ABSTRACT
This chapter introduces the concepts of the Gauge and Absolute measurement scales of pressure, and some of the techniques of measuring these parameters. Pressure can be used inferentially to measure other variables such as flow and level. Pressure is intimately bound up with the parameter flow. The most common method of measuring pressure is the Bourdon tube. Spiral and helical Bourdon tubes provide the means of measuring low and high pressures. Spiral Bourdon tubes are used on relatively low pressures, while helical Bourdon tubes are used on high pressures, the selection being dictated by the opposing requirements of high deflection and thick walls. The chapter identifies the general required data relating to the containment of process fluids relevant to pressure conditions. In determining the liquid pressure or level in closed vessels with a single instrument, the choice is restricted to differential-pressure systems only.
