Sistem Pemeliharaan (01)
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Sistem Pemeliharaan (01)






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    Sistem Pemeliharaan (01) Sistem Pemeliharaan (01) Presentation Transcript

    • SISTEM PEMELIHARAAN Bermawi P. Iskandar KK Sitem Manufaktur, FTI ITB
    • Products:[Support-Characteristics-Application]
      • 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.
      • 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.
      • 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
      • 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.
      • 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.