Transducer(센서; 변환기)로부터 발생하는 전하량은 미세한 차이를 표현해 주어야 하므로 세심한측정경로상에 주의가 필요하다. 특히 케이블의 노이즈나 설치오류에 의한 잡음 등은 치명적인 측정오류로이어질 가능성이 있다. 최근의 계측방식은 보다 컴팩트하고 정확하며 자기검정이 포함된 경우가 많다. 특히 과거에 사용하던 외부증폭기(Charger type)시스템은 작은 전하량을 중간에 증폭기(Amplifier)를사용하여 전기량을 증폭하여 사용하였다.
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일반적으로 압전형 가속도계는내부에 증폭회로(ICP, IEPE)가 내장되어 있다. 외부에서증폭기를 사용하던 Charger type방식은 측정의 복잡함(별도의증폭기)에 의해 고온 용도의 측정이외에 더 이상 특히 사용되지 않게 되었다.
힘이 먼저인가? 가속도가 먼저인가? ----------------------------------------------------------------------------------------------------------------------- 가속도센서의 원리를
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Coupling & Coupling effect
위에서 말한 설비의 각 기계 구성요소인 구동부(모터, 터빈, 내연기관)와 피동부(펌프, 팬, 압축기 등)를 연결해 주는 또 하나의 구성요소를 ‘커플링’이라고 한다. 이 커플링의 종류로는 직결플랜지, flexible, jaw, 고무, 기어, 벨트, 체인, 마그네틱 등이 있다. 이 단어는 기계를 조금만이라도 알고 있는 사람이라면....
Displacement means the maximum distance that has changed around
the reference line, so it is easy to intuitively judge the maximum amplitude of
vibration, and since the amount can represent and replace the magnitude of
stress, the main unit of vibration used in various standards (displacement,
speed, acceleration). In particular, it is widely used for direct deflection and
vibration of structures, vibration monitoring of pipes, and ‘online monitoring’
of shaft behavior using sleeve bearings. This is also the reason why
low-frequency acceleration sensors are widely used. The sensor used at this
time is accurate and good for evaluation if it directly outputs the
displacement, but on the other hand, there are many cases where its use is limited due to
limitations in its installation, orientation, and frequency.
Understanding the diversity and
weaknesses of displacement sensors
Type of Displacement sensor
Image
Disadvantages and Features
Eddy current principle ,
Proximity probe, Gap sensor
- Responds only to conductors
- Interference between nearby sensors and nearby conductors (a gap of at least 3 times the diameter of the sensor must be provided)
-Vibration measurement below the unit of mm
Linear measurement below -1000Hz
LVDT
-Linear variable differential transducer (measuring the amount of movement of protrusions, bar type, wire type, )
- When measuring absolute displacement, it is necessary to manufacture a jig for the reference position
- Suitable for low frequencies (below 50Hz)
Strain gauge
Measuring micro displacement, vulnerable to noise
Laser doppler
High-frequency measurements (40 kHz) are very expensive
An accelerometer is the easiest
transducer to measure vibration. Since the measurement direction of this
transducer has already been determined, the sensor must be placed in the
desired direction for measurement. It doesn't really matter if it's up or down.
This is because vibration is repeated and if you want to know the relative
movement, you have to use two or more sensors that measure it at the same time anyway.
In this case, the concept of a phase is only additionally required. However,
compared to a single axis vibration sensor, a triaxial vibration sensor
literally means a sensor having the ability to measure the magnitude of
vibration in three axes at the same time. It is
easy to measure and you will be able to identify vibrations in all directions
in a short time.
Advantages and disadvantages of
Triaxial Accelerometer
Triaxial is described as each three-dimensional orthogonal direction
in Z, X, and Y directions (H, V, A directions in the case of vibration
diagnosis of rotating equipment) that are perpendicular to each other. The axes
in each direction have an initial phase difference of 90 degrees from each
other, and the 3-axis vibration acceleration sensor outputs the amount of
vibration acceleration in each direction as voltage. Therefore, it can be said
that the 3-axis vibration sensor has the following advantages.
First of all, it is possible to measure the vibrations in all directions at the same time. It measures the
vibration in each axis direction at the same time without the need to measure
it sequentially with several different sensors or at different times, so it is
possible to prove the simultaneous state at the time and shorten the measurement
time.
Second, it is possible to measure -----
On the other hand, the 3-axis vibration acceleration sensor is at
least twice as high expensive as the combined
price of all three single-axis sensors, and the average probability of failure (MTBF) of the single-axis sensor is shortened to 1
year compared to the manufacturer's recommended 3 years. do. However, in fact,
the piezo-type accelerometer is more robust and less durable than expected, so
it is not easy to check the broken state. Recently, like a gyro sensor, a
modularized sensor capable of measuring 6-axis vibration has already appeared,
and like MEMS, which basically employs 3 axes,
new-technology vibration sensors with clear advantages
of low frequency have already started to lead in price. The day when
MEMS sensors will be used more often than piezos can be seen in the near
future.
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