Borehole logging apparatus for deep well drillings with a device for transmitting borehole measurement data

A borehole logging apparatus for deep well drillings, with a device for transmitting measured data obtained while drilling from a borehole through the drilling fluid to the earth's surface, with an elongated housing adapted for insertion in a drill string, a hydromechanical signal transmitter arranged in the housing and comprising a stator which is fixed to the housing and has at least one passage through which drilling fluid is routed from a side located upstream from the stator to a side located downstream from the stator, and a rotor mounted adjacent to the stator inside the housing for rotation about its longitudinal axis, said rotor having at least one continuous opening corresponding with the passage in the stator and being constructed to rotate either into a passing position in which the drilling fluid is allowed to pass through the passage and the opening aligned with it or into a throttling position in which a closed portion of the rotor throttles at least part of the flow through the passage in the stator, and a motor adapted to move the rotor repeatedly, in controlled intervals in response to signals indicative of the measured data to be transmitted, from the passing position into the throttling position and back into the passing position in order to generate in the drilling fluid a coded series of positive pressure pulses corresponding to the signals, characterized in that the housing has at its influx end a central inlet channel with an inlet opening and is sealed relative to the drill string by a sealing ring downstream from the inlet opening, that a feed pipe open at both ends with an outer diameter smaller than the inner diameter of the inlet channel is arranged to extend inside the inlet channel in the longitudinal direction of the inlet channel so that the current passing through it reaches the signal transmitter, that a bypass ring limiting the free annular cross section between the wall of the inlet channel and the feed pipe is arranged inside the inlet channel, and that downstream from the bypass ring the inlet channel has radial outlet openings through which a bypass current circulating around the feed pipe is routed out of the inlet channel into the drill string.