The amount of charge generated from the transducer
(sensor; converter) must express minute differences, so careful attention is
required on the measurement path. In particular, noise from cables or noise
caused by installation errors can lead to fatal measurement errors. Modern
measurement methods are more compact, more accurate, and often include
self-calibration. In particular, the external amplifier (Charger type) system used in the
past must amplify and use the amount of electricity by using an amplifier in
the middle in order to show a large amount of small charge.
When pressure is applied, electricity is generated... The
amount of charge generated by the 'piezoelectric effect' is very small,
and as you can imagine, it is not enough to perform the 'generating function'
that electricity will be generated when vibration is applied to the element.
Th
We are taught that light is faster than anything else,
so we miss the meaning of having powerful energy. Therefore, wherever the light
reached, there was hot energy. However, it was not always so where the sound
reached. I could hear the sound even in the dark. I heard it even though it was
blocked.
If sound and light are transmitted to an invisible
place, let's say that they can be seen as passing through an obstacle or being
reflected secondarily on another plane. But if you can hear sound in the back
corner where there is no such thing, how on earth can you explain this?
Huygens–Fresnel principle
Waves appear in the form
of light, sound, surface waves, earthquakes, vibrations, etc., and have
characteristics of reflection, refraction, and diffraction. Light is a
transverse wave in which the direction of vibration of the medium and the
direction of propagation of the wave are different, but sound is a longitudinal
wave having a wave of low density (low density, high density medium) in the
direction of propagation of the wave. If the sound propagation direction is
referred to as a sound ray, the perpendicular plane is called a 'wavefront' (a
plane obtained by connecting all points of the same phase when the wave
propagates).
The principle by which
sound can be heard in a confined, narrow, and dark place is explained by
Huygens' principle. “Each point on one wavefront becomes the point source of
the next wavefront, and a spherical wave is generated. The envelope that
touches all of the spherical waves created by these point sources becomes the
next wavefront.” Huygens' principle can be used to explain the phenomena
of reflection, refraction, interference, and diffraction of waves.
division
Refraction
Diffraction
explanation
bending of the sound ray
Propagation of sound in areas behind
obstacles
theory
Snell's
Law
When the
medium changes, the angle of incidence and angle of transmission change.
Huygens–Fresnel
principle
phenomenon
- deflects to the lower speed of sound
- Refraction towards the lower temperature.
- bends in the direction the wind blows
- The larger the wavelength, the more
diffraction occurs.
-The smaller the size of the obstacle (the
smaller the hole, the more diffraction.
The person in charge of vibration
technology is bound to hear the question, “What is
the current vibration state of the object in question (equipment, structure,
building, etc.)?” from the manager or the person in charge of
other technologies. You can even ask about the results when you have only
measured and delivered the data. So always have an answer ready for your
question.
Basically, evaluating the state of an
object requires comprehensive judgment based on absolute, relative, and mutual
standards, so it is not easy to answer at the time. . The
evaluation of the state of this absolute standard is mainly
divided into good / bad / unacceptable, and the various expressions and
standards have been summarized.
Level display of vibration evaluation
First of all, the method expressed in overseas standards
and reference standards using graphs is that the British type is mainly marked
with ABCDE 5 grades, and ......
In selecting a transducer, the most important priority
would be sensitivity and 'Frequency range'.
To
explain the vertical axis in the graph of amplitude and frequency, it would be
nice if one sensor could measure all amplitudes, but it can never be done
because it depends on the sensitivity. To explain the horizontal axis in this
way, if all sensors can measure all frequencies, there is no reason to select a
sensor. This is because each type of vibration sensor, further subdivided, each type of vibration sensor
(including an acceleration sensor) has its own frequency range of an area where
measurement is accurate. This is called the frequency range.
Frequency range
The sensor indicates the range of measurable frequencies
(e.g., acceleration sensor: 0.5 to 10 kHz), and the definition of this range is
slightly different depending on the user, so that the maximum and minimum frequency
ranges corresponding to the 'accurate zone' of the measurement can be selected.
This
frequency range is 'a reliable area where the sensor can output a properly
matched signal; It means 'the range of frequency response accuracy according to
the frequency sensitivity deviation', and although the meaning is slightly different from the
non-linearity of the sensor, this reliable area can be expressed as a linear
area.
