Method and apparatus for measuring time elapsed between events

Abstract

An apparatus and a method for determining the time difference between electrical events utilizes a sinusoidal signal as a reference from which to determine the elapsed time between events represented as electrical pulses. A sine wave and a cosine wave are multiplexed to produce the sinusoidal reference signal. When an event occurs, as indicated by an electrical pulse, the sine wave and the cosine wave are sampled to produce two digital values. A comparator determines which of the two digital values falls within a predetermined range, and transmits a select signal to multiplexer. The multiplexer selects the digital value which falls within the predetermined range. The selected digital value corresponds to an angle value which can be uniquely determined within one cycle of the sinusoidal reference signal. A cycle counter accounts for the number of full cycles which elapse until the next event is detected. The digital information for each event, including the angular position of each event within a cycle of the reference signal, and the number of cycles between events, is stored within a random access memory (RAM) and transmitted to a computer. The time difference between events is then advantageously calculated in real time within the computer using the known frequency of the effective reference signal.