The working principle of the bimetal thermometer is to use two kinds of metals with different temperature expansion coefficients. In order to improve the temperature measurement sensitivity, the metal sheet is usually made into a spiral shape. When the temperature of the multilayer metal sheet changes, the amount of metal expansion or contraction of each layer Not waiting to make the spiral roll up or loose.

Because one end of the spiral coil is fixed and the other end is connected with a pointer that can rotate freely, when the bimetallic piece feels the temperature change, the pointer can indicate the temperature on a circular graduation scale.

The temperature measurement range of this kind of instrument is generally between -80℃～+500℃, and the allowable error is about 1.5% of the scale range.

classification:

Ordinary bimetal thermometer, shockproof bimetal thermometer, electric node bimetal thermometer.

According to the connection direction of the bimetal thermometer dial and the protective tube, the bimetal thermometer can be divided into four types: axial type, radial type, 135°direction type and universal type.

①Axial type bimetal thermometer: The pointer plate is connected vertically to the protection tube.

②Radial type bimetal thermometer: The pointer disc is connected in parallel with the protection tube.

③135°direction bimetallic thermometer: the pointer disc and the protection tube are connected at 135°.

④Universal bimetal thermometer: The connection angle between the pointer plate and the protective tube can be adjusted arbitrarily.

Selection and use:

When selecting bimetal thermometers, full consideration should be given to the actual application environment and requirements, such as the diameter of the dial, the accuracy level, the installation and fixing method, the type of measured medium, and the environmental hazard. In addition, we must also pay attention to factors such as cost performance and maintenance workload.

In addition, the following points should be noted during the use of the bimetal thermometer:

A. The length of the bimetal thermometer protection tube immersed in the measured medium must be greater than the length of the temperature sensing element. Generally, the immersion length is greater than 100mm, and the immersion length of the 0-50℃ range is greater than 150mm to ensure the accuracy of the measurement.

B. Various types of bimetal thermometers should not be used to measure the temperature of the medium in an open container, and charged contact thermometers should not be used in the control circuit of occasions with large working vibrations.

C. In the storage, use, installation and transportation of the bimetal thermometer, avoid collision with the protective tube, do not bend the protective tube and use the watch as a wrench.

D. The thermometer should be inspected regularly under normal use. Generally every six months is appropriate. The electric contact thermometer is not allowed to work under strong vibration, so as not to affect the reliability of the contact.

E. The temperature at which the meter often works is best to be within 1/3 to 2/3 of the scale range.