• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권8호
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• pp.426-432
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• 2004

This paper presents a systematic approach of measurement, modeling and analysis of grounding system impedance in the field of lightning protection system and intelligent power equipments. The measurement and analysis system of ground impedance is based on a computer aided technique. The magnitude and phase of ground impedance were determined by the novel measurement and analysis using the revised fall-of-potential method. The ground impedances of the ground rod of 50 m long are considerably dependent on the frequency. The ground impedance is mainly resistive in the frequency range of 3-20 kHz. At higher frequencies, the reactive components of the ground impedances are no longer negligible and the inductance of the ground rod was found to be the core factor deciding the ground impedance. Although the steady-state ground resistance of the ground rod of 50 m was less than that of the ground rod of 10 m, the ground impedances of the ground rod of 50 m over the frequency range of more than 60 kHz were much greater than those of the ground rod of 10 m. Furthermore, the equivalent circuit model based on the measured data was proposed. and the calculated results were in approximately agreement with the measured data.

• Journal of Advanced Marine Engineering and Technology
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• 제21권5호
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• pp.579-583
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• 1997

A diesel Engine rotates vibratively because of alternative explosion strokes. Traditional measurement of a diesel engine speed is carried out by measuring output voltage of FV convertor from input signals of MPU(magnetic pickup unit) or of DC tachometer. Because these measurement include also vibrative rotation of a diesel engine, an analog filter is often used to eliminate high frequency noises due to periodic explosion stroke. But by this method these high frequency noises do not eliminated effectively because noise frequencies are changed according to diesel engine speed. In this paper, author proposes a new measurement method of a diesel engine revolution which read digital signal directly from MPU and prove the utility of proposed method through the real experiment.

• Journal of Biosystems Engineering
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• 제22권3호
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• pp.269-278
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• 1997

An automatic level measurement system was developed to level the land fer direct seeding of rice. A laser transmitter/receiver set was used to measure land-level. The inclination error occurred in level measurement on irregular land surface could be compensated by attaching rotating mass. The level measuring experiments were performed on three kinds of different shapes(step, random, sine). This system could accurately measure step level of which amplitude was 40mm in 0.5s, random level change within $\pm$ 5mm maximum measurement error, and sine level change of which spatial frequency was 0.5m-1. To verify performance of the inclination error compensation system, frequency transfer function(acceleration input vs. inclination error) was computed by spectral analysis. The inclination error was decreased about 20㏈ by error compensation system.

• Tribology and Lubricants
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• 제26권2호
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• pp.97-104
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• 2010

A new magnetoelastic technique of oil viscosity measurement, where the oil viscosity is estimated by frequency shift of natural oscillations of magnetoelastic ribbon, is implemented in this study. Laboratory tests of the detector prototype are performed for measurement of viscosity of base synthetic and mineral oils. It was found that measurement accuracy was better when damping factor was estimated in comparison with accuracy of frequency of damped oscillations. Thus the oil viscosity was calibrated as a function of number of pulses of the damped oscillations of magnetoelastic ribbon. Result generally showed that developed detector is promising for in line oil viscosity measurement in wide viscosity range from 10 cSt up to 600 cSt, while the viscosity measurement was relatively instable when the viscosity of test oil was over 400 cSt.

• 한국분무공학회지
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• 제7권2호
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• pp.1-6
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• 2002

It is necessary to develope a high frequency diode laser sensor system based on the absorption spectroscopy for the measurement of temperature of the spray flame. DFB diode laser operating near $2.0{\mu}m$ was used to scan over selected $H_2O$ transitions near $1.9{\mu}m\;and\;2.2{\mu}m$, respectively. The measurement sensitivity at wide range of sweep frequency was evaluated using multi-pass cell containing $CO_2$ gas. This diode laser absorption sensor with high temporal resolution up to 10kHz was applied to measure the gas temperature in the spray flame region of liquid-gas 2-phase counter flow flame. The successful demonstration of time series temperature measurement in the spray flame gives us motivation of trying to establish non-intrusive temperature measurement method in the practical spray flame.

• Journal of the Optical Society of Korea
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• 제9권2호
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• pp.54-58
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• 2005

A novel mode analysis method and differential mode delay measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. The differential mode delay (DMD) of the sample fiber was measured to be 16.58 ps/m with a resolution of 1.5 ps/m. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.503-507
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• 2004

This paper is concerned with the measurement of low-frequency vibrations of structures using the image processing method. To measure the vibrations visually, the measurement system consists of a camera, an image grabber board, and a computer. The specific target installed on the structure is used to calculate the vibration of structure. The captured image is then converted into a pixel-based data and then analyzed numerically. The limitation of the system depends on the image capturing speed and the size of image. In this paper, we discuss the methodology for the vibration measurement using the image processing method. The method enables us to measure the displacement directly without any contact. The resolution of the vibration measurement can be refined but limited to the sub centimeter displacement.

