Patent ID: 6484585
Filing Date: 2002-11-26
Classification: G01L

Abstract:
A pressure transmitter in a process control system for transmitting pressure on a process control loop, the transmitter comprising:a transmitter housing; an isolation diaphragm configured to couple to a process fluid; a pressure sensor body of a brittle material operably coupled to the housing and positioned in the housing, the pressure sensor comprising a first portion bonded to a second portion by a fusion bond, the fusion bond substantially free of foreign material, the pressure sensor body including a cavity formed between the first and second portions, the cavity having at least one dimension which changes in response to applied pressure thereby causing a change in the capacitance; first and second capacitive plates coupled to an interior wall of the cavity having a capacitance formed therebetween, the plates configured whereby a spacing between the plates changes as a function of the at least one dimension which changes in response to applied pressure; first and second electrical conductors extending from an exterior of pressure sensor body and electrically coupled to respective first and second capacitive plates; isolation fluid configured to fluidically couple the pressure sensor body to the isolation diaphragm to thereby couple the pressure sensor to a pressure of the process fluid; measurement circuitry in the transmitter housing coupled to the capacitance through at least one electrical conductor and having an output which is a function of capacitance; a loop interface in the transmitter housing coupled to the measurement circuitry configured to transmit a pressure related signal on the process control loop as a function of the capacitance.