GB1271245A - Ranging system - Google Patents

Abstract

1,271,245. Laser rangefinders. BOFORS A.B. 11 July, 1969 [12 July, 1968; 26 July, 1968], No. 35145/69. Heading H4D. Specification describes a pulsed laser rangefinder of the type wherein the transmission of a pulse 1 opens a gate 6, Fig. 1, coupling the output of a pulse oscillator 5 to a first pulse counter 7 and is arranged such that said one first counter can provide counts indicating the ranges of a plurality of targets including the selected target. Thus a plurality of registers 31, 32, 33 are connected to the counter 7, via gates 21, 22, 23 and opened in succession by the first, second and third echoes by means of distributer 40 fed by receiver terminal 2, whereby the count content of said counter is transferred to each register in turn, at the moment of echo receptions, said transferred counts thus indicating the respective plurality of ranges. So that near targets or clutter will not be received a gate 3 is placed in the line from receiver terminal 2 to distributer 40 and is opened only after an interval after the transmission of a pulse as determined by delay 4. Counter 7 is comprised of bi-stable circuits to give a binary coded decimal output. At the instant of reception of an echo, the bi-stable circuits of counter 7 may be in a state of switch over, which state if read out to a register would indicate an erroneous range. A second counter 14 may be thus provided commencing to count the oscillator 5 output on the reception of an echo pulse and also causing the simultaneous blockage of gate 6 and the stop of the count in counter 7. After a period long enough for the bi-stable circuits of counter 7 to settle, and determined by the count reached in counter 14, said counter 14 reopens gate 6 and recommences the count in counter 7 starting with a jump equal to said count reached. Counter 14 also then feeds a signal to distributer 40 such that the echo is then applied to the respective one of gates 21, 22, 23 whereby the "settled" state of counter 7 is passed to the register. In the arrangement of Fig. 2 only those two ranges of incoming echoes which bracket the suspected range of a target are stored in registers 31 and 32. Items 1 to 7, 21, 22, 31, 32 are as in Fig. 1. The suspected range Rs is fed into comparator 56 and is compared with the continually changing count in counter 7 to give an output at 58 indicating when the count range R is less than Rs and when it is greater than Rs. Said output is fed to control switch 52 such that the echoes for R<Rs are fed to gate 21 and the first only echo for R>Rs is fed to gate 22. Register 31 is cleared before the next opening of gate 21 such that the range which remains in it is that nearest to and just below Ri. The range in register 32 is that nearest to and just above Rs.