Thermometer Calibration

Prepare an ice-water bath:

1. Fill a container to the top with ice (preferably crushed, because there are fewer gap between pieces, but cubed will work too.)
2. Add water nearly to the top of the container (about 1 cm below the top.)
3. Gently stir the mixture and let it sit for a minute or two.

For an air temperature thermometer (digital or liquid-filled):

1. Put the thermometer into the ice-water bath. The bulb of the thermometer must be in the water. NOTE: This will not work for some digital thermometers that should not be immersed in water. Only immerse the probe part of a digital thermometer, if it has one.
2. Especially for a liquid-filled thermometer, you may need to leave the thermometer in the ice-water bath for a few minutes so that it has time to adjust.
3. Gently move the thermometer around in the ice-water bath so that it will be thoroughly cooled, and also avoiding it directly touching the side or bottom of the container.
4. Read the thermometer. If it reads between -0.5˚ C and +0.5˚ C, the thermometer is fine.
5. If the thermometer reads greater than +0.5˚ C, check to make sure that there is more ice than water in your ice-water bath. Remove water and/or add more ice if needed.
6. If the thermometer reads less than -0.5˚ C, check to make sure that there is no salt in your ice-water bath.
7. If the thermometer still does not read between -0.5˚ C and +0.5˚ C, replace the thermometer.

For an infrared thermometer (IRT):

1. Create a space of open water where no ice is floating or tamp the ice down so there is a layer of open water at the top of the container.
2. Hold the IRT so that the measurement opening is directly over and perpendicular to the ice-water bath surface. NOTE: You want to avoid the IRT being at an angle so that you aren't measuring the temperature of the sides of the container or the table underneath. Also pay attention to the distance from the surface - the manual (or the IRT unit itself) should indicate the spot size (field of view) for measurements at different distances. You want to make sure you are only measuring the water surface. If necessary, move the IRT closer or get a larger container. See the image below for one example of where you might find those specifications noted on the side of the IRT.
3. Depress the button on the IRT to take a measurement.
4. The ice-water bath should read within the accuracy specification for your specific IRT. (For example, a instrument advertising a +/- 2˚ C accuracy should read between -2˚ C and +2˚ C on the display.) If the reading is outside the specification, you may need to contact the manufacturer or replace the IRT.