On-line analyser systems are widely used in the Oil & Gas and (Petro) Chemical industry. They range from single component analysers like pH analysers to multi-component analysers like gaschromatographs and mass-spectrometers, from wet chemistry types to optical devices.

An on-line process analyser is generally a complex system if compared with other, more general purpose type of process instrumentation. It often needs an additional sample preparation – and sample disposal system, which in its own right might be complex. Hence, system design results often in a measurement system that is less stable than traditional process instruments thus needing more maintenance attention from better than average qualified maintenance staff.