Method and apparatus for correcting drift in the response of analog receiver components in induction well logging instruments

摘要

A method of determining amplitude and phase response of a receiver amplifier in an induction well logging instrument including the steps of generating an oscillating current at least one frequency, energizing a transmitter coil instrument with the oscillating current, generating a first test signal having a known phase and amplitude relationship with respect to the oscillating current and a different frequency than any frequency in the oscillating current, amplifying and detecting voltages induced in a receiver coil corresponding to electrical properties of an earth formation, conducting a portion of the first test signal to the receiver amplifier causing the amplifier to generate a combined output including the first test signal and a signal resulting from the induced voltages, combining the oscillating current with the first test signal to form a combined test/reference signal, spectrally analyzing the combined test/reference signal and spectrally analyzing the combined output, and comparing spectral analysis of the combined test/reference to spectral analysis of the combined output to determine the phase and amplitude response of the receiver amplifier at the frequency of the test signal. In a preferred embodiment, the method includes linear scaling of the response of the amplifier at the test signal frequency to derive the amplifier response at other frequencies in the voltages induced in the receiver coil corresponding to the electrical properties of the earth formation.