GB1285697A - Improvements relating to distance sensing systems - Google Patents

Abstract

1285697 Position-finding EMI Ltd 3 Oct 1969 [22 Oct 1968] 50068/68 Heading H4D [Also in Division G1] Acoustic signals transmitted through the air, between transmitter-receiver devices on a ship and one or more transponders located at one or more reference points, are used to determine the disposition of the ship in relation to the reference point(s). In the Fig. 2 system for assisting the berthing of a tanker 1 at jetty 2, two pulse transmitting/receiving devices X, Y each interrogate two transponders A, B at fixed locations on the jetty to determine at least some of the distances AX, AY, BX, BY. Additional receivers (e.g. at Y<SP>1</SP>) may also be used. An analog (details given) or digital computer derives the ship's disposition from these distances and, optionally, from compass data. The several distance measurements provide redundancy for resolving positional ambiguity and checking system operation. Velocity data is derived from a series of distance measurements. A predictive display, showing the distances between bow and stern respectively and jetty 2 at which zero velocity would be reached for a given deceleration, may be provided in addition to a CRT display showing the ship's outline in relation to jetty 2. The transponder responses are coded for identification, e.g. by using a pulse code or by operating at different carrier frequencies, and the transponders may shift the frequency between reception and re-transmission to avoid acoustic feedback. The pulse repetition period and pulse length may both be reduced as the measured distance reduces. In conjunction with the above apparatus, electrodes in the jetty may be used to measure small distances between the ship and jetty by sensing capacity changes.