Development of stepwise tolerances for efficient verification of automatic checkweigher

Abstract

The aim of this study is to calculate the risks of automatic checkweigher verification according to the specifications of the international recommendation OIML R51 developed by the International Organization of Legal Metrology (OIML) and to propose an alternative method for performing the verification efficiently.The risks posed by the OIML R51 method to the consumer and producer are calculated using the Monte Carlo method. The OIML R51 method was used to develop an alternative method with improved efficiency and almost equivalent risks. The alternative method involves calculating the sample mean and standard deviation of the error and makes acceptance/rejection decisions after weighing every 10 times. The tolerances of the alternative method are stepwise with the upper and lower limits. After weighing every 10 times, the sample mean and standard deviation were calculated, and if they were both less than the lower tolerance limit, the test was completed and a pass decision was made. Conversely, when the mean or standard deviation exceeded the upper tolerance limit, the test was completed and a failed decision was made.The Monte Carlo method was used to calculate the risks and a reduction in the required number of weighings by the alternative method.The alternative method was applied to an actual instrument to evaluate the efficiency of the method. For the instrument used in this study, the expected value of the required number of weighings is 20 in the weighing range of 400 g or more and one-third of the number stipulated in the international recommendation. This means that significant labor savings are possible.