The selection of temperature detection instruments should be based on process requirements, and the range and accuracy of the instrument should be correctly selected. The normal operating temperature range is generally 30%-90% of the instrument range.

The instrument for direct on-site measurement can be selected according to the process requirements. Glass liquid thermometers have the advantages of simple structure, easy use, accurate measurement, and low price, but poor strength and easy damage. They are usually used in places with high indication accuracy and no vibration on site. They can also be used for temperature alarm and position control. Bimetallic thermometers have the advantages of small size, easy use, clear scale, and high mechanical strength, but the measurement error is large. They are suitable for clear indication and vibration occasions. They can also be used for alarm and position control. There are three types of pressure thermometers: gas-filled, liquid-filled, and steam-filled. They can realize temperature indication, recording, adjustment, remote transmission, and alarm. The scale is clear, but the mechanical strength of the capillary is poor, and the measurement error is large. They are generally used for on-site centralized measurement or occasions requiring recording. Thermistor thermometers have the advantages of small size, high sensitivity, small inertia, and durability, but the characteristics of thermistors vary greatly. They can be used in occasions where the temperature of solid surfaces is intermittently measured.

Remote contact temperature measuring instruments are divided into two categories: thermocouples and thermal resistors. The appropriate type, inertia time, working pressure, structural form, connection method, compensation wire, and insertion depth of the protective sleeve of the thermocouple and thermal resistor should be correctly selected according to the process conditions and temperature measurement range. If used in special measurement occasions, special thermocouples and special thermal resistors can be selected. Thermocouples and thermal resistors have the characteristics of high measurement accuracy, simple structure, and easy use. They can be used for remote indication, recording, alarm and automatic control.

To measure the temperature of small objects and moving objects or to measure the temperature of objects that cannot be installed with temperature measuring elements due to high temperature, vibration, impact, etc., optical pyrometers, radiation temperature sensors and other radiation thermometers should be used. When measuring temperature with a radiation thermometer, the on-site environmental conditions must be considered. For example, if it is affected by water vapor, smoke, carbon monoxide, carbon dioxide, etc., corresponding measures should be taken to overcome interference. Optical pyrometers have the advantages of a wide temperature measurement range and are easy to use and carry, but they can only be visually observed and cannot automatically record or control the temperature. Radiation temperature sensors have the advantages of stable performance and ease of use. When used with display instruments, they can continuously indicate, record and control the temperature, but the measured object temperature is quite different from the actual temperature, so corrections should be made when using it. When measured with a sighting tube, the actual temperature can be measured.