2. Reliability Engineering Richard C. Fries, PE, CRE Corporate Manager, Reliability Engineering Baxter Healthcare Round Lake, Illinois

3. 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

4. Customers Definition of Reliability A reliable product: One that does what the customer wants, when the customer wants to do it

5. 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

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

7. Areas Covered by Reliability zElectrical zMechanical zSoftware zSystem

8. Electrical Reliability

9. Mechanical Reliability

10. Theoretical Software Reliability

11. Practical Software Reliability

12. System Reliability

13. Set the Reliability Goal zBased on similar equipment zUsed as the basis for a reliability budget zListed as Mean Time Between Failures (MTBF) in hours or cycles zMTBF = the time at which 63% of the units in the field will have failed zMinimum goal is ten years with a 98% reliability

14. Parts Count Prediction zUses MIL-HDBK-217 zIndicates whether the design approximates the reliability goal zIndicates those areas of the design with high failure rates

15. Chemical Compatibility zTest plastics with typically used chemical agents (alcohol, anesthetic agents, cleaning agents) zCleaning agents are the worst

16. Force Puller

17. Component Testing zCycle/life testing of individual components zComparison of multiple vendors of components zDetermine applicability for the intended use

18. Philosophy of Testing zTest to have the units pass zTest with the addition of stresses to check the margins of functionality

19. Types of Tests zTime terminated, failed parts replaced zTime terminated, no replacement zFailure terminated, failed parts replaced zFailure terminated, no replacement zTest until first failure zTest until all samples fail

20. Determining Sample Size zUses Chi-Square table zSS = Chi-square Value(MTBF goal)/2 zChi-square value includes confidence level and degrees of freedom = 2f+2 zComponent testing – 90% confidence level zLife testing – 95% confidence level

21. Sample Calculation zWant to test valves to be used for 2,000,000 cycles per year with a 10% failure rate after 10 years zReliability = e(-t/MTBF) zMTBF = -t/ln Reliability = -20,000,000/ln 0.90 = 389,914,514 cycles

22. Sample Calculation zMTBF = 389,914,514 cycles Number of SamplesNumber of Cyles 1089,777,817 50 17,955,563 100 8,977,782

23. Component Test Setup

26. Calculating Sample MTBF MTBF = (# of samples)(length of test) # of failures

27. Calculating MTBF Where No Failures Occur zA sample MTBF cannot be calculated zA lower one-sided confidence limit is calculated and the MTBF stated to be greater than that number One-sided limit = 2(#units)(test time) Chi square value for the confidence limit and 2 degrees of freedom

28. Sample Calculation for a No Failure Test z10 valves are tested for 10,000 cycles with no failures. Calculate using a 90% confidence level. One-sided limit = 2(10)(10,000) 4.605 = 43,431 cycles MTBF > 43,431 cycles

29. HALT zAcronym for Highly Accelerated Life Testing zUsed to find the weak links in the design and fabrication process zUsually performed during the design phase

30. HALT Testing zPossible stresses that can be applied: xrandom vibration xrapid temperature transitions xvoltage margining xfrequency margining zThe product is stressed far beyond its specifications zThe test can be set up to find the destruct limits

31. HALT Chamber

32. Goal of HALT Testing zOverstress the product zQuickly induce failures zBy 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 zThis test, if successful, will expose weak points in the design

33. Environmental Testing zOperating temperature/humidity zStorage temperature/humidity zEMC ySurges/transients yBrown-outs yElectrocautery yCell phones zESD zAltitude

34. Environmental Testing zAutoclave zShock zVibration zShipping zTip testing zThreshold testing

35. Temperature Chamber

36. Walk-In Temperature Chamber

37. Autoclave Testing

38. Customer Misuse zExcess weight on tabletop zFluid spillage zCross connection of wires zPulling unit by non-pulling parts zWrong order of pressing keys zKnowing how to operate the unit without reading the manual

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

40. Failure Analysis zFailure: device does not operate according to its specification zDetermine root cause of the failure zSuggest methods to address the failure

41. Prototype Front Panel

42. Plastic Structure

44. Autoclave Testing

45. Manifold Port

46. Prototype Port

47. Life Testing zOperate the device in its typical environment and application zUse appropriate on/off cycles zCan be used to verify the reliability goal or a specific period of time, such as the warranty period

48. Tracking Reliability Growth in the Field zCollect manufacturing data on how many units were manufactured by month zCollect field failure data, by month zDevelop a reliability growth chart

49. Reliability Growth Example

52. The Reliability Group You make it, Well break it