Communications – electrical: acoustic wave systems and devices – Echo systems
Reexamination Certificate
2001-02-02
2002-07-09
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
C367S099000, C367S903000, C367S908000
Reexamination Certificate
active
06418080
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to ultrasonic underwater detection apparatuses.
The invention will be explained as embodied in a fish finder installed in a ship, for detecting underwater conditions beneath the own ship.
FIG. 1
is a general block diagram of a conventional fish finder
51
comprising one transmit-receive channel. The fish finder is generally used in a bad environment having various background noises such as a ship's running noise and noises produced in the ship. A trap circuit
1
supplies a 50 kHz transmitting burst signal S fed from a transmitter
2
to a transducer
3
a
and delivers a received echo signal fed from the transducer
3
a
to a preamplifier
4
.
The transducer
3
a
is connected to the trap circuit
1
by means of two electric conductors. The length of the two electric conductors is, for example, more than five meters depending on the size of the own ship. The received echo signal from the transducer
3
a
mainly containing a 50 kHz component is mixed with a 300 kHz locally generated signal in a mixer
5
. A frequency-converted output signal of the mixer
5
is entered to a filter
6
, which passes only a 250 kHz analog received signal component whose frequency is equal to the difference between the frequencies of the raw received signal and the locally generated signal. The 250 kHz analog received signal is then amplified by a main amplifier
7
and converted into a digital signal by an analog-to-digital (A/D) converter
8
. The digital received signal output from the A/D converter
8
is converted into a video signal suited for on-screen display by a display circuit
9
and this video signal is stored in a video random-access memory (RAM) provided in the display circuit
9
. The video signal stored in the video RAM is converted back to an analog signal, which is delivered to a monitor
10
, whereby underwater situations under the ship detected along a track of the ship on which the fish finder
51
is installed are displayed.
The trap circuit
1
is essentially a resonant circuit formed of a coil L and a capacitor C, and has a single resonant frequency. For this reason, the trap circuit
1
is designed to have a resonant frequency of 50 kHz when the operating frequency of the transducer
3
a
is 50 kHz. Accordingly, only one transducer
3
a
having the same resonant frequency as the trap circuit
1
can be connected to the trap circuit
1
and, therefore, it has been necessary to replace the fish finder when the transducer
3
a
has been replaced with one having an operating frequency of 200 kHz, for example.
There have been used various frequencies such as 15 kHz, 28 kHz, 38 kHz, 50 kHz, 88 kHz, 150 kHz or 200 kHz to excite ultrasonic transducers for fish finders. Various fish finders corresponding to these kinds of transducers respectively have to be manufactured and provided to users.
When a transducer which had been installed in the ship is desired to be used, there could be used only one type of fish finder operating on the same frequency as the operating frequency of the transducer.
Sounding the same area with two different frequencies produces such an advantageous effect that a comparison of echoes taken with the two frequencies allow easy discrimination of fish species in fish schools X or of the nature of a sea floor. To enable dual-frequency sounding, a conventional dual-frequency fish finder has two channels of transmitting and receiving circuits, two transducers
3
a
of different frequencies connected to the respective channels, and a monitor
10
which presents echoes of the two frequencies side by side on a single screen divided into two display areas as shown in FIG.
2
.
Provision of the two-channel transmitting and receiving circuits, however, results in an increase in the mechanical size of the fish finder as well as in equipment cost.
SUMMARY OF THE INVENTION
The present invention has been made to solve the aforementioned problems of the prior art.
An object of the present invention is to provide an ultrasonic underwater detection apparatus which is capable of operating on a wide range of transducer frequencies and performing multi-frequency transmission and reception with a one-channel circuit configuration.
Another object of the invention is to provide an underwater detection apparatus which is capable of meeting demands from users in terms of frequency desired by the users.
Another object of the invention is to provide an underwater detection apparatus which simplifies manufacture and inventory control of fish finders, and the like.
Another object of the invention is to provide an underwater detection apparatus which can be connected to an ultrasonic transducer unit which is capable of transmitting or receiving signals having any one of carrier frequencies used in the fishing industry.
Another object of the invention is to provide an underwater detection apparatus which is capable of selecting and using an ultrasonic transducer unit having an operating frequency from a plurality of ultrasonic transducer units having mutually different operating frequencies.
Another object of the invention is to provide an underwater detection apparatus which is capable of selecting an operating frequency, or a combination of multiple operating frequencies, from a wide range of transducer frequencies and performing either single-frequency or multi-frequency transmission and reception with a one-channel circuit configuration, thereby eliminating the need to replace the fish finder when using a transducer having a different operating frequency.
According to an aspect of the invention, an underwater detection apparatus comprises a transducer for transmitting and receiving ultrasonic signals into and from the water, a transmitter for generating a transmission signal, a broadband trap circuit connected to the transducer by two conductive lines of a length more than five meters for transferring the transmission signal from the transmitter to the transducer and for passing an echo signal from the transducer, a preamplifier for amplifying the echo signal from the trap circuit, a mixer for converting the echo signal from the preamplifier into a signal of a specific frequency, a filter for selectively passing the signal of the specific frequency-band output from the mixer, a main amplifier for amplifying the echo signal from the filter, an A/D converter for converting the echo signal from the amplifier into a digital form, and an indicator for displaying the echo signal from the A/D converter.
Since the trap circuit does not include a resonant circuit, it has a broadband applicability, working independently of the frequency. Thus, operation of the trap circuit is not limited to any single transmitting frequency of the transmitter. Rather, the transmitting frequency of the transmitter may be determined according to the operating frequency of the transducer. If the transmitting frequency of the transmitter is freely variable, it would be possible to use a transducer having a desired operating frequency.
According to another aspect of the invention, an underwater detection apparatus comprises a first transducer for transmitting and receiving ultrasonic waves on its operating frequency F
1
, a second transducer for transmitting and receiving ultrasonic waves on its operating frequency F
2
, a transmitter for generating a transmitting signal, a trap circuit for transferring the transmitting signal fed from the transmitter to the transducers and for passing an echo signal fed from the transducers, a preamplifier for amplifying the echo signal fed from the trap circuit, a mixer for converting the echo signal fed from the preamplifier into a signal of a specific frequency, a filter for selectively passing the signal of only the specific frequency output from the mixer, a main amplifier for amplifying the echo signal fed from the filter, an A/D converter for converting the echo signal fed from the main amplifier into a digital form, and a display circuit for displaying the digitized echo signal fed f
Furuno Electric Company Limited
Jordan and Hamburg LLP
Lobo Ian J.
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