Rapid Processing Of Far Fieldeddy Current Testing Method And Circuit Design

The underground casing damage detection is always a focus in the field of oil well logging.But the current commonly used logging instruments can not detect the condition of casing’ outer wall but only the inner wall due to the overseas technology monopoly.In the "development of the multi-frequency eddy current detector of casing damage" project,this thesis has designed a far-field eddy current detection system which can be used to detect the inner and outer wall damage simultaneously.This instrument can work in a complex environment for a long period of time,and it has pretty good detection efficiency and precision.The thesis has analyzed the principle and phenomenon of far field eddy current detection,and the changes of the electromagnetic signal in the propagation.The relationship between the far field electromagnetic signal and the casing damage in the detection has been figured out.Then the thesis aims to calculate the phase difference of the detection signal quickly.And the effect of the instrument parameter on detection results also has been discussed.To accomplish the aim,three kinds of method to calculate phase difference of the detection signal have been discussed,and the thesis has improved disadvantages of the zero-crossing detection method.In the circuit system design of the thesis,the excitation signal circuit is responsible for generating initial signal.And the high voltage is controlled into drive coil to produce the far field eddy current signal by the initial signal.The signal processing circuit aims to improve the detecting signals that have carried the casing damage information.And finally the phase difference of the detection signal relatively to the reference signal is accomplished.Then in the thesis,the far field eddy current detection system has been tested in several ways.Test and analyze the signals in the circuit system,the statue of instrument in the high temperature environment,and the detection results of experimental casing pipes.The multi-frequency eddy current detector of casing damage is proved to accomplish the casing damage detection aim by these test reports,and the measurement method of signals’ phase and the circuit system are verified at the same time.