A Practical Guide to Adjusting Calibration Intervals

Abstract

It is the role of management to decide what method to use for adjusting calibration intervals. There are many methods and theories to calculate calibration intervals, such as those found in NCSL RP-1, Method S1 (Classical Method), Method S2 (Binomial Method), and Method S3 (Renewal time Method). As a result, it is very difficult to pick the right method to determine the interval. What is needed is the process that can help management decide the best method. To make the right decision, they need the right information. Why do we need to perform calibration on a regular basis? We calibrate to control uncertainty growth and reduce the risk of substandard performance of measuring and test equipment (MTE) during use. Over a period of time, the error probability starts to increase on MTE. The purpose of a calibration interval is not to prevent out-of-tolerances from occurring. It is to ensure we have an acceptable in-tolerance probability between calibrations. What is an acceptable in-tolerance probability? How do we determine in-tolerance probability targets for use in the calibration interval analysis? The optimal calibration interval is the one that not only saves management money and promotes cost effectiveness but can also help management maintain uncertainties at an acceptable level. This paper develops a simple process for the company to select the most appropriate method to adjust the calibration intervals.