Patent GB-798105-A (GB)
Title: Improvements in or relating to apparatus for determining the depth of an object in water
IPC: A01K79/00
Filed: 1956-01-23
Abstract: 798,105. Echo-sounding. RAYTHEON MANUFACTURING CO. Jan. 23, 1956 [Jan. 21, 1955], No. 2238/56. Class 118 (2). An echo-sounding system is arranged to give an audible alarm when an echo is received from a depth between predetermined limits, for example, from a school of fish. This is accomplished by keying a multivibrator by the transmission triggering impulse from the depth sounder indicator or recorder. The differentiated lagging edge of this multivibrator pulse is used to trigger a gating pulse generator that produces a pulse having a duration corresponding to the range of depths between a point somewhat below the water surface and a point somewhat above the expected bottom. Any echo signal occurring during this gating pulse opens a gate and, in addition to producing an indication on the indicator dial or a mark on the record, also keys an audio oscillator to give a burst of sound from a loud-speaker and may also operate a relay to ring a bell until attended to. Fig. 2 shows the invention applied to a recording type echo-sounder wherein a stylus 35 moves over a recording paper 33 and an associated arm 40 engages a contact 41 to trigger an oscillator 42 at the commencement of each sweep. The pulse of energy from oscillator 42 is fed to transducer 11 via transformer 43. Echo signals are fed via amplifier-detector 12, 13 to the recording stylus 35. A third winding 44 on the transformer 43 is connected to a rectifier and differentiator circuit 45 that produces a negative-going pulse to trigger a multivibrator 24. Alternatively the multivibrator 24 may be triggered more directly from the contact 41 as indicated by the broken lines and trigger generator 23. The pulse from multivibrator 24 is differentiated at 25 and the short pulse due to the lagging edge serves to trigger multivibrator 26 which produces a gating pulse having a duration corresponding to a depth somewhat less than the expected average depth of the bottom. This pulse is applied to a gate circuit 27 to which the output from the amplifier-detector 12, 13 is also applied. The purpose of the first multivibrator 24 and differentiator 25 is to delay the start of the gating pulse so that no signals will be passed for a short time after the pulse of compressional wave energy is propagated by transducer 11 in order to avoid false alarms. The device can be operated without this delay, but not as reliably. When an echo signal is received from an object within the depth range represented by the gating pulse an output is passed to multivibrator 28 which causes an audio oscillator 30 to produce a burst of oscillation which is heard as a " ping " from loud-speaker 31. This third multivibrator 28 is included to extend the period of oscillation since the actual duration of the echo would merely produce a click. A relay in the anode circuit of the oscillator valve in audio oscillator 30 has contacts which close the circuit of a bell 32 and further contacts which remove bias from the oscillator valve such that, after an initial echo, it oscillates continuously and the bell remains ringing until a switch is thrown to short out the relay coil. While this switch is closed only individual " pings " are heard on loud-speaker 31. In the embodiment of Fig. 1 (not shown) the invention is applied to an echo-sounder having an indicator of the rotating light type wherein the triggering arm 40 and contact 41 of Fig. 2 are replaced by a switch closed as the light passes the zero mark on the indicator scale. A circuit diagram of the blocks 23-28, 30 and 45 is given in Fig. 3 (not shown).