• Title/Summary/Keyword: noise measuring method

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Condition Monitoring of Low Speed Slewing Bearings Based on Ensemble Empirical Mode Decomposition Method (EEMD법을 이용한 저속 선회베어링 상태감시)

  • Caesarendra, W.;Park, J.H.;Kosasih, P.B.;Choi, B.K.
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.2
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    • pp.131-143
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    • 2013
  • Vibration condition monitoring of low-speed rotational slewing bearings is essential ever since it became necessary for a proper maintenance schedule that replaces the slewing bearings installed in massive machinery in the steel industry, among other applications. So far, acoustic emission(AE) is still the primary technique used for dealing with low-speed bearing cases. Few studies employed vibration analysis because the signal generated as a result of the impact between the rolling element and the natural defect spots at low rotational speeds is generally weak and sometimes buried in noise and other interference frequencies. In order to increase the impact energy, some researchers generate artificial defects with a predetermined length, width, and depth of crack on the inner or outer race surfaces. Consequently, the fault frequency of a particular fault is easy to identify. This paper presents the applications of empirical mode decomposition(EMD) and ensemble empirical mode decomposition(EEMD) for measuring vibration signals slewing bearings running at a low rotational speed of 15 rpm. The natural vibration damage data used in this paper are obtained from a Korean industrial company. In this study, EEMD is used to support and clarify the results of the fast Fourier transform(FFT) in identifying bearing fault frequencies.

Optical Characteristics of Bolometric Terahertz Sensor (볼로미터형 테라헤르츠 센서의 광학적 특성 연구)

  • Han, Myung Soo;Song, Woosub;Hong, Jung Taek;Lee, Donghee
    • Journal of Sensor Science and Technology
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    • v.27 no.5
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    • pp.335-339
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    • 2018
  • The optical characteristics of a terahertz (THz) antenna-coupled bolometer (ACB) detector were evaluated using a pulsed quantum cascade laser (QCL) and radiation blackbody sources. We investigated a method for measuring the responsivity and noise-equivalent power (NEP) of the THz detector using two different types of light sources. When using a QCL source with a frequency of 3 THz, the average responsivity of 24 devices was $1.44{\times}10^3V/W$ and the average NEP of those devices was $3.33{\times}10^{-9}W/{\surd}Hz$. The average responsivity and NEP as measured by blackbody source were $1.79{\times}10^5V/W$ and $6.51{\times}10^{-11}W/{\surd}Hz$, respectively, with the measured values varying depending on the light source. This was because the output power of each light source was different, with the laser source being driven by a pulse type wave and the blackbody source being driven by a continuous wave. The power input to the THz sensor was also different. Futhermore, the responsivity and NEP values measured using band pass filter (BPF) were similar to those measured when using only THz windows. It was found that ACB sensor responds normally in the THz region to both the laser and the blackbody source, and the method was confirmed to effectively evaluate the characteristics of the THz sensor.

A Study on Algorithm for Gear Profile Measurement Using a Standard Gear (표준기어를 이용한 기어 프로파일 정밀측정 알고리즘에 관한 연구)

  • Lee, Min-Ki;Lee, Eung-Suk;Kim, Kuang-Jung;Park, Hyun-Yoong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.5
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    • pp.555-561
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    • 2012
  • In this paper, a method to control the noise and vibration of a standard gear transmitting mechanical power in the transmission insides, to things regarding a way to inspect the gear which was processed minutely. In an algorithm used to accurately measure a work gear, the measurements of the master gear are considered as the basis. The existing method considers one rotation of the standard gear and monitor gear, and that carried out mastering work in frequency ways. In this study, an algorithm to measure standard gear and monitor gear is proposed along with methods to calculate an error of the monitor gear and to significantly increase the precision of gear measurement. Further, the algorithm is fast and is expected to be capable of accurately measuring for mastering processing.

An Accurate Direction Finding Technology Using a Phase Comparison and Time Difference of Arrival (위상비교와 시간차를 복합한 정밀 방향탐지 기술)

  • Lim, Joong-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.11
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    • pp.5208-5213
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    • 2011
  • In this paper, we proposed a new direction finding(DF) technology using TDOA(time-difference of arrival) and PDOA(phase difference of arriving signal) method. The proposed technology has a good DF accuracy without DF ambiguity. TDOA or PDOA technology is used to the most of intelligence systems in 21 century. The principle of TDOA is to receive a signal with two parallel antennas, measure the time difference of arrival signal, and converse the time difference to the direction of incident signal. Those technology make a DF system small size but the DF accuracy is low into short antenna installation distance. The principle of PDOA is similar to TDOA except measuring the phase difference of arrival signal, These technology get a good DF accuracy in short antenna installation distance but have a DF ambiguity. The proposed DF method is simulated into DF system operation environment with noise, and has a good DF accuracy.

