State Industries GFK-0827 manual Bumpless Switching, Synchronized CPUs, Effect on Scan Time

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the two CPUs and provides the communications path for the transfer of I/O data between the two units. An RCM must be configured in both the Primary PLC and the Secondary PLC. The RCM must reside in the CPU rack (rack 0) in a system and there can be no empty slot between the RCM and the CPU (there can be other modules).

Bumpless Switching

Bumpless switching occurs when the active unit fails and system control is transferred to the backup unit without affecting the operation of the process under control.

Synchronized CPUs

For bumpless switching to occur, the CPU in the active and backup units must operate in a synchronous fashion, that is, the operation of both units must occur at the same time (or as close to the same time as possible). There are two synchronization points in the sweep: one immediately after the input scan and the other immediately before the output scan.

Synchronization data is passed from the active to the backup unit at the first synchronization point, which occurs after the input scan. Specifically, after the inputs are scanned, the inputs that were just read (%I and %AI) are sent from the active to the backup unit and the synchronization message is passed after the input data.

The second synchronization point occurs immediately after the end of the logic solution before the output scan begins. During this time, all remaining control data, including the %Q, %AQ, %M and %R memories is transferred from the active unit to the backup unit.

Effect on Scan Time

When a system is operating normally (no faults exist in the system) redundancy adds about 21 ms (includes 5 ms default background window setting) per PLC scan. The effect on scan time depends on the system configuration. The following number of data points and registers is considered the base configuration on which the 21 ms was calculated.

512%I, 512 %Q, 512 %M

256%AI, 256 %AQ

2048 %R

Each additional 1K %I, %Q, or %M data points adds about 1.8 ms to the scan impact (add 25% for each %I or %Q reference if point faults enabled) and each additional 1K of %R, %AI, or %AQ registers adds about 5 ms to the scan impact (add 50% for each %AI or %AQ reference if point faults enabled).

Fail Wait Time

When the active CPU has a failure, the backup CPU will wait for a specified time (in milliseconds) before assuming that the link has failed. This time is referred to as the Fail Wait time. The duration of this time must be specified during configuration of both the Primary and Secondary units and can range from 60 ms to 400 ms (in increments of 10 ms), with the default value being 60 ms.

Switch to Backup Unit Time

The amount of time it takes to switch control from the active unit to the backup unit depends on what caused the switch to take place.

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Series 90-70 Hot Standby CPU Redundancy User's Guide ± December 1993

GFK-0827

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Contents GE Fanuc Automation GFL±002 Related Publications Content of this ManualWe Welcome Your Comments and Suggestions PrefaceContents Chapter System Components Chapter Configuration Chapter Operation System Operation Fault Detection and Control Actions Synchronized Hot Standby CPU Redundancy System Configuration Contents Hot Standby CPU Redundancy Product Chapter IntroductionGFK-0827 Benefits of the Hot Standby CPU Redundancy Product Features of the Hot Standby CPU Redundancy ProductCable Connections Systems for Hot Standby CPU Redundancy SystemsGenius I/O System Local I/O SystemControl Strategy Basic Hot Standby OperationSynchronized Hot Standby CPU Redundancy System Configuration Redundancy Communications Module Redundancy CPU ModuleEffect on Scan Time Bumpless SwitchingSwitch to Backup Unit Time Synchronized CPUsOn-Line Programming Configurable Backup Data SizeOn-Line Repair Programming Considerations Configuration RequirementsTerm Definition Definition of TermsAcronym Definition Commonly Used AcronymsRedundancy CPU Chapter System ComponentsCPU Architecture Watchdog TimerCapacities for Redundancy CPU, IC697CPU780 Redundancy CPU IC697CPU CPU FeaturesValid Operating Mode Selection CPU Mode SwitchBattery Connectors Memor y Protect KeyswitchCPU Status LEDs Expansion Memory Board Serial Port ConnectorExpansion Memory Boards for CPU Redundancy Communications Module RCM FeaturesBoard OK RCM System Status LedsUnit Selection Pushbutton RCM ConnectorsBus Transmitter Module LED Status IndicatorsBus Receiver Module BTM ConnectorsBRM Connectors Bus Signal TerminationGenius Bus Controller Genius Bus Controller User Features Racks GBC ConnectorsConfiguring a Hot Standby CPU Redundancy System Chapter ConfigurationRedundancy System Requirements Basic Redundancy System SetupLogicmaster 90 Configuration System ConfigurationMonitor or Online mode Screens for Fault Category ConfigurationHandling Folders Configuration with LogicmasterConfiguration of a Redundancy CPU Module GFK-0827 Redundant CPU Requirements Redund Type Normal Sweep ModeBackground Window Constant Sweep Mode Constant Window Sweep ModeFail Wait Ctrl StrgyShared I/O Shared I/O Reference Values Shared I/O Data ParametersReference Type ReferenceSize CalculationforNumberofBytes Transfer Data SizeConfiguring a CPU Expansion Memory Board Configuration of a Redundancy Communications Module Configuration Paired GBC Parameter Configuration of a Genius Bus ControllerSerial Bus Address Configuring a Primary Redundant PLC Select the Redundancy CPU Module Select an Expansion Memory Board Configure the Redundant Communications Module Configure a Genius Bus Controller Configuration Configure Genius I/O Blocks Configure the Bus Transmitter Module Configuring a Secondary Redundant PLC Change Redund Type GFK-0827 Chapter Operation Power-Up Sequence of a Redundant CPUIncompatible Configurations Resynchronization of the Redundant CPU Hot-Standby Redundancy Control Strategy First Data Transfer %I, %AI and Synchronization Synchronous ScanData Transfer from Backup Unit to Active Unit Second Data Transfer %Q, %AQ, %R, and %M Switching Control to Backup UnitRole Switch Svcreq Definition for% S Reference for Redundancy Status References for CPU RedundancyRedundancy CPU Considerations Differences in Operation for CPU RUN Disabled ModeRUN/ENABLED Locrdy Locact Remrdy Remact Configuration of Fault Actions Background Window Time Stop to RUN Mode TransitionWords per Sweep = Ovrpre %S Reference Timed ContactsGenius Bus Controller Switching Fault Categories Fault DetectionChanging Fault Category Actions Fault Zoom Help Text for Redundancy Error Codes PLC Fault TableFaulting RCMs, Losing Links, and Terminating Communications GFK-0827 Maskable Fault Group Descriptions Fault Actions in a CPU Redundancy SystemUserConfigurable Maskable Fault Group ActionsNon-Maskable Fault Action Descriptions Non-Maskable Fault Group DescriptionsMaintaining Parallel Bus Termination On-Line RepairOn-Line Repair Recommendations Redundancy Communications Module and Cables Power SupplyRacks Central Processor UnitBus Transmitter Module Redundancy Communications Link FailuresGenius Bus Controller GeniusBlocks Genius BusRedundancy Alternatives Appendix Redundancy AlternativesRedundancy Option Key See Table PLC RedundancyOptionsSeries 90-70 Redundancy Through Application Logic Index Index Index Index Index