Principle and structure of bimetallic thermometer

A bimetallic thermometer is a temperature sensor which is made of a hot bimetallic strip wound in a spiral shape and installed in a protective sleeve. One end of the protective sleeve is fixed, and the other end is connected with a thin shaft, which is called the free end.

The pointer is mounted on the free-end spool. When the temperature changes, the free end of the temperature sensing device rotates, driving the pointer on the thin shaft to change the angle and indicating the corresponding temperature on the dial.

The temperature range is -80~600C, which is suitable for temperature measurement when the accuracy requirement is not high in industry. As a temperature sensing element, bimetal can also be used for automatic temperature control.

Extended data:

I. Characteristics

1, the thermoelectric potential of bimetallic thermometer is only related to the thermoelectric properties of hot electrode materials and the temperature difference between the two ends.

2. Using the same homogeneous conductor or semiconductor to form a loop will not generate thermoelectric potential.

3. The temperature of two contact points of thermocouple is t, T0. If T=T0, the thermoelectric potential of the thermocouple is zero. The law of intermediate temperature lays the foundation for making thermocouple graduation table.

4. For many years, scientists have tried to study whether the relationship between the temperature at the hot end (measuring end) of the thermocouple and the thermoelectric potential generated by the thermocouple circuit can be expressed by functional relationship or even piecewise function, and finally failed.

5. If the thermoelectric consisting of two conductors A and B and the third conductor has a wide temperature measuring range, the physical and chemical properties will be stable after long-term use.

6. High conductivity and low temperature coefficient of resistance; The configured thermoelectric potential has high sensitivity, linear relationship between thermoelectric potential and temperature, easy replication, simple process and low price.

Second, the use and maintenance

1 and WSS series bimetallic thermometers should avoid collision with the protective tube during storage, installation, use and transportation, and the protective tube should not be bent or deformed. When installing, it is forbidden to distort the instrument shell.

2. The instrument should be able to work normally at the ambient temperature of -30℃ ~ 80℃.

3. The operating temperature of the instrument should be within 1/2 ~ 3/4 of the calibration range.

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

5. All kinds of bimetallic thermometers should not be used to measure the temperature of the medium in the open container, and charged contact thermometers should not be used in the control circuit in the case of large working vibration.

6, bimetallic thermometer in storage, use, installation and transportation, should avoid collision protection tube, don't bend the protection tube and watch as a wrench.

7. Under normal use, the thermometer should be checked regularly. Generally, once every six months is appropriate. Electric contact thermometer is not allowed to work under strong vibration, so as not to affect the reliability of contact.

References:

Baidu encyclopedia-bimetal thermometer