Calibration of measuring sensors and instruments

This chapter discusses that calibration consists of comparing the output of the instrument or sensor under test against the output of an instrument of known accuracy, when the same input is applied to both instruments. Calibration ensures that the measuring accuracy of all instruments and sensors used in a measurement system is known over the whole measurement range, provided the calibrated instruments and sensors are used in environmental conditions that are the same as those under which they were calibrated. Susceptibility to the various factors that can cause changes in instrument characteristics varies according to the type of instrument involved. Any instrument that is used as a standard in calibration procedures must be kept solely for calibration duties and must never be used for other purposes. To ensure that these conditions are met, the calibration function must be managed and executed in a professional manner. As far as management of calibration procedures is concerned, it is important that the performance of all calibration operations is assigned as the clear responsibility of just one person. The calibration facilities provided within the instrumentation department of a company provide the first link in the calibration chain. An essential element in the maintenance of measurement systems and the operation of calibration procedures is the provision of full documentation. An overriding constraint on the style in which the documentation is presented is that it should be simple and easy to read. This is often greatly facilitated by a copious use of appendices.