Data acquisition systems employing digital measuring and recording equipment are now being used in many scientific disciplines. To obtain maximum advantage from these systems it is essential to take into account considerations of the Sampling Theorem, the effects of a finite sampling aperture, and the various types of noise which can affect the signal being measured. This paper outlines these considerations and describes some of the digital techniques which have been used in practical systems e.g. cross-correlation methods such as digital synchronous rectification and computer averaging, photo-electron counting and multiplexing.
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