Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2001-08-23
2004-02-03
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S718000, C073S715000, C073S700000, C361S283100, C361S283200, C361S283300, C361S283400
Reexamination Certificate
active
06684711
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related generally to industrial process control transmitters, and particularly to a sensor excitation circuit for use in such transmitters.
BACKGROUND OF THE INVENTION
Industrial process control transmitters are used to measure process variables in field locations and provide standardized transmission signals as a function of the measured variable. The term “process variable” refers to a physical or chemical state of matter or conversion of energy, such as pressure, temperature, flow, conductivity, pH, and other properties. Process control transmitters are often operated in hazardous field environments to measure these variables and are connected by two-wire communication lines to a central or control station.
One such transmitter is described in U.S. application Ser. No. 09/312,411 filed May 14, 1999 by Roger L. Frick and David A. Broden for “Pressure Sensor for a Pressure Transmitter”, and assigned to the same assignee as the present invention. The Frick et al. transmitter employs a capacitive sensor having a deflectable sensing diaphragm and three or more capacitor electrodes forming separate capacitors with the diaphragm. Two of the capacitors are primary sensing capacitors that are arranged differentially so that the capacitances of the primary sensing capacitors change oppositely in proportion to the process variable. The third (and fourth, if used) capacitor is a compensation capacitor that provides signals representing certain offset errors associated with one or both of the primary sensing capacitors.
The Frick et al. transmitter includes a sigma-delta converter that acts as a capacitance-to-digital converter. An excitation circuit provides a charge packet to the capacitors of the sensor, which are charged by an amount based on the capacitance value of the capacitor. The charge is transferred to an integrator/amplifier of the sigma-delta converter to derive a signal representative of sensor capacitance. The signal is processed and a standardized transmission signal is transmitted to the central control station via the two-wire communication lines.
The excitation circuit of the Frick et al. application is operated such that each capacitor is charged by a charging voltage during a first phase and the charge is transferred to the integrator/amplifier during a second phase. The sensing capacitors and compensation capacitors are charged by the same charging voltage, necessitating the use of an inverting amplifier to invert one of the charges so that it may be subtracted from the other charge. The inverting amplifier introduces noise into the signal and consumes power.
SUMMARY OF THE INVENTION
The present invention is directed to a technique permitting the sensing and compensation capacitors to be charged oppositely so the need for a separate inverting amplifier is eliminated.
In accordance with the present invention, an industrial process control transmitter has a capacitive sensor with at least one sensing capacitor and at least one compensation capacitor. The sensing capacitor is charged with a first polarity during a first phase and the charge on the sensing capacitor is pumped to a sigma-delta capacitance-to-digital circuit during a second phase, mutually distinct from the first phase. The compensation capacitor is charged with a second polarity during the second phase and the charge on the second capacitor is pumped to the sigma-delta capacitance-to-digital circuit during a third phase.
In one form of the invention, the capacitive sensor includes a second sensing capacitor that is charged during the third phase.
A switch circuit selectively couples the sensing capacitors to a charging circuit to charge the sensor capacitors, and selectively couples the sensing capacitors to the sigma-delta circuit. The charge transferred is based on the charging level to the respective capacitor. A transmitter output circuit receives a digital output from the sigma-delta circuit and generates a standardized transmitter output for coupling to a remote receiver.
REFERENCES:
patent: 3701280 (1972-10-01), Stroman
patent: 3968694 (1976-07-01), Clark
patent: 4120206 (1978-10-01), Rud, Jr.
patent: 4125027 (1978-11-01), Clark
patent: 4238825 (1980-12-01), Geery
patent: 4250490 (1981-02-01), Dahlke
patent: 4287501 (1981-09-01), Tominaga et al.
patent: 4414634 (1983-11-01), Louis et al.
patent: 4419898 (1983-12-01), Zanker et al.
patent: 4446730 (1984-05-01), Smith
patent: 4455875 (1984-06-01), Guimard et al.
patent: 4485673 (1984-12-01), Stern
patent: 4528855 (1985-07-01), Singh
patent: 4562744 (1986-01-01), Hall et al.
patent: 4598381 (1986-07-01), Cucci
patent: 4602344 (1986-07-01), Ferretti et al.
patent: D287827 (1987-01-01), Broden
patent: 4644797 (1987-02-01), Ichikawa et al.
patent: 4653330 (1987-03-01), Hedtke
patent: 4677841 (1987-07-01), Kennedy
patent: 4745810 (1988-05-01), Pierce et al.
patent: D296995 (1988-08-01), Lee
patent: D297314 (1988-08-01), Hedtke
patent: D297315 (1988-08-01), Pierce et al.
patent: 4783659 (1988-11-01), Frick
patent: 4791352 (1988-12-01), Frick et al.
patent: 4798089 (1989-01-01), Frick et al.
patent: 4818994 (1989-04-01), Orth et al.
patent: 4825704 (1989-05-01), Aoshima et al.
patent: 4833922 (1989-05-01), Frick et al.
patent: 4850227 (1989-07-01), Luettgen et al.
patent: 4866989 (1989-09-01), Lawless
patent: 4881412 (1989-11-01), Northedge
patent: 4930353 (1990-06-01), Kato et al.
patent: 4958938 (1990-09-01), Schwartz et al.
patent: 4970898 (1990-11-01), Walish et al.
patent: 4980675 (1990-12-01), Meisenheimer, Jr.
patent: 5000047 (1991-03-01), Kato et al.
patent: D317266 (1991-06-01), Broden et al.
patent: D317269 (1991-06-01), Selg
patent: D318432 (1991-07-01), Broden et al.
patent: 5028746 (1991-07-01), Petrich
patent: 5035140 (1991-07-01), Daniels et al.
patent: 5058437 (1991-10-01), Chaumont et al.
patent: 5060108 (1991-10-01), Baker et al.
patent: 5070732 (1991-12-01), Duncan et al.
patent: 5083091 (1992-01-01), Frick et al.
patent: 5087871 (1992-02-01), Losel
patent: 5094109 (1992-03-01), Dean et al.
patent: D329619 (1992-09-01), Cartwright
patent: 5142914 (1992-09-01), Kusakabe et al.
patent: 5157972 (1992-10-01), Broden et al.
patent: 5162725 (1992-11-01), Hodson et al.
patent: 5187474 (1993-02-01), Kielb et al.
patent: 5227782 (1993-07-01), Nelson
patent: 5236202 (1993-08-01), Krouth et al.
patent: 5245333 (1993-09-01), Anderson et al.
patent: 5248167 (1993-09-01), Petrich et al.
patent: D342456 (1993-12-01), Miller et al.
patent: 5287746 (1994-02-01), Broden
patent: 5353200 (1994-10-01), Bodin et al.
patent: 5369386 (1994-11-01), Alden et al.
patent: 5377547 (1995-01-01), Kusakabe et al.
patent: 5381355 (1995-01-01), Birangi et al.
patent: D358784 (1995-05-01), Templin, Jr. et al.
patent: 5436824 (1995-07-01), Royner et al.
patent: 5448180 (1995-09-01), Kienzler et al.
patent: 5469150 (1995-11-01), Sitte
patent: 5471885 (1995-12-01), Wagner
patent: D366000 (1996-01-01), Karas et al.
patent: D366218 (1996-01-01), Price et al.
patent: 5495768 (1996-03-01), Louwagie et al.
patent: 5498079 (1996-03-01), Price
patent: 5524333 (1996-06-01), Hogue et al.
patent: 5524492 (1996-06-01), Frick et al.
patent: 5546804 (1996-08-01), Johnson et al.
patent: 5600782 (1997-02-01), Thomson
patent: 5606513 (1997-02-01), Louwagie et al.
patent: 5656782 (1997-08-01), Powell, II et al.
patent: 5665899 (1997-09-01), Willcox
patent: 5668322 (1997-09-01), Broden
patent: 5670722 (1997-09-01), Moser et al.
patent: 5710552 (1998-01-01), McCoy et al.
patent: 5754596 (1998-05-01), Bischoff et al.
patent: 5764928 (1998-06-01), Lanctot
patent: 5823228 (1998-10-01), Chou
patent: 5870695 (1999-02-01), Brown et al.
patent: 5899962 (1999-05-01), Louwagie et al.
patent: 5920016 (1999-07-01), Broden
patent: 5948988 (1999-09-01), Bodin
patent: 5954526 (1999-09-01), Smith
patent: 5955684 (1999-09-01), Gravel et al.
patent: 5973942 (1999-10-01), Nelson et al.
patent: 5988206 (1999-11-01), Bare et al.
patent: 6005500 (1999-12-01), Gaboury et al.
patent: 6006338 (1999-12-01), Longsdorf et al.
patent: 6038927 (2000-03-01), Karas
patent
Jenkins Jermaine L
Lefkowitz Edward
Rosemount Inc.
Westman Champlin & Kelly
LandOfFree
Three-phase excitation circuit for compensated capacitor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Three-phase excitation circuit for compensated capacitor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Three-phase excitation circuit for compensated capacitor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3348701