Servomechanism control system

Claim 1

IN AN ELECTRICAL LOGGING SYSTEM, THE COMBINATION OF AN ELECTRODE ARRAY COMPRISING A CENTRAL CURRENT EMITTING ELECTRODE, TWO PAIRS OF LONGITUDINALLY SPACED APART POTENTIAL PICKUP ELECTRODES DISPOSED SYMMETRICALLY ABOVE AND BELOW SAID CENTRAL ELECTRODE, THE INNER PICKUP ELECTRODES BEING ELECTRICALLY CONNECTED AND THE OUTER PICKUP ELECTRODES BEING ELECTRICALLY CONNECTED, AND TWO ELECTRICALLY CONNECTED AUXILIARY CURRENT EMITTING ELECTRODES PLACED SYMMETRICALLY ABOVE AND BELOW SAID CENTRAL ELECTRODE AND OUTSIDE OF SAID PICKUP ELECTRODES, A SOURCE OF ELECTRICAL ENERGY CONNECTED TO SAID CENTRAL CURRENT EMITTING ELECTRODE AND TO A RELATIVELY REMOTE REFERENCE POINT, AN ADJUSTABLE SOURCE OF ELECTRICAL ENERGY CONNECTED TO SAID AUXILITARY CURRENT ELECTRODES AND TO A RELATIVELY REMOTE REFERENCE POINT, SERVOMOTOR MEANS FOR CONTROLLING THE ADJUSTMENT OF SAID ADJUSTABLE SOURCE, SERVOAMPLIFIER MEANS RESPONSIVE TO THE POTENTIAL DIFFERENCES BETWEEN THE ELECTRICALLY CONNECTED PICKUP ELECTRODES COMPRISING SAID TWO PAIRS FOR ENERGIZING SAID AUXILIARY CURRENT ELECCURRENT TO BE EMITTED FROM SAID AUXILIARY CURRENT ELECTRODES TO REDUCE SAID POTENTIAL DIFFERENCES SUBSTANTIALLY TO ZERO, AND MEANS FOR PROVIDING INDICATIONS OF POTENTIAL DIFFERENCE BETWEEN A POINT INTERMEDIATE THE TWO ELECTRODES COMPRISING ONE OF SAID PAIRS OF PICKUP ELECTRODES AND A RELATIVELY REMOTE REFERENCE POINT.