• 한국군사과학기술학회지
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• 제22권2호
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• pp.233-240
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• 2019

High-altitude ElectroMagnetic Pulse(HEMP) is a high-power electromagnetic pulse caused by nuclear explosions at altitudes above 30 km. This pulse can cause serious damage to the electrical/electronic device. Therefore, there are a lot of studies on the effects of HEMP in the literature. When conducting studies on the effects of HEMP, it is essential to measure the simulated HEMP. Depending on the need for measurement, this paper focuses on the HEMP measurement method. This paper proposes a measurement method using frequency domain compensation to extract the correct waveform and solves the offset problem more efficiently than the conventional methods. The proposed method is verified by experiment using HEMP simulator and measurement system in ADD.

• 대한치과보철학회지
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• 제41권2호
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• pp.182-206
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• 2003

Statement of problem : Successful osseointegration of endosseous threaded implants is dependent on many factors. These may include the surface characteristics and gross geometry of implants, the quality and quantity of bone where implants are placed, and the magnitude and direction of stress in functional occlusion. Therefore clinical quantitative measurement of primary stability at placement and functional state of implant may play a role in prediction of possible clinical symptoms and the renovation of implant geometry, types and surface characteristic according to each patients conditions. Ultimately, it may increase success rate of implants. Purpose : Many available non-invasive techniques used for the clinical measurement of implant stability and osseointegration include percussion, radiography, the $Periotest^{(R)}$, Dental Fine $Tester^{(R)}$ and so on. There is, however, relatively little research undertaken to standardize quantitative measurement of stability of implant and osseointegration due to the various clinical applications performed by each individual operator. Therefore, in order to develop non-invasive experimental method to measure stability of implant quantitatively, the resonance frequency analyzer to measure the natural frequency of specific substance was developed in the procedure of this study. Material & method : To test the stability of the resonance frequency analyzer developed in this study, following methods and materials were used : 1) In-vitro study: the implant was placed in both epoxy resin of which physical properties are similar to the bone stiffness of human and fresh cow rib bone specimen. Then the resonance frequency values of them were measured and analyzed. In an attempt to test the reliability of the data gathered with the resonance frequency analyzer, comparative analysis with the data from the Periotest was conducted. 2) In-vivo study: the implants were inserted into the tibiae of 10 New Zealand rabbits and the resonance frequency value of them with connected abutments at healing time are measured immediately after insertion and gauged every 4 weeks for 16 weeks. Results : Results from these studies were such as follows : The same length implants placed in Hot Melt showed the repetitive resonance frequency values. As the length of abutment increased, the resonance frequency value changed significantly (p<0.01). As the thickness of transducer increased in order of 0.5, 1.0 and 2.0 mm, the resonance frequency value significantly increased (p<0.05). The implants placed in PL-2 and epoxy resin with different exposure degree resulted in the increase of resonance frequency value as the exposure degree of implants and the length of abutment decreased. In comparative experiment based on physical properties, as the thickness of transducer increased, the resonance frequency value increased significantly(p<0.01). As the stiffness of substances where implants were placed increased, and the effective length of implants decreased, the resonance frequencies value increased significantly (p<0.05). In the experiment with cow rib bone specimen, the increase of the length of abutment resulted in significant difference between the results from resonance frequency analyzer and the $Periotest^{(R)}$. There was no difference with significant meaning in the comparison based on the direction of measurement between the resonance frequency value and the $Periotest^{(R)}$ value (p<0.05). In-vivo experiment resulted in repetitive patternes of resonance frequency. As the time elapsed, the resonance frequency value increased significantly with the exception of 4th and 8th week (p<0.05). Conclusion : The development of resonance frequency analyzer is an attempt to standardize the quantitative measurement of stability of implant and osseointegration and compensate for the reliability of data from other non-invasive measuring devices It is considered that further research is needed to improve the efficiency of clinical application of resonance frequency analyzer. In addition, further investigation is warranted on the standardized quantitative analysis of the stability of implant.

• 한국광학회지
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• 제19권1호
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• pp.36-42
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• 2008

PZT형 파장가변 필터를 이용하여 파장스윕(wavelength-swept) 광원을 구성할 때 발진파장의 변화율을 일정하게 하려면 필터의 이력(hysteresis)특성을 알아야 한다. 이력특성을 무시하고 필터를 구동할 경우 파장스윕 광원을 사용하는 optical frequency domain reflectometry(OFDR) 시스템의 분해능이 떨어진다. 광스펙트럼 분석기(OSA)를 이용하여 필터의 이력특성을 측정할 수도 있지만 측정시간이 너무 길고 실제 구동조건에서의 이력특성은 측정할 수 없다는 문제가 있어 실제 구동조건에서 필터의 이력특성을 고속으로 측정할 수 있는 OFDR의 원리에 기초한 이력 측정법을 제시하였다. 파장스윕 광원과 간섭계, 신호처리 장치, 그리고 PC 프로그램으로 구성된 고속 이력측정장치를 구현하고, 이를 사용하여 필터 구동조건에서의 이력특성을 측정하였다. 마지막으로 측정된 이력특성을 파장스윕광원의 구동에 적용하여 선형적 파장변화를 얻음으로써 새로운 이력측정법의 유효성을 검증하였다.