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# Sistem Pemeliharaan (01)

## on Feb 06, 2010

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## Sistem Pemeliharaan (01)Presentation Transcript

• SISTEM PEMELIHARAAN Bermawi P. Iskandar KK Sitem Manufaktur, FTI ITB
•
• Products:[Support-Characteristics-Application]
• BASIC CONCEPTS OF RELIABILITY
• The National Aeronautics and Space Administration (NASA)[Smith (1977)] defines reliability as,
• The probability of a device performing adequately for the period of time intended under the operating condition encountered.
• British standards institution(1986) specifies reliability as, the probability that an item will perform a required function under stated conditions for a stated period of time.
• BASIC CONCEPTS OF RELIABILITY
• From the above two-definition, it is obvious that reliability of a device (an item or system) is the ability of the system to satisfy its intended function in probabilistic sense.
• BASIC CONCEPTS OF RELIABILITY
• Suppose that a device is required to operate satisfactorily under designed condition for a period given by (0,t).
• The device is said to have a high reliability if it performs its required function without failure during (0,t) with a sufficiently high probability.
• Otherwise, the device is said to have a low reliability and the device is deemed unreliable.
• Simple system & Complex system
• The device can be either:
• a very simple system consisting of a single component or
• a very complex system involving numerous components or subsystems. The components of the complex system may or may not interact with each other.
• Simple system & Complex system
• If the system is a single component system, its reliability depends only on the reliability of the component.
• In contrast, the reliability of a multi-component system depends not only on each component reliability but also on the relationship between components.
• In this case the configuration of the system affects the reliability of the system.
• Reliability is:
• A characteristic that describes how good a device is.
• Must be planned for, designed in both in terms of the initial product and in maintenance of that product.
• Failure is:
• The degradation of the performance of a device (process) outside of a specified value AND non-performance or inability to perform its function for a given time period within specified conditions.
• Defect: imperfection
• Deficiency: lack of conformance to specs
• Fault: Cause of failure
• Malfunction: unsatisfactory performance
• Failure Measures
• Real life failure: fact of life, define normal operation, anticipate worst, try to design out.
• Failure rate typically = #failures/unit time = failures/million hours for devices.
• Unreliability is:
• A measure of the potential for failure of a device (or process.)
• Leads to high cost, wasted time, inconvenience, poor reputation, unsafe operation, …
• - 9/9/99 more than 10,000 stepladders recalled by Home Depot – steps too short, improperly attached (RIDGID ladders, Louisville Ladder Co, Louisville KY)
• Electronic Reliability Infant Mortality <-Useful Life -> Wearout Joints, Welds, Contamination, Misuse Corrosion, Cracking, Wear, Crazing, Shorts Screening, Design, Burn-in --  Design, Preventive Maintenance, Replacement, Repair Time -> Failure Rate
• Mechanical Reliability Failure Rate Time-> Friction, Fatigue, Erosion, Corrosion, Cracking, Lack of PM PM, Replacement Misassembly <- Useful Life ->
• Software Reliability Failure Rate Time -> Debug errors, Spec. Errors, Special Cases
• System Reliability: Bathtub Curve Failure Rate Time -> QI QI PM Lawsuit Lawsuit
• NEED FOR HIGH RELIABILITY
• For large complex expensive systems the lack of adequate reliability can cause severe economic losses and/or social consequence.
• Breakdown of a numerically controlled machine tool, in an automated production line or cell can result in the loss of production; increased production time; increased production cost, customer dissatisfaction to name a few.
• In many cases (e.g. aircraft, spacecraft, chemical plant or nuclear reactor), unreliability affects personnel safety. Failure in operation can cause a dangerous situations e.g. Ieak of poisonous gas in a chemical plant can kill people; the effect is more devastating in the case of a leak in a nuclear reactor.
• NEED FOR HIGH RELIABILITY
• If an anti-aircraft missile fails to work when required the nation can suffer serious property and human loss as well as loss to national prestige.
• Considering the consequences of unreliability, the need to have highly reliable systems is paramount.
• For example, U.S. Air Force, through Reliability & Maintainability 2OOO,has established the reliability requirement that all new systems have twice the reliability than the system being replaced. [Piotrowski ( 1987 )]
• Approaches to ensure high reliability
• Using redundant components in a system is one way of achieving it.
• An integrated quality control also assures better reliability by ensuring that systems meet the design specification.
• Maintenance is also an effective way to control reliability, since it can prevent excessive deterioration of the system.
• Approaches to ensure high reliability
• However, all these methods are costly and in some cases difficult to achieve, especially for complex systems.
• This implies that there is a trade off between system reliability and the cost of assuring the reliability.
• The optimal trade off involves the use of quantitative method which is discussed in the next section.