Instrumentation is needed in process plants to obtain data that are essential to perform several activities. Among the most important are control, the assessment of the quality of products, production accounting and the detection of failures related to safety. In addition, certain parameters that cannot be measured directly, such as heat exchanger fouling or column efficiencies, are of interest. Finally, new techniques, such as on-line optimization, require the construction of reliable computer models for which the estimation of process parameters is essential.
There are different types of instrumentation used in process plants. They are flow rate, level, temperature, pressure, density, concentration, pH measurements instruments. It is also customary to include valves as part of instrumentation.
Reference: Miguel J. Bagajewicz, Process Plant Instrumentation: Design and Upgrade, Technomic Publishing Company (2001)

Management/Process Safety Information and Knowledge