Angular position detector

Claim 2

An angular position detector comprising a toothed wheel having a missing tooth, a sensor device producing a pulse train as the teeth of the toothed wheel pass it, and a discriminating circuit connected to said sensor device and producing a datum signal in response to recognition of the passage past the sensor device of the missing tooth by measuring the time intervals between the pulses of said pulse train, characterised in that said discriminating circuit recognises said missing tooth by detecting when an interpulse interval is significantly shorter than the preceding interval.

Claim 3

A detector as claimed in claim 1 said discriminating circuit includes a clock pulse generator and a micro-computer connected to the clock pulse generator and to the sensor device and programmed to count the number of clock pulses between successive pulses of the pulse train and to compare the number counted in each interval with a fraction of the number counted in the preceding interval.

Claim 4

A detector as claimed in claim 1 in which said discriminating circuit comprises a first programmable frequency divider for dividing the frequency of a fixed frequency pulse train by a divisor M, a first counter connected to said first programmable frequency divider to count pulses therefrom and to said sensor device so as to be periodically reset thereby, a second programmable frequency divider connected to divide the frequency of said fixed frequency pulse train by a number equal to the count in said first counter immediately before it was last reset, a second counter presettable to a number M.Q (where Q is less than one) and connected to count the output of the second frequency divider, means for supplying a signal representing the divisor M to the first frequency divider and a signal representing the number M.Q to the second counter and means for generating a datum signal if the number of signals received from the second frequency divider in any cycle exceeds the number M.Q.