Fish counter with scanning transducer

Claim 1

In a system for counting fish migrating in a body of water including sonar transducer means positioned in the water, electronic circuit means for providing transmit pulses to said transducer means and for receiving echo signals from said transducer means, said circuit means including a source of electrical power, an electric clock circuit connected to said source producing clock pulses at regular intervals to initiate said transmit pulses, receiver means, means responsive to a time interval after the initiation of said transmit pulses for enabling said receiver means to receive echo pulses, and counter means connected to receive and count the echo pulses from said receiver means: wherein the improvement comprises at least one acoustic focusing liquid lens transducer comprising a housing which is generally circular in at least one plane, acoustically transparent and filled with a low sound velocity liquid, a large numer of individual piezoelectric transducer elements arranged in the inside of said housing across an arc of the bottom thereof, said elements each transmitting and receiving from a very narrow beam width and being arranged such that said transmitted beams are side by side and successively illuminate a generally fan-shaped volume across said stream; a first binary coded decimal circuit which responds to said clock pulses to produce a large number of sequential binary signals and a first group of electronic switches each of which is connected to one of said transducer elements, said switches being successively closed by said binary signals to initiate said transmit pulses; time delay means responsive to said clock pulses initiating a delay period and then enabling said receiver for a set period to receive any echo signals resulting from the immediately preceding transmit pulse, means for amplifying said echo signals, a threshold detector for detecting only echo signals above a certain magnitude, and a signal conductor to which said signals are supplied; a second binary coded decimal circuit connected to receive said clock pulses in synchronism with said first binary coded decimal circuit to produce a large number of binary signals and a second group of electronic switches connected to said power source, which switches are successively closed by said binary signals, a plurality of AND gates each of which has one input terminal connected to one of said second group of electronic switches, a plurality of adjustable range gates connected to the other input terminal of said AND gates and having as input signals said timing pulses such that said AND gates conduct from a time initiated by said timing pulses to a time limit set on said range gates, a third group of electronic switches connected to receive input signals from the said AND gates and said signal conductor such that each of said electronic switches is closed to conduct said detected echo signals during a time period set on its respective range gate; a plurality of counters each connected to one of said third group of electronic switches to receive and count the echo signals from one of said transducer elements, and display means for displaying the counts from said counters.