• Journal of the Korean Society for Precision Engineering
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• v.26 no.11
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• pp.41-46
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• 2009

We present experimental data on the time response behavior of industrial platinum resistance thermometers (IPRT) to help with the selection of proper sensors in industry and research laboratories. Time constants of IPRTs were measured using a method specified in ASTM standards. Two different sensors of different protecting sheath diameters were tested in air, water and silicon oil at temperatures from $0^{\circ}C$ to $200^{\circ}C$. The time constant was the smallest in water and the highest in air. As the test temperature increased, time constants tended to decrease at all heat conducting media. For different diameters of sheath of IPRT at the same temperature, it was found that the IPRT of larger diameter showed higher time constant in air, but the opposite dependence was observed in water and oil. From the measured results, it was suggested that the sensor diameter and heat conducting medium should be considered if one wants to select proper thermometer to measure the dynamic temperature change in industry and research area.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.10
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• pp.563-570
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• 2003

When a fault occurs on railway feeders it is very important to detect the fault to protect trains and facilities. Because a DC railway system has low feeder voltage, The fault current can be smaller than the current of load starting. So it is important to discriminate between the small fault current and the load starting current. The load starting current increases step by step but the fault current increases at one time. So the type of $\Delta$I/ relay(50F) was developed using the different characteristics between the load starting current and the fault current. The load starting current increases step by step so the time constant of each step is much smaller than that of the fault current. First, to detect faults in DC railway systems, an algorithm using the time constant calculated by the method of least squares is presented in this paper. If a fault occurs on DC railway systems it is necessary to find a fault location to repair the faulted system as soon as possible. The second aim of the paper is to calculate the accurate fault location using Kirchhoff's voltage law.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.91-101
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• 2004

With the mathematic linear model of a combustor which consists of a combustion chamber and injectors, the analysis of low frequency dynamic characteristics of a liquld-propellant rocket engine combustor was performed. Propellant mass flowrate was varied by combustion chamber pressure feedback, therefore low frequency oscillation was appeared. Increasing the time constant of a combustion chamber and injector pressure differences and decreasing combustion time delay increased the combustor system stability. The variation of injector time constant little affected stability. The system was always stable, when there was no combustion time delay. Increasing combustion time delay decreased oscillation frequency and damping ratio, and the system eventually became unstable.

• Progress in Medical Physics
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• v.14 no.1
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• pp.54-67
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• 2003

The voltage-dependence of N-type calcium current inactivation is U-shaped with the degree of inactivation roughly mirroring inward current. This voltage-dependence has been reported to result from a purely voltage-dependent mechanism. However, $Ca^{2＋}$-dependent inactivation of N-channels has also been reported. We have investigated the role of $Ca^{2＋}$ in N-channel inactivation by comparing the effects of $Ba^{2＋}$and $Ca^{2＋}$ on whole-cell N-current in rat superior cervical ganglion neurons. For individual cells in-activation was always larger in $Ca^{2＋}$ than in $Ba^{2＋}$ even when internal EGTA (11 mM) was replaced with BAPTA (20 mM). The inactivation vs. voltage relationship was U-shaped in both divalent cations. The enhancement of inactivation by $Ca^{2＋}$ was inversely related with the magnitude of inactivation in $Ba^{2＋}$ as if the mechanisms of inactivation were the same in both $Ba^{2＋}$ and $Ca^{2＋}$. In support of this idea we could separate fast ( ${\gamma}$ ～150 ms) and slow ( ${\gamma}$ ～ 2500 ms) components of inactivation in both $Ba^{2＋}$and $Ca^{2＋}$ using 5 sec voltage steps. Differential effects were observed on each component with $Ca^{2＋}$ enhancing the magnitude of the fast component and the speed of the slow component. The larger amplitude of fast component indicates that the more channels inactivate via this pathway with $Ca^{2＋}$ than with $Ba^{2＋}$, but the stable time constants support the idea the fast inactivation mechanism is identical in $Ba^{2＋}$and $Ca^{2＋}$. The results do not support a $Ca^{2＋}$-dependent mechanism for fast inactivation. However, the $Ca^{2＋}$-induced acceleration of the slowly inactivating component could result from a $Ca^{2＋}$-dependent process.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.1
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• pp.90-98
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• 1998

This paper is to describe the improved vector control which can control the induction motor robustly in low speed. When the induction motor is drived with low speed, below 10 percent of the rated speed, an algorithm which can compensate the error of unit vector angle generated by the harmonics is proposed. Another algorithm which can be tuned to the rotor time constant so that nay be robust to the rotor parameter change in low speed and transient state was proposed. The ripple of flux and torque was reduced by the proposed vector control and then the stable output characteristics was obtained in low speed. When the input and output is sinusoidal, the proposed vector control, the direct vector control and the indirect vector control were analyzed and compared in the low speed characteristics. And each control characteristics is compared and analyzed in state of containing harmonics. The estimation and tunning performance of rotor time constant is confirmed with simulation. The whole control system is implemented by real hardware and experimented to compare the proposed vector control with the direct vector control. As a result of the experiment with two control methods in low speed, the torque ripple of the proposed vector control is improved by 45 percent than the direct vector control. And it is confirmed that the flux current ripple is reduced in 0.2 p.u. and torque current ripple is reduced in 0.6 p.u. It is confirmed that the rotor time constant by the estimation and the tunning algorithm is tunned by the real rotor time constant. Finally, it was confirmed that the validity and robustness for the proposed vector control in low speed existed.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1998.10a
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• pp.166-172
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• 1998

