Borehole surveying apparatus

Claim 1

Borehole survey apparatus comprising: a non-magnetic housing adapted for disposition in a borehole; a digital magnetic compass disposed within said housing and operative to provide a digital output signal representative of the azimuth orientation of said housing; wherein said digital magnetic compass includes: a normally stationary disk optically coded with a plurality of concentric tracks each having a different number of alternately light responsive and non-responsive segments representing respective bits of a multi-bit code; a compass magnet affixed to and rotatable with said disk; means for mounting said disk and magnet for rotation about a normally vertical axis to permit alignment of the magnet with the earth's magnetic field to provide a relative angular position of said disk indicative of compass heading; means for illuminating the coded tracks of said disk; and photosensor means including a photosensor array having a plurality of photosensitive elements each in alignment with a respective coded track and operative to receive light from the coded tracks of said disk and to provide in response thereto a plurality of digital signals corresponding to a multi-bit code representing the relative angular position of said disk with respect to said photosensor means; at least one digital inclinometer disposed in said housing and operative to provide a digital output signal representative of the inclination of said housing with respect to a predetermined vertical plane; wherein said at least one digital inclinometer includes: a normally stationary disk optically coded with a plurality of concentric tracks each having a different number of alternately light responsive and non-responsive segments representing respective bits of a multi-bit code; means for mounting said disk for rotation about a normally horizontal axis; a weight disposed at the lower portion of said inclinometer disk to define a normal position when said housing is vertically aligned; means for illuminating the coded tracks of said inclinometer disk; and second photosensor means including a photosensor array having a plurality of photosensitive elements each in alignment with a respective coded track and operative to receive light from the coded tracks of said inclinometer disk and to provide in response thereto a plurality of digital signals corresponding to a multi-bit code representing the relative angular position of said inclinometer disk with respect to said second photosensor means; and means disposed in said housing and operative to convey the digital output signals from said digital magnetic compass and from said at least one digital inclinometer to the surface of a borehole.