How to calibrate an immersion circulator

The beauty of an immersion circulator is it’s ability to hold the temperature of a water bath at a precise and stable temperature all the while circulating the water. The implications of being able to cook at such specific temperatures are vast and far reaching. Some of the best examples are eggs. But none of this matters if your circulator isn’t accurate.

I’ve suspected my circulator needs to be calibrated after a couple of run-ins with overcooked eggs. I tried making a crème anglaise which came out of the circulator broken. I also haven’t had much luck making sous vide scrambled eggs. Both recipes (from trusted sources) seemed to be cooked at too high of a temperature. So I set out to learn how to calibrate my immersion circulator.

So my circulator wasn't actually off by 1.1 degrees F, only about .4 C. But you get the picture.

I use the PolyScience Sous Vide Professional. These specific instructions are for that model, but the overall concept of how to calibrate a circulator will be the same no matter what make and model you are using. To make a long story short, you essentially make an ice water bath with a ton of ice. Let it sit for a few minutes and then put the circulator in the ice water. Turn the machine all the way down so it’s not heating. And then use the calibration function to calibrate the machine to either 32F or 0C. But here’s the long story…

To calibrate an immersion circulator:

  • Combine two parts ice to two parts water by volume to create a large ice bath. About 3 to 4 quarts. Allow to sit for five minutes.
  • Place the circulator in a tall and narrow container that will have just enough room for the circulator and the ice water.
  • Pour the ice bath into the container with the circulator.
  • Calibrate the machine to 32F or 0C.

To calibrate the PolyScience Sous Vide Professional:

  • Unplug the power cord from the wall.
  • Press and hold the menu button while plugging the machine back into the wall.
  • Press the menu button repeatedly until the screen says “offset calibration”.
  • Use the up and down buttons to change the offset.
  • Press the menu button again to exit the calibration mode.

notes:

  • Never try and use a home thermometer to calibrate an immersion circulator.  Most circulators have more accurate thermometers then home thermometers.
  • I found it easiest to calibrate the PolyScience on celsius as apposed to fahrenheit.  I could only get the offset calibration to show up in celsius.
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2 thoughts on “How to calibrate an immersion circulator

  1. Volition says:

    I do not recomend calibrating your circulator like this. You need a reference thermometer to calibrate. See greisinger thermometers for example. The problem is that Sous Vide is normally operated from 55c to 90c and this is the range that needs calibrating. A thermometer will have a different offset at different temperatures. And because we never sous vide at 0c calibrating at this mark is virtually useless. Sorry for the bad news look for a certification lab and see if they may help you calibrate.

    What i do is check every 2 months using two thermometers. One is a Thermapen the other is a cheap RTD. I log the temperatures down using a range of temperatures from 55c to 90c. Then when i do it again in 2 months I am expecting to see similar results. If I get a big change then it is time to re-calibrate. I have assumed that I received my unit calibrated to begin with.

    If you suspect your circulator is out you will need to seek out a better method to perform an inital calibration. Be it a lab or purchasing a reference thermometer that is calibrated as well.

    It is all very expensive in my eyes but if you chat to a calibrating lab they may help you.

    Don’t use this method, it is not reliable at all. When i think of a better way I’ll let people know. I’m trying to think of a visual reaction that occurs at a specific temp. Has anyone else got ideas.

    Vol

  2. Jonas says:

    This is a tricky question that I also asked some time ago when I first got my PolyScience circulator. After much research and some helpful guidance from PolyScience support, I finally came to understand.

    First, don’t assume that it’s your circulator that is out of calibration. Turns out that PolyScience immersion circulators that they sell to the laboratory world are very often used to create baths in which thermometers are calibrated – basically, PolyScience sets the temperature standard. All of the equipment they ship is calibrated using a super-accurate and really expensive digital RTD thermometer. If I remember right, the it’s accurate to either 1-thousandth or 1 ten-thousandth of a degree. That reference thermometer is then also verified regularly against a goverment-traceable standard.

    The part that makes this really tricky is that PolyScience uses highly accurate RTD probes. Most inexpensive digital thermometers, including the Thermapen, use a thermocouple. Inherently, an RTD is simply more accurate and has a more linear accuracy scale.
    What that means in a nutshell is that even if you calibrate your thermocouple based digital thermometer at one temperature and have it match the circulator, you are likely to find that at other temperatures, there is still a variance.

    To really get the most accurate results, you’ll need a high quality RTD based thermometer and consider calibrating the thermometer to match the Sous Vide Pro and not the other way around.

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