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Dial (Bimetal) Thermometers

Posted by Kenneth Kreiman on

Dial (bimetal) thermometers are simple to use, robust in design, and reasonably accurate in low and mid-range temperatures. They don’t require any power and are used in many different applications such as food and beverage quality control, general lab use, asphalt/concrete testing, and soil and compost testing. Stem lengths range from 5” to 48” and they can be calibrated in the field.

The bimetallic element inside a dial thermometer is constructed of two metal strips that are bonded together. The two strips are different metals that have different coefficients of thermal expansion. When the temperature changes, the two strips will expand/contract at different rates causing the connected strips to bend. One end of the element is attached to a rotating shaft that is attached to the pointer inside the dial face of the thermometer. This is what makes the dial move with temperature changes.

It is important to know how far you need to insert the stem in order to get an accurate reading. The bimetallic element is helix-shaped and for our thermometers it is about 2” in length at the bottom of the stem. Our thermometers have two dimples on the stem to indicate the top of the element. Your thermometer should be inserted at least this far for accurate readings.

 

Our dial thermometers include an adjustment screw for recalibration. Depending on the range of the dial, you can use an ice bath to calibrate at 32°F (0°C); or you can use boiling water to calibrate at 212°F (100°C). A temperature-controlled water bath can be used to calibrate at other temperatures.


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