BISOPE series 46 How do sound waves travel where there is no light refr...

BISOPE series 46- How do sound waves travel where there is no light? (refraction and diffraction)

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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.

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BISOPE series 37 Difference between shaft vibration and casing vibratio...

BISOPE series 37- Difference between shaft vibration and casing vibration(shaft vibration monitoring, bearing housing; casing vibration monitoring)

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If a dangerous state of a rotating machine is identified in advance or the machine suddenly breaks down, production is disrupted and huge asset losses occur. Therefore, in order to check the maintenance time while looking at the status (CBM), 'monitoring' must be performed and a 'monitoring system' must be installed or operated. As a monitoring method, the vibration of the facility is measured regularly in the field and sensing is performed by installing a continuous monitoring online system. But what is 'monitoring measurement technology'? The monitoring measurement technology is also divided into two parts as above, which are 'shaft vibration and casing vibration'. As for this distinction, even among those who specialize in vibration research, if you have not experienced the general field facility management method, you may not know the exact difference. This is very common in the current industrial field, but let's look at the direct differences in monitoring measurement technology that can never be confirmed theoretically.

 

Shaft & Casing, Housing vibration monitoring (shaft displacement vibration and bearing housing vibration)

 

Vibration in a rotating machine starts when the shaft rotates and excitation force (centrifugal force) is generated. Therefore, it is best to directly measure shaft vibration (shaft vibration measurement method), but this method has technical limitations. Therefore, a method of measuring where the shaft vibration is transmitted to the bearing housing or casing is often used, and this is commonly referred to as 'bearing housing vibration' or 'casing vibration'. This difference was sorted out.

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This data is very realistic and it is the result confirmed in the actual domestic industrial field, but it can be subjective and biased, so please refer to it.

 

All copyright  korea CBM  written by BISOPE , vs72@naver.com, 070-4388-0415,  www.kCBM.kr

 

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BISOPE series 35 The frequency range of the sensormeans the degree of f...

BISOPE series 35- The frequency range of the sensor(means the degree of frequency response accuracy)

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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 ..........

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 All copyright  korea CBM  written by BISOPE , vs72@naver.com, 070-4388-0415,  www.kCBM.kr

BISOPE series 31 Relation between type of vibration sensor and unit of ...

BISOPE series 31- Relation between type of vibration sensor and unit of amplitude (displacement, velocity, acceleration) Vibration measurement and evaluation

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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...

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BISOPE series 30 Noise and Vibration Stay away from it if you are tire...

BISOPE series 30- Noise and Vibration- Stay away from it if you are tired- What is sound distance attenuation?

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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, ............................

All copyright  korea CBM  written by BISOPE , vs72@naver.com, 070-4388-0415,  www.kCBM.kr

BISOPE series 29- Comparison of dB (dB) and % (Percent)

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'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'?............

All copyright  korea CBM  written by BISOPE , vs72@naver.com, 070-4388-0415,  www.kCBM.kr

BISOPE series 27 Equal loudness contours

What is Frequency? The number of cycles per second, that is, the number of repetitions per second, is used as a unit called ‘# Hertz (Hz)’. On the other hand, there is ‘#Octave’ as a filter that goes well with human listening ability, and this #filter is used to estimate the speed of sound that can be roughly distinguished by human ears. Therefore, if the horizontal axis is the octave-filtered Hz and the vertical axis is expressed as sound pressure or amplitudes, it is called a #frequency analysis graph (#spectrum analysis graph) because it can indicate which frequency of this wave is how large the amplitude is.

There is a limit to the frequency band that humans can hear, and even within that range, the sensitivity of listening differs depending on how many Hz the sound or vibration heard is. In other words, even if sound or #vibration of the same size (#sound pressure, #amplitude), according to the frequency (#low frequency? or #high frequency?), humans say 'the size is different'.

Phone curves - Equal loudness contours

Compared to animals with large ears, such as elephants, humans tend to be less able to hear in the low-frequency range. However, it can be sensitively noticed, especially around 3,900 Hz. The reason is that they saw the advantage of the resonance effect ............

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BISOPE series 25- About the bad and good points of vibration

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No matter how much people try to deny and avoid it, they cannot avoid the #wave that is transmitted through any form. A person hears because the eardrum vibrates, and sees the reflected form with the eyes because of the transmission by the wave of light. Breathing involves repetitive movements of the lungs, and walking is achieved by cyclic oscillating movements of the arms and legs. In addition, it speaks through the movement of the larynx and tongue, and it is possible to know that there is a call through sound or vibration. Early scholars in the field of vibration focused their efforts on the development of mathematical theories to understand natural phenomena, and were applied to the design of machines, structures, engines, and control systems in an engineering way, and focused on the design of motion, and safety, productivity, and asset management in the field. In order to efficiently proceed with vibration, vibration continues to be researched on the health and destruction of structures and machines, and human discomfort.

 

The damage of vibration and the use of vibration

 

Rotating machines (engines, fans, pumps, motors, etc.) generate #imbalance vibration due to poor design or current bad condition. The imbalance may cause a second large vibration when rotating at high speed, and the repetition of repeated motions leads to plastic deformation or fracture.

 

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All copyright  korea CBM  written by BISOPE , vs72@naver.com, 070-4388-0415,  www.kCBM.kr