Allen-Bradley AADvance T9110, Руководство по безопасности

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66 Rockwell Automation Publication ICSTT-RM446N-EN-P - April 2018
Chapter 4 AADvance Functional Safety System Implementation
• Sensor delay: 250ms
• Time for actuator (an ESD valve) to fully operate: 1750ms
In this example therefore, the setting of PST for the controller should be less
than or equal to 3000ms.
Choosing Controller PST Settings
The response time allocated to a logic solver such as the AADvance controller
needs to take account of delays within the operation of sensors and actuators.
In addition, the system's scan time should be considerably less than the process
safety time.
The value of the PST shall form part of the safety considerations for the
system. The value is defined by the process design authority; the system
integrator shall calculate and verify that the process safety time meets the stated
requirements.
• In an AADvance system the PST value is assigned to the system and can
be assigned to individual modules. The system PST value is enforced by
the processor modules and has priority over the module PST values.
When the system PST is not met the processor modules will fail-safe.
• The input PST is also enforced by the processor modules; when the PST
is not met, the processors will present fail-safe input values to the
application logic.
• Output PST is enforced by the output modules and when the output
PST is not met, the output module will assume the fail-safe state.
You must specify the process safety time for the whole controller. If desired,
you can specify additional process safety times for individual groups of I/O
modules. The setting for the whole controller is a top level setting, which you
make once for all the 9110 processor modules. Groups of I/O modules can
inherit this setting or, if desired, use individual process safety times instead.
NOTE The fail-safe state for all AADvance modules is de-energized.
NOTE • The minimum controller's PST must be at least twice the application
scan time.
• If you choose to specify a process safety time for a group of I/O
modules, the I/O modules use this setting instead of the top level
setting.
• If you do not specify a process safety time for a group of I/O modules,
the I/O modules use the top level setting.
• If you do not specify any process safety time, the controller will use a
default value of 2,500ms throughout.