Abstract

Pressure measurement spans the range from 1,380 MPa (200,000 psig) and higher to , ie, extreme ultrahigh vacuum. Pressure, particularly where it is monitored as opposed to being controlled, is generally measured by mechanical elements. Mechanical pressure gauges are reliable and inexpensive. They dominate process applications in older plants, and the sensing elements for many of the sophisticated electronic transmitters contain simple mechanical elements. The shift away from mechanical sensors to electronic sensors in the chemical process industries is a result of the superior accuracy and reliability of electronic instrumentation. Piezoelectric pressure elements, reluctive pressure transducers, strain gauges, piezoresistive sensors, and capacitive pressure transducers, the principal types of electronic sensors, are described herein. Conventional sensor technology is acceptable for pressure measurement in the low vacuum region, but esoteric technologies developed specifically for high vacuum, eg capacitance manometers, thermal conductivity gauges, and hot and cold cathode ionization gauges, are required for lower pressures. Smart pressure transmitters are revolutionizing industry's approach to pressure measurement. The rationale for replacing conventional transmitters with smart transmitters is discussed herein.