Validating the Readings on an Infrared Thermometer Using an Ice Bath
In the last blog post within our infrared thermometer series, we looked at how to correctly validate the accuracy of your instrument using a Thermometer Comparator. The comparator method allows devices to be validated at ambient room temperature, however we would not recommend conducting it at hot or cold temperatures as this lowers the accuracy of the readings. If you need to validate your thermometer at a cold temperature, you can use the ice bath method to achieve a fairly accurate result by following the guidelines below.
If you haven’t already, we would suggest reading the other blog posts in the infrared series before attempting this method as they explore emissivity, thermal stability and other factors that affect the accuracy of your readings.
What is an ice bath test?
An ice bath is a quick and simple method of checking the accuracy of any thermometer. Mixing crushed ice and water together in an insulated mug or container creates an environment where both ice and water can exist. The temperature of this environment is exactly 0.0°C which makes it perfect for checking the accuracy of your thermometer.
How to validate your infrared thermometer using an ice bath
Step 1: Fill an Ice Bath Mug to the very top with ice (crushed ice is preferred as our test below indicates this achieves the best results). If you do not have an Ice Bath Mug then any large glass or container would suffice.
Step 2: Add cold water until the water reaches about 1cm below the top of the ice.
Note: If the ice floats up off the very bottom of the container then the ice bath is likely warmer than 0.0°C. Pour off any excess water.
Step 3: Gently stir the ice mixture and let it sit for a minute or two.
Step 4: Create a well of open water where no ice is floating or push the ice down so there is a layer of open water at the top of the ice bath mug.
Step 5: Make sure your infrared thermometer is set to an emissivity setting of 0.97.
Note: All of our ETI manufactured infrared products allow you to change the emissivity. Please refer to the instrument’s operating manual for instructions on how to change this setting.
Step 6: Hold your infrared thermometer about 5cm above the top of the cup or 8cm from the surface of the water and make sure that the lens or opening is directly above and perpendicular to the surface of the ice bath.
Note: If you hold your infrared thermometer too far from the surface of the ice bath or hold it at an angle, your measurement will include the sides of the ice bath mug or even the table it is resting on and give you an inaccurate reading.
Step 7: Taking extra care to ensure that the “field of view” (the size and shape of surface area being measured) is well inside the sides of the ice bath mug, press the button on your infrared thermometer to take a measurement.
If you perform the test correctly, and your infrared thermometer is properly calibrated, it should read within your unit’s stated accuracy specification at 0.0°C (please refer to our website for specifications on your instrument).
Is an ice bath an accurate method of validating an IR thermometer?
We conducted an experiment to see how accurate using an ice bath to validate an infrared device is. We used three of our products — a Thermapen IR, RayTemp Blue and RayTemp 3 — to check the temperature of two ice bath mugs, one made with ice cubes and the other with crushed ice.
Following the steps above, we created an ice bath using one of our Ice Bath Mugs. To ensure that the bath had been made correctly, we used a Thermapen Professional to test the temperature of the water. As you can see from the image below our Thermapen was showing a temperature of 0.0°C.
The emissivities of all the infrared instruments were set to 0.97, apart from the RayTemp 3 which is fixed to 0.97 as default.
Using our UKAS calibrated Fluke 566 infrared thermometer we took reference readings from each ice bath three times and determined an average temperature. Noting this temperature down, we then used the same method for our Thermapen IR, RayTemp Blue and RayTemp 3.
Here are the results:
Using the reference readings from the Fluke 566 IR, we subtracted the average reading achieved from the instruments to show the “actual” result.
All of the instruments on test have an accuracy of ±1°C at 0.0°C, so as you can see from the results they were all within their stated accuracy specification when calculated from the average reference temperatures of the calibrated Fluke 566 IR.
In conclusion, if you perform the test correctly, and your infrared thermometer is properly calibrated with an emissivity setting of 0.97, it should read within your unit’s stated accuracy specification at 0.0°C.
Learn more about infrared thermometers: