US3698508A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Phase control of servo hydraulic vibrators
Assignee: BP America Production Co
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Filing: 1970-12-28
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Granted: 1972-10-17
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Expires: 1990-12-28
Abstract
Abstract In seismic geophysical surveying using a servo-controlled vibrator as the energy source for transmitting a predetermined varying-frequency seismic wave train into the earth, groundcoupling distortion and vibrator inefficiency at low frequencies cause loss of phase lock so that the vibrator no longer follows the reference or pilot signal. This problem is solved by interposing a filter with a varying frequency cutoff that passes the varying reference frequency in the feedback from the vibrator base plate, but rejects the distorting harmonic frequencies. The reference signal can be transmitted from a remote recording point, but preferably it is generated from a stored program or from frequency-change data at the vibrator vehicle, triggered from the remote recording point.
Inventors
- 👤 Ralph A Landrum Jr
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 08:19
CPC Classifications
G; G01; G01V; G01V1/00; G01V1/02; G01V1/04
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
193 words
In a system for maintaining substantially constant the phase relation between varying-frequency seismic signals induced in the earth by a servo-hydraulic vibrator and a reference signal controlling said vibrator, wherein a feedback signal representing said induced signals is phase-compared with said reference signal in a phase-comparing means which produces an error signal, and said error signal is used to produce a compensating phase shift of said reference signal tending to minimize the amplitude of said error signal, said feedback signal being amplified to a substantially constant level before passing to said phasecomparing means, the improvement comprisiNg passing said feedback signal through a first variable-pass filter prior to amplifying it to said substantially constant level, passing said reference signal through a second variable-pass filter substantially matching said first filter prior to entering said phase-comparing means, and, during the time of inducing said varying-frequency signals in the earth, varying the pass of said filters to pass said reference signal and maintain filter cut-off between the instantaneous frequency of said reference signal and the harmonics of said instantaneous frequency, whereby substantially only the fundamental frequency component of said reference signal is amplified to said constant level.
Claim 2
Dependent Claim
193 words
In a system for maintaining substantially constant the phase relation between varying-frequency seismic signals induced in the earth by a servo-hydraulic vibrator and a reference signal controlling said vibrator, wherein a feedback signal representing said induced signals is phase-compared with said reference signal in a phase-comparing means which produces an error signal, and said error signal is used to produce a compensating phase shift of said reference signal tending to minimize the amplitude of said error signal, said feedback signal being amplified to a substantially constant level before passing to said phasecomparing means, the improvement comprisiNg passing said feedback signal through a first variable-pass filter prior to amplifying it to said substantially constant level, passing said reference signal through a second variable-pass filter substantially matching said first filter prior to entering said phase-comparing means, and, during the time of inducing said varying-frequency signals in the earth, varying the pass of said filters to pass said reference signal and maintain filter cut-off between the instantaneous frequency of said reference signal and the harmonics of said instantaneous frequency, whereby substantially only the fundamental frequency component of said reference signal is amplified to said constant level.
Claim 3
Dependent Claim
39 words
In a system as in claim 1, the improvement as in claim 1 including the further step of varying the time constant of said constant-level amplification in proportion to the period of said instantaneous frequency of said reference signal.
Claim 4
Dependent Claim
82 words
In a system as in claim 1, the improvement as in claim 1 including the further steps of summing digital values representing an initial frequency and a series of subsequent frequency changes per digital time unit to obtain a series of first sums representing instantaneous frequencies, summing successive values of said first sum to obtain a second digital value representing phase angle, and applying said second digital value as input to a sine-function generator to obtain said reference signal as an output.
Claim 5
Dependent Claim
41 words
In a system as in claim 1, the improvement as in claim 3 including the further steps of converting said series of first sums to a proportional direct-current voltage, and applying said voltage to said filters to vary the pass thereof.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-17 | 1976-04-17 | 1976-10-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-17 | 1980-04-17 | 1980-10-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-17 | 1984-04-17 | 1984-10-17 | $7700.00 | Window Closed / Lapsed |