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A methodology has been developed for in situ diagnostic testing of dc-actuated solenoid-operated valves (SOVs) by analysis of the characteristics of the transient current waveform accompanying valve actuation. This waveform, which is used to identify abnormal operation, is obtained inductively by a small split-core current transformer clamped around one of the valve`s solenoid leads. The digitized waveforms are subsequently compared with similar waveforms obtained when the valve was known to be operating normally, and the results used to detect faulty valve operation. This methodology is noninvasive because direct access to the SOV is not required; also, the current transformer has negligible effect on the solenoid current and does not require the lifting of any electrical leads. Analysis is performed by first extracting various waveform features. A subset of these features is examined by diagnostic algorithms, tuned to identify faults for that valve type, that compare the features with those obtained from a previously acquired waveform for the particular valve under examination. Two methods of analysis have been examined. One utilizes fuzzy logic in an expert system diagnostic. The other performs pattern recognition using an artificial neural network approach. The overall analysis is robust in that it can deal with minor deviations of the waveform shape experienced during repeated operation of a normal valve while successfully identifying abnormal valve operation. In the present application, analysis has been specialized to SOVs used on space-based systems; however, the methodology has sufficient flexibility to be applicable to a wide variety of valves and other industrial electrically controlled components

Noninvasive testing of solenoid-operated valves using transient current signature analysis