• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1509-1510
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• 2006

ERA PD measuring system has been using for partial discharge evaluation of power appratus in test laboratories. So, the measurement uncertainty of PD measuring system (ERA), such as PD pulse calibrator rise and fall time, sacle factor(k) and linearity, transfer impedance etc, is very important factor of test result in test laboratory. In this paper, we describe tracebility and uncertainty improvement of PD measuring system in test laboratory based on IEC 60270.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2020-2021
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• 2003

Korea Research Institute of Standards and Science (KRISS) has developed a Web-based, remote, Internet calibration system to calibrate the Fluke 5700A/5720A calibrator using a transportable standard: specifically, multifunction transfer standard 4950. Although the uncertainty for the Internet calibration is up to two times larger than that using conventional manual calibration, it has many advantages: no need to transport the customer equipment, a reduction in the calibration service time, a directly enforced traceability to the national standards, convenience, and ease of use for the customers.

• Publications of The Korean Astronomical Society
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• v.37 no.1
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• pp.1-11
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• 2022

During the course of analysing both single-dish and very long baseline interferometry (VLBI) data obtained from the Korean VLBI Network (KVN), we found a systematic offset between flux density measurements from different antennas. We were able to attribute a majority of the systematic offsets to changes in the "a priori" antenna gains, which were found to have varied up to 10 percent at 22 GHz and up to 30 percent at 43 GHz. Using historical calibrator observations, we present a revised set of gains that may be applied to KVN data taken from 2015 August to 2019 January. Application of the revised gains to the KVN results in a consistency of correlated flux density measurements between the three baselines of approximately five percent. We found that images from the recalibrated data typically have a 50 percent higher dynamic range, with some cases showing an increase of dynamic range of up to a factor of three.

• Progress in Medical Physics
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• v.7 no.1
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• pp.79-89
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• 1996

The purpose of this study was to examine the dead time effects and derive the correction factor. Using the thyroid probe and lucite cylindrical phantom, $^{99m}Tc$ 10.50mCi and $^{123}I$ 2.08mCi were counted with medical spectrometer at intervals of 2 hours for 43hrs and 79 hours. respectively. $^{123}I$ 2.06mCi was counted at intervals of 6 hours for 910 hours. To measure the starting point of dead time effect, the radioactivity was measured with dose calibrator in each time. The dead time effects started at about 0.80mCi at all distances for $^{99m}Tc$, and about 1.00mCi for $^{123}I$. The radioactivity corresponding to 20％ counts loss is 1.29(center), 1.28(2cm), 1.31(4cm), 1.13(6cm)mCi for $^{99m}Tc$ and 1.39mCi for $^{123}I$. The correction factors for 2mCi of radioactivity as an example were 1.52(center), 1.52(2cm), 1.50(4cm), 1.58(6cm) for $^{99m}Tc$ and 1.58 for $^{123}I$.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1769-1776
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• 2016

For on-line partial discharge (PD) monitoring of rotating machines, a novel sensor is proposed, which can be installed on the power lead inside the terminal box of the machine. The sensor has been designed to have high capacitance, and minimal reflection of measured pulses. As a sensitivity of the sensor, transfer impedance $Z_t$ has been measured and compared to conventional coupler-type sensors. A simple method is presented for measuring $Z_t$ of coupler sensors, using a vector network analyzer and a practical lead-cable of rotating machine. Through this method, it became possible to measure the $Z_t$ of coupler sensors including the installation environment of them. The $Z_t$ of the proposed sensor is higher than that of same sized other conventional couplers at frequencies between 30 and 92 MHz. Another sensitivity test has been performed using a PD calibrator as a test pulse source. The proposed sensor has higher measured peak voltage than the conventional coupler type sensors when the same charges were input.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.12
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• pp.1699-1707
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• 2003

Coriolis mass flowmeter(CMF), which can measure the mass flow directly, is getting rapid attention for the industrial and custody transfer purpose. In order to study the characteristics and the applicability of CMF, it is tested with the national flow standard system. Two types of sensing tube, U-type and straight type, are employed in the test. Water, spindle oil and viscosity Standard Reference Material whose viscosities are 1, 20 and, 67 $\textrm{mm}^2$/s, respectively, are studied. It is shown that the linearity of CMF is getting deteriorated as the fluid viscosity increases, which is due to the zero drift and the relaxation time of the fluid. To test its applicability in the case of high pressured gas, it is calibrated using compressed air, It shows 1∼l.6 % deviations compared to the calibration results using water. It concludes that the fluid velocity in CMF should be lower than the sonic velocity. In addition, the effects of the vibration from the pipeline and pump on CMF as well as the long term stability are studied.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.637-640
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• 2005

