The instrument type must meet the requirements of the process. For example, whether remote transmission, automatic recording, or alarms are required; whether the properties of the measured medium (such as temperature, viscosity, corrosiveness, dirtiness, flammability, or explosiveness) impose special requirements on the instrument; and whether the on-site environmental conditions (such as humidity, temperature, magnetic field strength, and vibration) impose specific requirements on the instrument type. Therefore, correctly selecting the instrument type based on process requirements is crucial for ensuring proper function and safe production.
For example, the spring tube of ordinary pressure gauges is often made of copper alloy (high-pressure gauges use alloy steel), while the spring tube of ammonia pressure gauges is made of carbon steel (or stainless steel). Copper alloys are not permitted. Because ammonia and copper react chemically, which can cause an explosion, ordinary pressure gauges cannot be used for ammonia pressure measurement.
Oxygen pressure gauges can be identical to ordinary pressure gauges in structure and material, but oxygen pressure gauges must not be oil-free. This is because oil entering the oxygen system can cause an explosion. During calibration, oxygen pressure gauges must not be calibrated with oil as the working medium, as is the case with ordinary pressure gauges. Furthermore, oxygen pressure gauges must be stored away from oil contaminants. If you must use an existing oily pressure gauge to measure oxygen pressure, you must clean it repeatedly with carbon tetrachloride before use and carefully check it until there is no oil.
