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MTBF Calculation for all the machines/equipments

May 25, 2017 at 06:22 PM

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Former Member

Hi Everyone,

I have read several posts and documents regarding MTBF calculation. But I had a doubt regarding MTBF calculation for all the equipment existing in my system.

Formula which I know is: (Available time for equipment - Down Time)/ Number of Breakdown

Suppose I have total working 10 equipment and available time for each equipment is 24 hours.

Now if suppose 2 of them had a breakdown of 2 hours each.

- Will MTBF formula consider available hours for all 10 equipments i.e. 240 hours? MTBF will be: (240-4)/2 = 236/2 = 118

or will MTBF be calculated on the basis of only 2 equipments for which breakdown occurred i.e. 48 hours? MTBF will be (48-4)/2 = 44/2 = 22

Thanks!

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2 Answers

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Former Member May 27, 2017 at 06:52 AM
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Hi Madhur,

I have done the same thing on one of my client. i.e.

suppose you have 10 equipment and you want to calculate the MTBF for April month then the calculation will be like:

Thare are two things one is If you want to calculate the MTBF equipment wise and another one is overall equipment wise MTBF.

Formula:

Plan Time = No of Days * 24 * No of Equipment

MTBF = (Plan Time-Breakdown duration)/No. of Breakdown

For single Equipment:

Plan time = 30 * 24 * 1 = 720

Breakdown duration of single equipment = 10 hour

No of breakdown of 1 equipment = 4

MTBF = ( 720 - 10 ) / 4 = 177.5

For Overall 10 Equipments:

Plan time = 30 * 24 * 10 = 7200

Breakdown duration of 2 equipment = 15 hour

No of breakdown of 2 equipment = 7

  • MTBF = ( 7200 - 15 ) / 2 = 1026.42

Let's wait for other expert answer.

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Former Member

Hi Ramesh,

Thanks for responding. But don't you think considering the equipment for MTBF for which failure never happened is not correct.

e.g. If there are 2 equipments, first one with total working hours 720 hours, 4 hours breakdown and 2 notifications

MTBF = (720 - 4)/2 = 716/2 = 358.

Second one with no failure/breakdown will be: (720 - 0) /0 which will be infinite.

Moreover considering both of them: (1440 - 4) /2 = 1436/2 = 718. Which as per my understanding is not correct. MTBF should be calculated for only equipments which generate notification or which have a failure.

Please feel free to correct me if my understanding is not correct.

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Former Member May 29, 2017 at 06:15 AM
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Hi Madhur,

If you are calculating MTBF, not a single equipment wise than all the equipment will be considered. That is suggested by my client in my last project.

We can wait for other expert opinion.

Regards,

Ramesh

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