Sistem Pemeliharaan (01)

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Sistem Pemeliharaan (01)

  1. 1. SISTEM PEMELIHARAAN Bermawi P. Iskandar KK Sitem Manufaktur, FTI ITB
  2. 3. Products:[Support-Characteristics-Application]
  3. 4. BASIC CONCEPTS OF RELIABILITY <ul><li>The National Aeronautics and Space Administration (NASA)[Smith (1977)] defines reliability as, </li></ul><ul><li>The probability of a device performing adequately for the period of time intended under the operating condition encountered. </li></ul><ul><li>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. </li></ul>
  4. 5. BASIC CONCEPTS OF RELIABILITY <ul><li>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. </li></ul>
  5. 6. BASIC CONCEPTS OF RELIABILITY <ul><li>Suppose that a device is required to operate satisfactorily under designed condition for a period given by (0,t). </li></ul><ul><li>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. </li></ul><ul><li>Otherwise, the device is said to have a low reliability and the device is deemed unreliable. </li></ul>
  6. 7. Simple system & Complex system <ul><li>The device can be either: </li></ul><ul><ul><li>a very simple system consisting of a single component or </li></ul></ul><ul><ul><li>a very complex system involving numerous components or subsystems. The components of the complex system may or may not interact with each other. </li></ul></ul>
  7. 8. Simple system & Complex system <ul><li>If the system is a single component system, its reliability depends only on the reliability of the component. </li></ul><ul><li>In contrast, the reliability of a multi-component system depends not only on each component reliability but also on the relationship between components. </li></ul><ul><li>In this case the configuration of the system affects the reliability of the system. </li></ul>
  8. 9. Reliability is: <ul><li>A characteristic that describes how good a device is. </li></ul><ul><li>Must be planned for, designed in both in terms of the initial product and in maintenance of that product. </li></ul>
  9. 10. Failure is: <ul><li>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. </li></ul><ul><li>Defect: imperfection </li></ul><ul><li>Deficiency: lack of conformance to specs </li></ul><ul><li>Fault: Cause of failure </li></ul><ul><li>Malfunction: unsatisfactory performance </li></ul>
  10. 11. Failure Measures <ul><li>Real life failure: fact of life, define normal operation, anticipate worst, try to design out. </li></ul><ul><li>Failure rate typically = #failures/unit time = failures/million hours for devices. </li></ul>
  11. 12. Unreliability is: <ul><li>A measure of the potential for failure of a device (or process.) </li></ul><ul><li>Leads to high cost, wasted time, inconvenience, poor reputation, unsafe operation, … </li></ul><ul><li>- 9/9/99 more than 10,000 stepladders recalled by Home Depot – steps too short, improperly attached (RIDGID ladders, Louisville Ladder Co, Louisville KY) </li></ul>
  12. 13. 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
  13. 14. Mechanical Reliability Failure Rate Time-> Friction, Fatigue, Erosion, Corrosion, Cracking, Lack of PM PM, Replacement Misassembly <- Useful Life ->
  14. 15. Software Reliability Failure Rate Time -> Debug errors, Spec. Errors, Special Cases
  15. 16. System Reliability: Bathtub Curve Failure Rate Time -> QI QI PM Lawsuit Lawsuit
  16. 17. NEED FOR HIGH RELIABILITY <ul><li>For large complex expensive systems the lack of adequate reliability can cause severe economic losses and/or social consequence. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>
  17. 18. NEED FOR HIGH RELIABILITY <ul><li>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. </li></ul><ul><li>Considering the consequences of unreliability, the need to have highly reliable systems is paramount. </li></ul><ul><li>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 )] </li></ul>
  18. 19. Approaches to ensure high reliability <ul><li>Using redundant components in a system is one way of achieving it. </li></ul><ul><li>An integrated quality control also assures better reliability by ensuring that systems meet the design specification. </li></ul><ul><li>Maintenance is also an effective way to control reliability, since it can prevent excessive deterioration of the system. </li></ul>
  19. 20. Approaches to ensure high reliability <ul><li>However, all these methods are costly and in some cases difficult to achieve, especially for complex systems. </li></ul><ul><li>This implies that there is a trade off between system reliability and the cost of assuring the reliability. </li></ul><ul><li>The optimal trade off involves the use of quantitative method which is discussed in the next section. </li></ul>

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