Abstract: A system for automatically suppressing any ground noise present in the detection of periodic phenomena comprising detecting means for detecting the signal occurring just prior to the occurrence of the periodic phenomena, which signal is representative of ground noise, converting means for converting the sensed signal to a usable D.C. level signal, sampling means for sampling the signal resulting from the occurrence of the periodic phenomena, and summation means for algebraically adding the converted D.C. signal to the sampled signal for eliminating any ground noise present in the sampled signal, thereby providing an output signal representative of the periodic output phenomena free of any ground noise.

Abstract: A system is disclosed through which knocking in an internal combustion engine is quantitatively measured by detecting engine vibrations with an accelerometer, transmitting the accelerometer signal to an elaboration network including an amplifier and a filter, transmitting an ignition pulse to a control network, transmitting the output from the elaboration network through a gate only during coincidence of a signal from the control network, the output of the control network corresponding to the angle of revolution of the crankshaft during which knocking usually occurs, and detecting the output signal from the gate.