State Industries GFK-0827 manual Fault Actions in a CPU Redundancy System

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Fault Actions in a CPU Redundancy System

Fault actions in the Hot Standby CPU Redundancy System are handled differently than those in a non-redundancy (Simplex) system. Whenever there is a ºreadyº backup unit configured in the system, the fault actions in the active unit will not be those normally specified by the user. For an active unit with a ready backup, any fault which will cause a degradation in performance, or loss of control of I/O which does not cause a similar degradation of performance or loss of control of I/O in the backup will be considered a FATAL fault in the active unit and cause the active unit to transition to STOP mode.

The configurable fault actions will be applied whenever the system is running in stand-alone mode in case you prefer fault tolerance (availability) versus safety (depending on the application). The following tables (1) define the Fault Groups and (2) show the fault groups and their fault action defaults. There are three fault actions shown in Table 11: Fatal, Non-Fatal, and Conditionally Fatal. Fatal always stops the PLC, Non-Fatal never stops the PLC and Conditionally Fatal stops the PLC depending on other information in the fault.

Table 9. Maskable Fault Group Descriptions

		Table
	Fault Group	Type	Description
	LOSS_RACK	CPU	Lossof or Missing Rack
	LOSS_IOC	I/O	Loss of or Missing IOC
	LOSS_IO_MOD	I/O	LossoforMissingI/OModule
	LOSS_OTHR_MOD	CPU	Loss of or Missing Option Module
	ADD_RCK	CPU	Addition of or Extra Rack
	ADD_IOC	I/O	Addition of or Extra IOC
	ADD_IO_MOD	I/O	AdditionoforExtraI/OModule
	ADD_OTHR_MOD	CPU	Additionof, Reset of, or Extra Option Module
	IOC_FAULT	I/O	IOC or I/O Bus Fault
	IO_MOD_FAULT	I/O	I/OModule Fault
	CNFG_MIS_MTCH	Both	SystemConfigurationMismatch
	SYS_BUS_ERROR	CPU	System Bus Error
	CPU_HARDWR	CPU	CPU Hardware Failure
	MOD_HARDWR	CPU	Module Hardware Failure (e.g. Serial Port Failure on PCM)
	IOC_SOFTWR	I/O	IOC Software Failure
	MOD_OTHR SOFTWR	CPU	Option Module Software Failure
	PRG_BLK_CHKSUM	CPU	ProgramBlockChecksumMismatch
	LOW_BATTERY	CPU	Low Battery in the System
	CNST_SW_EXCD	CPU	Constant Sweep Exceeded
	PLC_FTBL_FULL	CPU	PLC System Fault Table Full
	IO_FTBL_FULL	CPU	I/OFault Table Full
	APPLICATION_FLT	CPU	UserApplicationFault
GFK-0827	Chapter 4 Operation		77