[li] Patent Number: 4,986,121  Date of Patent: Jan. 22, 1991
 APPARATUS FOR MEASURING THE VERTICAL MOTION OF A FLOATING PLATFORM
 Inventor: John Luscombe, Oxford, England
 Assignee: Technical Survey Services Ltd., Bicester, England
 Appl. No.: 406,312
 Filed: Sep. 12, 1989
 Int. a.5 G01C 21/16; GO IP 15/00
 U.S. a 73/170 A; 73/178 R
 Field of Search 73/170 A, 178 R
 References Cited
U.S. PATENT DOCUMENTS
3,840,726 10/1974 Harrison 73/178 R
4,038,527 7/1977 Brodie 244/3.2
4,515,013 5/1985 Hue 73/170 A
FOREIGN PATENT DOCUMENTS
0106777 4/1984 European Pat. Off. .
0411124 5/1934 United Kingdom .
0518546 3/1940 United Kingdom .
1307310 2/1973 United Kingdom .
1548794 9/1979 United Kingdom .
Primary Examiner—Donald O. Woodiel
Attorney, Agent, or Firm—Marjama & Pincelli
An apparatus and method for measuring the vertical motion of a floating platform e.g. a survey vessel, caused by wave action. The apparatus includes a sensor having three accelerometers (11,12,13) arranged on mutually perpendicular axes (Ax,Ay,Az) so that one accelerometer acts in a vertical plane and the other two act in a horizontal plane. Output signals (S1,S2,S3) from the accelerometers are continually sampled through a multiplexer (14) and are passed through an ADC (19) and a shift register (21) to provide output signals for a data processor (D) which provides a signal A indicative of the vertical position of the platform. In the method, the accelerometer output signals (S1,S2,S3) are corrected for offsets by use of a reference signal (So) and the corrected signals are used to derive the signal (A) which may be double integrated to obtain the final signal (A3) relating to vertical displacement.
13 Claims, 3 Drawing Sheets