Allen-Bradley 1756-L61S ControlLogix 5561S, Справочное руководство

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Rockwell Automation Publication 1756-RM093J-EN-P - April 2018 17
Safety Integrity Level (SIL) Concept Chapter 1
PFD and PFH values are associated with each of the three primary elements
making up a safety-related system (the sensors, the logic element, and the
actuators). Within the logic element you also have input, processor, and output
elements.
Figure 2 - PFH Example
To determine the logic element PFH for each safety loop in the simple example
system shown in the PFH Example, sum the PFH values for each component in
the loop. The
PFH Equations by Safety Loop table provides a simplified example
of PFH value calculations for each safety loop shown in the PFH Example
illustration.
When calculating PFH values, you must take into account the specific
requirements of your application, including proof test and diagnostic test
intervals.
Safety Integrity Level (SIL)
Compliance Distribution and
Weight The GuardLogix controller and I/O system may conservatively be assumed to
contribute 10% of the reliability burden. A SIL 3 system may need to incorporate
multiple inputs for critical sensors and input devices, as well as dual outputs
connected in series to dual actuators dependent on SIL assessments for the safety
related system.
DeviceNet EtherNet Logix5562S Logix55LSP
Sensor
Sensor
Sensor
1791DS-IB12
GuardLogix Controller
1791DS-IB8XOB8
1791DS-IB4XOX4
Actuator
Actuator
LOOP 1
LOOP 2
Table 5 - PFH Equations by Safety Loop
For this loop Sum the PFH values of these components
Total PFH for loop 1 = 1791DS-IB12 + GuardLogix cont 1791DS-IB4XOX4
Total PFH for loop 2 = 1791DS-I GuardLogix cont 1791DS-IB4XOX4