Reliability & Maintainability Engineering An Introduction Robert Brown Electrical & Computer Engineering Worcester Polytechnic Institute

Reliability / Maintainability *-ability Reliability – Probability that a device will operate within specifications for the specified duration Reliability – Probability that a device will operate within specifications for the specified duration Maintainability – Amount of resources required to remove faults Maintainability – Amount of resources required to remove faults –Diagnose-ability – The ability to locate faults –Repair-ability – The ability to remove faults Availability Probability that a device is operationally ready

Why is it important? Reliability & Maintainability Engineering Mission Success - The product correctly operates for the duration of the mission Mission Success - The product correctly operates for the duration of the mission Customer Satisfaction – Perceived product quality Customer Satisfaction – Perceived product quality –Brand loyalty, customer loyalty Competitive Products – Market requirements Competitive Products – Market requirements Safety Safety Support Legal & Contractual Requirements Support Legal & Contractual Requirements Reduce Cost of Ownership Reduce Cost of Ownership –Reduce Product Cost – Warranty –Reduce Service Cost – Service delivery cost –Insurance

Bathtub Curve Failures over Time InfancySteady StateWearout Failure Rate Time Workmanship Contamination Burn-In Quality Control Random Failures Overload Improper Usage Thermal Fatigue Oxidation Cracking-Shrinking Friction Wear Warranty Period

Product Life Cycle Activities Reliability & Maintainability DesignDevelopDeployManage Identify competitive market requirements Design for reliability Failure analysis Reliability predictions Reliability testing Maintainability testing Develop service strategy Ongoing reliability testing Engineering changes Maintenance releases End of product life End of service life Logistics strategy

Reliability Developing reliable products Quality materials Quality materials Stability – mechanical / electrical Stability – mechanical / electrical Design for anticipated load Design for anticipated load Design for operating environment Design for operating environment Cooling Cooling Redundancy Redundancy –Full functionality –Reduced functionality Self-healing Self-healing

Series and Parallel Predicting System Reliability System requires device “A” AND device “B” to operate R S = R 1 * R 2 * R n Series R S = 0.8 * 0.9 = 0.72 System requires device “A” OR device “B” to operate R S = 1 – ( 1 - R 1 ) * ( 1 – R N ) Parallel R S = 1 – ( ) * ( ) R S =

Complex Configuration Predicting System Reliability System includes series and parallel device configuration R S = R 1 * R 2 * R n R S = R A * R BC R S = 0.8 * 0.98 = R S = 1 – ( 1 - R 1 ) * ( 1 – R N ) R BC = 1 – ( ) * ( ) R BC = 0.98 A B C ABC

Reliability Metrics Reliability Metrics Reliability is specified and measured in several ways Failure Rate  Count of failures during a time period.  Usually 10 6 hours MTBF or MTTF Reliability %  Mean Time Between Failures  Mean Time To Fail  Stated in hours  MTBF =  MTBF = 1 /  Usually MTBF =  Usually MTBF = 10 6 /  R(p) =  e - t  t = Mission time

Reliability Reliability Calculating MTBF Component Duty CycleComponent Failure Rate  100 %CPU   100 %Power Supply  20 %Floppy  MTBF = hrs= Note: in 10 6 Hours  Total 1 =

Maintainability MTTR – Mean Time To Repair MTTR – Mean Time To Repair Measured in hours Measured in hours Major activities Major activities –Diagnoses –Repair Focus on labor and materials Focus on labor and materials Resources required to remove faults

Diagnose-ability Developing diagnose-able products User and service documentation, tools and training User and service documentation, tools and training Operator indicators and error messages. Preserved state indicators accessed by repair depot. Operator indicators and error messages. Preserved state indicators accessed by repair depot. Test points Test points Device error and state change logging Device error and state change logging Environmental measurements Environmental measurements Diagnostic and failure detection tools Diagnostic and failure detection tools –Local and remote diagnosis –“Call Home” –Designed for technical and non-technical users Product labeling and revision management Product labeling and revision management Quickly and Correctly Locate the Fault

Repair-ability Developing repair-able products Repair or replace? Repair or replace? Remote and On-site repair? Remote and On-site repair? –Firmware, software, micro-code Limit specialized tools Limit specialized tools Limit adjustments Limit adjustments Hot-Swap Hot-Swap Larger, functionally dense sub-assemblies Larger, functionally dense sub-assemblies Physical layout Physical layout –Easier to replace less reliable components –Minimal disruption to replace a component Quickly Remove the Fault

Economics Reliability & Maintainability Population (units)20,000 Reliability MTBF Hr10,00015,00010,00015,000 Repair cost$ $ Duty Cycle 12/24 Day = 50% 50 % Operating Time (12*365*20000) 87,600,000 Repair Calls ( /MTBF) 8,7605,8408,7605,840 Service Cost (Calls*Cost) $ 219,000$ 146,000$ 109,500$ 73,000 Savings$ 73,000$ 109,500$ 146,000 Annual

Resources Applied Reliability by Dave Trindade Applied Reliability by Dave Trindade Reliability Magazine magazine.com/index.php Reliability Magazine magazine.com/index.phphttp:// magazine.com/index.phphttp:// magazine.com/index.php IEEE Reliability Society IEEE Reliability Society