• Journal of the Korean Society of Safety
• /
• v.18 no.3
• /
• pp.154-160
• /
• 2003

Uncertain time delay happens when the process reads the sensor data and sends the control input to the plant located at a remote site in distributed control system. As in the case of data network using TCP/IP, VDN that integrates both device network and data network has uncertain time delay. Uncertain time delay can cause degradation in performance and stability of distributed control system based on VDN. This paper first investigates the transmission characteristic of VDN and suggests a control scheme based on the Smith's predictor to minimize the effect of uncertain varying time delay. The validity of the proposed control scheme is demonstrated with real-time velocity control of DC servo motor located in remote site.

• Journal of the KSME
• /
• v.33 no.8
• /
• pp.739-745
• /
• 1993

60년대 이후 경제개발과 더불어 건설된 화력발전소는 장기사용 및 주기 운전 (cycling operation)에 따라 경년열화가 상당히 진행된 상태로 가동되고 있다. 또한 설비운용 기 술도 고장보수(failure maintenance), 예방보수(protective maintenance) 단계를 거쳐 80년대 후 반기부터는 예측보수(predictive maintenance)에 주안점을 두게 되었으며 사회변화에 따른 신규 발전설비의 건설부지 확보, 환경 규제의 엄격 등이 당면 과제로 대두되었다. 따라서 경년화력의 장수명화, 고효율, 저공해 발전방식의 실용화 등이 현실적인 대책이므로 경년화력의 정밀진단 및 평가기술의 고도화 신형발전설비의 개발 등이 연구개발의 주측이 되고 있다. 이 글에서는 국내 에서 추진되고 있는 이들 기술개발의 현황과 향후계획을 제시하여 산 . 학 . 연의 보다 긴밀한 연구활동에 기여하고자 한다.

• Proceedings of the KIEE Conference
• /
• 1991.07a
• /
• pp.81-85
• /
• 1991

The distribution facilities fault has been anually shown about 13% all of the total distribution faults. Therefore, to prevent, the distribution facilities we have to manage them properly during their life time and enhance their quality and advance preventible maintenance, that is predictive maintenance or condition based maintenance. This paper presents the aging characteristics and the degenerating factors. Accordingly, improving the enhanced quality of distribution facilites is expected to contribute the electric power operation constantly.

• Proceedings of the KSR Conference
• /
• 2006.11b
• /
• pp.1436-1441
• /
• 2006

In this paper, Computer-aided Maintenance Equipments, which are being used in High Speed Line Train Control System, are applied to analyze failures in train control systems, resulting in long time delays of trains. It can be expected to extend and apply CAMS(Computer Aided Maintenance System) in the hereafter efficient operation and maintenance of high speed railway train control systems, by comparison between the analysis result of fundamental causes, from high speed railway train control system failure occurred during the operational process, and predictive result of failure causes, based on the recording data of CAMS when failures were occurred.

• Proceedings of the KIEE Conference
• /
• 2006.07a
• /
• pp.22-24
• /
• 2006

The installations of power quality monitoring system have increased drastically over the past several decades. These systems have been effectively used to monitor, analyze and diagnose the conditions of power system, and furthermore can be used to improve the present asset maintenance policy, scheduled (time-based) method, into the advanced, cost-effective and labor-effective maintenance methods, such as condition-based maintenance, predictive maintenance and reliability centered maintenance. As an approach to this, this paper introduces the statistical methods, three kinds of control charts (Shewhart chart, CUSUM chart and EWMA chart), and discusses the applicability of these methods to recognize the changing trends of power quality indices and to estimate the system's condition, using Matlab.

• Journal of the Korean Society of Systems Engineering
• /
• v.18 no.1
• /
• pp.1-13
• /
• 2022

The Yongin Light Rail train was manufactured by Bombardier Transportation in Canada in 2008 and is a privately invested railway line that has been operating in Yongin-si, Gyeonggi-do, since 2013. When the frequency of train failure increases due to aging, and there is a delay in the delivery period of imported parts used in the Bombardier manufactured trains, timely vehicle maintenance may not be performed due to lack of parts. To solve this problem, it is necessary to build a 'vehicle parts maintenance demand forecasting system' that analyzes the accurate and actual maintenance demand annual based on the condition of vehicle parts. The full scope of analysis in this paper analyzes failure data from various angles after opening of Yongin light rail vehicle to analyze failure patterns for each part and identify replacement cycles according to possible failures and consumption of parts. Based on this study, it is expected that Yongin Light Rail's maintenance system will change from the existing time-based replacement (TBM) concept to the condition-based maintenance (CBM) concept. It is expected that this study will improve the efficiency of the Yongin Light Rail maintenance system and increase vehicle availability. This paper is a fundamental for establishing of a system for predicting the replacement timing of vehicle parts for Yongin Light Rail. It reports the results of data analysis on some vehicle parts.

