A manufacturer of touch screens for tablets wants a MTBF of

A manufacturer of touch screens for tablets wants a MTBF of at least 50 000 hours. Recent test results for 10 units were one failure at 10 000 hrs, another at 25 000 hrs, and two more at 45 000 hrs. The remaining units were still running at 60 000 hours. Determine the following:

a.      Percentage of failures

b.      Number of failures per unit-hour

c.      MTBF at this point in the testing

Solution

There are 4 failures out of total 10 units.

Therefore . Percentage of failures = 4/ 10 x 100 = 40 %

PERCENTAGE OF FAILURS = 40%

Unit hour run by first unit = 10,000 hours

Unit hour run by second unit = 25,000 hours

Unit hours run by 3^rd and 4^th unit cumulatively = 2 x 45000 hours = 90,000 hours

Cumulative hours run by balance 6 units at 60,000^th hour = 6 x 60,000 = 360,000 hours

Therefore,

Total hours run by 10 units = 10,000 + 25,000 + 90,000 + 360,000 hours = 485,000 hours

Corresponding number of failures during this unit-hours = 4

Therefore, number of failures per unit hour = 4/485,000 = 0.00000824

NUMBER OF FAILURES PER UNIT HOUR = 0.00000824

At this point in testing,

4^th failure has occurred at 45,000 hours

Thus, Mean Time Between Failures ( MTBF) = 45,000/ 4 = 11250 Hours

MTBF AT THISPOINT IN TESTING IS 11250 HOURS