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Safety-instrumented system in single-channel operation (SIL 2)
Automation system
Transmitter
Final controlling
P$
P$
Figure 10-1 Safety-instrumented system in single-channel operation
The combination of pressure transmitter, automation system and final controlling element
forms a safety-instrumented system that performs fail-safe behavior. The focus of this
description is on the pressure transmitter. For information on requirements for the automation
system or final controlling element, please refer to the corresponding standards.
The pressure 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 device is required for single-channel operation for SIL 2.
Safety-instrumented system in multi-channel operation (SIL 3)
Automation system
Transmitter
Final controlling elements
P$
P$
Figure 10-2 Safety-instrumented system in multi-channel operation
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 process-related measured values that are transferred to the
automation system. The automation system monitors these measured values. In the event of
a fault, the automation system generates shutdown signals for connected final controlling
elements that set the associated valve to the defined safety position. Faults are:
● Violations of the preset high or low limits
● Deviations between the two measured values
The automation system program must monitor the measured values of both SITRANS
P devices. As soon as the measured values differ by e.g. 2% or more, the system must be
brought into the safe state and the fault must be located.
Functional Safety
10.1 Safety concept
SITRANS P320/P420 with 4 to 20 mA/HART
Operating Instructions, 11/2019, A5E44852162-AC
161