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Reliability Engineering for Medical Devices

Reliability Engineering for Medical Devices. Richard C. Fries Manager, Reliability Engineering Datex-Ohmeda Madison, Wisconsin. Definition of Reliability. The probability, at a desired confidence level, that a device will perform a specified function, without failure,

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Reliability Engineering for Medical Devices

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  1. Reliability Engineering for Medical Devices Richard C. Fries Manager, Reliability Engineering Datex-Ohmeda Madison, Wisconsin

  2. Definition of Reliability The probability, at a desired confidence level, that a device will perform a specified function, without failure, under stated conditions, for a specified period of time

  3. More General Definition of Reliability A reliable product: one that does what the customer wants, when the customer wants to do it

  4. Reliability Basics Reliability cannot be tested into a product It must be designed and manufactured into it Testing only indicates how much reliability is in the product

  5. Purpose of the Reliability Group Determine the weaknesses in a design and correct them before the device goes to the field

  6. Areas Covered by Reliability • Electrical • Mechanical • Software • System

  7. Electrical Reliability

  8. Mechanical Reliability

  9. Theoretical Software Reliability

  10. Practical Software Reliability

  11. System Reliability

  12. Set the Reliability Goal • Based on similar equipment • Used as the basis for a reliability budget

  13. Parts Count Prediction • Uses MIL-HDBK-217 • Indicates whether the design approximates the reliability goal • Indicates those areas of the design with high failure rates

  14. Chemical Compatibility • Test plastics with typically used chemical agents (alcohol, anesthetic agents, cleaning agents) • Cleaning agents are the worst

  15. Component Testing • Cycle/life testing of individual components • Comparison of multiple vendors of components • Determine applicability for the intended use

  16. HALT • Acronym for Highly Accelerated Life Teing • Used to find the weak links in the design and fabrication process • Usually performed during the design phase

  17. HASS • Acronym for Highly Accelerated Stress Screen • Uses the highest possible stresses as determined by HALT testing • Performed on 100% of the units being manufactured

  18. HALT Testing • Possible stresses that can be applied: • random vibration • rapid temperature transitions • voltage margining • frequency margining • The product is stressed far beyond its specifications • The test can be set up to find the destruct limits

  19. Goal of HALT Testing • Overstress the product • Quickly induce failures • By applying the stresses in a controlled, stepped fashion, while continuing monitoring for failures, the testing results in the exposure of the weakest points in the design • This test does not demonstrate that a product will function in its intended environment • This test, if successful, will expose weak points in the design

  20. Goals of HALT Testing • The goal is more effectively met by testing at the lowest possible subassembly, typically individual PC boards • Card cages are not usually used due to the dampening effect of the cage on vibration • Cages also can block air flow, thus reducing stresses

  21. Environmental Testing • Operating temperature/humidity • Storage temperature/humidity • EMC • Surges/transients • Brown-outs • Cell phones • ESD • Altitude

  22. Environmental Testing • Autoclave • Shock • Vibration • Shipping • Tip testing • Threshold testing

  23. Customer Misuse • Excess weight on tabletop • Fluid spillage • Cross connection of wires • Pulling unit by non-pulling parts • Wrong order of pressing keys • “Knowing” how to operate the unit without reading the manual

  24. Making a Design Foolproof The biggest mistake engineers make when trying to make a design completely foolproof is underestimating the ingenuity of complete fools

  25. High Performance Air Compressor

  26. Prototype Front Panel for Ventilator

  27. Plastic Structure

  28. Plastic Structure

  29. Plastic Structure

  30. Manifold Port

  31. Prototype Switch

  32. Autoclave Testing

  33. Critical Care Ventilator

  34. Critical Care Ventilator

  35. Life Testing • Operate the device in its typical environment and application • Use appropriate on/off cycles • Can be used to verify the reliability goal or a specific period of time, such as the warranty period

  36. Tracking Reliability Growth in the Field • Collect manufacturing data on how many units were manufactured by month • Collect field failure data, by month • Develop a reliability growth chart

  37. Reliability Growth Example

  38. Reliability Growth Example

  39. Reliability Growth Example

  40. Failure Analysis • Failure: device does not operate according to its specification • Determine root cause of the failure • Suggest methods to address the failure

  41. The Reliability Group You make it, We’ll break it

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