• Nutrition Research and Practice
• /
• v.11 no.4
• /
• pp.340-346
• /
• 2017

BACKGROUND/OBJECTIVES: Despite the importance of consuming sufficient amounts of vegetables, daily vegetable intake among adolescents in Korea is lower than the current dietary recommendation. The objective of this study was to examine determinants affecting vegetable preference in order to suggest a stage-tailored education strategy that can promote vegetable consumption in adolescents. SUBJECTS/METHODS: Adolescents (n = 400, aged 16-17 years) from two high schools participated in a cross-sectional study. Survey variables were vegetable preference, the social cognitive theory (SCT) and stages of change (SOC) constructs. Based on vegetable preference, subjects were classified into two groups: a low-preference group (LPG) and a high-preference group (HPG). SOC was subdivided into pre-action and action/maintenance stages. To compare SCT components and SOC related to vegetable preference, chi-squared and t-tests, along with stepwise multiple-regression analysis, were applied. RESULTS: In the LPG, a similar number of subjects were classified into each stage. Significant differences in self-efficacy, affective attitudes, and vegetable accessibility at home and school were detected among the stages. Subjects in the HPG were mainly at the maintenance stage (81%), and there were significant differences among the stages regarding self-efficacy, affective attitudes, and parenting practice. In the predictions of vegetable preference, self-efficacy and parenting practice had a significant effect in the "pre-action" stage. In the action/maintenance stage, outcome expectation, affective attitudes, and vegetable accessibility at school had significant predictive value. In predicting the vegetable preference for all subjects, 42.8% of the predictive variance was accounted for by affective attitudes, self-efficacy, and vegetable accessibility at school. CONCLUSION: The study revealed that different determinants affect adolescent vegetable preference in each stage. Self-efficacy and affective attitudes are important determinants affecting vegetable preference. Additionally, school-based nutrition intervention that focuses on enhancing affective attitudes, self-efficacy, and vegetable exposure may constitute an effective education strategy for promoting vegetable consumption among adolescents.

• Journal of the Institute of Convergence Signal Processing
• /
• v.6 no.3
• /
• pp.143-147
• /
• 2005

Monitoring and diagnosis of the operating machines are very important for safety operation and maintenance in the industrial fields. These machines are most rotating machines and the diagnosis of the machines has been researched for long time. We can easily see the faulted signal of the rotating machines from the changes of the signals in frequency. The Linear Predictive Coding(LPC) is introduced for signal analysis in frequency domain. In this paper, we propose fault detection and diagnosis method using the Linear Predictive Coding(LPC) and residual signal energy. We applied our method to the induction motors depending on various status of faulted condition and could obtain good results.

• Proceedings of the KIEE Conference
• /
• 2005.10b
• /
• pp.56-58
• /
• 2005

This paper for the Train control system which has been used in the railway system for the purpose of headway control is regarded as safety-critical system, which is based on embedded controller. Therefore, for the maintainability, the maintenance time shall be predicted correctly in order to improve availability of railway system and the predictive values shall be proved through the test. In conclusion, for the maintainability of train control system, the solution for exact prediction based on related international standard and the system for justification of derived predictive values shall be proposed.

• The Journal of Korean Medicine
• /
• v.37 no.3
• /
• pp.62-73
• /
• 2016

Objectives: Dropout and weight regain are common problems in most obesity treatments. The purpose of this study was to review previously published study results of the predictive factors associated with dropout during weight loss treatment and weight loss maintenance after successful weight loss. Methods: Authors searched for the articles related to dropout and weight loss maintenance, published from 2007 to 2016 found on Pubmed, Scopus, RISS, and KISS. A total of 19 articles were finally selected. From the study results, unchangeable and changeable predictors were extracted, and these predictors were examined according to dropout and weight loss maintenance categories. Results: The unchangeable predictors of dropout were younger age, lower education level and female, whereas the changeable predictors of dropout were lower initial weight loss, symptoms of depression and body dissatisfaction. The strongest factor for predicting the dropout was initial weight loss. The unchangeable predictors of weight loss maintenance were old age, male and family history of obesity, whereas the changeable predictors of weight loss maintenance were regular exercise, dietary restraint, self-weighing and low depressive symptoms. Initial weight loss, depressive symptoms, body image, dietary restraint, physical activity, weight loss expectation and social support were considered to be dominant factors for weight loss treatments. Conclusions: Our review results suggest that unchangeable and changeable predictors of dropout and weight loss maintenance should be carefully examined during treatments of obesity.