Method and apparatus for maintaining phase relation

Claim 1

APPARATUS FOR MAINTAINING A CONSANT PHASE RELATIONSHIP BETWEEN A SERIES OF SEISMIC WAVE OUTPUT SIGNALS GENERATED IN THE EARTH BY A SEISMIC TRANSDUCER IN RESPONSE TO A SERIES OF REFERENCE SWEEP SIGNALS, THE APPARATUS COMPRISING: MEANS FOR GENERATING THE SERIES OF REFERENCE SWEEP SIGNALS; PHASE SHIFT CIRCUIT MEANS OPERATIVELY CONNECTED TO THE MEANS FOR GENERATING THE SERIES OF REFERENCE SWEEP SIGNALS AND TO THE SEISMIC TRANSDUCER FOR IDUCING A PHASE LAG IN THE REFERENCE SWEEP SIGNALS PROPORTIONAL TO THE MAGNITUDE OF A PHASE SHIFT SIGNAL APPLIED TO THE PHASE SHIFT CIRCUIT MEANS AND APPLYING THE REFERENCE SWEEP SIGNALS TO THE SEISMIC TRANSDUCER TO PRODUCE THE SEISMIC WAVE OUTPUT SIGNALS; FEEDBACK CIRCUIT MEANS FOR PRODUCING AN OUTPUT FEEDBACK SIGNAL IN A PREDETERMINED, CONSANT PHASE RELATIONSHIP WITH THE SEISMIC OUTPUT SIGNAL; MULTIPLIER MEANS OPERATIVELY CONNECTED TO THE FEEDBACK CIRCUIT MEANS AND TO THE MEANS FOR GENERATING THE SERIES OF REFERENCE SWEEP SIGNALS FOR MULTIPLYING THE REFERENCE SIGNAL AND THE OUTPUT FEEDBACK SIGNAL TO PRODUCE AN ERROR SIGNAL WHEN THE TWO SIGNALS ARE OTHER THAN 90 DEGREES OUT-OF-PHASE; INTEGRATOR MEANS OPERATIVELY CONNECTED TO THE MULTIPLIER MEANS AND TO THE PHASE SHIFT CIRCUIT M EANS FOR INTEGRATING THE ERROR SIGNAL OVER A TIME PERIOD AND PRODUCING A PHASE SHIFT SIGNAL EQUAL TO THE INTEGRAL SUM OF THE ERROR SIGNAL PLUS A PREDETERMINED VALUE AND APPLYING THE PHASE SHIFT SIGNAL TO THE PHASE SHIFT CIRCUIT MEANS FOR INDUCING A PHASE LAG IN THE REFERENCE SWEEP SIGNAL; AND, INTEGRATOR RESET CIRCUIT MEANS OPERATIVELY CONNECTED TO THE MEANS FOR GENERATING THE SERIES OF REFERENCE SWEEP SIGNALS AND TO THE INTEGRATOR MERANS FOR RESETTING THE PHASE SHIFT SIGNAL FROM THE INTEGRATOR MEANS AT THE PREDETERMINED VALUE PREPARATORY TO EACH REFERENCE SWEEP SIGNAL, WHEREBY THE OUTPUT FEEDBACK SIGNAL WILL CONSTANTLY LAG THE REFERENCE SWEEP SIGNAL BY $/2+N$ DEGREES WHERE N IS AN INTEGER DEPENDING UPON THE PREDETERMINED VALUE OF THE PHASE SHIFT SIGNAL.