Calibration is the determination of the correlation between an input and an output quantity. All measurement instruments, such as voltmeters, manometers, Vernier calipers, etc., must be calibrated to determine the variation of their reading from the absolute quantity. In radiometry, the input quantity is provided by standard lamps and optical radiation detector standards. Because of the many different measurement quantities involved, calibration standards for each quantity are required if an optical radiation calibration laboratory hopes to cover the whole range of possible calibrations. A “traceable” lab calibration standard should show an unbroken chain of links to national (better international) standards. However, this in itself does not guarantee accuracy or ability of the lab to meet its calibration uncertainty claims. Since calibration standards are subject to change with age and use, the calibration of the standards themselves must also be checked periodically. This at times means replacing the standards in order to maintain the calibration and traceability quality. The end user of the calibrated product may be required to audit the calibration facility to ensure its competency and traceability. In Germany, the Deutsche Kalibrierdienst (DKD, the German accreditation institution) and the Physikalisch-Technische Bundesanstalt (the German national standard laboratory) offer an accreditation service for industrial calibration laboratories where the lab‘s calibration standards, calibration procedures and the stated re-calibration intervals are subject to auditing. This accreditation ensures that the traceability of the calibration is on an absolute level. The DKD also ensures the international acceptance of its accredited calibration laboratories. More information on national calibration organizations.
Fig. 1: Gigahertz-Optik calibration engineer