Looking at the criterion of error amplitude related to
the frequency domain, select the rate of change of the amplitude limit that can
be judged by the presence or absence of an error, eg) ±3dB, ±5%, ±10%, etc.,
and the applicable frequency at this time is ..........
If
the desired 'unit' of vibration is selected as a result for the evaluation, the
next step is to select an appropriate 'sensor'. First of all, it is necessary
to check whether contact attachment is possible at the location to be
measured... or whether the attachment method is appropriate. For example, in
the case of high frequency (more than 5000Hz), the magnetic attachment method
is not appropriate, and if you want to measure the behavior of an axis, it is
difficult to use a contact sensor. Also, if you try to measure the speed and
measure 5 Hz using a coin type speed sensor, you will get an amplified error
signal. This is because the characteristics of each sensor are different depending
on the amplitude band, frequency band, resonance band, etc.
Selection of displacement, velocity, and acceleration sensors
such as amplitude units
Since the output voltage or current is proportional to
each unit, the selection of the unit is not very different from the selection
of the sensor. Sensors mainly used for diagnosing and monitoring equipment
1. Eddy current type displacement sensor (Proximity) that
directly measures the behavior of a shaft supported by a sleeve bearing in a
non-contact manner.
2. Accelerometer, which propagates shaft vibration to
rolling bearing and measures it indirectly by contact method outside the
bearing housing (indirectly transmitted to the housing by impact of the bearing
connected to the shaft)
3. There is a velocity transducer that works without power.
However, among these, the speed sensor is very precise,
but has a weakness limited to the range of 10 to 1000 Hz because it has a
natural frequency in the upper and lower frequencies, which is why displacement
sensors and acceleration sensors are widely used. (If it is out of this frequency
range, an erroneous or amplified value is output.)
A sensor (transducer) is one of the components
of a system that is mainly used by companies that use sensors to research,
diagnose or manufacture monitoring equipment. Since the manufacturer has
selected a sensor that fits a specific principle, the manufacturer has
accumulated a lot of engineering grounds for this. In many cases, the level of
engineering is considerably deeper than that of academia because it must be
required and the reliability of the measurement needs to be verified.
Above all, this principle can be considered as the most
basic sensor selection method. The reason why a displacement sensor is
called a displacement sensor and an acceleration sensor is called an
acceleration sensor is that each sensor generates an electrical output
'proportional to the amplitude unit'. It's because you do it. For example, since the value
converted to displacement by outputting acceleration vibration with an
acceleration sensor and integrating twice is not very accurate (especially when
it is not a sine wave), it is better to measure acceleration vibration with an
acceleration sensor, and displacement vibration It is basic to measure with a
displacement sensor. However, there are cases where it is absolutely necessary to
evaluate the health of a machine or the vibration of a building with the
'velocity' value, which is used as the most evaluation unit in academia and
industry, so this only allows integration from the acceleration sensor once.
Because the speed sensor isn't cool...
평가를 위해서 결과로 원하는 진동의 '단위'가 선택되었다면 그 다음으로는 적절한 '센서'를 선택해야 한다. 우선 측정하고자 하는 위치에 접촉부착이 가능한지... 또는 부착방법이 적절한지...를 확인해야 한다. 간단히 예를들어서 만약에 고주파(5000Hz이상)일 경우에는 자석식의 부착방법은 적절하지 못하며 축의 거동을 측정하고 싶었다면 접촉식센서로는 곤란하다. 또한 속도를 측정하려 했는데 동전식 속도센서를 사용하여 5Hz를측정한다면 증폭된 오류신호를 얻게 된다. 이러한 이유는 센서를 선택함에 있어 각 센서의 특성이 진폭대역, 주파수대역, 공진대역 등에 따라 각각 다르기 때문이다
진폭단위와 같은 변위, 속도, 가속도 센서의 선택
각 단위별로 출력전압 또는 전류가 비례하므로 단위의 선택은 센서의 선택과 크게 다르지 않다. 설비를 진단하고 상태를 감시하는 용도로 주로 사용되는 센서는
1. 슬리브베어링으로 지지된 축(shaft)의 거동을 비접촉으로 직접 측정하는 Eddy current방식의 변위센서(Proximity).
