How to Calibrate a thermometer | Ice water vs boiling water vs Dry-block Calibrator

Using ice and boiling water to calibrate temperature is easy and fast. However, the water method can be inaccurate because of variations in altitude, atmospheric pressure and water purity -- and the inaccuracies are unknown. When you're calibrating you want to avoid as many unknowns and inaccuracies as possible.

Using a dry-block calibrator is a far better way to calibrate temperature. A dry-block provides a better measurement because it has a known accuracy.

In this brief video I will calibrate a digital thermometer with ice water and boiling water. Next I'll do the same calibration using Fluke Calibration 9100S and 9102S Handheld Dry-Wells.

Then we'll see how the two methods measure up against each other.

Transcript:

Let's experiment with a couple of different ways calibration we're going to use the common methods here of ice water and boiling water. I've got everything set up here we're going to do a quick check with these and then we're going to compare against our dry wells and see how we measure up.

I've got the unit under test sitting in an ice bath and right now you can see we're measuring approximately 0.6 a little bit off from where we want to be, so now let's make a quick adjustment get this dialed into our ice bath.

Here I've made a quick adjustment to the ice bath right at about zero, now I'm going to move over and try this at the boiling point and see how we're doing on the linear side going up.

It looks like we're wobbling around about 95 and some change so let's make a quick adjustment on the top end.

Now I've got it close to a hundred degrees Celsius so now what I'd like to do is repeat this, this time we're going to use the 90, 100 s and the 90, 102's and see how we measure up.

Now what we're going to do is use our 90 100 s and 90 102's let's see how we compare just a few seconds ago you saw me make the adjustments using the water method but now you can see we're a little bit out of spec again.

Those common methods can net you some errors in the neighborhood of several degrees.

The benefit of moving to a dry well is that these are calibrated certified and you know the uncertainty you're working with. William Water depends not only on the elevation but also barometric pressure, Ice water and building an ice bath there is some technique to it and the purity of the water will also make a difference.

So let's make another adjustment to the thermometer now and see what our results are, I've moved right over into the hundred point. That's kind of where we left off and you can see here from the boiling water to the drywall we're almost four degrees and some change high.

So what we're going to need to do now is make an adjustment again for this time we're going to bring it back down, so you can see how I've made the high side adjustment and again we've pulled it back from the boiling water which was reading roughly 104.

Now I've brought it down to right at 100 degrees Celsius.

All right we've allowed a few minutes for the device under test to kind of come down to zero and stabilize. We're actually right on with what the drywall is reading, so again we had to make a slight adjustment of about four degrees at the top end versus the boiling water it looks like at our low end we're pretty linear and so we know at this point we're within 0.25 degrees C of our reading which is well within a type K uncertainty.

Again we're confident even at the top end now with the adjustment that we've got an uncertainty of 0.25 there as well, so again you can see the difference between using water technique versus a dry well.

The big benefit here is you're working with a known uncertainty versus an unknown to learn more about our dry Wells and how they can help you improve your sensor.

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