Pressure transmitter with simplified pressure sensing head

Abstract

A differential pressure to electrical signal transmitter has a pair of flat barrier diaphragms and a central control diaphragm located between the barrier diaphragms. First chambers between one of the barrier diaphragms and the control diaphragm, and a first length of capillary tubing connected between the first chambers and one chamber of a remotely located sensor capsule, are filled with a first incompressible fill liquid. Second chambers between the other barrier diaphragm and the control diaphragm, and a second length of capillary tubing connected between the second chambers and another chamber of the sensor capsule, are filled with a second incompressible fill liquid. The fill liquids are made to pump up their respective flat barrier diaphragms to cause the latter to have a dome shape and hence to be free from 'oil canning.' A chamber on the outside of one barrier diaphragm is pressurized with a first fluid, and a chamber on the outside of the other barrier diaphragm is pressurized with a second fluid. The pressures of the two fill liquids act on the opposite sides of a minute displacement sensing element, located between the two sensor chambers, to displace the element and cause it to produce an electrical output signal which is dependent upon the difference between the fill liquid pressures, and hence upon the difference between the pressures of the first and second fluids.