Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/562664
AGGREGATES MANAGER September 2015 28 However, it is important to understand that this initial calibration does not come with a guarantee of continued accuracy. Calibration can never be guaranteed, because ac- curacy is highly dependent on the way a scale is used and maintained. Weather, use, and wear are just a few of the factors that can change the accuracy of a weighing device. That is why periodic calibration is so essential. Test fre- quency depends on a variety of factors, including: • Number of weighments per day, • Price of the product being weighed, • Number of days the scale is used annually, and • Acceptable error rate. What's the potential loss from a poorly calibrated scale? Seemingly minimal errors can substantially cut into profits over time. Take the Acme Aggregate Co. example shown in Figure 1, in which 200 pounds may appear miniscule, since a typical truckload of sand or gravel can exceed 80,000 pounds. However, when one does the math, the truth is revealed — an annual revenue variance of about $345,000. Figure 1. Acme Aggregate Co. Weighing volume 500 trucks per day Weighing frequency Five days per week Five days per week $26.50 per ton Scale inaccuracy -200 pounds Lost annual revenue $344,500 Five components of a good scale maintenance program 1. Use a state-licensed service provider. It is important to understand that the state weights and measures organiza- tion is the only entity that can issue a scale certification. A commercial scale company cannot certify a scale — but it does have the authority to recalibrate and reinstate an in- accurate scale that has been "tagged-out" by the state, as long as the scale company is state-licensed and registered in good standing. (Tagged-out means the scale has failed a state weights and measures accuracy test, so the state has attached a lockout tag to the scale, rendering it unusable for commercial trade.) So make sure the commercial scale company shows you its valid license. 2. Conduct calibration using state-certified test weights. Calibration must be completed using state-certified test EQUIPMENT MANAGEMENT Initial calibration of a scale is not a guarantee of continued accuracy. How a scale is used and maintained affect its accuracy.