Safety Manual
Operating Instructions, 06/2012, A5E03433511-05
13
Device-specific Safety Instructions
3
3.1 Applications
The SITRANS SL is suitable for use in a safety-instrumented function of Safety Integrity
Level (SIL) 1, low demand mode, within a 1oo1 architecture.
The safety-related characteristics listed in the respective "SIL Declaration of Conformity"
may be used in the relevant calculations required for IEC 61508 / 61511 safety-instrumented
system compliance.
3.2 Safety function
The safety function at SITRANS SL refers to the measurement of gas concentrations.
The concentration is converted into an analog measured value and supplied over a
4 ... 20 mA (NAMUR) analog output. Fault tolerance allowances must be made, because the
measured value transferred to the automation system by SITRANS SL can deviate from the
physical value. The total tolerance (safety function) is calculated as follows:
Total tolerance (safety function) = ± [application-specific measuring error at operating
conditions + 5 % safety accuracy of full-scale value].
The application-specific measuring error at operating conditions is calculated from the
application-specific measuring error under reference conditions and the measuring error
caused by the influencing variables which depend on the operating conditions. The
application-specific measuring error under reference condition is 2 % of the full-scale value.
For the calculation of the measuring error of the influencing variables and external sensors
contact SIEMENS support providing the operating conditions of the measurement point.
Safety accuracy of the SITRANS SL: the maximum effect of a single failure on the measured
value, which is classified to have no effect.
The diagnostics function responds within 10 seconds in the worst-case scenario.
WARNING
The mandatory settings and conditions are listed in the "Settings (Page 16)" and "Safety
char
acteristics (Page 20)" sections.
These conditi
ons must be adhered to in order to fulfill the safety function.
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