Stewart Hughes Limited

Richard P Dudley

Maxwell Richard Hadley

This invention relates to apparatus for producing a periodic output signal having a predetermined period ratio (a/b) relative to a periodic input signal. Signals from a tachometer on a gearbox are received by a counter timer unit, the counter timer unit evaluates the number of clock pulses k.sup.o received from a clock within each period of the tacho signal. A control unit receives values of k.sup.o from the counter timer and employs an algorithm based on the following equation to calculate a count value n.sup.o to be loaded into a register for the next tacho period. ##EQU1## where dK represents k.sup.-1 -k.sup.o. An accumulator is connected via an adder to the register and at receipt of each clock pulse from the clock adds the count stored in register into the accumulator. An output is produced on line when the accumulator overflows.

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Southampton, United Kingdom

Richard P Dudley