Glossary · Automation fundamentals, platforms and components
Reliability
German: Zuverlässigkeit
In dependability engineering, reliability is the ability of an item to perform as required, without failure, for a given time interval, under given conditions. It is often quantified by measures such as failure rate, mean time to failure (MTTF) or mean time between failures (MTBF).
- Automation components
- Standards
In one sentence
Reliability is the ability of an item to perform as required, without failure, for a given time under given conditions (IEC 60050-192).
Example
The pump supplier states an MTBF of 50,000 hours for continuous duty at 40 °C; at higher ambient temperatures the value is lower.
How it applies
- Engineering: Reliability is designed in through component selection, derating, Redundancy and robust design, and is checked with analyses such as FMEA and reliability prediction.
- Maintenance: Maintenance strategies use failure data to choose intervals; field data improves predicted values over time.
- Documentation: Reliability figures are only meaningful with their conditions (duty cycle, temperature, load). Quote them together in data sheets and manuals.
Reliability vs. safety
A reliable machine rarely fails; a safe machine does not cause unacceptable risk, even when it fails. A very reliable function can still be unsafe, and a safety function may deliberately stop the machine and reduce availability. In functional safety, the relevant figure is the probability of dangerous failure, for example Mean time to dangerous failure (MTTFd), not overall reliability.