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JPS5364491

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DESCRIPTION JPS5364491
Specification 1 The name of the invention.
Acoustic detector
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acoustic
detector adapted to improve the signal-to-noise ratio. When a solid plastically deformed and
broken, it is stored until then and I / L nine strain energy is emitted as a sound. Therefore, if this
sound is detected by an acoustic detector, destruction of the structure can be predicted. By the
way, as the sound detector provided for the purpose as described above, one generally
configured as shown in FIG. 1 is used. That is, in the figure, 1 is a container formed of a metal
material, for example, stainless steel, and a bottom wall 13 of the container 1 is formed of an
elastic wall which can be displaced when a sound pressure is applied from the outside. Further,
an annular projecting wall 2 is provided in the inside of the container J, and a piezoelectric
element formed of a crystal similar to lithium niobate (LINbOs) or the like between the projecting
wall 2 and the bottom wall 1a. A false-tongue-acoustic transducer 3 is provided. The electroacoustic transducer 3 has the − side in close contact with the inner surface of the bottom 111 a
via a conductive adhesive. Then, an electrode plate 4 is closely provided on the other side surface
of the electro-acoustic transducer S, and a ring 5 made of a 2 flange material is interposed
between the electrode plate 4 and the projecting wall 1; The position is fixed by this ring 5. On
the other hand, a hole 6 is provided in the soil wall of the EndPage: 1 container l, and one end
side of the sheathed cable 7 is inserted into the hole 6. The sheath 8 of the sheathed cable 7 is
airtightly fixed to the inner surface of the hole 6 by welding, and the core 9 is connected to the
electrode plate 4. In the figure, 10 indicates an insulating material, and I indicates a welding
portion for facilitating assembly. Thus, the acoustic detector configured as described above fuses
the outer surface of the bottom wall 1B of the container 1 to the surface of the observed member
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via the acoustic transmission medium, and outputs between the sheath 8 and the core wire 9 A
resistor is connected, and an output signal is taken out from both ends of the output resistor.
However, the conventional acoustic detector configured as described above has the following
problems. That is, in the conventional sound # detector, the container 1 is formed of a metal
material in order to sufficiently reduce the acoustic resistance, and this container J is also used as
one electrode for extracting the output of the electro-acoustic transducer 3 ing. Therefore, when
the observation member is, for example, a grounded metal material, the container 1 is also
grounded. On the other hand, in the case where the sheathed cable 1 is extended by hundreds of
US, it is difficult to completely float the sheath 8 from the ground, and some portions of the
sheath 8 are grounded.
When the sheathed cable 7 is elongated as described above, it is difficult to keep the grounded
container 1 and the container 1 grounded at the same potential via the observed member. In
particular, it is extremely difficult in reactor facilities and high-pressure large-current facilities. As
described above, when there is a potential difference between the ground portions, noise appears
across the output resistance and the SN ratio is degraded. That is, if this pattern is shown by the
evaluation circuit, it becomes as shown in FIG. In FIG. 2, ES indicates the signal generated by the
electro-acoustic transducer J, and ZI indicates the internal impedance of the electro-acoustic
transducer 3. Assuming that the cover of the electro-acoustic transducer 3 is C1, Zl is 7. i = t'pQ,
Further, in the figure, EN indicates a noise signal appearing between the ground points, and R
indicates an output resistance. Now, assuming that the impedance of the sheathed cable 7 is Zc,
the noise signal en appearing between a and b in the drawing is I, and ZcllR represents a parallel
resistance of Zc and R. As described above, in the conventional acoustic detector, when a
plurality of grounding points are formed, the SN ratio becomes extremely troublesome, and as a
result, there is a disadvantage that the signal processing circuit is complicated. The present
invention has been made in view of circumstances such as a coin, and the purpose thereof is to
make it possible to sufficiently improve the SN ratio even when the grounding points are set to
be formed at a plurality of places, It is an object of the present invention to provide an acoustic
detector suitable for telemetry and the like. The details of the present invention will be described
below with reference to the illustrated embodiments. FIG. 8 shows a detector according to the
present invention, and the same parts as FIG. 1 are indicated by the same reference numerals.
Therefore, the description of the overlapping parts is omitted. The detector according to the
present invention is different from the conventional one in that a condenser 2 is provided in the
container 1 so that one end side is electrically connected to the container J, and a sheath type
cable 1a having a two core Are connected to the electrode plate 4 while the other is connected to
the other end of the capacitor 2). That is, the capacitor 2 is formed of an insulating material 22
having an electrical constant equal to that of the electro-acoustic transducer 3, and for example,
in the case of using a crystal plate of LINbO as the electro-acoustic transducer 3, insulation As
the material 2z, a crystal plate of non-polarized LINbO having the same size as the electroacoustic transducer S is used. The capacitor J1, that is, the insulating material 2j, is bonded to the
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projecting wall 2S of which the-side surface is protruded from the inner surface of the earth wall
of the container J by a conductive adhesive and is electrically connected to the container J The
electrode plate j4 is adhered.
Further, one end side of one core line EndPage: 29 b of the sheathed two-core cable yl is
connected to the electrode 24. One end side of the other core wire 9 a is connected to the
electrode plate 4. Also, the capacitance of the ring 5 is set to be almost negligible. Thus, in actual
use of the acoustic detector configured as described above, the outer surface of the bottom wall
1a is contact-fixed to the surface of the observed member via the acoustic transmission medium
and the sheath 8 is grounded. An output resistance is connected between the core wires 9B and
9b, and an output signal is obtained from between the output resistances. With such a
configuration, even if the observation member is a metal material and grounded, the SN ratio can
be greatly improved as compared with the conventional one. That is, when the observed member
is a metal material and is used in a grounded state, the circuit at this time is as shown in FIG. In
the figure, Es represents the output signal of the electroacoustic transducer S, and EN represents
a noise signal. Further, Zl indicates the internal impedance of the electro-acoustic transducer J,
zP indicates the internal impedance of the capacitor 2 and R indicates the output resistance. As
apparent from the figure, the noise signal flows on the one hand through the impedance between
the capacitor 21 to the core wire 9b to the core wire 9b and the sheath 8 and on the other hand
the electro-acoustic transducer S to the core wire 9a to the core wire 9a and the sheath It flows
through the impedance between 8 and. As described above, since the electro-acoustic transducer
S and the capacitor x1 have the same electrical constant, and the impedance between each core
wire and the sheath I is also equal, the noise current flowing in each core wire 9 @, 9b eventually
becomes The potential difference between the core wires 9a and 9b becomes equal to zero due
to the noise current. Therefore, the potential difference between both ends of the output resistor
R corresponds to only the signal Es, and does not include noise. According to the experiment, the
SN ratio is -60! , B could be less. As described above in detail, according to the present invention,
the SN ratio can be greatly improved in a state where the electro-acoustic transducer is used with
maximum efficiency, and the signal processing circuit can be simplified. In addition, since the
detection unit is housed in the container, it can be used without any problem even in a liquid or
the like, and an acoustic detector with a high degree of freedom of use can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a conventional
detector of this type, FIG. 2 is an equivalent circuit diagram when the detector is used, and FIG. 8
is a longitudinal sectional view of one embodiment of the present invention FIG. 4 is a circuit
diagram of evaluation when the same embodiment is used. ! ... Container 3 ... Electro-acoustic
conversion element 2 ... ... Condenser 1 a ... Sheath type cable Applicant agent Attorney Takeshi
Suzue 1 Faction 2 Figure EndPage: 3
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