An Method for Inferring Fine Dust Concentration Using CCTV (CCTV를 이용한 미세먼지 농도 유추 방법)

  • Hong, Sunwon;Lee, Jaesung
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.23 no.10
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    • pp.1234-1239
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    • 2019
  • This paper proposes a method for measuring fine dust concentration through digital processing of images captured by only existing CCTVs without additional equipment. This image processing algorithm consists of noise reduction, edge sharpening, ROI setting, edge strength calculation, and correction through HSV conversion. This algorithm is implemented using the C ++ OpenCV library. The algorithm was applied to CCTV images captured over a month. The edge strength values calculated for the ROI region are found to be closely related to the fine dust concentration data. To infer the correlation between the two types fo data, a trend line in the form of a power equation is established using MATLAB. The number of data points deviating from the trend line accounts for around 12.5%. Therefore, the overall accuracy is about 87.5%.

A Study on Selection of Optimal Imaging Diagnostic Device for Cerebral Angiography: Focusing on MRA, CTA, and DSA Imaging Diagnosis Devices (뇌혈관 검사 시 최적의 영상 진단장치 선정에 관한 연구: MRA, CTA, DSA, 영상 진단장치 중심으로)

  • Byun, Jung-Su;Goo, Eun-Hoe
    • Journal of the Korean Society of Radiology
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    • v.11 no.7
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    • pp.637-645
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    • 2017
  • The objective of this study was to find the optimum test device for the cerebral blood vessels by comparing and analyzing the SNR and CNR methods for images of three devices (i.e., MRA, CTA, and DSA). The study targeted 90 patients who underwent cerebral angiography from November 2016 to May 2017. The measuring parts were measured by using Rt MCA, Lt MCA, and ACA Image J. The results of quantitative analysis showed that the mean SNR of MRA, the CNR of MRA, the signal strength of MRA, the mean SNR of CTA, the CNR of CTA, the signal strength of CTA, the SNR of DSA, the CNR of DSA, and the signal strength of DSA were evaluated as 254.87, 178.13, 326.81, 74.75, 62.2, 356.66, 26.85, 25.89, and 4400.69, respectively (p<0.05). As a result, both SNR and CNR methods measured it in the order of MRA>CTA>DSA. Statistical significance was determined by using ANOVA analysis at p<0.05 and Bonferroni method was used as a post-hoc analysis SPSS. In conclusion, the results of this study revealed that the optimum imaging devices were MRA, CTA, and DSA after evaluating randomly selected patients with cerebrovascular disease.

A study on the standard for determining airborne sound insulation performance of sound barrier panels (방음판의 음향투과손실 측정규격에 관한 연구)

  • Oh, Yang Ki
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.3
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    • pp.302-311
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    • 2022
  • Sound barrier walls are one of the most effective alternatives for reducing environmental noise on roads and railways in the city center. The insertion loss of the sound barrier against road traffic noise is the sum of the sound transmission loss, sound absorption loss, and sound energy reduction due to the diffraction attenuation of the sound barrier. The sound transmission loss of the sound barrier is one of the important factors that determine the insertion loss of the sound barrier and is a basic indicator that determines the performance of the sound barrier. Nevertheless, there is not a separate standard in Korea for measuring the acoustic transmission loss of sound barrier panels. There are only a few conditions in KS F 4770 series that stipulates on the general material of sound barrier panels. This thesis examines the necessity of the acoustic transmission loss measurement and evaluation standards of sound barrier walls, and seeks a measurement method in a free sound field (anechoic chamber) sound receiving room considering the characteristics of sound barrier walls installed in external spaces, unlike indoor building materials. In addition, a single number evaluation method using a reference spectrum was proposed so that the sound insulation effect according to various installation places such as roadside or railroad side can be easily displayed.

