Abstract: A telemetry system employs a periodic pseudorandom training sequence to effectively initialize an adaptive digital FIR filter-equalizer for optimal communications between a surface modem and downhole measuring equipment, without requiring any changes to the normal logging configuration or any special operator intervention. In a "training mode", an electronic source in a downhole sonde transmits a predetermined training sequence to a surface modem via a cable. The source preferably transmits the training sequence continuously until the surface modem has acclimated itself to the characteristics of the multiconductor cable by adaptively configuring the filter-equalizer, thereby enabling the surface modem to accurately interpret data received from the sonde despite attenuation, noise, or other distortion on the cable. The filter-equalizer adjusts itself in response to an error signal generated by comparing the filter-equalizer's output with a similar training sequence provided by a training generator.

Abstract: In a well logging tool forming a data stream for telemetry to the surface, an encoding system is located downhole cooperative with surface located decoding equipment. The encoder converts serial data into NRZ symbols, then duobinary code of seven levels and then into quadrature modulating signals on a complex carrier. The decoder at the well surface receives the quadrature modulated complex carrier, forms inphase and quadrature components and decodes the two components. The decoder includes circuit means removing the intersignal distortion and also intersymbol smearing. This enables very significant telemetry ratio.

Abstract: The operation of hostile environment logging tools at temperatures up to 250.degree. C. stresses not only the tools, it also places severe demands upon the wireline telemetry due to the wide variations in the logging cable transmission characteristics. A robust adaptive wireline telemetry system for use in hostile environments has been developed that combines sophisticated digital communication methods with modern Digital-Signal-Processing (DSP) techniques. The downhole telemetry transmitter outputs a multilevel signal. The uphole receiver includes an adaptive transversal-filter equalizer (TFE) that is continually optimized to correct for changing signal distortion. The system operates robustly at high data rates over the temperature range of 0.degree. to 250.degree. C.

Abstract: A magnetic mark on a cable is subject to loss of intensity. The present disclosure provides for remarking. It utilizes a detector which responds to passage of a magnetic mark on the cable. A coil for remarking is located at a specified and measured distance from the detector. Through the use of measuring wheels in contact with the cable providing data to a computer, the cable traverses from the detector to the marking coil, and a marker control circuit is timely operated to place a new mark on the cable. The new mark is placed coincident over the prior mark and has greater intensity to renew the magnetic marks on the cable.

Abstract: A stretch corrected wireline depth measuring system is set forth including method and apparatus. It forms a log quality indication which indicates those occasions where the tool velocity is outside acceptable limits. The apparatus utilizes calibrated encoder wheels, preferably a redundant and duplicate pair, to form pulse trains indicative of surface wireline velocity. Additional measurements are made of wireline tension, and magnetic marks on the wireline are observed. All of this data is input to a CPU which determines the raw depth, and adjusts this value with depth corrections. The device calculates wireline stretch as a function of tension and total wireline in the borehole. This enables formation of output data as a function of depth including cable tension, tool speed, depth correction and log quality in the event that tool velocity is outside an acceptable range.

Abstract: The present disclosure is directed to an improved telemetry system and data recovery telemetry receiver apparatus for installation with a logging cable supported sonde. In the sonde, a data stream is modulated onto a carrier after conversion by an encoder. Encoding involves conversion from a stream of binary data into four state symbols which are then encoded into seven duobinary levels. The availability of redundant levels permits correlation between encoded symbols and adjacent symbols. This is transmitted up the monocable to the surface and is recovered. The recovery involves amplification by an automatic gain control amplifier, conversion from an analog to digital form in an ADC, demodulation and reconstruction of the transmitted signal by means of a adaptive transversal filter equalizer featuring fractionally spaced sampling. Reconstructed output levels are then provided, and a slicer adjusts those values to the permitted seven levels. The data is then decoded.