Thermometers - Which is most accurate & Calibration Question

For our first few batches we used a Polder digital thermometer which read about 4 degrees lower than the adhesive thermometer strips we have on our fermenters. I just received two new thermometers from AHS and did a side by side test with all three of them last night. The two new thermometers are a glass lab thermometer and a dial type probe thermometer. The lab thermometer and the Polder digital thermometers read the same and the dial thermometer read three degrees higher (at approx 65 degrees). So the questions are:

- Is the glass lab thermometer the standard that I should use for accuracy?

- There's a nut right against the back of the dial on the dial thermometer. Is this how the thermometer is adjusted?

- It was getting too late for me to fill a fermenter with water to check the accuracy of the adhesive strip thermometers against the others. Has anyone tested the accuracy of the adhesive strip thermometers?

There can be only one!

The nut on the back is to adjust it. Just calibrate it against known constants like boiling water and ice water that has reached a steady state. At the very least, checking both of your thermometers against those will tell you which one is off, and by how much.

Make an ice slushy mix in a glass and insert thermos. Whichever ones read 32F are the accurate ones. Then stick them in boiling water and depending on your altitude the ones that read 212F or so pass the test. Hopefully they are accurate at both extremes.

I was looking for the boiling water correction for altitude and came across this article. It looks like a bi-metallic thermometer is only truly accurate at the temperature it is calibrated. I guess ideally a mash thermometer would be calibrated at about 153 degrees. According to the article, at least one manufacture calibrates at 100 degrees. It seems that if I calibrated at 32 I would introduce more error than I might already have. So, it seems that accuracy is unobtainable with the equipment that I have. I just need to learn to brew consistently with what I have. I'll probably just calibrate my dial thermometer to match the lab thermometer at 153'ish and go with that. Thanks for the responses.

I use a Taylor Precision thermometer and I can calibrate it at both extremes. I guess I'm lucky. I followed the procedures this article suggested. I guess it worked for me!

Boiling water test is only accurate if you have an accurate barometric pressure reading. http://en.wikipedia.org/wiki/Boiling_point
Altitude does not matter, because in effect when you change altitude, water only feels the change in pressure.

That Thermoworks looks good, but for the money you could buy two (McMaster-Carr product number 3569K58 from www . mcmaster . com catalog page 581).
They are more accurate, and have a longer probe length.

B Long reach with NIST Certificate -58° to +302° F ±0.4° F 8" SR44 coin cell 3569K58 $48.50

or a DS18S20 for $4.

GatorDad said:

or a DS18S20 for $4.

Click to expand...

With that particular sensor, I would be concerned about the +/- 2*C accuracy listed in the specs. That and the fact that you would necessarily have to buy the receiver component that receives the signal and I am sure that would push the cost way above $4. Unless, of course, you happen to already have some type of receiver that would accept that type of sensor.

Jameco has the accuracy data wrong. It's 0.5 (http://www.maxim-ic.com/datasheet/index.mvp/id/2815).

See link in my sig for the "receiver" side. It's a "roll your own" gig.

I thought that +/- 2*C spec. was awfully wide.