GE Mark VIe System Manual page 53

1.7.5 Designated Controller
Although three controllers, R, S, and T, contain identical hardware and software, some of the functions performed are unique.
A single designated controller can perform the following functions:
• Supply initialization data to the other two controllers at start-up
• Keep the master time clock
• Supply variable state information to the other controllers if one fails
For the purposes of deciding which controller is to be the designated controller, each controller nominates itself on a
weighting algorithm. The nominating values are voted among the controllers and the majority value is used. If there is a tie, or
no majority, the priority is R, then S, and then T. If a designated controller is powered down and later powered up, the
designated controller will move and not come back if all controllers are equal. This ensures that a toggling designated
controller is not automatically reselected.
Designated controller selection is based on:
• Control state
• UDH connectivity
• IONet connectivity
• NVRAM health
1.7.6 Communication Loss
Each output pack monitors the IONet for valid commands from one or two controllers. In the event that a valid command is
not received within an expected time the pack declares the communication as being lost. Upon loss of communication the
pack action is configurable. The pack can continue to hold the last commanded value indefinitely or it can be commanded to
go to a specified output state. The default action is to go to a power-down state, the same as if the power were removed from
the pack.
Note Refer to specific I/O pack documentation in Mark VIe and Mark VIeS Control Systems Volume II: System Guide for
General-purpose Applications (GEH-6721_Vol_II).
For critical loops, the default action is the only acceptable choice. The other options are provided for non-critical loops, where
running liability may be enhanced by an alternate output.
1.7.7 State Exchange
To keep multiple controllers in synchronization, the Mark VIe control efficiently exchanges the necessary state information
through the IONet. State information includes calculated values such as timers, counters, integrators, and logic signals such as
bi-stable relays, momentary logic with seal-in, and cross-linked relay circuits. State information is voted in TMR controllers
and follows the designated controller in dual or faulted TMR systems.
1.7.8 Voting
Voting in the Mark VIe control is separated into analog and logic voting. Additionally, fault detection mechanisms directly
choose owned inputs and designated states.
Control System Overview
Public Information
GEH-6721_Vol_I_BP System Guide 53