MTBF CALCULATION
MTBF(MEAN TIME BETWEEN FAILURE):是指产品在使用过程中前一个故障至后一个故障的平均时间，称为平均寿命时
间，又名平均无故障时间。采用MIL-STD-781(POISSON) CONFIDENCE LEVEL 90%计算。
MTBF?n?TL?FCC?Ft?FCCC.L?
(Tr-Ta)/10
NOTE: n: Numbers Of Test Sets. TL: Total Life Test Time FCC = 2
Tr: Room Temperature.(40?C) Ta: Environment Temperature (25?C)
Ft: Hours Before Defect Occurred C.L?= Confidence Level(90%)
举例说明(C.L.值见下表)
例 S785P机种将24台放入40?C加温室B/I 2000Hrs(常温25?C), 1.若Failure Number=0时,MTBF为多少? 2.若在600Hrs Failure 1台,则MTBF为多少?
3.若600HrsFailure 1台,1100Hrs又 Failure 1台,则MTBF为多少? 解:1.Failure number=0时
MTBF=[(n*TL*FCC)+(Ft*FCC)]/C.L?
(40-25)/10
+0Hrs*2(40-25)/10]/2.3026=58952Hrs =[24*2000Hrs*2
2.Failure number=1时
MTBF=[(n*TL*FCC)+(Ft*FCC)]/C.L?
(40-25)/10
+600Hrs*2(40-25)/10]/3.8897=33880Hrs =[(24-1)*2000Hrs*2
3.Failure number=2时
MTBF=[(n*TL*FCC)+(Ft*FCC)]/C.L?
(40-25)/10
+(600+1100)Hrs*2(40-25)/10]/5.323=24282Hrs =[(24-2)*2000Hrs*2
C.L. FAILURE NUMBER 0 1 2 3 4 5 6 90% 2.3026 3.8897 5.3223 6.6808 7.9936 9.2742 10.5321
General Exponential Model(For Time-Terminated Tests) Number of Failures Conf. level 0 1 2 3 4 5 6 7 8 9 7 11.7709