PD 제어기는 산업현장에 가장 널리 운영되는 제어알고리즘이지만 지금까지 보편적으로 사용되고 있는 PID 파라메터 동조방법인 Ziegler-Nichols 동조법으로는 화학공정 같은 비선형 특성이 크거나, 시정수가 큰 플래트에서는 좋은 성능을 얻을 수 없다. 본 논문에서는 릴레이 동조 실험을 통하여 임계 이득과 발진주기를 구하고, 이 값들로부터 Z-N 동조법을 적용하여 초기 동조값을 구한다. 이 값에 의해서 얻어진 공정 출력의 오차와 오차변화율을 입력으로 한 퍼지 동조기를 통하여 PID 제어기의 비례이득과 적분시간을 구하는 동조 방법을 제시한다.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.2
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• pp.141-151
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• 2013

This study presents a modeling of aerosol extinction vertical profiles in Korea by using the Moderate Resolution Imaging Spectro-radiometer(MODIS) derived aerosol optical thickness(AOT) and ground based visibility observation data. The method uses a series of physical equations for the derivation of aerosol scale height and vertical profiles from MODIS AOT and surface visibility data. The modelled results under the standard atmospheric condition showed small differences with the standard aerosol vertical profile used in the radiative transfer model. Model derived aerosol scale heights for two cases of clean(${\tau}_{MODIS}=0.12{\pm}0.07$, visibility=$21.13{\pm}3.31km$) and hazy atmosphere(${\tau}_{MODIS}=1.71{\pm}0.85$, visibility=$13.33{\pm}5.66km$) are $0.63{\pm}0.33km$ and $1.71{\pm}0.84km$. Based on these results, aerosol extinction profiles can be estimated and the results are transformed into the KML code for visualization of dataset. This has implications for atmospheric environmental monitoring and environmental policies for the future.

• Journal of the Korean Geographical Society
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• v.45 no.1
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• pp.119-143
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• 2010

Local administrative districts in Japan have extensively reformed over the last 10 years and have decreased by 40 percent. This study examines the process of the municipal mergers in Japan from the perspective of the politics of space, in addition to a focus on the formation of Tobichi (enclaves). The background and progress of municipal mergers in Japan revealed that the reformation of administrative districts progressed under 'restruction' rather than 'decentralization' to manage a financial crisis of government. As a result, the municipal mergers of Japan have progressed in spatiotemporal inequality. The municipal mergers of the study areas are analyzed in multi-dimensional spatial politics composed of financial and demographic properties, locationality, territoriality, placeness, and the politics of decision making. Administrative districts have a spatial property; the reformation of them should be considered with the specialty and generality of the region.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.3
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• pp.52-61
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• 2020

This study developed a legibility distance(LD) model for three colors used in VMS according to luminance under foggy conditions through experiments. For this, a simulated environment was created, and LD values of red, green, and yellow color were collected by increasing the luminance. From the test results, the LDs for red at luminance levels of 2,000 cd/㎡ and 20,000 cd/㎡ and a visibility distance of 10m were 10.2m and 18.8m, respectively, which was an improvement of 84%. The LD was improved by 34% and 17% at a visibility distance of 20 m and 30 m, respectively. For green, the LD was improved by 69%, 63%, and 19% at visibility distance of 10m, 20m, 30m, respectively. For yellow, the LD was improved by 100%, 47%, and 36% at visibility distance of 10m, 20m, 30m, respectively. The LD models for three colors were developed by using two independent variables, luminance value and visibility distance. The adjusted coefficients of the red, green, and yellow model equations were calculated as 0.982, 0.978, and 0.915, respectively, and the explanatory power of all models was very high.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.88-100
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• 1990

Since sea state changes engine load instantaneously, the speed governing apparatus is essential for marine engine to maintain constant speed regardless of the load. As governing apparatuses, mechanical, pneumatic, and electric governors have been employed. But, recently, according to the introduction of low speed-ling stroke engines to increase thermal efficiency, the development of governor which has better response characteristics is requisite. In this paper, to design the governor that meets above requirement, author made a performance test for the existing PID control digital governor with the aid of computer simulation, and investigated digital governor applying the optimal control algorithm, then, executed computer simulation by the same way. As the result of simulations, found that the former let engine have large overshoot and long settling time at low speed, on the other hand, the latter made engine have better response. If we design and invent a good observer for delay time element so that the optimal control theory can be applied, better governor will be expected.