Chapter 2 – Instrument Types and Performance Characteristics

The chapter first compares active/passive, null/deflection, analog/digital, indicating/signal output types, smart/non-smart instruments and considers how the differences affect their typical usage. Following this, the various static characteristics of instruments are discussed. These define the quality of measurements when an instrument output has settled to a steady reading and include parameters like accuracy (measurement uncertainty), precision (repeatability), range (span), linearity, measurement sensitivity, resolution, threshold, sensitivity drift, zero drift (bias), hysteresis, and dead-space. Some important lessons arise out of this coverage such as that high precision does not necessarily mean high accuracy. The final topic covered in the chapter is then the dynamic characteristics of instruments. These define the behavior of an instrument before its output reading settles to a steady value which takes one of three forms, zero-order, first-order or second-order. The typical characteristics of each type are examined, and discussion follows about the effect that the dynamic characteristics have on the applicability of various types of instrument in different applications.