The level of performance achievable by an instrumentation scheme is limited by various factors. Noise is a primary factor. All round improvement in technology results in better levels of precision and repeatability of components used. To achieve compatible levels of system performance, more attention need to be paid to noise, its effects and ways and means of reducing them. This forms the subject matter of this chapter. In any instrumentation scheme, any voltage or current that contaminates the main signals of interest, can be termed noise. The origin of noise can be due to factors external to the instrumentation scheme as well as those internal to it. The external factors — barring lightning, background radiation etc., — are all of human origin. They are mostly periodic in nature. Their effects can be totally eliminated or substantially reduced by care in design and engineering. Unfortunately, the case with internal noise is different. Firstly, it is random in nature; only its distribution characteristics can be predicted and analysed. Secondly, it can neither be eliminated nor reduced substantially. Only its effects can be reduced by design.
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