MTBF stands for the Mean Time Between Failures. It is an indicator defining
time between failures; it also allows you to determine how reliable the
production process is. The MTBF is used in a number of industry branches in
the context of maintenance. It is also one of key performance indicators (KPIs)
used in a TPM system, allowing companies to verify failure time as well as
Introduction to the MTBF: what is failure?
If one wants to discuss the MTBF indicator (or other key performance indicators
remaining in the TPM system), it is essential to specify what failure actually is.
There are two basic definitions of failure which will in turn allow you to
understand what the MTBF indicator is.
Failure could be one of the following scenarios:
- certain elements are not functioning
- the product as a whole is not functioning
Letʼs look at an example: failure of a UPS power inverter caused the power
supply to switch to a bypass mode. Despite the component failure, the power
supply is still able to function and supply the critical device.
Another example of failure might be failure of a redundant array of disc (RAID)
which will cause an inability to deliver key data within the Net infrastructure.
As a consequence, the disc will stop working entirely.
Naturally, the above examples are not complicated enough and the definition of failure based upon them is quite straightforward. The problem to define failure might occur when it is essential to verify the MTBF indicator as part of complex and complicated structures and processes.
Which is why companies need to define failures on their own terms; in
accordance with their own regulations and estimates based upon production
processes and maintenance. It is necessary to interpret definitions individually.
Only in the context of failure clarified, can the MTBF indicator be interpreted.
What is an MTBF indicator and what does it communicate to the company?
An MTBF indicator impacts not just dependability but also availability of a
machine in a production process. It is worth mentioning the difference between
availability and dependability.
In accordance with IEEE 90, availability is the
degree of the system activity when its usage is required. Dependability is an
ability of a system to function under a certain set of circumstances and for a
certain period of time. So a high availability always goes hand in hand with high dependability.
The Key Performance Indicator (KPI)– which is what the MTBF is, described as a mean time between failures- is a basic estimate of a systemʼs dependability.
It is usually defined in hours; the higher the number, the higher the
dependability of the product or of the production process. In other words, the
MTBF indicator determines how often statistically, will the system failure take
place. In practice, companies usually use this indicator to estimate the
frequency of machine park maintenance as preventive measures.
The MTBF indicator can be described as the total of the MTTR and the MTTFso
the total of mean time from failure and mean time from failure to repair.
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