Apparatus and method for measuring the frequency of a pulse signal

Abstract

An apparatus for measuring the frequency of a pulse train signal and method therefor applicable to a speedometer of a vehicle are disclosed in which a count value C of at least one counter which counts number of pulses in the pulse train signal for predetermined counting intervals of time .DELTA.T (=T/n, wherein T denotes a frequency measuring time interval and n denotes a calculation constant) is updated to a value related to the count value for each predetermined counting interval of time .DELTA.T and stored and outputted for each predetermined counting interval of time .DELTA.T so that the same or better performance as that using a stagger ring method can be achieved. The value is expressed by (C-C/.alpha.) in a first preferred embodiment (wherein .alpha. denotes the calculation constant preferably equal to n), by (C-C.times.m/.alpha.+D) in a second preferred embodiment (wherein m denotes the number of counters and D denotes the latest count values of the m counters during .DELTA.T at the time of update), by (C-M.sub.1 .times.C/.alpha.+M.sub.2 D) in a third preferred embodiment (wherein M.sub.1 and M.sub.2 denotes values determined according to a change rate of the count value C of the counter with respect to time and D denotes the latest count value of the counter for .DELTA.T at the time of update), and by (C-C/M) in a fourth preferred embodiment (wherein M denotes a value determined according to a change rate of the count value C of the counter with respect to time).