Well logging apparatus having detector means in a rotatable casing mounted within a drill string for simultaneous drilling and logging

Claim 1

IN WELL LOGGING APPARATUS COMPRISING THE COMBINATION OF AN ALTERNATING CURRENT GENERATOR INCLUDING A COMMUTATOR, A PAIR OF ELECTRODES, AND MEANS FOR COUPLING SAID ELECTRODES TO SAID GENERATOR, THE IMPROVEMENT WHEREIN AT LEAST ONE OF SAID ELECTRODES IS COUPLED TO SAID COMMUTATOR BY MEANS OF A COMMUTATOR BRUSH CONSISTING ESSENTIALLY OF 85-95 PERCENT SILVER AND 5-15 PERCENT COPPER, AND WHEREIN ONE OF SAID ELECTRODES IS A CONDUCTIVE HOUSING AND WHEREIN SAID COUPLING MEANS COMPRISES GROUND CONTACT MEANS FOR COUPLING SAID GENERATOR TO SAID CONDUCTIVE HOUSING, SAID GROUND CONTACT MEANS INCLUDING AN ADDITIONAL BRUCH MOUNTED IN FIXED RELATION TO SAID HOUSING AND ELECTRICALLY CONNECTED THERETO.