Capacitive pressure transmitter

• US 6,843,133 B2
• Filed: 05/15/2003
• Issued: 01/18/2005
• Est. Priority Date: 06/18/2002
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Broden, David A., Horky, David A.
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): ALLEN, ANDRE J
• Application Number:
  US10/438,446
• Publication Number:
  US 20040025594A1
• Time in Patent Office: 614 Days
• Field of Search: 737/18, 737/24, 361/283.1, 702/713.8
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A capacitive pressure transmitter is provided. In one aspect, the transmitter includes a capacitive pressure sensor coupled directly to the measured media without any intervening fluid isolation. A filter is preferably used to keep particulates from reaching the measuring diaphragm. In another aspect, a capacitive pressure transmitter is provided with at least one self-contained isolator interposed between a process connection and the capacitive pressure sensor. In both aspects, the capacitive pressure transmitter is relatively small and preferably constructed from materials that facilitate low-cost manufacture.

Claims

1. A capacitive pressure transmitter comprising:

a capacitive pressure sensor having a first and second sensor inlets, wherein each inlet is fluidically coupled to a side of a conductive deflectable measuring diaphragm;

a self-contained isolator having a process fluid inlet, and an isolator fluid outlet operably coupled to the first sensor inlet, the self-contained isolator also having an isolator diaphragm disposed to fluidically isolate the process fluid inlet from the isolator fluid outlet while providing a pressure at the isolator fluid outlet related to a pressure at the process fluid inlet;

a second transmitter inlet operably coupled to the second sensor inlet;

sensor circuitry coupled to the capacitive pressure sensor to generate a sensor signal based upon the capacitance of the capacitive pressure sensor; and

transmitter circuitry coupled to the sensor circuitry to transmit information relative to the sensor signal over a process communication loop.

2. The transmitter of claim 1, wherein:

the second transmitter inlet is part of a second self-contained isolator, the second self-contained isolator having an isolator fluid outlet operably coupled to the second sensor inlet, the self-contained isolator also having an isolator diaphragm disposed to fluidically isolate the second transmitter inlet from the isolator fluid outlet while providing a pressure at the isolator fluid outlet related to a pressure at the second transmitter inlet; and

wherein the second transmitter inlet is adapted to couple to a source of process media; and

wherein the sensor signal is indicative of differential pressure between the process media inlet and the second transmitter inlet.

3. The transmitter of claim 1, wherein the self-contained isolator includes a fill fluid.