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About MTBF

  • 1.  About MTBF

    Posted 06-22-2023 05:21 AM

    First all,thanks for your helping.

    Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

    What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

    Which number is right?

    Thanks



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    Yi Sun
    Huizhou
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  • 2.  RE: About MTBF

    Posted 06-23-2023 07:41 AM
    Edited by Jesse Day 06-23-2023 07:41 AM

    I think when reading the question I would clue in on the dates listed "from installation". The MTBF can also be considered Mean Life where the life of the asset in this case starts at installation. MTBF = Operating time / Number of Failures. This interpretation would use 23 months / 3 events.

    I hope I am not leading you down the wrong path but this is how I would approach the problem. 



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    Jesse Day

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  • 3.  RE: About MTBF

    Posted 06-23-2023 08:07 AM

    I ignore the time from first operation to the 9th months.

    So the corrective formula is (9-0)+(16-9)+(23-16)=9+7+7=23 ( which is not the 23rd months) ,

    then MTBF = 23/3=7.7.

    Regards



    ------------------------------
    Yi Sun
    Huizhou
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    Original Message


  • 4.  RE: About MTBF

    Posted 06-23-2023 07:54 AM

    Hi Yi,

    The interval from install to the first break down was 9 months.  That raises the interval from the 7 to the 7.7.  

    Jason Ball



    ------------------------------
    Jason Ball PMP, SSGB
    Maintenance Manager
    TechmerPM
    Clinton TN
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  • 5.  RE: About MTBF

    Posted 06-23-2023 08:15 AM

    Hi Yi,

    I think it is 7.7 for two reasons:

    1- the first interval is 9 months not seven, so the average of the three intervals will be the average of 9, 7, and 7.

    2- by definition the MTBF = total running hours / total number of failures. So the total running hours are 23, and total failures are 3.

    I hope this has replied your question. 



    ------------------------------
    Ahmed Mohamed Helmy Khattab
    Almanzala
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  • 6.  RE: About MTBF

    Posted 06-23-2023 08:22 AM

    My approach would be to ignore the "intervals" as a consideration for this question. By definition, MTBF = Operating time (hours) / Number of Failures.



    ------------------------------
    KAMARIA DUNCAN
    Mechanical Technician III
    P.P.G.P.L
    Point Fortin
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  • 7.  RE: About MTBF

    Posted 06-23-2023 10:21 AM

    MTBF=Total running hours/ number of failure.

    In above question,total operating time is given in terms of months. Hence,the formula shall be considered as below.

    MTBF=Total running months/ number of failure.

    MTBF=23 months/3

    Ans:7.7 months.



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    Muthukumar Pandian
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  • 8.  RE: About MTBF

    Posted 06-23-2023 12:03 PM

    Averaging the intervals works, but you left out the first one (9 months).  The average of 9, 7, 7 is 7.7 months. 



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    Daniel K Corman, CMRP
    Houston, Texas, USA
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  • 9.  RE: About MTBF

    Posted 06-23-2023 09:30 PM

    Yes,I recognize the point that neglected the first 9 months.

    Thanks for your reply,that helps me a lot.



    ------------------------------
    Yi Sun
    Huizhou
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    Original Message


  • 10.  RE: About MTBF

    Posted 06-23-2023 02:22 PM

    I believe you could interpret this question a couple different ways. The first way is the first failure occurred at in 9 months and the next failure occurred 16 months later and the last failure occurred 23 months later. If that's the case the formula would be (9+16+23)/3=16 months MTBF. 

    Second interpretation, this is how I'm understanding the question, the first failure occurred in 9 months and the next failure occurred during the 16th month which is 7 months later and the last failure occurred during the 23rd month which was 7 months later than the 16th month. The formula would be (9+7+7)/3=7.67 months MTBF

    I hope this helps. 


    Daniel Sallings



    ------------------------------
    Daniel Sallings
    Tech Manager of Operations
    Michelin
    Lexington SC
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  • 11.  RE: About MTBF

    Posted 06-23-2023 09:27 PM

    Thanks for your help,

    I understand my falut that ignore the first 9 month,the correct fomula will be (9+7+7)/3=7.7

    Regards



    ------------------------------
    Yi Sun
    Huizhou
    ------------------------------

    Original Message


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