Siemens SITRANS P DS III Operating Instructions Manual page 146

Functional safety
8.1 Safety function
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 binding settings and conditions are listed in the chapters "Settings (Page 149)" and
"Safety characteristics (Page 150)".
Please observe the applicable conditions to ensure the safety function.
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 emphasis of this description
is on the transmitter. For information on requirements for the automation system or final
controlling element, please refer to the corresponding standards.
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 violates the high or low limit, the automation system generates a shutdown signal for
the connected final controlling element, which switches the corresponding valve to the
specified safety position.
Only one SITRANS P DS III device is required for single-channel operation for SIL 2.
Safety-instrumented system in multi-channel operation (SIL 3)
Figure 8-2
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WARNING
Safety-instrumented system in single-channel operation
Safety-instrumented system in multi-channel operation
SITRANS P DS III with HART
Operating Instructions, 06/2013, A5E00047092-09