| abstract |
An embodiment of the invention transmits signals from a borehole logging sonde through an armored cable to the earth''s surface. In order to transmit different logging information signals through the cable, a time division multiplexing system is used. Individual time slots in a repeated sequence are each allocated to respective information signals. Although an information pulse will not appear in each of these time slots, one time slot is set aside for a sync pulse that does recur in each sequence. On the earth''s surface, a demultiplexing circuit synchronizes itself with the downhole multiplexer through the assumption that any first-received pulse is the sync pulse. In response to this pulse, the demultiplexer segregates and distributes the succeeding time slot information in accordance with a predetermined program. The demultiplexer, on termination of the first sequence, once more reproduces the signal distribution cycle in response to the very next-received pulse. Because the sync pulse is the only pulse that is certain to occur in every sequence, the demultiplexer quickly locks into phase with the downhole multiplexer. |