GB1494626A - Navigation aids - Google Patents

Abstract

1494626 Navigational aid B R V Z DE FERRANTI and R M S MURRAY 7 Feb 1975 [7 Feb 1974] 05778/74 Heading G1A and G1F In a navigational aid for indicating a deviation of a vessel from a predetermined fixed compass heading, a bar magnet 44 is suspended from an arm 42 mounted on a conical pivot 43. The arm 42 carries a part spherical encoder surface 45 that is marked with alternating reflective and absorptive stripes. Radiation from a light emitting diode 48 in a reading unit 47 is periodically received by two photo-detectors 49 and 50 when the magnet moves relative to the ship. The photo-detectors are spaced apart in the direction of rotation of the member 45 by an odd number of half stripe widths so as to provide signals phase displaced by 90 degrees. The outputs of the detectors 49 and 50 are fed by way of pulse shaping and level changing amplifiers 27, 28, Fig.3 to a direction discriminator 29 which supplies output signals on lines 30, 31 depending on the direction of movement of the encoder surface. The signals on these lines 30, 31 pass via a combined reset and reversing switch 32 to a reversible counter 33 which will count up or down (from its initial half full count) depending upon the setting of switch 32. The counter's output is fed via a D/A converter to a pair of comparators 35, 38 which are also connected as shown to two potentiometers 36, 39. The comparators actuate an audible alarm 37 or 40 when the signal input from the photo-detectors is greater than the level set by, say, potentiometer 39. A similar embodiment Figs.2a and 2b (not shown) is disclosed wherein the diode and detectors are on either side of an encoder disc with alternating transparent and opaque marks on the edge, the disc being moved by the magnet when the ship's orientation changes.