Measuring instruments for pressure and temperature are employed in almost all regions of industrial manufacturing. Because of continuous mechanical, chemical and thermal loading, these instruments age and can therefore not guarantee the correctness of the measured values over the course of time. Through timely calibration, however, the alteration of the measured value can be determined.
In the process of calibration, the displayed value of the measuring instrument is weighed against the measuring result of a different measuring device that is recognized to function correctly and accurately and which itself has been designed to coincide directly or indirectly with a national (or international) reference instrument. In short, in order to compare measuring results, they need to be ?traceable? to a national or international standard via a chain of comparative measurements. The calibration hierarchy shown in the picture (using the example of Germany) depicts the traceability of an inspection equipment in an organization up to national standard at the PTB (German national metrology institute).
In order to ensure traceability in practice, the following points must be observed, among others:
The chain of comparison must not be interrupted.
The measurement uncertainty should be known in each stage of the calibration chain in order that the total measurement uncertainty could be calculated. Generally, a superordinate measuring instrument must have a measurement accuracy three to four times higher.
Each part of the calibration chain should be documented, like the measurement results.
All bodies following a stage in the chain must prove their competence by means of accreditation.
Calibrations should be repeated at appropriate intervals. The periods depend on the demanded measurement accuracy and the technical requirements
Note
The WIKA calibration laboratory is accredited by the German Accreditation Body (Deutsche Akkreditierungsstelle ? DAkkS) in accordance with DIN EN ISO / IEC 17025 for the measurands temperature, pressure, DC current, DC voltage and DC resistance. Further information on our calibration laboratory or an on-site calibration with the WIKA calibration van are available on the WIKA website. When Meltdown are interested in our services, please feel absolve to contact us via e-mail.
Find out about the differences between factory calibration and traceable calibration in the next video: