Elaborato finale di laboratorio di Affidabilità realizzato con il supporto della military handbook

R4 (x1) 2,44E-03 2,44E-03

S1,2 (x2) 1,88E-02 1,88E-02

XS1,2 (x2) 7,40E-03 7,40E-03

Z1,4 (x4) 1,61E-01 4,70E-02

PCB (x1) 2,73E-02 2,73E-02

C1,10 (x10) 1,14E-04 1,14E-04

D1,3 (x3) 7,73E-03 7,73E-03

IC1 (x1) 9,98E-02 2,91E-02

J1 (x1) 2,55E-03 2,55E-03

Total Failure Rate 3,53E-01 1,68E-01

As we can see from figure 2 and figure 3, the components which have the highest impact on the total failure

rate are the Integrated Circuit (IC1) and especially the Zener diodes (Z1,4). In order to improve this value, we

decided to change both their quality factor from JAN to JANTXV, resulting in a major improvement in the total

failure rate, but also causing a cost increase of the final product.

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2,55E-03 2,44E-03

7,40E-03

1,85E-02 7,40E-03

1,88E-02

9,98E-02

2,73E-02 1,61E-01

7,73E-03

1,14E-04

R1,2 (x2) R3 (x10) R4 (x1) S1,2 (x2) XS1,2 (x2) Z1,4 (x4) PCB (x1) C1,10 (x10) D1,3 (x3) IC1 (x1) J1 (x1)

Figure 2. Components’ Failure Rate (40°) pre optimization

2,55E-03

7,40E-03 1,85E-02

2,91E-02 2,44E-03

7,73E-03

1,14E-04 1,88E-02

7,40E-03

2,73E-02 4,70E-02

R1,2 (x2) R3 (x10) R4 (x1) S1,2 (x2) XS1,2 (x2) Z1,4 (x4) PCB (x1) C1,10 (x10) D1,3 (x3) IC1 (x1) J1 (x1)

Figure 3. Components’ Failure Rate (40°) post optimization

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2.3 Failure Rate and MTBF vs Temperature

In order to observe how failure rate and temperature are related to each other in the same environment, in our case

Ground Fixed, we chose different values of for each component varying the temperature from 30°C to 90°C with

10°C step, in accordance to the components’ performances.

The results in figure 4 show that there is an evident increase of the components’ failure rate due to the temperature

increase.

Components (GF) 30° 40° 50° 60° 70° 80° 90°

R1,2 (x2) 6,79E-03 7,40E-03 8,01E-03 8,63E-03 9,25E-03 9,86E-03 0,0105

R3 (x10) 1,70E-02 1,85E-02 2,00E-02 2,16E-02 2,31E-02 2,47E-02 2,62E-02

R4 (x1) 2,24E-03 2,44E-03 2,64E-03 2,84E-03 3,05E-03 3,25E-03 3,45E-03

S1,2 (x2) 0,0188 0,0188 0,0188 0,0188 0,0188 0,0188 0,0188

XS1,2 (x2) 5,55E-03 7,40E-03 0,01 0,014 0,018 0,023 0,0296

Z1,4 (x4) 3,70E-02 4,70E-02 5,74E-02 6,72E-02 7,73E-02 9,07E-02 1,08E-01

PCB (x1) 0,02731 0,02731 0,02731 0,02731 0,02731 0,02731 0,02731

C1,10 (x10) 1,43E-04 2,05E-04 2,92E-04 4,20E-04 6,14E-04 8,70E-04 1,23E-03

D1,3 (x3) 2,80E-03 3,73E-03 5,13E-03 7,00E-03 9,10E-03 1,17E-02 1,49E-02

IC1 (x1) 0,02548 0,02912 0,03822 0,04914 0,06188 0,07826 0,09646

J1 (x1) 1,93E-03 2,55E-03 3,24E-03 4,07E-03 5,18E-03 6,42E-03 8,28E-03

1,20E-01

1,00E-01

8,00E-02

[FAILURES/(10^6)HOURS] 6,00E-02

4,00E-02

RATE 2,00E-02

FAILURE 0,00E+00 30° 40° 50° 60° 70° 80° 90°

TEMPERATURE [°C]

R1,2 (x2) R3 (x10) R4 (x1) S1,2 (x2) XS1,2 (x2) Z1,4 (x4)

PCB (x1) C1,10 (x10) D1,3 (x3) IC1 (x1) J1 (x1)

Figure 4. Components’ Failure Rate vs Temperature

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Considering all the assumptions and conditions previously specified (serial model, random failures, indipendent

failures) we can obtain the following results concerning the system’s failure rate and MTBF:

System's Parameter 30° 40° 50° 60° 70° 80° 90°

Failure Rate 1,45E-01 1,64E-01 1,91E-01 2,21E-01 2,54E-01 2,95E-01 3,44E-01

MTBF 8 6,94 5,88 4,98 4,27 3,62 3,08

4,00E-01 3,44E-01

3,50E-01

[FAILURES/(10^6)HOURS] 2,95E-01

3,00E-01 2,54E-01

2,50E-01 2,21E-01

1,91E-01

2,00E-01 1,64E-01

1,45E-01

1,50E-01

RATE 1,00E-01

5,00E-02

FAILURE 0,00E+00 30° 40° 50° 60° 70° 80° 90°

TEMPERATURE [°C]

Figure 5. System’s Failure Rate vs Temperature

9 8

8 6,94

7 5,88

6

HOURS] 4,98

5 4,27 3,62

[10^6 4 3,08

3

MTBF 2

1

0 30° 40° 50° 60° 70° 80° 90°

TEMPERATURE [°C]

Figure 6. System’s MTBF vs Temperature

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