Safety Integrity Level (Sil) - Siemens SIPART PS2 Operating Instructions Manual

Functional safety

8.3 Safety Integrity Level (SIL)

Situations in which it is not possible to depressurize the actuator on demand or in the case of
a fault represent a dangerous failure.
Disregarding conditions for fulfilling the safety function
Disregarding conditions can result in a malfunction of the process system or application, for
example, process pressure too high, maximum level exceeded.
The mandatory settings and conditions are listed in sections Settings (Page 142) and Safety
characteristics (Page 143).
● These conditions must be met in order to fulfill the safety function.
The pneumatic block of the positioner pressurizes and depressurizes the actuator. The
pneumatic block contains two pilot valves. The characteristic service life of the pneumatic block
depends on the load. On average it is approx. 200 million switching cycles for each of the two
pilot valves with symmetrical load. The number of control procedures for the switching cycles
is called in the local display or via the communication function. For more details, see Diagnostic
value '42.VENT1' / '43.VENT2' (Page 264).
Safety-instrumented system in single-channel operation (SIL 2)
Figure 8-1
The combination of transmitter, automation system and final controlling element forms a safety-
instrumented system that performs a safety function.
The transmitter generates a process-related measured value that is transferred to the
automation system. The automation system monitors this measured value. If the measured
value exceeds the range of the high or low limit, the automation system generates a shutdown
signal for the connected final controlling element, which switches the associated valve to the
specified safety position.
8.3 Safety Integrity Level (SIL)
The international standard IEC 61508 defines four discrete Safety Integrity Levels (SIL) from
SIL 1 to SIL 4. Every level corresponds to a probability range for the failure of a safety function.
140
WARNING
Transmitter
Safety-instrumented system in single-channel operation
Automation system
Operating Instructions, 02/2016, A5E00127926-AB
Final controlling element
SIPART PS2 with PROFIBUS PA