# How to Properly Calculate System Availability

Recently received a request for my opinion concerning the calculation of system availability using the classic formula

$\displaystyle A=\frac{MTBF}{MTBF+MTTR}$

The work is to create a set of goals for various suppliers and contractors to achieve. The calculation values derive from vendor data sheets and available information concerning MTBF and MTTR. The project is in the design phase thus they do not have working system’s available to measure actual availability.

How would you go about improving on this approach? Continue reading Calculating System Availability

# What should we use instead of MTBF?

Giving a presentation last week and asked if anyone uses an 85/85 type test, and a couple indicated they did. I then asked why?

The response was – just because. We have always done it, or it’s a standard, or customers expected it. The most honest response was ‘I don’t know’.

They why is the test being done? Who is using the information for a decision? What is the Continue reading What should we use instead of MTBF?

# MTBF free Availability

The classic formula for availability is MTBF divided by MTBF plus MTTF. Standard. And pretty much wrong most of the time.

Recently working for a bottling plant design team we pursued the design options to improve availability and throughput of the new line. The equipment would remain basically the same, filler, capper, labeler, etc. So we decided to gather the last 6 months or so of operating data which included up and down time. Furthermore the data included time to failure and time to repair information. Continue reading MTBF free Availability