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Exercise: „Reliability and availability“

Additional task 1:

The system with the machines of availability types A, B and C represented below is to be

tested for its total availability.

The used machine types have the following availabilities:

Typ B: VB = 0,95

Typ C: VC = 0,9

The total availability of system is to be VSYS=0,9. For machines of availability tpye A an

average time for repairs can be ensured in case of machine failure.

Which demands have to be made on the downtime behavior of the machine with

availability type A?

2

!74,19908,01

2908,0

2908,0

908,0

908,09914,0

9,0

9914,0

9914,0

9914,0)855,01()9405,01(1

855,09,095,0

9405,099,095,0

99,0)9,01()9,01(11

failurestwobetweentimeAveragehh

MTBF

hMTBFMTBF

MTTRMTBF

MTBFA

sys

A

Asys

BC

BCunten

BCoben

C

Additional task 2:

A lifting-sinking station was investigated by an analysis of the current state. Thereby, the

following data were gained:

Number of repairs M = 6

Number of failures N = 7

cumulated operating time tE = 520 [h]

cumulated downtime tA = 39 [h]

What is the value with which the availability of the lifting-sinking station can be estimated

with an error probability of α = 0,05?

3

909,034,335,33

35,33

34,3)!(336,23

392

35,33)!(845,28

)39520(2

975,02

05,01

21

2

)(2

,

2

)2

1(;2

2

)2

1();1(2

u

o

u

M

Ao

n

AEu

ou

uu

TabelleausMTTR

TabelleausMTBF

tMTTR

ttMTBF

wobeiMTTRMTBF

MTBF

Source: Universität Karlsruhe

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