Excel 2007 : How to calculate Mean Time between Failures

**Icehockey44** · 02-17-2012, 12:59 PM

Hi All,

i have been putting this off for months, but my client is now hastling me for it!!!

I have attached a spread sheet with example data (not much)

Basically in 1 month we had X amount of machines have calls logged against them for a breakdown, of this X, Y of them have logged another call within 26 days of the previous breakdown call. ( we repair within 8 hours of call logged).

i need to show what is the mean time between each failure per month.

Each month will have a different set of machines and numbers, so do i only use the number of machines that have l;ogged a call in each month, or should i base it on our whole machine estate for the clients account?

Please see attched spread sheet and have a play.

i am really looking forward to your help on this one!!

Donnaexample 1.xlsx

**Fotis1991** · 02-17-2012, 01:08 PM

Hi Dona

As i understand it, i would say...

=E4/E6

**shg** · 02-17-2012, 03:02 PM

Divide the number of operating machine-days by the number of failures.

So if there are 200 machines operating for 31 days, and 10 fail (and are immediately replaced), the MTBF is 200*31/10 = 620 days.

**Icehockey44** · 02-21-2012, 08:20 AM

Hi guys,

Thanks for this, not sure how much you know about this (I don't know much!!) but would i use the whole estate of machines in the equation, or just the ones that have had breakdowns on?

Both of your suggestions work, but give different answers, which it would as one is just the number of days in the period/the no of multiple failures, where as the other is the number of Machines * days in the period/no of multiple failures.

Look forward to your help and advice on this one.

Cheers

Donna