Contactless measurement of external ignition engine revolution rate - using coils detecting ignition coil magnetic field outside car

摘要

A contactless revolution rate measurement arrangement for vehicle external ignition combustion engines enables simple high precision measurements to be made at a point remote from the vehicle body. This enables final assembly checks to be made quickly as required in a factory. An electrical signal is induced in a measurement coil (3,4) by the magnetic field set up by the engine ignition coil. The signal is amplified in a noise-free amplifier (6,7) and fed to a low pass filter (8,9) passing an output signal frequency component proportional exclusively to the engine revolution rate. The low pass filter output is processed into a revolution rate signal by a correlating revolution rate counter (12). Two measurement coils (3,4) may be used, one either side of the car. In this case the two filter (8,9) outputs are added.