System and method for digitally transmitting well logging information

Abstract

A data transmission system, for a well logging system having a logging tool logging a borehole traversing an earth formation and surface equipment adjacent to the borehole for making a well log, includes a sync word generator located in the logging tool, which periodically provides a predetermined digital signal corresponding to at least one sync word. A phase encoder located in the logging tool receives the data in serial digital form and the sync word. The phase encoder provides a phase encoded signal, corresponding to the data and to the sync word, at a predetermined frequency. A cable drive receives the phase encoded signal and provides it to a cable for transmissin up-hole. The surface equipment includes a phase decoder connected to the cable for decoding the phase coded signal to provide at a serial digital signal. An output circuit at the surface provides parallel digital signals in accordance with the serial digital signal corresponding to the sync words and the data.