In many heating systems and installations in the home and in production, a bimetallic thermometer is used, showing the temperature change in a gaseous or liquid medium. This is a universal device. It can be installed in enclosed spaces, and indoors, and in open areas. It is used in nuclear power plants, oil refineries, military vessels, etc.
A bimetallic thermometer works on the basis of the following physical law: "Various metals expand or contract differently when the temperature of their environment changes." The sensitive element of the thermometer is a bimetallic spring (or plate), consisting of two different metals, pressed together. Since they have different expansion coefficients, as the temperature of the medium rises or falls, they deform. Deformation of metals causes the thermometer to turn and show the temperature value on the scale.
The bimetallic thermometer consists of a chrome-plated steel case, a sensitive bimetallic element (spring or plate), enclosed in a brass thermoball, a dial and a kinematic mechanism with an arrow. The dial and the arrow are covered by glass. A conventional thermometer can show a temperature in the range from -70 ° C to + 600 ° C.
All bimetallic thermometers, depending on the mounting axis of the dial, are divided into two groups: basic and radial. The axis of the dial of the axial bimetallic thermometer is parallel to the axis of the bulb. A radial bimetallic thermometer differs from an axial in that its axis is located at an angle of 90 ° to the axis of the bulb.
Types of bimetallic thermometers can also be classified according to the purpose of the device, at its place of work. Depending on the purpose, thermometers are tube and needle. A bimetallic pipe thermometer measures the temperature of a pipe in a heating system from its surface. Bimetallic needle thermometers measure temperature with a special needle probe immersed in the medium.
Depending on the place of use, the devices are divided into household and industrial bimetal thermometers. The range of temperature measurement by household devices is much smaller than that of industrial bimetal thermometers. In the manufacture of household options take into account the conditions in which they have to work.
Industrial bimetal thermometers are manufactured both with highly specialized capabilities and with universal ones. They can work in any phase state and in a very wide temperature range.
A bimetallic thermometer is a great alternative to liquid. Its disadvantages consist only in the fact that it is more expensive to manufacture and has a longer temperature measurement.
When purchasing a bimetallic thermometer, you need to pay attention to the presence of a certificate of conformity and a passport for the device. When working with the device, it is necessary to observe the temperature range indicated in the thermometer certificate.