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gold Here is some Here is some eTCL starter code for calculating the failure rate of electronic devices in failures per billion device-hours or Failures In Time (FIT). This report will use less strict definitions and not consider confidence levels for FIT, since the main interest is developing a simple and quick calculator. The impetus for these calculations was reported failure rates in some light emitting diode (LED) lightbulbs. Most of the testcases involve replicas or models, using assumptions and rules of thumb.
In planning any software, it is advisable to gather a number of testcases to check the results of the program. The results of the testcases were estimated using the hand calculator and then checked in the eTCL calculator. Additional significant figures are used to check the eTCL calculator, not to infer the accuracy of inputs and product reports. For the 3 testcases, there were sets of trials lasting up to 1000 hours. If the device lasted 1000 hours, a new device was switched in. The first testcase was 592, 642, 595, 1000, and 1000 hours. The hand calculator returned an average failure rate of 3 failures /(592+ 642+595+ 1000+ 1000) hours, 3/3829, or 0.0007834 failures per hour. Converting, the failure rate was 0.0007834*1E6, 783.4 failures per million hours and 0.0007834*1E9, 0.783 failures per billion hours (FIT) . The eTCL calculator returned 0.7349 FITS. The second testcase was 592, 642, 595, 1000, and 1000 hours. In the hand calculator, the average failure rate was 3/(592+ 642+595+ 1000+ 1000),3/3737, 0.0008027 failures per hour. The conversion by 1E6 and 1E9 was 802.7 f/1E6 hours and 0.8027 FITS, respectively. On the second testcase, the eTCL calculator returned 0.802 FITS. The third testcase was 3/(644+ 604+650+ 1000+1000) or 0.0007696 failures per hour. The conversion by 1E9 was 0.77 FITS in the hand calculator. The eTCL calculator returned 0.769 FITS for the third testcase.
The mean time between failures, abbreviated as MTBF, equals 10E9*(1/FIT). The analysis made some trial estimates for MTBF. For the first testcase, the trial MTBF is 10E9*(1/FIT), 10E9*(1/0.783), or 12.77E9 hours. For the second testcase, the trial MTBF is 10E9*(1/FIT), 10E9*(1/0.8027), or 12.45E9 hours. For the third testcase, the trial MTBF is 10E9*(1/FIT), 10E9*(1/0.769), or 13.00E9 hours.
For comparison, the MTBF in the testcases was compared with the understanding of the mean time to failure, MTTF. The MTBF in the first testcase was 5*1000/3, 1666 hours per failure. The MTTF was 5*1000/5, 1000 hours per failure. For a disk drive used continuously, the MTBF was 15E5 hours. There were 365 days*24 hours, or 8760 hours in a year. Converting, the drive MTBF was 15E5 hours/ 8760 hours per year, 171.23 years. The percent failure was (1/ MTBF years)*100., (1/171.23)*100, or 0.5840 percent. Meaning, 0.584 percent of the population or drives in service were expected to fail per the average year.
For the push buttons in the eTCL calculator, the recommended procedure is push testcase and fill frame, change first three entries etc, push solve, and then push report. Report allows copy and paste from console. For testcases in a computer session, the eTCL calculator increments a new testcase number internally, eg. TC(1), TC(2) , TC(3) , TC(N). The testcase number is internal to the calculator and will not be printed until the report button is pushed for the current result numbers. The current result numbers will be cleared on the next solve button.
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