Definition:
An Application Program is the specific logic developed and loaded into a safety logic solver or safety PLC to implement a Safety Instrumented Function (SIF). It is the software the user develops and should not be confused with the embedded software already on the device.
This ties with the three IEC 61508/61511 programming categories
- fixed programming language (FPL) – use is limited to adjustment only. Such as a smart logic module.
- limited variability language (LVL) – most common in SIS engineering, uses pre-configured function blocks within the safety PLC programming language platform.
- full variability language (FVL) – rarely needed in a SIS, full breadth of programming requiring IEC 61508-3 compliance
Within these programming categories, one can use different programming languages like ladder diagram (LD), function block diagram (FBD), structured text (ST), instruction list (IL), sequential function chart (SFC).
Key Points:
- Must be created following strict software development life cycle (SDLC) principles.
- Typically programmed using LVL in languages like Function Block Diagram (FBD) or Ladder Diagram (LD).
- Subject to functional safety software standards like IEC 61511-1 §12
Example:
An emergency shutdown sequence is programmed in a safety PLC using pre-defined function blocks. These blocks process inputs from instruments and outputs to ON/OFF valves. This would be an example of an LVL application program type.
See Also: V-Model, FPL, LVL, FVL
Cited Source:
- IEC 61508-3:2010, §7.4.
- IEC 61511-1:2016, §12