Table of Contents
Overview
Chapter 1
Fault State
The DG safety relay and the taps have two fault states: recoverable and
non-recoverable. When a fault occurs, the taps and DG safety relay are in a safe
state. Diagnostic information is provided by the indicators. The DG safety
relay also sends diagnostic information to the EtherNet/IP interface.
Recoverable faults can be cleared by cycling the faulted input devices. Non-
recoverable faults require the power to the cycled and can also require
troubleshooting and correction of the fault. When an EtherNet/IP interface is
used, the machine control system can issue a fault reset (equivalent to a power
cycle).
GuardLink Transition from Safe State to Operational State
When the GuardLink signal is in the safe state, the DG safety relay holds the
CLU signal in the high or dynamic unlocking state. The DG safety relay puts
all taps in the safe state. For the GuardLink signal to return to the operational
state, the DG safety relay must know that all taps are ready to go to the
operational state. If the taps are ready to go, the CLU signal is set to LO.
Now that the CLU is set to LO, the last tap generates the safety signal. Each
successive upstream device verifies that the previous device is in a safe state,
confirms that its own device is in a safe state, and sends an inverted safe state
signal to the next device.
When the DG safety relay receives the safety signal, the GuardLink circuit is in
an operational state, and the DG safety relay continues with the evaluation of
the other inputs, output monitoring, and reset inputs.
GuardLink Transition from Operational State to Safe State
Once an input device has a demand on its safety function, the tap stops sending
the safety signal. When the DG safety relay no longer detects the safety signal,
the CLU signal is set to HI to make all taps enter the safe state.
GuardLink Fault Reset Command
Devices with OSSD outputs can sometimes go to a fault state that requires
power cycling. The Ethernet interface can be used to send a fault reset signal
from the machine control system to individual or all devices. This reset signal
cycles the power to the device connected to the specified tap.
17
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018
Table of Contents
