• Journal of the Optical Society of Korea
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• 제4권2호
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• pp.94-99
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• 2000

Optical monitoring using the chromatic aberration of focusing optics is applied to auto-focus control in laser welding. The spectral transmittance of thermal radiation from a weld pool through an aperture depends on the wavelength of the spectral band and on the distance of the weld pool from the focusing optics. Its dependence has been used to monitor the focus shift in laser welding by measuring the spectral band signals filtered by the aperture. The difference between pulsed and continuous laser welding is analyzed. Furthermore, the dependence of the focus shift monitoring on the weld pool size variation is optimized to monitor the focus shift independently from the laser power change at the weld pool. The performance of the auto-focus control with chromatic filtering is presented for pulsed laser welding.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.242-243
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• 2015

Fault detection using optical emission spectra with modified K-means cluster analysis and principal component anal ysis are demonstrated for inductive coupl ed pl asma cl eaning processes. The optical emission spectra from optical emission spectroscopy (OES) are used for measurement. Furthermore, Principal component analysis and K-means cluster analysis algorithm is modified and applied to real-time detection and sensitivity enhancement for fluorocarbon cleaning processes. The proposed techniques show clear improvement of sensitivity and significant noise reduction when they are compared with single wavelength signals measured by OES. These techniques are expected to be applied to various plasma monitoring applications including fault detections as well as chamber cleaning endpoint detection.

• ETRI Journal
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• 제35권2호
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• pp.253-258
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• 2013

We propose and demonstrate an efficient power-saving optical network unit (ONU) based on upstream traffic monitoring for 10-Gb/s wavelength division multiplexed passive optical networks (WDM-PONs). The power-saving mode controller uses a ${\mu}$-processor and traffic monitoring modules followed by the proposed power-saving processes to operate the sleep mode ONU. The power consumption of the ONU is effectively reduced from 19.3 W to 6.4 W when no traffic from the users is detected. In addition, we design a power-saving mechanism based on a cyclic sleep mode operation to allow a connectivity check between the optical line terminal and ONU. Our calculation results show that the WDM-PON ONU reduces the power consumption by around 60% using the proposed mechanism.

• 전자통신동향분석
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• 제19권5호통권89호
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• pp.125-133
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• 2004

파장분할 다중방식 광통신망(WDM -PON) 운영의 신뢰성을 높이기 위해 각 광 채널의 파장과 파워, 그리고 광섬유로 이어진 링크(link)의 절단상태 등을 모니터링(monitoring)하는 것은 필수적이다. 본 원고에서는 이러한 목적을 효율적이고 경제적으로 달성하기 위해 제시되고 검증되었던 방법들을 pilot tone을 이용한 방법, AWG, FBG, tunable filter 등의 파장 선택성 소자를 이용한 방법, electrical processing을 이용한 방법 등의 세 가지로 나누어 소개한다.

• 한국전자통신학회논문지
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• 제9권8호
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• pp.841-846
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• 2014

FBG센서는 터널, 교량, 선박과 같은 구조물의 변형을 측정하고 활용된다. 본 논문은 구조물의 상태를 FBG센서를 이용하여 원격모니터링 하기 위한 광전변환시스템의 개발 구현에 관한 것이다. 개발한 광전변환시스템은 원격 모니터링을 위하여 유선과 무선통신 기능으로 각각 CAN과 Zigbee를 포함한다. 광전변환시스템은 광회절격자에 의하여 분광된 FBG센서의 반사광을 선형 이미지센서로 입사하여 파장의 변이를 FPGA를 이용하여 측정한다. FBG센서신호에 대한 처리와 원격모니터링을 위한 데이터 전송을 위하여 DSC(digital signal controller)를 이용한다. 개발한 광전변환시스템이 구조물 변형 측정에 효율적임을 실험을 통하여 확인하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.17-20
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• 2005

In-situ structural health monitoring of filament wound pressure tanks were conducted during water-pressurizing test using embedded fiber Bragg grating (FBG) sensors. We need to monitor inner strains during working in order to verify the health condition of pressure tanks more accurately because finite element analyses on filament wound pressure tanks usually show large differences between inner and outer strains. Fiber optic sensors, especially FBG sensors can be easily embedded into the composite structures contrary to conventional electric strain gages (ESGs). In addition, many FBG sensors can be multiplexed in single optical fiber using wavelength division multiplexing (WDM) techniques. We fabricated a standard testing and evaluation bottle (STEB) with embedded FBG sensors and performed a water-pressurizing test. In order to increase the survivability of embedded FBG sensors, we suggested a revised fabrication process for embedding FBG sensors into a filament wound pressure tank, which includes a new protecting technique of sensor heads, the grating parts. From the experimental results, it was demonstrated that FBG sensors can be successfully adapted to filament wound pressure tanks for their structural health monitoring by embedding.