Comparison of the I-V Characteristic as Various Composition ratio of Iodine in a-Se of $BrO_2/a-Se$ based Radiation Conversion Sensor ($BrO_2/a-Se$ 구조의 방사선 변환센서에서 a-Se에 첨가된 조성비 변화에 따른 I-V 특성 비교)

  • Choi, Jang-Yong;Park, Ji-Koon;Gong, Hyun-Gi;Ahn, Sang-Ho;Nam, Sang-Hee
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.11a
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    • pp.440-443
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    • 2002
  • Present1y the X-Ray diagnosis system is a real condition that is changing by digital ways in it's existent analog ways. This digital radiation detector is divided by the direct method and the indirect method. The indirect method of applied voltage has special qualities that the resolution is low than direct method by diffusion effect that happens. The conversion process ( radiation${\rightarrow}$visible ray${\rightarrow}$electrical signal of two times, has shortcomings that the energy conversion efficiency of electrical signal is low. The direct method has shortcomings that need strong electric fie1d to detect electrical signal efficiently. This research achieved to develop digital detector of the Hybrid method that have form that mixes two ways to supplement shortcoming of direct. indirect method. A studied electrical characteristic by Iodine's Mixture ratio change is added to selenium in the detector which has a multi-layer structure (Oxybromide + a-Se). There are 8 kinds of Manufactured compositions to amorphous selenium Iodine each 30ppm, 100ppm, 200 ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm by a doped photoconductor through a vacuum thermal evaporation method. The phosphor layer is consisted of Oxybromide ($BrO_2$) which uses optical adhesives multi-layer structure. The manufactured compositions calculates and compares Net Charge and signal to noise ratio measuring Photocurrent about Darkcurrent and X-ray. When doped Iodine Mixture ratio is 500ppm to the multi-layer structure (Oxybromide + a-Se), applied voltage of $3V/{\mu}m$, leakage current of compositions $2.61nA/cm^2$ and net charge value by 764pC/$cm^2$/mR then the best result appeared.

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Algorithm Development and Experimental Verification of Acoustic Emission First-arrival-time Determination for the Source Location (정확한 미소파괴음의 발생위치 분석을 위한 신호 도달시간 결정 알고리즘 연구 및 실험적 검증)

  • Jang, Hyun-Sic;Choi, Jun-Young;Jang, Bo-An
    • The Journal of Engineering Geology
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    • v.25 no.4
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    • pp.587-598
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    • 2015
  • We examined various existing threshold methods for the determination of the first arrival time of acoustic emission (AE), and developed a new variable threshold method that could determine the first arrival time of AE more accurately and more quickly than existing methods. The new method, a modification of an existing threshold method, does not fix the threshold, but applies variable thresholds for the AE signals according to noise analysis. Two- and three-dimensional models were established to test the effectiveness of the new method. It could determine source locations of AE in a two-dimensional model 38.3% more accurately than the pre-existing threshold methods. Its accuracy improvement over the existing methods in a three-dimensional model was about 15.2%. A practical test involved measuring the source locations of AE during three-point bending tests of granite cores. The new method placed the sources closer to the fracture plane than did the pre-existing methods, indicating its superior (and quicker) ability to determine the source locations of AE.

Development of Quantification Method for Bioluminescence Imaging (발광영상에 대한 정량화 방법 개발)

  • Kim, Hyeon-Sik;Choi, Eun-Seo;Tak, Yoon-O;Choi, Heung-Kook;Lee, Ju-Young;Min, Jung-Joon;Lee, Byeong-Il
    • Nuclear Medicine and Molecular Imaging
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    • v.43 no.5
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    • pp.451-458
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    • 2009
  • Purpose: Optical molecular luminescence imaging is widely used for detection and imaging of bio-photons emitted by luminescent luciferase activation. The measured photons in this method provide the degree of molecular alteration or cell numbers with the advantage of high signal-to-noise ratio. To extract useful information from the measured results, the analysis based on a proper quantification method is necessary. In this research, we propose a quantification method presenting linear response of measured light signal to measurement time. Materials and Methods: We detected the luminescence signal by using lab-made optical imaging equipment of animal light imaging system (ALIS) and different two kinds of light sources. One is three bacterial light-emitting sources containing different number of bacteria. The other is three different non-bacterial light sources emitting very weak light. By using the concept of the candela and the flux, we could derive simplified linear quantification formula. After experimentally measuring light intensity, the data was processed with the proposed quantification function. Results: We could obtain linear response of photon counts to measurement time by applying the pre-determined quantification function. The ratio of the re-calculated photon counts and measurement time present a constant value although different light source was applied. Conclusion: The quantification function for linear response could be applicable to the standard quantification process. The proposed method could be used for the exact quantitative analysis in various light imaging equipments with presenting linear response behavior of constant light emitting sources to measurement time.