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 will therefore not guarantee the correctness of the measured values during the period of time. Through Missing Out , 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 which 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 via a chain of comparative measurements. The calibration hierarchy shown in the picture (utilizing the example of Germany) depicts the traceability of an inspection equipment in a company up to a national standard at the PTB (German national metrology institute).
So as to ensure traceability used, the following points should be observed, among others:
The chain of comparison should not be interrupted.
The measurement uncertainty must be known in each stage of the calibration chain in order that the total measurement uncertainty can be calculated. Generally, a superordinate measuring instrument must have a measurement accuracy 3 to 4 times higher.
Each step in the calibration chain should be documented, including the measurement results.
All bodies carrying out 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. More info on our calibration laboratory or an on-site calibration with the WIKA calibration van are available on the WIKA website. Should you be interested in our services, please feel free to contact us via e-mail.
Find out more about the differences between factory calibration and traceable calibration in the following video: