METHOD AND APPARATUS FOR
AUTOMATIC OFFSET COMPENSATION IN
 Inventors: Eugene R. Jornod, Caledonia; James G. Mueller; Matthew S. Solar, both of Rockford, all of 111.
 Assignee: Barber-Colman Company, Rockford, 111.
 Appl. No.: 892,131
 Filed: Jul. 30, 1986
 Int. CI.* G01C 25/00; G01N 7/00;
 U.S. a 364/571.03; 364/558;
73/4 R; 73/765; 73/861.01
 Field of Search 364/178, 179, 550, 551,
364/558, 571, 573, 509; 73/1 R, 3, 4 R, 708, 765, 766, 861.01, 861.02, 861.03
 References Cited
U.S. PATENT DOCUMENTS
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4,384,925 5/1983 Stetter et al 73/1 G X
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Application Note TN-001, dated Mar. 1985, published by IC Sensors, Inc.
Application Note TN-002, dated Mar. 1985, published by IC Sensors, Inc.
An articles by Jim McDermott entitled "Silicon Fabri-
cation Techniques Extend Sensor Ranges and Designs",
appearing at pp. 106-113 of EDN, Dec. 27, 1984.
A product known as DATA PRO (a multiple channel
data logger) marketed about 1980 by Barber-Colman
Company and described in an unpublished Engineering
Report dated Apr. 30, 1980. The Report is submitted as
describing what was physically in the product which is
acknowledged to be in prior art, but the Report itself is
not admitted as constituting prior art.
Primary Examiner—Parshotam S. Lall
Assistant Examiner—Joseph L. Dixon
Attorney, Agent, or Firm—Leydig, Voit & Mayer, Ltd.
Methods and apparatus by which a transducer is employed to create a digital signal representing numerically the value of a changeable physical parameter. The signal from the transducer is subject to large and unpredictable amounts of offset due to either or both (i) manufacturing tolerance departures from the desired target of creating a zero output signal value when the sensed parameter is zero and (ii) changes in offset due to changes in one or more physical conditions (other than the sensed parameter) to which the transducer and its associated electrical components are subjected. A bistate device is associated with the transducer and controlled so as (a) to first apply substitutionally to the transducer a known, and preferably zero, value of the parameter—with the output signal value being stored so as to represent the then-existing offset, and then (b) to apply the changeable physical parameter to the transducer. The stored value of the transducer output signal is, in effect, subtracted from the output signal obtained in the second instance, to produce an accurate final signal numerically representing the existing actual value of the sensed parameter. A programmed microcomputer is preferably employed to carry out the necessary steps in the sequence, and apparatus of that character is described.
13 Claims, 6 Drawing Sheets