GB1079242A - Improvements in or relating to distance measuring apparatus - Google Patents

Abstract

1,079,242. Echo-sounding. MINISTER OF TECHNOLOGY. May 17, 1965 [May 20, 1964], No. 20790/64. Heading H4D. In a pulse-echo ranging system, a quantity proportional to the echo-time is derived for each transmitted and received pulse and the largest quantity derived for a given number of successive echo-time measurements is stored to provide an indication of the target range, thereby eliminating disturbances of the measurement due to reflecting objects whose ranges are less than that of the target. In an embodiment for providing a digital measurement of the depth of a river, e.g. for determining the timevarying profile of silt on the river bed, acoustic pulses having a carrier frequency of 1 Mc/s. and a repetition frequency of 200 c/s. are transmitted and received by a transducer 1 in pulse trains of 2¢ seconds duration separated by a ¢-second interval. The echo-time for each pulse is determined by passing clock pulses to a counter 7 through a gate 5. The number in counter 7 and the number in a store 10 are compared by a digital comparator 11 after each count, and if the number in counter 7 exceeds that in the store 10 it is substituted for the number in the store. The counter 7 is reset to zero after each comparison. The number in store 10 at the end of a 2¢ second pulse train corresponds to the greatest depth recorded during the train, and ensures that lower values corresponding to reflections from weed, fish and the like are ignored. In the ¢-second following a pulse train, the number in store 10 may be read out to a computer. The clock pulse frequency is such that the read-out number gives the depth directly in units of 1/10 of an inch for a water temperature of 45‹ F. If the number in counter 7 reaches a value greater than that corresponding to the maximum depth for which the gauge is designed, e.g. due to non-reception of an echo pulse which would normally close gate 5, transfer of the counter number to store 10 is inhibited. The pulse trains may be produced by transmitting pulses as trains, or by transmitting pulses continuously and gating the receiving circuits. The invention may be applied to a multiplexing system for cyclically connecting each of an array of transducers to the transmitting/ receiving apparatus so as to read out the depth recorded by each transducer in turn.