Siemens SIPART Series Operating Instructions Manual page 144

Functional safety
8.2 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 operations for
each of the two pilot valves with symmetrical load. The number of control procedures for the
switching operations is called in the local display or via HART communication. Refer to the
diagnostics parameters "40 VENT1" and "41 VENT2" under the following "see also" link.
See also
Meaning of the diagnostics values (Page 211)
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.
142
Safety-instrumented system in single-channel operation
SIPART PS2 with and without HART
Operating Instructions, 10/2013, A5E00074631-11