In addition to the top five factors discussed in part one, which can be viewed here, several other factors need to be consider when calibration pressure gauges.
When calibrating a pressure gauge, it is important to be conscious of adiabatic effect. For example, adiabatic effect can be present in a closed system that consists of a pressure media made up of gas. The temperature of the gas will affect the volume of the gas, which in turn has an effect on the pressure. In situation as such, pressure can increase quickly, causing the temperature of the gas to rise. When the temperature of the gas rises, the gas will begin to expand, thus having a bigger volume and a higher pressure. After the temperature of the gas starts to cool, the volume of the gas then starts to become smaller, which then causes the pressure to drop. While the pressure dropping may seem like a leak, it is really just an adiabatic effect.
Another important factor to consider when calibrating a pressure gauge is torque force, especially when it comes to torque sensitive gauges. It’s essential to ensure that excessive force is not used when connecting the pressure connectors to the gauge. If excessive force is used, it is likely that the gauge endure damage. Proper tools and appropriate adapters/ seals should be used.
Calibration mounting position should also be taken into consideration when calibrating a pressure gauge. Pressure gauges are mechanical instruments; therefore, their positioning during calibration will affect the reading. It is strongly recommended to calibrate a pressure gauge in the same position it is used in process. It’s also vital to check all manufacturer specifications revolving around operation/mounting positions.
In order to properly calibrate a pressure gauge, pressure must be generated in order to apply needed pressure to the gauge. There are multiple ways this can be done:
- A pressure hand pump
- A pressure regulator with a bottle
- A dead weight tester
Pressure gauges are a mechanical structure and are known to have some friction in their movement. This friction can cause changes the gauges behavior over time; therefore, it is recommended to “work it out” before calibration. This should specifically be done if the gauge has not been applied with pressure in some time. To exercise a gauge before calibration, a nominal max pressure should be applied to the gauge. This pressure should sit for a minute and then it should be vented. This process should be repeated up to three times before performing the pressure gauge calibration.