Classification (Sil Level) System Time Constraint; Without System Time Constraint Dual Final Elements - ABB Triguard SC300E Safety Manual

3.3.2.6 Hot Repair Adapters
Wherever dual slot hot repair facilities are required, the hot repair adapter boards must be fitted
on the chassis backplane.

3.4 Classification (SIL level) System Time Constraint

The Triguard SC300E Safety PLC is a fault tolerant system that inherently tolerates and reports
a first major fault (for example a processor failure).
The system diagnostics of a digital output module are not fully available after a first fault is found
on the module. The time allowed to repair this module before a shutdown to the safe state is
required is the system time constraint.
The Triguard SC300E System may be configured with or without time constraint dependent on
the safety output configurations used.
In systems configured with single outputs and final elements, then a time constraint will apply.
The time constraint has been conservatively calculated by TUV dependent on the SIL level (low
demand) and based on worst case of all outputs used.
Time constraint for SIL 3 systems is 2353 hours
Time constraint for SIL 2 systems is 7440 hours
Time constraint for SIL 1 systems is 23528 hours
Time constraint may be extended if less than 32 outputs are safety related, for extended time
constraint values refer to the table Appendix 2.
3.4.1

Without System Time Constraint Dual Final Elements

In AK6 (SIL 3) classified safety loops it is probable that the safety loop final element has at least
two possible operational paths (Figure 3 shows a typical configuration).
Providing each final element is driven from a separate SC300E digital output on separate digital
output modules, the system will have no time constraint.
Issue 5 - September 2006
MDO Card 1
SC300E TMR
System
MDO Card 2
Dual Valve Example
MDO Card 1
SC300E TMR
System
MDO Card 2
Dual Solenoid Example
TC
ESD Valve 1
TC
ESD Valve 2
TC
Dual
Solenoid
Valve
TC
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