• 한국산학기술학회논문지
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• 제19권7호
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• pp.252-257
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• 2018

본 논문에서는 군용 냉각형 열상장비의 중요한 부품인 냉각기의 MTTF를 개선하기 위한 방법을 제시한다. 일반적인 전자장비는 전자소자의 특성으로 인해 온도, 습도 등 환경요인에 의해 고장발생 가능성이 높다. 그러나 일부 군용과 같이 특수목적용의 장비(열상장비 등)들은 다양한 환경요인들에 노출되어 운용하기 때문에 환경요인을 극복할 수 있도록 설계한다. 다양한 군용 장비 중 지속적으로 사용가능 해야 하는 장비 중 가장 널리 사용되는 장비로 열상장비를 꼽을 수 있다. 특히 화질을 우선시하는 군용의 특성상 냉각형 열상장비를 많이 사용한다. 이러한 군용 냉각형 열상장비는 항시 운용 가능해야 하기 때문에 MTTF는 장비의 중요한 파라미터다. 군용 냉각형 열상장비의 MTTF에 가장 중요한 영향을 미치는 부분은 냉각기 부분이다. 냉각기의 MTTF는 장비 내부 열과 연관이 있으며 열을 저하시켜 MTTF를 증가시킬 수 있다. 이를 위해 기존 장비의 내부열에 대한 시뮬레이션을 수행하였고 이로부터 개선점을 확인할 수 있었으며 내부 구조를 개선하는 방법을 제안하였다. 제안한 개선방법의 효과는 시뮬레이션 및 MTTF계산을 통해 확인한다.

• 전기학회논문지P
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• 제59권4호
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• pp.467-472
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• 2010

In this study, an analysis of the used RCD's condition is conducted to assess the effect on environment of installation area, terms of use, corrosion, contamination etc. According to KS C 4613, the used RCDs were tested to get date which is the RCD's life time. And then, the date is analysed using Minitab which is a statistical program for reliability analysis. As a result, The RCD's MTTF for the all samples is $12.7{\pm}0.23$ years. and the MTTF of RCDs which are used indoor area is $12.9{\pm}0.34$ years, the MTTF of RCDs which are used outdoor area is $11.9{\pm}0.30$ years. Futhermore, the MTTF of RCDs which are used in dry area is a $13.1{\pm}0.26$ years, the MTTF of RCDs which are used in dust area is $13.0{\pm}0.57$ years, the MTTF of RCDs which are used in moisture area is $8.4{\pm}0.77$ years.

• 대한안전경영과학회지
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• 제25권1호
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• pp.15-21
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• 2023

In modern society, the delivery service market has grown explosively due to rapid changes in social structure and the recent COVID-19 pandemic. Therefore, various problems such as injury to workers and an increase in human accidents are occurring due to the loading and unloading of parcels. In order to solve this problem, domestic company n is developing a "robot-based cargo loading and unloading system". In developing a new technology system, quantitative reliability targets should be set for efficient operation and development. In this paper, reliability analysis was conducted through field data for the pneumatic gripper of the "robot-based cargo loading system". The reliability of the failure data was analyzed to estimate the distribution parameters and MTTF. Random data was derived for the probability of occurrence of a failure with the estimated value. By repeating the simulation to predict the number and year of failures according to the estimated parameters of the probability distribution, it was proposed as a method that reflects realistic probabilities rather than calculating with simple arithmetic using the average MTTF previously used in the field.

• 산업공학
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• 제4권2호
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• pp.35-42
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• 1991

Many authors derived MTTF/MTBF for an operating system by analyzing its actual life time data. However, it is difficult to derive MTTF/MTBF when few breakdowns accur throughout a year. In this paper, we address a new approach to solve that problem under a preventive maintenance policy, in which few breakdowns occur, and also introduce a case study using the results obtained.

