Engine rotational speed measurement system.

摘要

A speed measurement system for an engine includes a magnetic pick-up (10) positioned adjacent an engine-driven gear (12) having a substantial number of teeth so that the pick-up produces a number of speed pulses per revolution of the gear. These pulses are shaped into square waves by a signal conditioning circuit (14) and the square waves applied to a synchronizing circuit (16) which responds to the trailing edge of each square wave to produce a triggering pulse, with each triggering pulse supplied to a tooth counter (18). A high speed clock is connected to a second counter (20) which is reset with each triggering pulse. A sampling signal (IT) which controls the flow of tooth counts to the tooth counter (18) is produced in an associated control system, said sampling signal being not coordinated with the speed pulse but being longer in duration than any of the speed pulses. Memory circuits (34,36) associated with the second counter (20) retain the high speed counts measuring the intervals (Ti-1) and (Ti) between a triggering pulse and the beginning of a sampling signal (IT) and between the end of the sampling signal (IT) and the triggering pulse immediately preceding, respectively. Another counter (42) counts the high speed counts occurring during the sampling signal period. These counts are combined to provide a high speed count of a new measuring interval T = IT (Ti - Ti-1) exactly related to the speed pulse count and which is combined with the speed pulse count (TCT) to provide a digital signal which accurately represents a desired function of engine rotational speed.