In this paper, we investigate the characteristics of a piezoresistive AFM cantilever in the range of $0\~30{\mu}N$ by using nano force calibrator (NFC), which consists of a high precision balance with resolution of 1 nN and 1-D fine positioning stage. Brief modeling of the cantilever is presented and then, the calibration results are shown. Tests revealed a linear relationship between the probing force and sensor output (resistance change), and the force vs. deflection. From this relationship, the force constant of the cantilever was calculated to 3.45 N/m with a standard deviation of 0.01 N/m. It shows that there is a big difference between measured and nominal spring constant of 1 N/m provided by the manufacturer s specifications.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1610-1611
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• 2011

실선로 전력 케이블의 부분방전 측정은 주위 전력설비의 신호들이 혼합되면 정확한 부분방전 진단이 어려운 면이 있다. 본 논문에서는 15kV급 EPR 난연 케이블을 대상으로 거리에 따른 부분방전 신호를 검출 및 감쇄 정도 확인 시험을 통하여 발생 위치 추정 기준을 마련하고자 한다. 이를 위해 길이 500m의 EPR 난연 케이블을 제작하여 모의 선로를 구성하였고, IEC60270에 적합한 Calibrator를 이용하여 신호를 인가한 후 HFCT 센서를 사용하여 일정한 거리를 두고 방전 신호를 검출하고, Techimp사(社)의 PDBASE와 OMICRON사(社)의 MPD600을 이용하여 부분방전 신호를 분류하였다. 전압 인가 지점에서 단계적인 거리증가에 따른 부분방전 신호 감쇄 현상 및 일정 길이(300[m])에 대한 주입 신호별 감도 측정을 분석하였다. 본 논문의 시험대상인 15kV급 EPR 난연 케이블은 원자력 발전소의 배전선으로 사용하기 위해 제작된 것으로, 포설 후 절연체 내에 B/D가 발생했다고 가정했을 때, PD신호의 검출 및 대략적인 위치의 추정은 안전을 최우선시 하는 원자력 발전 및 배전 부문에서 주요한 문제로 부각 될 것이다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1380-1383
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• 2004

The scanning type XY stage is frequently used these days as precision positioning system in equipment for semiconductor or display element. It is requested higher velocity and more precise accuracy for higher productivity and measuring performance. The position accuracy of general stage is primarily affected by the geometric errors caused by parasitic motion of stage, misalignments such as perpendicular error, and thermal expansion of structure. In the case of scanning type stage, H type frame is usually used as base stage which is driven by two actuators such as linear motor. In the point view of scanning process, the stage is used in moving motion. Therefore, dynamic variation is added as significant position error source with other parasitic motion error. Because the scanning axis is driven by two actuators with two position detectors, 2 dimensional position errors have different characteristic compared to general tacked type XY stage. In this study 2D position error of scanning stage is analyzed by 1D heterodyne interferometer calibrator, which can measure 1D linear position error, straightness error, yaw error and pitch error, and perpendicular error. The 2D position error is evaluated by diagonal measurement (ISO230-6). The yaw error and perpendicular error are compensated on the base stage of scanning axis. And, the horizontal straightness error is compensated by cross axis compensation. And, dynamic motion error in scanning motion is analyzed.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1752-1758
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• 2015

This paper presents partial discharge localization in stator winding of generators using multi-conductor transmission line (MTL) and RLC ladder network models. The high-voltage (HV) winding of a 6kV/250kW generator has been modeled by MATLAB software. The simulation results of the MTL and the RLC ladder network models have been evaluated with the measurements results in the frequency domain by applying of the Pearson’s correlation coefficients. Two PD generated calibrator signals in kHz and MHz frequency range were injected into different points of generator winding and the signals simulated/measured at the both ends of the winding. For partial discharge localization in stator winding of generators is necessary to calculate the frequency spectrum of the PD current signals and then estimate the poles of the system from the calculated frequency spectrum. Finally, the location of PD can be estimated. This theory applied for the above generator and the simulation/measured results show the good correlation for PD Location for RLC ladder network and MTL models in the frequency range of kHz (10kHz<f<1MHz) and MHz (1MHz<f<5MHz) respectively.