Bimetal thermometers are by far the most common thermometers around. Their simple design makes them easy to mass produce, and even though they have a low price point, they are still fairly accurate. But how do you know when you should calibrate it? Or is there simply no need to? In this blog, we check out why and when you should calibrate your bimetal thermometer.
Bimetal thermometers work by converting the temperature increase or decrease into mechanical displacement through a bimetallic strip inside of the thermometer stem. The bimetallic strip is made up of two metals attached to each other. The metals used can include copper. brass or steel. Because the two metals expand or contract differently when the temperature increases or decreases, the difference causes the indicator to move. The difference in expansion is also explained as a difference in coefficients of thermal expansion. The indicator is attached to a dial at the front of the thermometer, with temperature indications alongside the dial. When the indicator is moved by a temperature increase, we can see that visually by inspecting the dial.
Calibration is most easily explained as making sure a thermometer is accurate. This is done by testing whether the bimetal thermometer indicates what it should indicate by comparing it to something you know the temperature of. In the case of bimetal thermometers, you can adjust the thermometers with the nut located below the dial. Calibration should be important when you need to be sure of your thermometer’s measurement. For more common questions, read our recent blog on temperature calibration.
Bimetal thermometers can suffer a loss in accuracy from various sources. When you suspect that one of the following is the case, you should probably perform a simple calibration to see what is up:
The reasons are simple, so the cure is just as simple. There is an easy way to calibrate bimetal thermometers, as they have a nut on the back of the dial that can be adjusted manually. To calibrate, you first set up a glass or bucket (depending on the size of the insert) and fill it all the way with ice. You then add cold water to fill it up entirely and let it sit for a couple of minutes. After a few minutes have passed, you can insert the thermometer. Make sure the stem of the thermometer is as much submerged as possible, or the surrounding air will influence your reading. When the indicator settles down, check that it should indicate 0°C. If it does not, adjust the nut (while the thermometer is still in there) so that the thermometer indicates 0°C. Now you are done. The thermometer should now be as accurate as you can make it without using calibrated equipment.
If there are strict requirements for your thermometer, you may consider more precise temperature calibration. You can read more on temperature calibration in our other article about the 4 main steps to calibrate temperature instruments.
So you calibrated your thermometer, but the response time is now lacking! How to fix this? Go and check out WIKA’s blog about the response time differences between gas-actuated and bimetal thermometers and check whether you may want to upgrade to a gas-actuated thermometer.