Abstract: A method and apparatus for autocalibrating the transfer function of a digital induction logging tool is disclosed. A plurality of test calibration signals of differing amplitudes are generated and periodically substituted for the normal formation signals. An expression for the transfer function of the tool using standard circuit analysis is obtained for the tool. From the tool output measurements taken for the various test calibration inputs, a linearization correction function is obtained for the tool transfer function as the tool is being used in normal logging operations.

Abstract: A floating point analog-to-digital converter for use in a digital induction logging tool is disclosed. Floating point samples of phase quadrature components of the receiver signal are obtained. Each sample contains a digital word representing the exponent of a floating point number and digital word representing its magnitude. A voltage-to-frequency converter produces an output frequency proportional to the magnitude of the component signal. The resulting frequency signal is counted over a predetermined time inverval. At the completion of each time interval, the count is shifted until a predetermined magnitude is reached. The number of shift pulses required to reach this magnitude represents the exponent. The resulting shifted count represents its magnitude.