Lecture 9 - Functional Safety: Standards and Terminology Flashcards
1
Q
Umbrella standard
A
REFER TO SLIDES
2
Q
What is a control system and equipment under control
A
- System that responds to INPUT signals from process and/or from an operator and generates OUTPUT signals causing the EUC to operate in the desired manner.
- Equipment under Control (EUC)
- equipment, machinery, apparatus or plant used for manufacturing, process, transportation, medical or other activities.
3
Q
What are the demands on the safety functions?
A
- During normal operations, machines have safety functions that are expected to either operate in:
- Low demand – less than once a year activation
- High/Continuous demand – more than once a year activation
- IEC 62061 & ISO 13849 only designs safety function in High Demand (e.g. activated more than once per year)
4
Q
What is low and high complexity?
A
- Complexity of components: High vs Low
- It depends on the Failure mode
- High complexity - Failure modes of individual components cannot be completely defined -> IEC 62061
- # Examples include Safety PLC, microprocessor
- Low complexity – Failure modes of individual components are well
defined -> ISO 13849 - Examples include mechanical devices, relays, contactors
5
Q
How do you determine what standard to use?
A
REFER TO SLIDES (SLIDE 10)
6
Q
What is the SIL Definition?
A
REFER TO SLIDES
7
Q
What is the Risk Reduction Factor (RRF)?
A
- Normally used in low-demand mode.
- It is the inverse of the required probability of failure on demand.
- REFER TO SLIDES
8
Q
What is the PL Definition?
A
REFER TO SLIDES
9
Q
What are some common misconceptions in functional safety in regards to the above content?
A
- Meeting probability of system failure (PFD / PFH) is sufficient
- # Need to follow selection of good components and minimum hardware fault tolerance
- High SIL is always better
- # Higher SIL – higher insurance premium, higher maintenance cost
- SIL can be achieved by device only
- Safety functions require input / logic / output
