Unit 21: Maintenance
LO3: Be able to analyse reliability-centred
maintenance data
MTBF, MTTF and MTTR
Learner activity sheet
Activity 1
The life of a component, product or system can be described using a bath tub curve. The bath tub curve
shows failure rate against time (or life).
Explain what the bath tub curve below tells us about the life of a component/system, including the
significance of regions 1, 2 and 3.
Failure rate
3
1
2
Time
Version 1
Activity 2
Mean Time Between Failures (MTBF), Mean Time To Failure (MTTF) and Mean Time To Repair (MTTR)
are commonly used metrics relating to reliability that inform reliability-centred maintenance strategies.
They can be calculated using data.
Define the terms below, giving a formula for how each can be calculated:
1.
MTBF
2.
MTTF
3.
MTTR
Version 1
Activity 3
Problem 1
A batch of 10 air compressors is tested for 500 hours before being sent to the customer. During the test
2 of the compressors fail. Estimate the MTBF.
Problem 2
A batch of 10 lambda oxygen sensors is tested for 500 hours. During the test 2 sensors fail. Estimate
the MTTF.
Comment on your solutions to Problem 1 and Problem 2 – what is different about the two cases given
(the compressor and the lambda sensor) and why are the results different?
Version 1