Allen-Bradley GuardPLC 1753, Справочник по безопасности

Страница: 71 / 120

Publication 1753-RM002C-EN-P - September 2008 71
DeviceNet Safety I/O for the GuardPLC Control System Chapter 6
Input and Output Line Conditioning
DeviceNet safety I/O modules provide pulse test and monitoring
capabilities. If the module detects a failure, it sets the offending input
or output to its Safety state and reports the failure to the controller.
The failure indication is made via the input or output point status, and
is maintained for a configurable amount of time, or until the failure is
repaired, which ever comes first.
DeviceNet Connection Loss
This section describes input and output connection losses.
Input Connection
If an input connection loss is detected, the safety data is set to the
defined safety state (0). The corresponding connection fault bits are
set to one. The application logic must react appropriately to all safety
data from a DeviceNet safety connection being set to the safety state
fault. The scanner continuously attempts to reestablish the input
connection.
Output Connection
If an output connection is lost, the connection is reported as faulted
by the safety Scanner to the controller via the connection status bits.
The application logic must react appropriately to the connection fault,
and the output device must react appropriately to the loss of the
connection and must perform its safety action. The scanner
continuously attempts to reestablish the output connection.
Your application should monitor the HSP and DeviceNet connection
status bits. Since connections often recover automatically, make sure
this occurrence does not result in an unsafe machine state. Your
application should drive safety outputs to their safe state when the
connection faults or goes idle, and remains in the safe state until a
manual reset occurs. This prevents unexpected output transitions from
low/off to high/on when a connection recovers from a faulted or idle
state.
IMPORTANT
Logic must be included in the application program to latch
these I/O point failures and ensure proper restart behavior.
Allen-Bradley Parts