Bore hole logging apparatus of the focussed current type for providing a pulse spacemodulated record

Claim 1

BORE HOLE LOGGING APPARATUS COMPRISING A HOUSING ADAPTED TO BE MOVED LENGTHWISE IN A BORE HOLE, ELECTRODE MEANS SECURED TO SAID HOUSING TO BE LOWERED THEREWITH, MEANS PROVIDING A GROUND CONNECTION TO THE EARTH SURROUNDING THE HOLE BEING LOGGED, SAID ELECTRODE MEANS INCLUDING A POTENTIAL ELECTRODE AND A PAIR OF ELONGATED CURRENT ELECTRODES RESPECTIVELY ABOVE AND BELOW SAID POTENTIAL ELECTRODE AND SPACED THEREFROM, MEANS IN SAID HOUSING PROVIDING CURRENT TO THE EARTH THROUGH BOTH OF SAID CURRENT ELECTRODES IN PARALLEL AND SAID MEANS PROVIDING A GROUND CONNECTION, MEANS IN SAID HOUSING ADVANCING A RECORD MEMBER AT A REAT INDEPENDENT OF THE RATE OF MOVEMENT OF THE HOUSING IN A BORE HOLE, AND MEANS IN SAID HOUSING PICKING UP THE POTENTIAL OF SAID POTENTIAL ELECTRODE PRODUCED BY SAID CURRENT AND PROVIDING WITHIN SAID HOUSING A PULSE SPACE MODULATED RECORD OF SAID POTENTIAL ON SAID RECORD MEMBER, THE CYCLES OF WHICH RECORD HAVE A SUBSTANTIALLY CONSTANT LENGTH ALONG THE RECORD MEMBR.