Measuring instruments for pressure and temperature are used in almost all regions of industrial manufacturing. As a result of continuous mechanical, chemical and thermal loading, these instruments age and can therefore not guarantee the correctness of the measured values during the period 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 compared with the measuring result of another measuring device which is known to function correctly and accurately and which itself has been made to coincide directly or indirectly with a national (or international) reference instrument. In short, to be able to compare measuring results, they need to be ?traceable? to a national or international standard via a chain of comparative measurements. ไดอะแฟรม ซีล shown in the picture (utilizing the exemplory case of Germany) depicts the traceability of an inspection equipment in an organization up to a national standard at the PTB (German national metrology institute).
To be able to ensure traceability in practice, the following points must be observed, among others:
The chain of comparison should not be interrupted.
The measurement uncertainty should be known in each stage of the calibration chain so the total measurement uncertainty could be calculated. As a rule, a superordinate measuring instrument must have a measurement accuracy 3 to 4 times higher.
Each part of the calibration chain should be documented, including the measurement results.
All bodies following a stage in the chain must prove their competence through accreditation.
Calibrations must be repeated at appropriate intervals. The periods be determined by the demanded measurement accuracy and the technical requirements
Note
The WIKA calibration laboratory is accredited by the German Accreditation Body (Deutsche Akkreditierungsstelle ? DAkkS) relative to DIN EN ISO / IEC 17025 for the measurands temperature, pressure, DC current, DC voltage and DC resistance. More info on our calibration laboratory or an on-site calibration with the WIKA calibration van are available on the WIKA website. For anyone who is thinking about our services, please feel free to e mail us via e-mail.
Read more about the differences between factory calibration and traceable calibration in the following video: