Five commonly used temperature detection instruments

1. Expansion thermometer

Temperature detection instruments made using the principle that objects expand according to a certain rule when heated. Such as: glass liquid thermometer, rod-shaped expansion thermometer, bimetallic thermometer. The most commonly used is the glass liquid thermometer, which uses mercury and alcohol as working liquids. It has the characteristics of simple use and low price. The temperature measurement range is between -80 and +500℃.

2. Pressure thermometer

An instrument manufactured based on the principle that the pressure of liquid or gas in a closed container changes with temperature. Its advantage is that the indicated value can be transmitted over a long distance (about 30 meters) through a capillary tube. It has a simple structure, is resistant to vibration, and can be completely explosion-proof. But it must be calibrated frequently. The temperature measurement range is between -50 and +400℃, and it is not widely used.

3. Resistance thermometer

A temperature measuring instrument designed and manufactured based on the principle that metals or alloys change their resistance according to a certain rule as the temperature changes. It consists of a temperature sensing element and a display instrument, with a temperature measurement range of -20 to +500°C, and can measure the surface temperature of liquids, gases, steam and solids. The output of this thermometer is a resistance signal, which can be transmitted remotely and participate in automatic adjustment, and is widely used. Such as copper resistance and platinum resistance.

4. Thermoelectric pyrometer

Two different metal or alloy wires are welded together at one end, and a thermoelectric potential is generated after heating. This is the principle of the thermocouple. The thermoelectric pyrometer is composed of a thermocouple and a secondary instrument connected to it. The measurable temperature range is 0 to 1600°C. Thermoelectric pyrometers have sufficiently high accuracy, which is convenient for centralized temperature inspection and can also be directly involved in recording. Since the thermocouple outputs a millivolt signal, after amplification and transformation, the thermoelectric pyrometer can not only indicate and record, but also directly participate in the temperature automatic adjustment system. It is widely used in high-temperature detection, especially in the metallurgical industry.

5. Radiation pyrometer

The working principle of the radiation pyrometer is to utilize the relationship between the radiation energy and temperature of a hot object. There are two types: optical pyrometer and radiation pyrometer. Optical pyrometers detect temperature based on the brightness of hot objects. They only use a very narrow section of the spectrum (monochromatic radiation), so optical pyrometers are also called local radiation pyrometers. Radiation pyrometers measure temperature based on the thermal radiation effect and use all the energy of radiation. Radiation pyrometers are non-contact pyrometers with a high starting point for measuring temperature, but the highest temperature they can measure is also high, up to about 3000°C.