MTBF. Reliability Predictions. The objective of a reliability prediction is to determine if the equipment design will have the ability to perform its required functions for the duration of a specified mission profile.
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Why are Spares so important?
You do fix the ones that fail, but that takes time. The equipment is unavailable while the repair is made.
MTTR = Mean Time To Repair
MLDT = Mean Logistics Delay Time
Equip = Ni(gQ)i
Equip= Total equipment failure rate
g = Generic failure rate for the ith generic part
Q = Quality factor for the ith generic part
Ni = Quantity of the ith generic part
n = # of different generic part categories in equipment
Res(RLR) = Ni(gQ)
Res(RLR) = 47 X (.033 X .1)
Res(RLR) = .1551 fails/million hours
NOTE: This is the failure rate associated with only this type
of resistor. To get the complete failure rate for the
board, the failure rates for all other resistor types and
for all other components would have to be added.
p = b RQ E
p = (C1T + C2E)Q L
p = (C1T + C2E + cyc)Q L
MIL-HDBK-217 Parts Stress equation for this type of part is:
p = b RQ E
R6 = b RQ E
b = .0011
R = 1.0
Q = 0.1
E = 18
R6 = .0011 X 1.0 X 0.1 X 18 = .00198 fails/million hours
(Based on RAC Survey)Reliability PredictionsPRISM
included in Raytheon
System-level process grade multiplier
(approximately 1.0 for “average” processes)Reliability PredictionsPRISM Failure Rate Models
lP(Inherent) = lIA (PPPIMPE + PDPG + PMPIMPEPG + PSPG +PW) + lSW
lP(Logistics) = lIA (PPPIMPE + PDPG + PMPIMPEPG + PSPG +PI+ PN + PW) + lSW
PI Induced process grade factor
PN No-defect process grade factor
This is the preferred method if good data exists.
MTBF Prediction for ABX Radar
Modified by removing failures
with C/A in place.
Modified to account for more
severe ABX environment.