ABSTRACT
Data signals can be sub-divided into two classifications: deterministic and random. Such data come from real processes which may themselves be deterministic or random. There are many occasions when the data produced from some phenomenon is random. The most commonly used statistical parameter is the average or mean. For a time-dependent signal such calculations need to be taken over the cycle. When amplifying low-level signals, amplifiers having low noise levels in their input stages must be sought. Phase-sensitive detection is a generic technique that can be implemented in a number of forms. Phase-sensitive detectors can be built from discrete elements but it is usually more cost-effective to use commercially available systems, which are described as lock-in amplifiers. One powerful application of correlation is to the recovery of signal information using auto-correlation. Some sensors need to be driven by an a.c. supply or have an a.c. signal conditioning circuit.
