The document describes the strongly recommended regular checks and recalibrations for radiation thermometers.
VDI/VDE 3511 Blatt 4.2-2002 history
2014VDI/VDE 3511 Blatt 4.2-2014 Temperature measurement in industry - Radiation thermometry - Maintenance and intended operation of radiation thermometers
2002VDI/VDE 3511 Blatt 4.2-2002 Temperature measurement in industry - Maintenance of the specification for radiation thermometers
2000VDI/VDE 3511 Blatt 4.2-2000 Technische Temperaturmessungen - Ergaenzungen - Erhaltung der Spezifikation von Strahlungsthermometern