• 한국신뢰성학회지:신뢰성응용연구
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• 제18권3호
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• pp.250-259
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• 2018

Purpose: Previously, missile reliability prediction is based on theoretical failure prediction model. It has shown that the predicted reliability is inadequate to real field data. Although an MTTF based reliability prediction method using real field data has recently been studied to overcome this issue. In this paper, we present a more realistic method, considering MTBF concept, to predict missile reliability. Methods: In this paper we proposed a modified survival model. This model is considering MTBF as its core concept, and failed missiles in the model are to be repaired and redeployed. We compared the modified model (MTBF) and the previous model (MTTF) in terms of fitness against the real failure data. Results: The reliability prediction result of MTBF based model is closer to fields failure data set than that of MTTF based model. Conclusion: The proposed MTBF concept is more fitted to real failure data of missile than MTTF concept. The methodology of this study can be applied to analyze field failure data of other similar missiles.

• 전기학회논문지
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• 제62권1호
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• pp.109-119
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• 2013

This paper presents the design of the Safety Programmable Logic Controller (SPLC) used in the Nuclear Power Plants, an analysis of a reliability for the SPLC using a markov model. The architecture of the SPLC is designed to have the multiple modular redundancy composed of the Dual Modular Redundancy(DMR) and the Triple Modular Redundancy(TMR). The operating system of the SPLC is designed to have the non-preemptive state based scheduler and the supervisory task managing the sequential scheduling, timing of tasks, diagnostic and security. The data communication of the SPLC is designed to have the deterministic state based protocol, and is designed to satisfy the effective transmission capacity of 20Mbps. Using Markov model, the reliability of SPLC is analyzed, and assessed. To have the reasonable reliability such as the mean time to failure (MTTF) more than 10,000 hours, the failure rate of each SPLC module should be less than $2{\times}10^{-5}$/hour. When the fault coverage factor (FCF) is increased by 0.1, the MTTF is improved by about 4 months, thus to enhance the MTTF effectively, it is needed that the diagnostic ability of each SPLC module should be strengthened. Also as the result of comparison the SPLC and the existing safety grade PLCs, the reliability and MTTF of SPLC is up to 1.6-times and up to 22,000 hours better than the existing PLCs.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 추계학술발표회논문집(1)
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• pp.244-250
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• 1997

The mean time to failure (MTTF) expressing the mean value of the system life is a measure of system effectiveness. To estimate the remaining life of component and/or system, the dynamic mean time to failure concept is suggested. It is the time-dependent Property depending on the status of components. The Kalman filter is used to estimate the reliability of components using the on-line information (directly measured sensor output or device-specific diagnostics in the intelligent sensor) in form of the numerical value (state factor). This factor considers the persistency of the fault condition and confidence level in measurement. If there is a complex system with many components, each calculated reliability's or components are combined, which results in the dynamic MTTF or system. The illustrative examples are discussed. The results show that the dynamic MTTF can well express the component and system failure behaviour whether any kinds of failure are occurred or not.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.324-327
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• 2003

The needs for the cryocooler which has high reliability and long MTTF are increased in the military and commercial thermal imaging system The gas contamination wear, leakage of the working fluid, fatigue and etc. have the significant effects on the reliability and MTTF(Mean Time To Failure) or MTBF(Mean Time Between Failure) of the Stirling cryocooler. In the KIMM, the Stilting cryocooler with the linear compressor was released after the several performance tests were performed. This paper describe the experimental facility for the MTTF evaluation and some typical results of the Stilling cryocooler.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.824-829
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• 1998

In regard to the very stringent-going requirements applied to power supply systems is nowadays applications, the reliability of typical UPS redundency systems are investigated. Several resonable assumptions are made to build up the probability models. The reliabilities of the typical UPS redundency systems are analysed. Their relating Relaibility and MTTF (Mean Time To Faults) are evaluated. It is resulted in that the MTTF of today's UPS redundency systems is unlikely to be beyond 1,000,000 hours.

• Communications for Statistical Applications and Methods
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• 제19권2호
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• pp.219-224
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• 2012

This article considers the mean time to failure(MTTF) of a dependent parallel system. We study how the degree of dependency components influences the increase in the mean lifetime for this system. The results are illustrated by tables and figures.