COST EFFECTIVE MASS STANDARD CALIBRATION INTERVALS

National Institute of Standards and Technology (NIST) traceable standard weights serve as the foundation of mass measurement control programs. These standards are normally recalibrated annually at a cost of approximately $100 per weight. The Savannah River Site (SRS) has more than 4,000 standard weights. Most have recalibration intervals of 1 year. The cost effectiveness of the current practice was questioned. Are these mass standards being calibrated too often, and are all of these standards needed for calibration and QC activities? Statistical analyses of data from the calibration histories were performed on a random sample of eight weight sets. The analyses indicated no time effects or significant trends in the weight masses for periods of from 5 to 8 years. In other words, calibration Table 1: WEIGHT SET: WL-1017 checks were being performed too frequently. Also, current electronic balance technology does not require the traditional weights that cover a balance's entire weighing range. At the most, only 2 or 3 standards are needed for most weighing systems. Hence, by increasing weight set recalibration frequencies from 1 to 3 years, and by reducing the number standards calibrated by 80%, annual cost savings of over $400,000 are attainable at SRS. Details of the data analysis, technological advances, and cost savings are included in the paper.