• KSTLE International Journal
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• 제8권1호
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• pp.1-6
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• 2007

Chromatic device was developed using light emitting diodes, optic fibers and photodiodes. Chromatic ratio and total contamination parameters based on transmitted light intensity in Red, Green, and Blue wavelengths were used for oil chemical and particulate contamination assessment. Chromatic ratio criterion was found independent of the particulate contamination of oil; but depended on chemical degradation, being more sensitive for synthetic than mineral hydraulic oil. Total contamination index of the sensor depended on both the chemical degradation and particulate contamination of the oil; being most sensitive in blue wavelength, and least in the red. Test results for synthetic hydraulic oils monitored corroborated with results of other tests such as viscosity, total acid number, elemental optical emission spectroscopy, particulate counts and UV-VIS photospectrometry. Chromatic ratio showed a clearer indication of oil degradation, compared to key monitoring parameters such as total acid number, viscosity and particle counts. The results showed that these parameters are effective criteria for the condition monitoring of synthetic hydraulic oils.

• International Journal of Precision Engineering and Manufacturing
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• 제6권3호
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• pp.19-23
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• 2005

To minimize the weld defect in manufacturing of the welded tube by using $CO_2$ laser, the monitoring of the welding quality and the seam tracking along the butt-joint lengthwise to the tube axis are studied. The longitudinal butt-joint is shaped from $60kgf/mm^2$ grade steel sheet by 2 roll bending method, and welded by the $CO_2$ laser welding system equipped with the seam tracker and plasma sensor. The laser welded tube has the thickness of 1.5mm, diameter of 105.4mm and length of 2000mm. The precise positioning of the laser beam on the butt-joint to be assembled is obtained within $200{\mu}m$ by the laser vision sensor. The artificial defects in the butt-joint are well observed by the signal of plasma intensity measured from the plasma sensor of UV wavelength range within 400nm. The developed $CO_2$ laser tube welding system has the function of the precision seam tracking and the real-time monitoring of the welding quality. In conclusion, the laser welded tube can be used for manufacturing of automobile chassis and components after hydro-forming.

• 한국통신학회논문지
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• 제36권10B호
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• pp.1216-1221
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• 2011

본 논문은 코드 분할 다중방식을 이용하여 외부로부터 선박에 가해지는 변형 및 온도 변화를 모니터링 할 수 있는 광섬유 브라그 격자 (FBG) 기반의 센서 네트워크를 제안하였다. 선박에 변형이 발생 하거나 온도의 변화가 일어날 때 FBG는 본래 가지고 있는 중심 파장이 이동하며 이는 외부 변형 크기에 비례하여 증가된다. 중심파장의 변화량을 측정함으로써 센서에 가해지는 변형이나 온도의 크기를 알 수 있다. 제안된 센서 네트워크는 코드분할 다중방식을 이용하였으며 광원에서 발생되는 신호를 직접 변조하여, 변조된 신호를 센서로 보내고 센서로부터 돌아오는 신호를 검출하여 상태를 모니터링하게 된다. 또한 슬라이딩 자기상관 기법과, 파장-시간 변환 기법을 이용하여 빠른 센싱과 넓은 범위의 센싱이 가능하도록 하였다.

• 전기학회논문지
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• 제60권11호
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• pp.2088-2092
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• 2011

The accelerated thermal aging of CSPE(chloro sulfonate polyethylene) of test cables were carried out for the period equal to 10, 20 and 30 years in air at $100^{\circ}C$, respectively. The CSPE cables(TAIHAN electric wire Co. Ltd) which installed in nuclear power plant for three years were used as starting materials. Condition monitering methods of the accelerated thermal aging of CSPE cables were estimated through indenter modulus and OIT(oxidation induction time) of IEC 62582, and those were newly estimated through volume electrical resistivity, ultrasound reflection time, density, FE-SEM(field emission scanning electron microscopy), XPS(x-ray photoelectron spectroscopy), EDS(energy dispersive spectroscopy), and WD-XRF(wavelength dispersive x-ray fluorescence). A new condition monitoring methods of the accelerated thermal aging of CSPE cables were generally coincident with trend of indenter modulus expect EDS, XPS and XRF. A volume electrical resistivity among new condition monitoring methods of the accelerated thermal aging of CSPE cables is excellent. It is considered that life-time of CSPE cable can be predicted through volume electrical resistivity, if CSPE jacket was aged for period such as more than 20 years.