Abstract: A method and apparatus is presented for measuring the azimuth angle of a borehole being drilled, the data for determining the azimuth angle being obtained while the drillstring is rotating.

Abstract: A method is presented, for use in borehole drilling, for correcting errors in azimuth determination resulting from variations in the earth's magnetic field to which a measuring instrument is exposed. The method distinguishes between variations in the earth's magnetic field caused by the drillstring and variation caused by external sources, and the method corrects only for errors caused by the drillstring. If the error is caused by the drillstring, an azimuth correction is made based on dip angle data, thereby reducing errors caused by scale factor variations since dip angle is a ratio quantity of magnetic field components.

Abstract: A system for measuring the displacement of a workpiece from a reference coordinate system. Position information with respect to the various axes of the coordinate system is acquired by rotary resolver assemblies that measure the angular position of rotatable elements. Each resolver assembly includes a coarse and a fine resolver. Signals representative of the SIN and COS of the angles of the coarse and fine resolvers for each rotor assembly (or referred to as a channel) are applied to a multiplexer. The multiplexer sequentially selects the appropriate channel and the signals are then converted into angular information for each channel. An accurate count of the number of revolutions of the rotatable elements is then obtained. Offset error correction may be provided for each channel. The number of counted revolutions, corrected for offset error, may be multiplied by a scaler for conversion into a linear displacement.