CROSSCOUPLING COMPUTER

• US 3,610,900 A
• Filed: 11/24/1969
• Issued: 10/05/1971
• Est. Priority Date: 11/24/1969
• Status: Expired due to Term

• Current Assignee: Manik Talwani
• Original Assignee: Manik Talwani
• Inventors: Talwani, Manik
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Wise, Edward J.
• Application Number:
  US04/879,469
• Time in Patent Office: 680 Days
• Field of Search: 73/382 235/150.26,150.27,151.3 346/8
• US Class Current: 702/93
• CPC Class Codes: G01V 7/16 specially adapted for use on moving platforms, e.g. ship, aircraft
• CPC Class Codes: G06G 7/48 Analogue computers for specific processes, systems or devices, e.g. simulators
• CPC Class Codes: G06G 7/78 for direction-finding, locating, distance or velocity measuring, or navigation systems

Abstract

A crosscoupling computer is disclosed which generates a signal that is subtracted from the output of a highly damped beam gravimeter to eliminate the crosscoupling acceleration errors introduced into the gravity measuring system by horizontal forces acting on the beam. In gravity measurements made at sea, these forces are produced by the motion of the ship in which the gravimeter is mounted.

Claims

1. Apparatus for computing crosscoupling errors introduced into the measurement of local gravitational fields by a beam gravimeter and for eliminating these errors from the gravity measurement, comprising;

means for generating a signal having an amplitude proportional to accelerations to which said beam is subjected which are collinear with the longitudinal axis of said beam;

means for multiplying said signal with a signal having an amplitude proportional to the angular orientation of said beam relative to a reference position;

means having a transfer function corresponding to the mechanical damping function of said gravimeter for filtering the signal resulting from said multiplication; and

means for subtracting said filtered signal from the signal generated by said gravimeter so as to produce a signal proportional only to said local gravitational field, whereby crosscoupling errors in the signal generated by said gravimeter are automatically eliminated from the gravity measurement.

2. Apparatus for computing crosscoupling errors introduced into the measurement of local gravitational fields at sea by a beam gravimeter and for eliminating these errors from the gravity measurement, comprising:

means for measuring the beam deflection angle of said gravimeter and for generating a first signal whose amplitude is proportional to said deflection angle;

means for generating a second signal having an amplitude proportional to accelerations collinear with the longitudinal axis of said beam to which the beam of said gravimeter is subjected;

means for multiplying said first and second signals together to produce a crosscoupling error signal;

means having a transfer function corresponding to the mechanical damping function of said gravimeter for filtering said crosscoupling error signal; and

means for subtracting said filtered signal from said first signal so as to produce a signal proportional only to said local gravitational field, whereby crosscoupling errors in said first signal thereafter are automatically computed and eliminated from the gravity measurement.

3. The apparatus as recited in claim 2 wherein the high-frequency components of said first signal are attenuated immediately prior to multiplication with said second signal.

4. The apparatus as recited in claim 3 wherein said means for multiplying includes an analog multiplier requiring positive and negative representations of the two signals to be multiplied and wherein the high-frequency components of said first signal are attenuated by a high filter which generates positive and negative signals for use with said analog multiplier corresponding to positive and negative representations of said beam deflection absent any long term of DC components, said high-pass filter comprising:

a reference potential;

a first operational amplifier coupled to said first signal at a first input having a second input coupled to said reference potential, said amplifier having a high-pass filter in its feedback circuit, thereby coupling only high frequency signals back to said first input in phase with said first signal, the output of said first operational amplifier providing a positive representation of said beam deflection angle;

means for inverting the output of said first operational amplifier to provide a negative representation of said beam deflection angle; and

means for coupling low frequency components of said inverted signal to said first input such that said low frequency components are subtracted from the input signal to said first operational amplifier, causing said amplifier to amplify only high frequency components of said input signal, said last-mentioned means comprising a second operational amplifier having its output coupled to said first input having high-pass filter in the feedback path between its output and the input thereto for coupling only high frequency signals from its output to its input, and means for connecting the input to said second operational amplifier to said inverted signal, said means including a high-pass filter coupled between the input to said second operational amplifier and said reference potential for shunting the high frequency components of said inverted signal to said reference potential.

5. The apparatus as recited in claim 3 wherein said first signal and said filtered crosscoupling error signal are filtered by similar low-pass filters to remove signals associated with sea motions.

6. Apparatus for eliminating crosscoupling error from the output signal of a beam gravimeter introduced by the motion of a seagoing vessel within which said gravimeter is mounted, comprising means for producing from the output signal of said gravimeter an amplified signal whose magnitude is proportional to the angular position of the beam of said gravimeter;

means for filtering high-frequency components from said amplified signal so as to remove any component due to heave of the vessel and produce a first signal representing the local gravitational filed and including acceleration due to crosscoupling;

means for filtering low-frequency components from said first signal and for producing second and third signals corresponding, respectively, to the positive and negative components of the filtered positioned of said beam;

means for generating fourth and fifth signals corresponding, respectively, to the positive and negative components of the horizontal acceleration to which said beam may be subjected in a direction colinear with the longitudinal axis of said beam;

means for multiplying said second, third, fourth and fifth signals together so as to obtain an analog signal;

means having a transfer function equal to the mechanical damping function of said gravimeter for filtering said analog signal so as to produce a sixth signal;

means having the same filter characteristic as the means which filters high-frequency components from said amplified signal for filtering said sixth signal so as to produce a seventh signal; and

means for subtracting said seventh signal from said first signal so as to develop an output signal corresponding to the gravitational acceleration unaffected by any crosscoupling error.