Errors during the measurement process

This chapter discusses the various errors in measurement systems that can be divided into those that arise during the measurement process, and those that arise due to later corruption of the measurement signal by induced noise during the transfer of the signal from the point of measurement to some other point. It is extremely important in any measurement system to reduce errors to the minimum possible level and then to quantify the maximum remaining error that may exist in any instrument output reading. Systematic errors in the output of many instruments are due to factors inherent in the manufacture of the instrument, arising out of tolerances in the components of the instrument. The prerequisite for the reduction of systematic errors is a complete analysis of the measurement system that identifies all sources of an error. Once all practical steps have been taken to eliminate or reduce the magnitude of systematic errors, the final action required is to estimate the maximum remaining error that may exist in a measurement due to systematic errors. Random errors in measurements are caused by unpredictable variations in the measurement system. Errors in measurement systems often arise from two or more different sources, and these must be aggregated in the correct way to obtain a prediction of the total likely error in output readings. The final case to be covered is where the final measurement is calculated from several measurements that are combined together in a way that involves more than one type of arithmetic operation.