The online analyzer is becoming more prevalent. This trend is stimulated by the technological advances and corre sponding price reductions for analyzers and by the growing insistence on real-time analysis for processors (Procyk 1991).

For batch processing, analyzers that do not require elaborate sampling systems or the constant attention of a maintenance crew are recommended. Analyzers for pH, conductivity, and resistance generally meet those criteria. However, if measuring color, moisture, spectroscopic properties, or the presence of ions is necessary, the analyzer is more likely to require a sampling system with some stream conditioning, such as filtering to remove suspended particles.

Some or all of these analyzers may be needed in any typical processing step. However, many process industries need a special analyzer. For example, the fermentation batches in pharmaceutical or other plants using biotechnology must monitor the oxygen content and cell density and growth. In many cases, analyzers for qualitative properties do not exist, and a plant must try to correlate those properties with ones that can be measured using DCS.

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