17 May How accurate should my scale be?
A measuring instrument must comply with the requirements of the Metrology Act (“be calibrated”) and be suitable for its intended purpose. Accuracy is one of the factors that play a role in this.
From the regulations, it can be deduced that the error in measuring the quantity of a product must not exceed 1/5 of the maximum allowable error of the nominal quantity.
Based on this, the following relationship between the nominal quantity and the verification unit (e) of scales was established in 1980:
| nominal quantity of the prepackaging | verification unit (e) of the scale |
| 5 g or ml or higher | 0,1 g or smaller |
| 15 g or ml or higher | 0,2 g or smaller |
| 35 g or ml or higher | 0,5 g or smaller |
| 125 g or ml or higher | 1,0 g or smaller |
| 350 g or ml or higher | 2,0 g or smaller |
| 1.750 g or ml or higher | 5,0 g or smaller |
| 3.500 g or ml or higher | 10,0 g or smaller |
| 7.000 t/m 10.000 g or ml | 20,0 g or smaller |
This means that the indication of a scale with a verification unit of 1g can be accepted without further correction for nominal quantities starting from 125g. It also means that a scale with a larger verification unit can be used if the measurement result is corrected.
Other aspects that fall under “suitable for the intended purpose” include:
Regular calibration Method of recording measurement results (if the scale has that capability) Reject mechanism or other means to distinguish rejected prepackagings from approved ones (in the case of checkweighers) Guarantee that all dosed product goes into the packaging and that the machine stops if no combination can be made (in the case of multiheads) Correct functioning of software calculations used by the packager for assessing the acceptance or rejection of batches with prepackagings, and correct functioning of algorithms that control the acceptance or rejection of individual prepackagings.