TABLE OF CONTENTS Pressure instruments are used to determine the pressure in a vessel and sometimes the level of a vessel. It is necessary to measure pressure for safety reasons, such as over-pressuring a vessel or controlling the pressure of a vessel. Pressure instruments can also be used to measure flow, such as a differential pressure transmitter across an orifice. Pressure instruments can also measure vacuum. The pressures may be calibrated in gage or absolute pressure.
Flow instruments may be the differential pressure instrument across an orifice or one of the more sophisticated mass flowmeters, magnetic flowmeters, turbine flowmeters, vortex meters, or many other types.
Also explained in this chapter are level transmitters. Some level transmitters use the pressure method; others use the capacitance and electromechanical methods.
