List of Type Approvals > Type Approved Programmable Electronic Systems (PES) (PLC's)
System Structures
The nomenclature for system structures describes the possible degradation
behaviour after fault detection and fault localisation for the central processing units.
Variations are possible due to different implementation possibilities. This table shall
give a first guideline.
In the I/O area different degradation mechanisms are possible and implemented on the different
systems.
|
Fault-free system
|
Degradation 1
|
Degradation 2
|
Degradation 3
|
System structure
|
|
2oo4
|
1oo2
|
1oo1*
|
Shutdown
|
Safety related and fault tolerant
*with time restriction |
|
2oo4
|
1oo2
|
Shutdown
|
Safety related and fault tolerant
|
|
|
1oo3
|
Shutdown
|
Safety related
|
||
|
2oo3
|
1oo2
|
1oo1*
|
Shutdown
|
Safety related and fault tolerant
*with time restriction |
|
2oo3
|
1oo2
|
Shutdown
|
Safety related and fault tolerant
|
|
|
1oo2D
|
1oo1D
|
Shutdown
|
Safety related and fault tolerant with time
restriction
|
|
|
1oo2
|
Shutdown
|
Safety related
|
||
|
2oo2
|
1oo1
|
Shutdown
|
Safety related and fault tolerant
|
|
|
1oo1
|
Shutdown
|
Safety related
|
Part 4 of the IEC 61508 gives the defintion of
MooN : M out of N channel architecture (for example 1oo2 is 1 out of 2 architecture, where either of the two channels can perform the safety function)
MooND : M out of N channel architecture with diagnostic
© by TÜV Rheinland Industrie Service GmbH/ last change: 20.03.2004