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JPS63118620

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DESCRIPTION JPS63118620
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
apparatus for detecting a vibration of an object to be measured, electrically converting the
vibration and outputting it as a signal to a predetermined device. [Prior Art] In various devices
and plants, it is widely practiced to monitor the vibration of a predetermined part or device
continuously or intermittently to grasp the state of these devices or plants. The vibration
detection devices used for these are all devices that convert vibration into an electrical signal, but
when roughly classified, the "strain gauge system" that utilizes the change in resistance of the
element generated by the vibration, and the dielectric It becomes two of the "piezoelectric and
electrostriction system" which utilizes the electric charge generated by the distortion added to
the. The strain gauge method is mainly used for measurement of low frequency vibration, and in
the case of measurement of ultrasonic vibration, a piezoelectric / electrostrictive method is often
used. However, there are many cases where the operating temperature range is 100 ° C. or less
in any of these two systems. For example, the device used under high temperature environment
of about 500 ° C. has various product heat resistance means and the product yield is bad. It is
an expensive device. Here, also in the thermal power plant in recent years, for example, whether
the large valve is opened and closed normally, the flow of the internal fluid is normal, there is no
leakage of the internal fluid, or the defect of the material of the valve In order to monitor the
presence or absence, etc., vibration converters have often been installed for valves and piping
systems to be observed. In this case, it is necessary to measure the vibration state of the
observation target in a high frequency region of several tens of kilohertz or more, and the use of
such vibration transducers is also increasing. Among the above-described measurement methods,
a piezoelectric / electrostrictive vibration transducer is used in this ultrasonic frequency range.
[Problems to be Solved by the Invention] FIG. 4 shows this piezoelectric / electrostrictive
vibration converter. Reference numeral 1 is a vibration conversion element, 2 is a storage case
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constituting the apparatus main body, 3 is a vibration conversion element mounting metal plate
connected to the vibration conversion element 1, and 4 is an electrical signal output connector.
In this configuration, the diameter of the contact portion to be measured of the vibration
converter is relatively large, for example, 10 m 1. For this reason, there is no problem in bringing
the transducer into contact with a flat measuring object, but when the object is a curved surface
or a spherical surface, the contact state becomes defective and the measurement accuracy is
lowered. That is, as shown in FIG. 3, when the vibration converter 10 is brought into contact with
the measurement object 11 which is a tube, a gap is generated between the vibration conversion
element and the measurement object, and the measurement accuracy is lowered. For example,
when the diameter of the vibration conversion element is 10 mm and the vibration of a cylinder
with a radius of 50 m is measured, a gap of 0.5 mm at maximum is generated between the
vibration conversion element and the cylinder.
For this reason, the measurement accuracy is reduced, and it is practically impossible to measure
on a cylindrical surface or the like having a radius of less than 501 °. Therefore, in such a case,
a method is employed in which a flat plate is fixed on the surface of a cylinder to be measured
and a vibration converter is installed on the flat plate portion. However, in this method, the
vibration of the object to be measured is measured via the flat plate, so the vibration of the object
to be measured is attenuated at this flat plate portion, and the measurement accuracy naturally
decreases, eventually a good measurement of the sensitivity can be made. It was not. If the
diameter of the vibration converter is made smaller than 10 mm, the adhesion to the object to be
measured will be improved, but if the diameter of the vibration converter is made smaller, the
accuracy of the vibration converter itself will be reduced. It has not been done. Second,
conventional arrangements have made it difficult or impossible to use the device in high
temperature environments. That is, in order to protect the device main body from high heat, the
vibration converter main body is disposed at a position separated from the measurement object,
and a waveguide metal plate is interposed between the measurement object and the vibration
converter to It transmits to a vibration converter via this waveguide metal plate. However, in this
method too, for example, the ultrasonic wave is attenuated about half with a 50 cm-long
waveguide metal plate, and there is a large problem in practical use due to the large attenuation
of the ultrasonic wave. In addition to this, in the conventional configuration, there is also a
problem that the vibration transmission surface of the vibration converter can not be disposed
when the measurement part to be measured is a slit or the like. [Means for Solving the Problems]
The present invention has been made in view of the above-mentioned problems, and the
vibration conversion element of the vibration converter and the object to be measured have heat
resistance and vibration damping is extremely high. The device is characterized in that it is
configured to be connected by a heat-resistant glass-based material which is a small material.
[Operation] The present invention connects a vibration transmitter made of a material such as
quartz fiber or the like having a high vibration transmission coefficient and heat resistance to an
object whose vibration is to be measured, and transmits the vibration of the measurement target
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through this vibration transmitter. The vibration is transmitted to the vibration converting
element of the vibration converter connected to the other end, the converted vibration is
converted into an electric signal in the vibration converting element, and the electric signal is
output to a predetermined device. Embodiments of the present invention will be described in
detail with reference to the drawings. In FIG. 1 and FIG. 2, 1 is a vibration conversion element, 2
is an apparatus main body which is a case for housing the vibration conversion element 1, 3 is a
metal plate for mounting the vibration conversion element (hereinafter simply referred to as
"metal plate"), An electrical signal output connector 4 outputs the measured vibration of the
measured object as an electrical signal. A metal sleeve 5 is screwed to the metal plate 3 by a
screw portion 9 and fixed to the metal plate 3.
The metal sleeve 5 is inserted and one end of the metal-coated quartz fiber 6 is in close contact
with the vibration conversion element 1 (see FIG. 2). Further, the other end of the metal-coated
quartz fiber 6 is connected by spot welding 8 to a measurement target (the boiler furnace electric
heat pipe shown in the drawing) 7. Incidentally, since this metal-coated quartz fiber 6 is a quartz
fiber coated with aluminum, it can be welded to the object to be measured. Next, the metal-coated
quartz fiber will be specifically described among the above-described configurations. This metalcoated quartz fiber is obtained by melt-coating a metal such as aluminum with a quartz fiber
having a fiber diameter of 11 n or less, and by making the thickness of the metal coating 20% or
more of the fiber diameter, the same as the optical fiber The entire fiber can be made flexible.
Further, since the coating is a metal, the entire fiber can be used continuously in a high
temperature environment of 500 ° C. or higher, and sufficient heat resistance can be obtained.
Also, although quartz does not match the quartz used as an ultrasonic transducer or its
transmission line, the transmission loss of ultrasonic transmission line compared to carbon steel,
for example, at the frequency of I MHz, will be explained as an example. It becomes 1/1000 or
less, which is a good ultrasonic wave transmission path. The higher the frequency of the
ultrasonic wave, the larger the difference from the transmission path by the metal body, and
quartz is more advantageous. FIG. 5 shows the frequency characteristics of the ultrasonic
absorption coefficient in quartz glass and carbon steel. As apparent from the diagram A showing
the characteristics of quartz glass and the diagram B showing the characteristics of carbon steel,
the relative absorption coefficient increases with the increase in the frequency of ultrasonic
waves for both quartz glass and carbon steel, and hence the absorption loss becomes large.
However, in the case of quartz glass with respect to carbon steel, its loss is 1/1000 or less at the
same frequency range, and it can be seen that it has an extremely high ultrasonic wave
transmission capability as compared to carbon steel. Although the mechanism of ultrasonic
absorption is not clear yet, it is said to be related to the crystal grain size, hardness, etc. of the
ultrasonic wave transmitter. The ultrasonic absorption loss of quartz glass attenuates to 6.5 db /
m at 10 MHz, that is, about 22% when transmitted 1 m. Quartz has the advantage of having an
absorption coefficient smaller than this by more than an order of magnitude, but on the other
hand there is also the critical problem that fiber processing can not be performed. Therefore,
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quartz glass can be said to be the best material in consideration of the attenuation characteristics
of ultrasonic waves and the fiber processability. However, in addition to this, Pyrex glass also has
an ultrasonic wave transmission characteristic substantially equal to that of quartz glass, and can
be used as an ultrasonic wave transmission path.
