Schneider Electric 890USE17700 manual Island Fallback Scenarios, Heartbeat

Advanced Configuration Features

Island Fallback Scenarios

Introduction	In the event of a communications failure on the island or between the island and the
	fieldbus, output data is put into a safe fallback state. In this state, output data is
	replaced with pre-configured fallback values, ensuring that a module’s output data
	values are known when the system recovers from a communications failure.
Fallback	There are several scenarios in which Advantys STB output modules go into their
Scenarios	fallback states:
	loss of fieldbus communications—Communications with the PLC are lost.
	loss of island bus communications—There is an internal island bus
	communications error, indicated by a missing heartbeat message from either the
	NIM or a module.
	change of operating state—The NIM may command the island I/O modules to
	￿switch from a running to a non-running (stopped or reset) state.
	missing or failed mandatory module—The NIM detects the absence or failure of
	a mandatory island module.
	Note: If a mandatory (or any other) module fails, it needs to be replaced. The
	module itself does not go into its fallback state.
	In all of these fallback scenarios, the NIM disables the heartbeat message.
Heartbeat	The Advantys STB system relies on a heartbeat message to ensure the integrity and
Message	continuity of communications between the NIM and the island modules. The health
	of island modules and the overall integrity of the Advantys STB system are
	monitored through the transmission and reception of these periodic island bus
	messages.
	Because island I/O modules are configured to monitor the NIM’s heartbeat
	message, output modules will go into their fallback states if they do not receive a
	heartbeat message from the NIM within the defined interval.

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