A particularly frequently used design for temperature measurement is the bimetallic thermometer. The basis of the measuring process is based on a mechanical change, which is caused by heat or cold. The result of this – the coefficient of thermal expansion – is then transferred to a scale by means of a pointing device and displayed. The actual measuring instrument is made of a bimetallic sensor. This usually consists of two firmly interconnected metal strips, which consist of different thermally conductive materials such as iron, nickel, chromium or manganese.
Since the two different metals also behave differently to heat or cold, the bimetal deforms accordingly in different directions. This sensor element is usually designed as a spiral spring, which is firmly anchored on one side with the meter. The free end of the spiral will now expand or collapse depending on the temperature change. This linear motion is then transferred to a pointer work and displayed on a scale of values.
Designs and measuring ranges
Classic bimetallic thermometers are offered in a circular design with appropriate scaling and an immersion sleeve. The ferrule is led out to the rear or below the display when. Another variant is offered with an installable or weldable protective sleeve. One can also do justice to the materials used in the sensors, such as the use in media such as water, oils, gases or chemical media.
The measuring ranges of the bimetallic thermometers are standard – 80 ° C up to + 600 ° C. Usually they are used at temperatures of – 50 ° C up to + 400 ° C. The bimetal thermometers are particularly popular in heating, ventilation and plant engineering and have established themselves there as a quasi-standard. The easy handling, robust and proven design and the uncomplicated use make the bimetallic thermometer still the first choice. Even today you can see these thermometers in commodities such as refrigerators and freezers and here and there even in cheap ovens.