Calibration World Issue 1-2007 - Beamex - #10

Calibrating weighing insbume

From the point of view of the owner, weighing instruments, usually called scales or balances, should provide the correct weighing results. How the weighing instrument is used and how reliable the weighing results are can be very different. Using weighing instruments for legal purposes must have legal verification.

If a weighing instrument is used in a quality system, the user must define the measurement capability of it. In any case, it is the owner or the user of the instrument that carries the final responsibility of measurement capability and who is also responsible for the processes involved. (S)He must select the weighing instrument and maintenance procedure to be used to reach the required measurement capability.

From a regulatory point of view, the quality of a weighing instrument is already defined in OIML regulations, at least in Europe. Calibration is a means for the user to obtain evidence of the quality of weighing results, and the user must have the knowledge to apply the information achieved through calibration.

Calibration and legal verification

Weighing instruments may also possess special features. One of these features includes making measurements for which legal verification is required, for example when invoicing is based on the weight of a solid material. The features may vary slightly from country to country, but in the EU they are the same, at least at the stage when the weighing instrument is being introduced into use.

Verification and calibration abide by a different philosophy. Calibration depicts the deviation between indication and reference (standard) including tolerance, whereas verification depicts the maximum permissible amount of errors of the indication. This is a feasible practice for all weighing. The practical work for both methods is very similar and both methods can be used to confirm measurement capability, as long as legal verification is not needed.

The terminology and practices used previously for verifying measurement capability, and for weighing technology in general, are based on these practices of calibrating and verifying, even if it was a question of general weighing (non­legal).

Confirmation is the collecting of information

Confirming the capability of weighing

CALIBRATION WORLD 01- 2007 www.beamex.com/calibrationworld