At what interval should I calibrate my instruments? It's a question we're always asking ourselves, to make sure we're on the right track in terms of quality and even quantity.
In practice, however, the most frequently asked question is how to determine whether recalibration is required.
In general, the operator is responsible for determining calibration intervals. If internal specifications for recalibration are available, for example in the quality management manual, then these will be the official source for calibration schedules. For some applications, these specifications may also be present in general standards (e.g., ISO 376 for instrument strength, or certification of measurement vehicle exhaust emissions).
For measurements where the highest demands are placed on precisely known measurement properties, it should be noted that calibration cannot make valid statements at the time of implementation. Consequently, an extremely complicated process is required: calibration must be carried out both before and after each important measurement. Examples of such demanding applications are measurements as part of DAkkS accredited calibration of equipment, or measurements as part of certification.
If a pragmatic recommendation is followed in industrial practice, it is of course more sensible to allow a greater number of measurements or a specific time interval between two calibrations. If the deviations measured during a calibration from the previous calibration lie within the metrological requirements, the measurement results obtained with the measuring instrument are justifiable. If, however, the deviations are greater, then the question is whether measurements are only significant to a limited extent and should be repeated. The decision on the duration of a calibration interval must therefore take into account how high the costs are, on the one hand, for more frequent calibration (including lost time) and, on the other hand, for possibly worthless measurement results, repeat measurements, reminder actions, etc., and how much they are likely to cost.
