Understanding Vacuum Calibration

Finding the proper vacuum calibration service is not easy. Especially for those in a highly regulated industry who require NIST traceability, it can be extremely hard to find the right vacuum calibration lab. The best way to start your search for a vacuum calibration lab is by understanding vacuum calibration itself.

Why do we calibrate?
Calibration is the standardization of an instrument to ensure that it is working properly every time. Whenever you step into an elevator, you are trusting that the sign stating “can hold up to 1,000 pounds” is correct. Those elevator cables which hold the weight of the elevator are calibrated to ensure they truly can hold up to 1,000 pound without failing. Without calibration, a lot of the items we use and trust could be extremely dangerous.

There are two different types of gas flow rates that a vacuum calibration can be based on.

Piston Flow Meter
The piston flow meter creates flow by allowing gas at a known temperature and pressure to leak out of a small container. A piston is inserted into the vessel to hold the pressure constant. The molar flow rate is yielded by combining gas pressure and temperature with the piston.

Bellows Flow Meter
The bellows flow meter uses an oil filled chamber, containing both a piston and a gas-filled metal bellows. When the piston is inserted, the chamber causes the volume of the bellows to change equally.

There are also two types of vacuum calibrations, the high vacuum standard and transition range vacuum standard. High vacuum standard is used for ion gauges at low pressures. The transition range vacuum standard is used for vacuum calibration of spinning rotor gauges at pressures in the transition range. These two standards have been identified by NIST and will be practiced by those vacuum calibration labs who are traceable to NIST.

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