In
order to diagnose motors (electric motors), you must understand the operating
principles of the motor, but first you must know the corresponding terminology.
If you cannot understand the terminology used by motor experts and public
affairs and maintenance teams (electrical, relay, mechanical), you will
inevitably have poor data for important analysis. Then comes the diagnosis. Of
course, there are diagnostic terms, but it can be said to be the same way a
doctor learns basic anatomy and learns medical terminology first. Here,
motor-related electrical terms and terms for vibration diagnosis are defined.
Motor terminology
number
of revolutions
It
is the degree of rotation speed and is expressed as RPM (Revolution Per
Minute).
Torque
It
refers to rotational force and is expressed as kgfm or Nm.
Inertia
It
refers to the property of an object to maintain its state of motion unless an
external force acts on it.
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
기어박스는 변속을 하여 피동부에 동력을 전달하는 기계요소(벨트, 체인 등)중의 하나로서 다른 유사 요소와 가장 큰 특징은 강한 토오크를 전달할 수 있다는 것이다. 따라서 고속의 동력으로 저속의 강한 토오크를 필요로 하는 곳은 대부분 강한 부하를 받는 곳이다. 기어박스는 특히 시멘트의 견인 및 파쇠, 타이어의 파쇠 및 압출, 열차의 빈번한 동력전달 등에서 감속기로 활용된다. 반면에 가스생산의 고압 토출에 사용되는 기어박스는 증속기로서의 회전변경을 위해 사용되는 경우도 있다. 다시 한번 살펴보면 기어박스는 절대로 홀로 움직여서 활용될 수 있는 기계요소가 아닌 것을 확인할 수 있다. 그래서 진동이 발생한다.
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...
Whatever
it is, power (#Power, output) itself is constant, but energy (#Energy,
work) gets smaller as the distance increases; As you move, the energy gets
smaller and smaller.
Noise and vibration are lost as kinetic energy and
potential energy are transformed into thermal energy or other energy. That is,
the wave energy must go through a process of attenuating and disappearing. If
you apply this, ............................
'dB (dB, decibel)', which is used as the most common way
to determine the level of amplitude, is often used when trying to explain 'to
what extent to be compared', especially for the evaluation of linearity, which
is the usable frequency range of vibration and noise, measuring instruments or
sensors. there is. Explain again how this differs from '%'.
The
reason why the linear section of the graph is selected as dB or % is used when
setting standards for reliability in various applications (mathematics,
physics, measurement, medicine, statistics, etc.). In particular, it is an
essential confirmation condition for accurate measurement and selection in the
sensor field. At this time, dB and % can be understood in terms of mathematical
principles, but they can be difficult to compare in practice, so they are
compared and explained.
dB and % are comparison methods.
dB is an amplitude value expressing log (ratio of change
rate), and % is a method of expressing the size of a linear (arithmetic) value. If % has changed by 50%,
this is self-explanatory and easy to understand. But what does it mean that dB
'changed by 3dB'?............
