thermometer in my brewing (all-grain), and I've previously checked it againist a known accurate thermometer here at work at a temperature of 65 degrees. The two thermometers read the same (which I was pretty pleased about). I performed this check about 18 months ago.

Well last night for something to do I decided to do another quick check of my thermometer in an ice bath, and then in some boiling water. I made up an ice slurry of about 50% crushed ice and 50% water - mixed up well and left to stand for a few mintues. Put the termometer in to the indicated submersion depth and it read -1 degree. Slightly out at the lower end of the scale it seems.

Next I brought a pot of water to the boil on the stove and measured the temp of the liquid once it was at a gentle rolling boil. 102 degrees. For this measurement I did my best to keep the bulb of the thermometer around 50mm off the bottom of the pot - which meant tilting the thermometer a bit and doing my best to keep the submersion line at the water's surface.

So using a little spreadsheet I was able to work out what "true" temp would be for an indicated temperature on my thermometer - which resulted in my thermometer typically reading 1 degree high around mash temperatures. Not a huge problem, but probably something I'll allow for on my next brew day.

Has anyone else performed a calibration procedure like this on a spirit filled thermometer? Do my results sound similar/reasonable?

Benniee

 

[Fourstar]

Has anyone else performed a calibration procedure like this on a spirit filled thermometer? Do my results sound similar/reasonable?

For accurate calibration regardless of altitude.

Stick it up your butt and see if it reads true 37 degrees :lol:

 

[beerbog]

Stick it up your butt and see if it reads true 37 degrees :lol:

Unless you have a slight fever, could throw the calibration out. :beerbang:

 

[unrealeous]

Stick it up your butt and see if it reads true 37 degrees :lol:

Beware of Fourstar's chocolate stout

 

[katzke]

Mine is on in ice and high at boiling. Last time I checked it was higher then what you get.

I was very disappointed that my spirit thermometer was off so did some searching. I found out that as you say they have an immersion mark on them and need to be used at the depth. I also found out that they need to be stored vertical and not lying down. I need to check again but after properly storing it, it was closer to expected then the last time I checked it.

I also discovered that they do go off and need to be checked. I bought it thinking it would solve the problem of wonky dial thermometers. I was half-correct in that they can be calibrated or compensated for using an easy to make graph. A spirit thermometer may be off at 0C and or off at 100C and still be predictable at mash temp. I had a bi-metal dial that was not predictable at any temp. I have also heard of brewers that say if in doubt tap a dial to get a better reading. I want a bit more precision in my mash temp then that.

 

[Tony M]

I have done the same with three digital thermometers I have. Only one was spot on at 0C & 100C, One read 1C low at both ends and the last was -2 at 0C and +1 at 100C. I dropped the spot on one on the ground the other day and it shifted by 2 degrees. I pulled it apart looking for a trimpot or something but observed nothing I could make sense of. The moral of this story is that you check the calibration regularly.

 

[katzke]

I have done the same with three digital thermometers I have. Only one was spot on at 0C & 100C, One read 1C low at both ends and the last was -2 at 0C and +1 at 100C. I dropped the spot on one on the ground the other day and it shifted by 2 degrees. I pulled it apart looking for a trimpot or something but observed nothing I could make sense of. The moral of this story is that you check the calibration regularly.

I know that bi-metal dial thermometers can be way off at mash temp and close at 0 and 100. I am not sure about digitals so it would be a good idea to check them at mash temp against a known good thermometer.

Spirit thermometers are what we are talking about for calibrating.

 

[Thirsty Boy]

As long as you are fairly aware - it doesn't actually matter if your thermometers are out a little, as long as they are cosistent (or you know the differences) between them. So you aren't measureing one brew with one - and the next with something thats 2 degrees off it.

I calibrate all my thermos in ice slurry, in boiling water, at 37 (under my tounge) and then plot them in cooling water against each other across the mash range. about every 6 months - should do it more often but I am slack.

 

[Benniee]

As long as you are fairly aware - it doesn't actually matter if your thermometers are out a little, as long as they are cosistent (or you know the differences) between them. So you aren't measureing one brew with one - and the next with something thats 2 degrees off it.

I calibrate all my thermos in ice slurry, in boiling water, at 37 (under my tounge) and then plot them in cooling water against each other across the mash range. about every 6 months - should do it more often but I am slack.

I don't really have a problem with the thermometer as long as the calibration data I've collected stays fairly stable. I'll check it again in a couple of months. The fact it was reading high partly explains why some of my beers have been attenuating more than expected.

I don't know how I'd go getting the correct immersion depth for the thermometer by putting it under my tongue - and I'm not going to consider any other location to measure body temperature (Fourstar - I'm looking at you)

Good idea on monitoring some temps in cooling water as a comparison. At the moment I only have one thermometer - so I can't really do that. And I'll have to assume that the capilliary within it is precise enough to ensure a linear response across the temperature range.

It's highly probably that the "known good" thermometer at my work is not as good as they have made out.

I do store mine upright - but I'm not sure how that would alter the readings over time. With a correctly sealed system I can't imagine that the nitrogen and spirit would changes places or form bubbles in the capilliary - but I'm happy to be educated by someone who knows better.

Benniee