Seismic vibrator phase detector

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,

• improved phase-comparing means comprising:
• delay means for receiving said reference signal and providing an output signal having a 90.degree. phase shift relative to said reference,
• a first multiplier having inputs for receiving said reference signal and said feedback signal and an output for providing a signal proportional to the product of said reference signal and said feedback signal,
• a second multiplier having inputs for receiving the output of said delay means and said feedback signal and an output for providing a signal proportional to the product of said delay means output signal and said feedback signal,
• first and second integrators coupled to said first and second multiplier outputs, respectively, and to said reference signal for integrating the output signals of said multipliers during one full cycle of the reference signal, said integrators having outputs for providing signals proportional to the integrals of said multiplier output signals, and
• a divider coupled to said first and second integrator outputs and to said reference signal for providing an output proportional to the quotient of the integrals after one full cycle of reference signal.

In a system for maintaining a substantially constant-phase relation between varying frequency seismic signals induced in the earth by a servo-hydraulic vibrator and a reference signal controlling said vibrator, wherein said reference signal is a sequence of digital words which are coupled to the vibrator through a digital phase shifter, a feedback signal representing said induced signals is digitized to provide a feedback word for each reference word, a sequence of said reference and feedback words are coupled to a phase-comparing means which produces an error signal and said error signal is coupled to the phase shifter to produce a compensating phase shift of the reference signal tending to minimize the amplitude of the error signal, improved phase-comparing means comprising:

• digital delay means having an input for receiving said reference signal and an output for providing the same sequence of digital words as said reference signal, delayed by one-fourth of the period of one full cycle of reference signal,
• a first digital multiplier having a first input for receiving said reference signal digital words and a second input for receiving said digitized feedback words, and an output for providing the digital product of each pair of input words,
• a second digital multiplier having a first input for receiving digital words from said delay means and a second input for receiving said reference signal digital words and an output for providing the digital product of each pair of input words,
• first and second digital adders, each having an input coupled to said first and second multiplier outputs, respectively, for sequentially adding each product generated by said multipliers for one full cycle of said reference signal, and
• a divider coupled to said first and second adders for providing an output equal to the quotient of the sums generated by said adders over one full cycle of reference signal.