For safety and quality-relevant measurement tasks, it is crucial that the measurement results are within the specified measurement uncertainty. In order to fulfil this fundamental requirement, it is necessary to regularly determine the measurement uncertainty, i.e. to calibrate the measuring equipment.

This raises the question for the user as to how often calibration should be carried out. In principle, measuring equipment for safety and quality-relevant measuring tasks should be procured with a calibration certificate. The first recalibration can be scheduled based on the manufacturer's recommendation (often 1 year).

For tough operating conditions:

• High operating hours
• Alternating load operation
• Extreme temperature conditions
• Dirt and moisture
• Frequent mounting and dismounting of the sensor

the initial interval should also be shortened in deviation from the manufacturer's recommendation (e.g. to ½ year). The subsequent calibration intervals can be set dynamically. For this purpose, the changes in the previous calibrations are evaluated. If the measured value is close to the uncertainty limit and the last change was so large that the measured value in the next interval is likely to run outside the specified uncertainty range, the interval should be shortened accordingly. If the measured value is stable and the changes are small compared to the specified uncertainty range, the interval can be extended accordingly.

DIN EN ISO 376 provides the following explanation:

Within the scope of this International Standard, the period of validity of the certificate shall not exceed 26 months. A force gauge must be recalibrated if it has been subjected to an overload greater than the test overload (see B.1) and after it has been repaired.

B.1 Overload test
An overload is applied to the force gauge four times in succession, which should be at least 8 % and at most 12 % greater than the maximum load. The overload lasts 1 min to 1.5 min. At least one overload test should be carried out by the manufacturer before the measuring device is released for calibration or use.