Rockwell Automation iTRAK, User Manual

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Rockwell Automation Publication 2198T-UM002C-EN-P - March 2019 113
Functional Safety Chapter 7
contact is held open, which breaks the reset circuit. The system must not be
restarted until appropriate measures have been taken.
Considerations for Category 1
Stop If there is a malfunction, it is possible that stop category 0 can occur. When
designing the machine application, timing and distance must be considered for
a coast to stop and the possibility of the loss of control of a vertical load. The
malfunction that causes this condition maybe when a signal to the output
contactor coil were to go low. A low can happen when a wire falls off or control
power fails before the iTRAK system has a chance to come to a complete stop.
Use additional protective measures if this occurrence can introduce
unacceptable risks to personnel.
Overall System Stopping
Performance ISO 14119 6.2.1 stipulates that the overall system stopping time for a
hazardous machine that is safeguarded by an interlock must be less than the
access time. If the overall system stopping performance is equal to or greater
than the access time, an interlock with guard locking must be used, the distance
from the safeguard to the hazard must be increased, or another, more suitable
method must be used to safeguard the hazard.
The overall stopping performance of these applications is the sum of the
following.
• Response time of the safety input device.
• Safety logic devices.
• Any delay that is configured in the safety logic devices.
• The safety reaction time of the output contactors used.
• The coast-to-stop time of the hazardous motion.
The response and reaction times can be taken from the product support
literature.
The sum response and reaction time of the safety logic devices, output
contactors, and worst-case, coast-to-stop portion of the overall system-
stopping performance is the same regardless of the input device used.
It is useful to estimate how fast the hazardous motion must coast to a stop
before the safeguarded system is available for testing.
IMPORTANT Determine the overall system stopping performance of a safeguarding
system by actual system testing and measurement. The worst-case, overall
system stopping performance from these tests and measurements must be
used to evaluate the safety distance requirements.