Among metals, aluminum has a relatively low ultrasonic absorption coefficient, and aluminum is
suitable as a fiber metal material. There is almost no study on the ultrasonic wave transmission
characteristics of bare quartz fiber without metal coating, but the speed of sound in quartz is
about 500 (im / sec), and the wavelength λ = 5 fl at a frequency of 1 mHz. Therefore, even if the
fiber shakes or the like occurs in the middle of the transmission metal-coated quartz fiber, the
transmission loss does not significantly increase unless deformation having a curvature radius of
5 dragons or less occurs. When the ultrasonic frequency to be measured is about I MHz, the
length of the quartz fiber can be practically used up to about 10 m. In this embodiment, uniform
refractive index quartz is used as the metal-coated quartz fiber, but good transmission
characteristics can be expected in the same manner with quartz-based fibers having a refractive
index distribution adopted for quartz-based optical fibers, and mass production It is possible to
reduce the price by diversion of fiber. Next, the details of the configuration for connecting the
metal-coated quartz fiber 6 to the vibration conversion element 1 will be described with
reference to FIG. The tip of the metal-coated quartz fiber 6 is inserted through the metal sleeve 5
and the metal-coated quartz fiber 6 and the metal sleeve 5 are connected and fixed with an
adhesive. In this state, the metal sleeve 5 is screwed to the metal plate 3 so that the end of the
metal-coated quartz fiber 6 is in close contact with the vibration conversion element 1. However,
a gap of about 10 μm may occur between the end of the metal-coated quartz fiber 6 and the
vibration conversion element 1 only by such mechanical connection, so the occurrence of such a
gap is prevented. Therefore, it is desirable to impregnate the contact surface with machine oil or
the like. The operating state of the device having the above configuration will now be described.
The vibration of the object to be measured 7 is transmitted to the vibration converter side via the
metal-coated quartz fiber 6 spot-welded to one end of the furnace heat transfer tube which is the
measurement object 7 under high temperature environment. That is, the vibration of the object
to be measured 7 propagates with low loss mainly through the quartz fiber of the metal-coated
quartz fiber 6 and is transmitted to the vibration conversion element 1. Here, it is converted into
an electrical signal by the piezoelectric / electrostrictive effect, and is output to a predetermined
device through the electrical signal output connector 4. In this case, although the vibration also
propagates in the metal-coated portion of the metal-coated quartz fiber, most of the vibration
reaching the vibration conversion element 1 is the quartz fiber portion because the transmission
loss is about 1000 times larger than the quartz fiber portion. There are propagations. Next, as a
constituent material of the vibration conversion element 1, a piezoelectric / electrostrictive
material such as pzT1 barium titanate or lithium niobate (LiNbO: +) is used.
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In addition, since the vibration converter body can be arranged away from the high temperature
environment by the use of metal coated quartz fiber, the vibration conversion element itself using
these materials does not have to consider heat resistance too much, and a room temperature type
element is used. be able to. With the above configuration, continuous use in a high temperature
environment of 500 ° C. is possible, and since the melting point of aluminum is about 660 ° C.,
if it is several hours, it is in a 600 ° C. environment. Measurement is also possible. [Effect] As
described above, the present invention has heat resistance such as metal-coated quartz fiber and
vibration damping of the vibration converting element of the vibration converter and the object
to be measured. Since it is configured to be connected with a heat-resistant glass-based material,
which is a small material, it is possible to use the device under high temperature environment
and provide a device with high measurement accuracy at a low price. In addition, since it is
possible to dispose a vibration transmitter such as a metal-coated quartz fiber even at narrow
portions and the like which can not be measured conventionally, the object to be measured can
be greatly expanded.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a longitudinal sectional view of a vibration converter showing an embodiment of the
present invention, and FIG. 2 is an enlarged sectional view of a vibration conversion element part
showing a state of attachment of metal coated quartz fiber to the vibration converter body, FIG. 4
is a longitudinal sectional view of the conventional apparatus shown in FIG. 3, and FIG. 5 is an
ultrasonic frequency and relative absorption of ultrasonic waves in carbon steel and quartz glass.
It is a diagram which shows the relationship with a coefficient.
1 ... vibration conversion element 2 ... vibration converter main body 6 ... metal-coated quartz
fiber 7 ... measurement object Fig. 1 Fig. 2
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