GB1431783A - Tracking systems - Google Patents

Abstract

1431783 Optical tracking BRITISH AIRCRAFT CORP Ltd 22 Nov 1973 [24 Nov 1972] 54449/72 Heading H4D In a tracking system which includes a tracker having a split photosensitive screen divided into two equal areas such that a light strip incident on the screen and originating from the object being tracked will produce a pair of pulses having the same characteristic shape but relative amplitudes depending on the proportion of light strip incident in the respective areas, the two pulses having equal amplitudes when the object is centred on the screen, an out of balance error signal is obtained from the proportional difference in amplitude of the two pulses. Coincident pulses of similar shape are obtained, one from each electrically separate triangular photo-electric area A, B, Fig. 1 of screen 16 upon which is focused a light strip 10 produced by aiming a cylindrical lens system at the engine flare of a missile. The amplitude A, B, Fig. 2, of the pulses will be equal when the missile is in the centre of the field of view, i.e. when the light strip is co-incident with the centre line 11. The circuit of Fig. 2 generates an out of balance control voltage proportional to (A - B)/ (A + B) to maintain this condition. Pulses A and B are amplified at 12, 13 respectively, the gain of which amplifiers, is controlled by an AGC so that A+B>V REF where V REF is a fixed reference voltage. The pulse leading edges are extended by filters and the amplitudes summed at 14, which sum is applied to the AGC and also compared with V REF in a comparator so that when A + B>V REF the sample and hold circuits for each pulse are enabled, and the difference of the outputs thereof is produced at the output of amplifier 15, to produce the control voltage.