Updated 2016-05-01 18:23:26 by gold

Electronic Failure Rate FITS and eTCL Slot Calculator Demo Example  edit

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gold 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.

Pseudocode and Equations

  price? = raw materials + labor  +  profit
  price? = raw materials + heat process
  price? = raw materials + labor 
  average price per unit  = revenue  / units sold

Testcases Section

Testcase 1

table 1printed in tcl wiki format
quantity value comment, if any
testcase number:1
t1 hours til failure:592.0
t2 hours til failure:642.0
t3 hours til failure:595.0
t4 hours til failure:1000.0
t5 hours til failure:1000.0
t6 hours til failure:0.00078349
per million : 783.49
per billion (FIT): 0.78349


Testcase 2

table 2printed in tcl wiki format
quantity value comment, if any
testcase number:2
t1 hours til failure:655.0
t2 hours til failure:480.0
t3 hours til failure:602.0
t4 hours til failure:1000.0
t5 hours til failure:1000.0
t6 hours til failure:0.00080278
per million : 802.78
per billion (FIT): 0.80278


Testcase 3

table 3printed in tcl wiki format
quantity value comment, if any
testcase number:3
t1 hours til failure:644.0
t2 hours til failure:604.0
t3 hours til failure:650.0
t4 hours til failure:1000.0
t5 hours til failure:1000.0
t6 hours til failure:0.0007696
per million : 769.62
per billion (FIT): 0.76962


Screenshots Section

figure 1.


References:

  • Failure rate ref. Dr. A.K. Nema
  • NIST/SEMATECH e-Handbook of Statistical Methods [1]

Appendix Code edit

appendix TCL programs and scripts

        # pretty print from autoindent and ased editor
        # Electronic failure rate FIT calculator
        # written on Windows XP on eTCL
        # working under TCL version 8.5.6 and eTCL 1.0.1
        # gold on TCL WIKI, 20oct2014
        package require Tk
        namespace path {::tcl::mathop ::tcl::mathfunc}
        frame .frame -relief flat -bg aquamarine4
        pack .frame -side top -fill y -anchor center
        set names {{} {t1 hours til failure :} }
        lappend names {t2 hours til failure :}
        lappend names {t3 hours til failure :}
        lappend names {t4 hours til failure :}
        lappend names {t5 hours til failure :}
        lappend names {answers: average failure per hour: }
        lappend names {failure per million hours: }
        lappend names {failure per billion hours, FIT:}
        foreach i {1 2 3 4 5 6 7 8} {
            label .frame.label$i -text [lindex $names $i] -anchor e
            entry .frame.entry$i -width 35 -textvariable side$i
            grid .frame.label$i .frame.entry$i -sticky ew -pady 2 -padx 1 }
        proc about {} {
            set msg "Calculator for Electronic Failure Rate FIT              
            from TCL WIKI,
            written on eTCL "
            tk_messageBox -title "About" -message $msg }       
        proc calculate {     } {
            global answer2
            global side1 side2 side3 side4 side5
            global side6 side7 side8
            global testcase_number
            incr testcase_number 
            set side1 [* $side1 1. ]
            set side2 [* $side2 1. ]
            set side3 [* $side3 1. ]
            set side4 [* $side4 1. ]
            set side5 [* $side5 1. ]
            set side6 [* $side6 1. ]
            set side7 [* $side7 1. ]
            set side8 [* $side8 1. ]
            set average_rate [/ 3.  [+ $side1 $side2 $side3 $side4 $side5 ]  ] 
            set side6 $average_rate 
            set side7 [* $average_rate 1.E6 1. ]
            set side8 [* $average_rate 1.E6 .001 1. ]                    
                  }
        proc fillup {aa bb cc dd ee ff gg hh} {
            .frame.entry1 insert 0 "$aa"
            .frame.entry2 insert 0 "$bb"
            .frame.entry3 insert 0 "$cc"
            .frame.entry4 insert 0 "$dd"
            .frame.entry5 insert 0 "$ee"
            .frame.entry6 insert 0 "$ff" 
            .frame.entry7 insert 0 "$gg"
            .frame.entry8 insert 0 "$hh" 
             }
        proc clearx {} {
            foreach i {1 2 3 4 5 6 7 8 } {
                .frame.entry$i delete 0 end } }
        proc reportx {} {
            global side1 side2 side3 side4 side5
            global side6 side7 side8 
            global testcase_number
            console show;
            puts "%|table $testcase_number|printed in| tcl wiki format|% "
            puts "&| quantity | value| comment, if any|& "
            puts "&| testcase number:|$testcase_number | |&"
            puts "&|  t1 hours til failure:|$side1|   |&"
            puts "&|  t2 hours til failure:|$side2| |& "
            puts "&|  t3 hours til failure:|$side3| |& "
            puts "&|  t4 hours til failure:|$side4|  |&"
            puts "&|  t5 hours til failure:|$side5|  |&"
            puts "&|  t6 hours til failure:|$side6|  |&"  
            puts "&|per million :| $side7 |  |&"
            puts "&|per billion (FIT):| $side8 |  |&"
         }
        frame .buttons -bg aquamarine4
        ::ttk::button .calculator -text "Solve" -command { calculate   }
        ::ttk::button .test2 -text "Testcase1" -command {clearx;fillup 592. 642.0 595.0 1000.   1000. .000783 783. .783}
        ::ttk::button .test3 -text "Testcase2" -command {clearx;fillup 655. 480.0 602.0 1000.   1000.  8.03E-4 802.78 .8028 }
        ::ttk::button .test4 -text "Testcase3" -command {clearx;fillup 644. 604.0 650.0 1000.   1000. 7.69E-4  769.6 0.769 }
        ::ttk::button .clearallx -text clear -command {clearx }
        ::ttk::button .about -text about -command about
        ::ttk::button .cons -text report -command { reportx }
        ::ttk::button .exit -text exit -command {exit}
        pack .calculator  -in .buttons -side top -padx 10 -pady 5
        pack  .clearallx .cons .about .exit .test4 .test3 .test2   -side bottom -in .buttons
        grid .frame .buttons -sticky ns -pady {0 10}
        . configure -background aquamarine4 -highlightcolor brown -relief raised -border 30
        wm title . "Electronic Failure Rate FIT  Calculator "


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Comments Section edit

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