Dft - Accelerated Life Test Report

VEM

Accelerated Life Testing of De-frost Timers

Reliability Engineering

VEM

Reliability Engineering

VEM Test Procedure : DFT are tested at the rated supply at high temperatures 80°C and 90°C. The De-frost and Compressor timings are noted for each cycle by the LEDs. Judgment Criteria: Timer Stops and Timings more than the specs is considered as failure. Software Used in analysis : MINITAB for Data Analysis, Dplot for Graphs Test Facilities :

Reliability Engineering

VEM Test Data at 80°C

Sample 1 2 3 4 5 6 7 8

Failed after 1 2 2 110 110 110 110 123*

* indicated censored Sample

Reliability Engineering

VEM Test Data at 90°C

Sample 1 2 3 4 5 6 7

Failed after 1 2 78 106 121 121 121 *

* indicated censored Sample

Reliability Engineering

VEM

For Data Analysis, the following are the parameters considered 1. Distribution : Weibull 2. Temp. Relation : Arrhenius 3. Approximation : Maximum Likelihood Estimation

Reliability Engineering

VEM Probability Plot (Fitted Arrhenius) for Failure T Weibull Distribution - ML Estimates - 95.0% CI Censoring Column in Censor 80

Percent

99

90

95 90 80 70 60 50 40 30

Shape

Scale

AD*

F/C

0.5906

56.195

6.50

8/1

0.5906

84.216

7.55

6/1

Design Value = 35.0000 0.5906

20

6.5756

10 5 3

Probability of failure for 80°C is more than 90°C

2 1

0

0

0

0

0

0

0

0

1

10

100 1000 10000100000 1000000

Failure T

Reliability Engineering

VEM

As the probability of failures in 80°C is more than 90°C, which is not suggested, the data has to be modified. Neglecting the early life failures (1 cycle failures) the data is again analyzed.

Reliability Engineering

VEM Modified Test Data at 80°C

Sample 1 2 3 4 5 6

Failed after 2 110 110 110 110 123*

* indicated censored Sample

Reliability Engineering

VEM Modified Test Data at 90°C

Sample 1 2 3 4 5 6

Failed after 2 78 106 121 121 121*

* indicated censored Sample

Reliability Engineering

VEM Probability Plot (Fitted Arrhenius) for Failure T Weibull Distribution - ML Estimates - 95.0% CI Censoring Column in Censor 80

Percent

99

90

95 90 80 70 60 50 40 30

Shape

Scale

AD*

F/C

1.2015

112.77

8.91

5/1

1.2015

109.82

8.59

5/1

Design Value = 35.0000 1.2015

20 10 5 3 2 1

0

0

1

10

100

1000

10000

Failure T

Reliability Engineering

100000

129.80

VEM

When doing accelerated life testing, you subject units to levels of an accelerating variable far exceeding normal field conditions to accelerate the failure process. But most likely, the information you ultimately want is, How do the units behave under normal field conditions? Ask Minitab to extrapolate information gained from the accelerated situation to the design value, or common field condition. Percentile is How long it takes for 10% of the units to fail, 20% of the units to fail, 20% of the units to fail............

Reliability Engineering

VEM

Test Data Extrapolated to use temperature 35°C

So, The No. of Cycles required for 10 % of the samples to fail are 20 Cycles, for 50 % of failure is 95 Cycles and for 90 % of the sample to fail is 259 Cycles.

Percent 10 20 30 40 50 60 70 80 90

Reliability Engineering

Temp 35 35 35 35 35 35 35 35 35

Percentile 19.95 37.25 55.04 74.21 95.67 120.69 151.48 192.87 259.85

VEM

Test Data Extrapolated to use temperature 27°C

So, The No. of Cycles required for 10 % of the samples to fail are 20 Cycles, for 50 % of failure is 98 Cycles and for 90 % of the sample to fail is 267 Cycles.

Percent 10 20 30 40 50 60 70 80 90

Reliability Engineering

Temp 27 27 27 27 27 27 27 27 27

Percentile 20.54 38.36 56.67 76.42 98.52 124.29 156.00 198.63 267.60