Systems for acoustic velocity logging of earth formations

Claim 1

IN A SYSTEM FOR MEASURING THE ACOUSTIC VELOCITY OF EARTH FORMATIONS ADJACENT A BOREHOLE, THE COMBINATION OF AN ACOUSTIC PULSE TRANSMITTER MOVABLY POSITIONED IN SAID BOREHOLE FOR GENERATING AND TRANSMITTING TO SAID FORMATIONS A TRAIN OF ACOUSTIC PULSES AND FOR CONCURRENTLY GENERATING A TRAIN OF SYNCHRONIZING PULSES, A GENERATOR FOR PRODUCING A SIGNAL OUTPUT WAVEFORM THE AMPLITUDE OF WHICH VARIES MONOTONICALLY AS A FUNCTION OF TIME FOR A PREDETERMINED TIME INTERVAL, MEANS CONNECTED TO RECEIVE SAID SYNCHRONIZING PULSES AND FOR INITIATING GENERATION OF SAID WAVEFORM RESPONSIVE TO EACH SAID SYNCHRONIZING PULSE, FIRST, SECOND AND THIRD ACOUSTIC ENERGY RECEIVERS MOVABLY POSITIONED IN SAID BOREHOLE AND SPACED DIFFERENT FIXED DISTANCES LONGITUDINALLY OF THE BOREHOLE FROM EACH OTHER AND FROM SAID TRANSMITTER, FIRST, SECOND AND THIRD MEANS RESPECTIVELY ASSOCIATED WITH THE FIRST, SECOND AND THIRD RECEIVERS AND RESPONSIVE TO THE OUTPUT OF SAID GENERATOR AND EACH ACQUIRING AND STORING A SIGNAL LEVEL WHICH IS PROPORTIONAL TO THE INSTANTANEOUS MAGNITUDE OF SAID WAVEFORM AT THE OF ARRIVAL OF FIRST ACOUSTIC ENERGY AT THE ASSOCIATED RECEIVER, MEANS CONNECTING THE OUTPUT OF SAID GENERATOR TO ALL OF THE LAST NAMED MEANS, MEANS FOR CONNECTING THE FIRST, SECOND AND THIRD RECEIVER OUTPUTS TO SAID FIRST, SECOND AND THIRD MEANS, SIGNAL PRODUCING MEANS IN CIRCUIT WITH SAID FIRST, SECOND AND THIRD MEANS FOR GENERATING A PLURALITY OF DIFFERENCE SIGNAL LEVELS, EACH SAID DIFFERENCE SIGNAL LEVEL BEING PROPORTIONAL TO THE ALGEBRAIC SUM OF THE OUTPUT SIGNAL LEVELS OF A DIFFERENT PAIR OF SAID FIRST, SECOND AND THIRD MEANS, AND MEANS CONNECTED TO THE SIGNAL PRODUCING MEANS FOR RECORDING EACH OF SAID DIFFERENCE SIGNAL LEVELS AS A DUAL RECEIVER LOG, THEREBY TO PRODUCE A PLURALITY OF SUCH LOGS FOR COMPARISON.