Siemens SIPART PS2 FF Betriebsanleitung Seite 21

WARNING
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 chapters "Settings (Page 22)" and "Safety-related characteristics
(Page 23)".
● 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 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 SIPART PS2 FF diagnostics values (Page 23)
Safety-instrumented system in single-channel operation (SIL 2)
Figure 2-1 Safety-instrumented system in single-channel operation
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.
2.3 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.
Description
The following table shows the dependency of the SIL on the "average probability of dangerous failures of a safety function of
the entire safety-instrumented system" (PFD
required a maximum of once per year on average.
Table 2-1 Safety Integrity Level
SIL
4
3
2
1
Functional safety for SIPART PS2 FF
A5E00489774-02, 10/2013
). The table deals with "Low demand mode", i.e. the safety function is
AVG
Interval
10 ≤ PFD < 10
-5 -4
AVG
10 ≤ PFD < 10
-4 -3
AVG
10 ≤ PFD < 10
-3 -2
AVG
10 ≤ PFD < 10
-2 -1
AVG
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