Demodulation of instantaneous rotational speed of diesel engine based on Hilbert transform

To measure diesel engine rotational speed, special 84-teethed wheel is fixed across the engine output shaft, and magnetoelectric transducer mounted above the wheel. The induced electromotive force between the tooth and the sensor is measured, whose frequency characteristics contains the engine speed information. Engine instantaneous speed is extracted by counting process method and Hilbert demodulation method respectively, and their differences are analyzed. Taking no tooth wheel indexing mismachining tolerance into consideration, the time resolution from the counting process mainly lies on the teeth number. While the number is limited, the result cannot be satisfactory. And its amplitude error can be guaranteed within need only by greater sampling frequency. Comparatively, time resolution of the engine instantaneous speed from the Hilbert methods depends on the sampling frequency, so it is relatively fine. And its error mainly results from the signal processing, avoiding high sampling frequency demand.