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Calibration Traceability and Pressure Standards
Source: | Author:SW | Published time: 2025-01-03 | 46 Views | Share:

Calibration Traceability

A traceable calibration is a calibration in which the measurement is traceable to the International System of Units (SI) through an unbroken chain of comparable measurements to a National Metrology Institute (NMI).  This type of calibration does not indicate or determine the level of competence of the staff and laboratory that performs the calibrations. It mainly identifies that the standard used in the calibration is traceable to an NMI. NMIs demonstrate the international equivalence of their measurement standards and the calibration and measurement certificates they issue through the framework of CIPM Mutual Recognition Arrangement (CIPM MRA).

Primary vs. Secondary Pressure Standards

There seems to be a good deal of confusion on the difference between primary and secondary standards, mainly because of a lack of technical distinction between the two.
Pressure is a unit derived from fundamental SI units so any pressure device could never be a primary standard. The lowest uncertainty pressure devices available are considered fundamental pressure standards and are typically ultrasonic interference manometers and piston gauges. They are often referred to as primary standards even though technically, they are not.
 
The term primary standard is also sometimes used when referring to the most accurate pressure standard within a facility. In most cases, these are traceable to the best fundamental pressure devices at NMIs. The instruments at these institutes are also called primary standards and are probably more deserving of the title because they are at the pinnacle of accuracy in the chain of traceability.  
 
To further complicate the issue, calibration laboratories frequently call their lowest uncertainty pressure devices their primary standards. Secondary standards are devices either calibrated by, or traceable to, the aforementioned primary standards, or even other secondary standards.
 
Find out more about traceability and the hierarchy of bureaus and institutes in the unbroken chain linking to SI.