Transmission circuits for well logging systems

Claim 1

IN AN ACOUSTIC VELOCITY WELL LOGGING SYSTEM HAVING A DOWNHOLE TRANSMITTER AND FIRST AND SECOND DOWNHOLE RECEIVERS AND A TIME INTERVAL MEASURING MEANS UPHOLE FOR MEASURING THE TIME INTERVAL BETWEEN THE RECEIPT OF A TRANSMITTER-GENERATED ACOUSTIC PULSE BY THE FIRST RECEIVER AND THE RECEIPT OF THE SAME PULSE BY THE SECOND RECEIVER, AND IN WHICH THE TIME INTERVAL MEASURING MEANS INCLUDES MEANS RESPONSIVE TO SIGNALS FROM THE FIRST RECEIVER FOR STARTING THE MEASUREMENT OF THE TIME INTERVAL AND MEANS RESPONSIVE TO SIGNALS FROM THE SECOND RECEIVER FOR ENDING THE MEASUREMENT OF THE TIME INTERVAL, A TRANSMISSION LINE HAVING ONE END FOR ELECTRICAL CONNECTION TO THE MEASURING MEANS AND HAVING A DOWNHOLE END FOR ELECTRICAL CONNECTION TO THE RECEIVERS FOR TRANSMITTING TO THE MEASURING MEANS ELECTRIC SIGNALS FROM THE RECEIVERS PRODUCED IN RESPONSE TO THE ARRIVAL OF THE ACOUSTIC PULSE, A LIMITER CONNECTED IN CIRCUIT BETWEEN A FIRST OF THE RECEIVERS AND THE DOWNHOLE END OF SAID TRANSMISSION LINE FOR LIMITING THE MAGNITUDE OF THE SIGNAL APPLIED TO THE TRANSMISSION LINE BY THE FIRST RECEIVER, AN AMPLIFYING MEANS CONNECTED IN CIRCUIT BETWEEN THE SECOND RECEIVER AND THE DOWNHOLE END OF SAID TRANSMISSION LINE FOR INCREASING THE SIGNAL FROM THE SECOND RECEIVER TO A LEVEL SUBSTANTIALLY ABOVE THAT OF THE LIMITED LEVEL OF SIGNAL FROM THE FIRST RECEIVER, MEANS IN CIRCUIT BETWEEN SAID ONE END OF SAID TRANSMISSION LINE AND THE MEASURING MEANS FOR APPLYING FIRST RECEIVER SIGNALS TO THE STARTING MEANS, AND AN AMPLITUDE SELECTIVE MEANS UPHOLE IN CIRCUIT BETWEEN SAID ONE END OF SAID TRANSMISSION LINE AND THE MEASURING MEANS FOR BLOCKING THE FIRST-RECEIVER SIGNAL FROM AND FOR APPLYING THE SECONDRECEIVER SIGNAL TO THE MEASUREMENT ENDING MEANS OF THE MEASURING MEANS.