When measuring special media such as viscosity or acid base, diaphragm pressure gauges, stainless steel spring tubes, stainless steel movements, stainless steel housings, or bakelite housings should be selected. According to the different media tested, the pressure gauge should have a specified color code and indicate the name of the special media. The oxygen gauge must be marked with the words "No Oil" in red, the hydrogen should use a dark green lower horizontal line color code, and the ammonia should use a yellow lower horizontal line color code.

The selection of instrument type must meet the requirements of process production. For example, whether remote transmission, automatic recording, or alarm are required; Whether the properties of the measured medium (such as the temperature, viscosity, corrosivity, dirt, flammability, and explosiveness of the measured medium) have special requirements for the instrument, and whether on-site environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) have requirements for the type of instrument. Therefore, selecting instrument types correctly according to process requirements is an important prerequisite for ensuring normal operation and safe production of instruments.