The static characteristics of sensors

The selection of the most suitable instrument for a required measurement from a range of commercially available instruments necessitates the knowledge of certain important factors. These can be divided into the static and dynamic characteristics of the instrument. The dynamic properties of instruments are fundamentally no different from those of any other system or process and are described, therefore, by the analysis of system dynamics presented in Chapter 7. Static properties, which are specific to instrumentation, are discussed in this section. 

There is a wide variety of important static terms and properties related to instrumentation which require careful definition and understanding. Some of these are frequently used in a misleading or even incorrect context. Expressions such as the accuracy of an instrument or its precision or its sensitivity are often employed by manufacturers in a casual or imprecise manner. A brief description of the more common terms follows. 

The range of an instrument is the region over which a quantity may be measured or received (input range) or transmitted (output range) and is defined by stating the 

This is often termed the full scale deflection (FSD) and is the magnitude of the range of the instrument. In the above example, the input span of the thermocouple is 150°C and the output span is 6 mV. 

This is defined as the minimum difference in the values of a quantity that can be discriminated by a device. In essence this is the largest change in input that can 

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