Temperature gauges measure the thermal state of a homogeneous substance. The measuring system must be brought as closely together as possible with the body to be measured. The most widely used measuring methods rely on temperature-dependent physical and material characteristics.
Bimetal temperature gauge
Bimetal temperature gauges operate with a measuring system in the form of a helical or spiral tube. The measuring system consists of two sheets with different expansion coefficients, which are inseparably joined. Through the mechanical deformation of the bimetal strips in the aforementioned tube types, a rotational movement results, caused by temperature changes. If one end of the bimetal measuring system is firmly clamped, the other end will rotate the pointer shaft. Bimetal temperature gauges are available with a scale range of -70 ... +600 °C in accuracy classes 1 and 2 in accordance with EN 13190.
Expansion temperature gauge
An expansion temperature gauge consists of a temperature sensor, a capillary and a Bourdon tube. The measuring system itself is filled with a liquid. If the temperature changes, the internal pressure of the temperature gauge will change as well. The pressure is transferred via a tube to a pointer shaft and thus the temperature value is indicated on the scale. Using remote capillaries from 500 ... 10,000 mm long, measurements can also be taken from remote measuring locations. The scale ranges for expansion temperature gauges lie between -40 ... +400 °C with class 1 and 2 accuracies in accordance with EN 13190.
Gas-actuated temperature gauge
With a gas-actuated temperature gauge the stem, the capillary and the Bourdon tube are joined together into one unit. The instrument is filled with inert gas. If the temperature changes, the internal pressure will also change. The pointer is moved by the action of the pressure via a measuring tube. To compensate for the ambient temperature, a bimetal element is mounted between the movement and the measuring tube. Gas-actuated temperature gauges are available with scale ranges between -200 ... +700 °C in accuracy class 1.
Machine glass temperature gauge
These temperature gauges are suitable for the monitoring of temperatures in gases, vapours and liquids in vessels and pipelines. The thermometer is housed in a case with a cutout for the scale display. Machine glass thermometers are often used with a V-shaped case.