In measurement technology, calibration refers to the traceability of the findings of a measurement device to a standard via which the measured variable is defined. Here, the reading indicated by the measurement device is compared with the "true" value, i.e. the standard. This also includes the documentation of measurement errors or measurement accuracy as well as a calculation of the measurement uncertainty. In Germany, regulatory monitoring of the traceability of a measurement to a comparison standard is carried out by the Federal Physical-Technical Institute (PTB).
In the calibration of an infrared temperature measurement device, black bodies, which can reproducibly reach various temperatures with a high degree of accuracy, are employed. To guarantee traceability to a standard, for the calibration of its devices Optris uses transfer standard pyrometers which are traced back to the ITS-90 international temperature scale at regular intervals. As the measurement geometry can influence the reading due to the so-called size-of-source effect, calibration is generally carried out for a specifically defined geometry (distance and aperture diameter of the radiation source). As a result, in the technical documentation a defined value is usually given for the measurement field size; usually 90% or 95%.