5.3 Introduction to signal processing
Signal processing is concerned with improving the quality of the reading
or signal at the output of a measurement system, and one particular aim is to
attenuate any noise in the measurement signal that has not been eliminated by
careful design of the measurement system as discussed above. However, signal
processing performs many other functions apart from dealing with noise, and the
exact procedures that are applied depend on the nature of the raw output signal
from a measurement transducer. Procedures of signal filtering, signal
amplification, signal attenuation, signal linearization and bias removal are
applied according to the form of correction required in the raw signal.
Traditionally, signal processing has been carried out by analogue
techniques in the past, using various types of electronic circuit. However, the
ready availability of digital computers in recent years has meant that signal
processing has increasingly been carried out digitally, using software modules
to condition the input measurement data.
Digital signal processing is inherently more accurate than analogue
techniques, but this advantage is greatly reduced in the case of measurements
coming from analogue sensors and transducers, because an analogue-to-digital
conversion stage is necessary before the digital processing can be applied,
thereby introducing conversion errors. Also, analogue processing remains the
faster of the two alternatives in spite of recent advances in the speed of
digital signal processing. Hence, both analogue and digital processing are
considered in this chapter, with analogue processing being considered first
because some preliminary analogue processing is often carried out even when the
major part of the processing is carried out digitally.
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