ABSTRACT
Process control is the method by which a particular process variable, for example temperature, is maintained at a level determined by such factors as product quality and production rate. It is an area which has seen enormous change in the last forty years with mechanical and pneumatic controllers being challenged first by electronic and then by microprocessor control. Manual control, with its attendant problems of inconsistency and poor product quality becomes increasingly uncommon and results improve as control is further removed from the operator. The attempting a review of a very broad field we have necessarily had to be both selective and superficial. The range of process variables with which the control engineer may become involved is extensive. Temperature, pressure, flow, humidity, fluid level, acidity (pH) is some of these variables, and each area has sub-divisions. Flow control involves, amongst others, orifice plates, venturis, turbines and Vortex meters.
