Instrument type selection must meet the requirements of the production process. Such as the need for remote transmission, automatic recording or alarm; by the nature of the medium (such as the measured temperature of the medium temperature, viscosity, corrosion, dirt, whether flammable and explosive, etc.) on the instrument made special requirements, Environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) on the instrument type requirements. Therefore, according to process requirements, the correct choice of instrument type is to ensure the normal work of the instrument and an important prerequisite for safe production.

       For example, ordinary pressure gauge spring tube to use more copper alloy (high pressure alloy steel), and ammonia pressure gauge spring tube materials are used carbon steel (or stainless steel), does not allow the use of copper alloy. Because ammonia and copper chemical reaction, will explode, so ordinary pressure gauge can not be used for ammonia pressure measurement.

       Oxygen pressure gauge and the general pressure gauge in the structure and material can be exactly the same, but oxygen must be prohibited with a pressure gauge. Because the oil into the oxygen system can cause an explosion. The oxygen pressure gauge used in the calibration, not as ordinary pressure gauge as the use of oil as the working medium, and oxygen pressure gauge in storage to strictly avoid contact with oil. If it is necessary to measure the oxygen pressure with an existing oil pressure gauge, it must be repeatedly cleaned with carbon tetrachloride before use and carefully checked until no oil is present.