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.
Along the way of calibration, the displayed value of the measuring instrument is weighed against the measuring consequence 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, to be able to compare measuring results, they must be ?traceable? to a national or international standard with a chain of comparative measurements. The calibration hierarchy shown in the picture (using the exemplory case of Germany) depicts the traceability of an inspection equipment in a company up to a national standard at the PTB (German national metrology institute).
To be able to ensure traceability in practice, the following points should be observed, amongst others:
The chain of comparison must not be interrupted.
Crushing must be known in each stage of the calibration chain so that 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 step in the calibration chain should be documented, like the measurement results.
All bodies conducting a stage in the chain must prove their competence through 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. More info on our calibration laboratory or an on-site calibration with the WIKA calibration van can be found on the WIKA website. If you are interested in our services, please feel free to e mail us via e-mail.
Know more about the differences between factory calibration and traceable calibration in the next video: