Instrumentation for non-contact I.C. engine test and monitoring
Steve Hadden, L. R. Hulls, E. M. Sutphin · 1976
Instrumentation has been developed for obtaining engine speed and diagnostic information for a diesel engine without mechanical or electrical connections to the engine. This non-contact technique has the potential for making diesel engine power measurement and fault diagnosis extremely simple and rapid. The method employs a single transducer held near the engine and special purpose circuitry which extracts the engine speed information from the signal and performs spectral analysis for diagnostic purposes.