GB1362740A - On-speed detection arrangement - Google Patents

Abstract

1362740 Speedometers ITT CREED Ltd 7 Dec 1972 56486/72 Heading G4D [Also in Division G1] An on-speed detection circuit for monitoring a pulse train, e.g. to sense when a shaft has run up to its correct speed, comprises a cyclic counter 5 driven continuously by a clock pulse generator 6, the counter 5 giving an output pulse at 8 whenever it reaches a predetermined count, and being reset to zero by each pulse of the pulse train being monitored, a first toggle 7 set by a pulse from the counter output terminal 8 and cleared by each pulse of the pulse train, and a second toggle 10 set by a second pulse from the counter output terminal 8 when the counter has not been reset by a pulse of the pulse train between said second pulse and the preceding first pulse from the counter, and cleared by the coincidence of the first toggle 7 in its cleared condition with a pulse of the pulse train, which cleared condition of the second toggle 10 indicates that the repetition rate of the pulse train is up to the correct speed. As shown, the shaft carries a disc 1 having markings or teeth to be detected by a photo-electric or magnetic sensor 2 which produces an output as each mark or tooth passes to cause a pulse generator 3 to produce a pulse. The markings or teeth have a gap at at least one part of the disc 1 to provide a regular datum gap in the pulse train from the generator 3. The output lines from the toggle 7 pass via delay elements 12, 13 respectively to AND gates 9, 14 and thence to the toggle 10. When the counter 5 reaches a second predetermined count greater than the first, the datum gap in the pulse train being great enough to allow this second count to be reached when the pulse train is not below its correct speed, the counter produces a pulse in a line 16 to an AND gate 15 between the toggle 10 and a third toggle 11. The third toggle 11 is set by the occurrence of two consecutive pulses from the counter output terminal 8, as detailed above, and is cleared by the coincidence of the second toggle 10 in its cleared condition with the occurrence of a pulse from the counter output terminal 16. The third toggle, when set, inhibits actions not to be performed while the shaft is below speed, and when cleared enables these actions to be performed in correct timing with respect to the shaft rotation.