Description

Although pressure-type thermometers belong to the expansion-type thermometers, they do not reflect temperature through changes in volume or size caused by the expansion of a substance when heated. Instead, they rely on the increase in pressure of a liquid or gas in a sealed container when heated to indicate the measured temperature. Therefore, the indicating instrument of this type of thermometer is essentially an ordinary pressure gauge. The main characteristics of pressure thermometers are simple structure, high strength, and good vibration resistance.

A pressure-type thermometer is primarily composed of a temperature bulb, a capillary tube, and a pressure-sensitive element (such as a Bourdon tube, a capsule, a bellows, etc.), as illustrated in Figure 2.2.3. The internal cavities of the temperature bulb, capillary tube, and Bourdon tube together form a sealed container filled with a working substance. The temperature bulb is directly in contact with the measured medium and is responsible for fully transmitting temperature changes to the internal working substance. Therefore, its material should possess corrosion resistance and exhibit good thermal conductivity. To enhance sensitivity, the thermal expansion of the temperature bulb itself should be significantly less than that of its internal working substance, necessitating a material with a low bulk expansion coefficient.

In addition, it should possess sufficient mechanical strength to withstand a significant pressure difference between the internal and external pressures on the relatively thin container wall. Typically, the bulb is made of stainless steel or brass, with brass only being used in non-corrosive media. When the bulb is heated, it causes the internal working substance to increase in temperature and pressure. This pressure is transmitted through the capillary tube into the Bourdon tube, causing it to deform and, through the transmission system, drive the pointer to indicate the corresponding temperature value.

Currently, pressure thermometers in production can be divided into gas-filled pressure thermometers and vapor-filled pressure thermometers based on the different working substances filled into the closed system.

Relevant Qualifications