Automating Manufacturing Systems - Process Control and ...

plc software - 32.21
32.7.1 IEC 61508/61511 safety standards
REF: McCrea-Steele, R., "Proven-in-Use: Making the right choices for process
safety", Hotlinks, Invensys, Summer 2003.
REF: Eberhard, A, "Safety in Programmable Applications", Automation World,
Nov., 2004.
- these standards cover electrical, electronic, and programmable electronic systems.
- three categories of software languages covered by the standard
- FPL (Fixed Programming Language) - a very limited approach to programming.
For example the system is programmed by setting parameters.
- LVL (Limited Variability Language) - a language with a strict programming
model, such as ladder logic.
- FVL (Full Variability Language) - a language that gives full access to a
systems, such as C.
- Safety Integrity Level (SIL) - the safety requirements for a function in a system
Low demand:
level 4: P = 10^-4 to 10^-5
level 3: P = 10^-3 to 10^-4
level 2: P = 10^-2 to 10^-3
level 1: P = 10^-1 to 10^-2
High Demand or continuous mode:
level 4: P = 10^-8 to 10^-9
level 3: P = 10^-7 to 10^-8
level 2: P = 10^-6 to 10^-7
level 1: P = 10^-5 to 10^-6
- System safety levels are defined as,
SIF (Safety Instrumented Function) - The SIL for each function is chosen
to ensure an overall system functionality.
SIS (Safety Instrumented System) - A combined system with one or more
logic processors.
SFF (Safe Failure Fraction) - the ratio of safe and dangerous detected failwww.PAControl.com