Triconex Trident, Planning And Installation Manual

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Fault Tolerance 3
Chapter 1 Theory of Operation
Fault Tolerance
Fault tolerance, the most important capability of the controller, is the ability to
detect transient and steady-state error conditions and take appropriate corrective
action online. Fault tolerance provides an increase in safety and the availability of
the controller and the process being controlled.
The Trident controller provides fault tolerance through TMR architecture. The
controller consists of three identical channels (except for the power modules which
are dual-redundant). Each channel independently executes an application in
parallel with the other two channels. Voting mechanisms qualify and verify all
digital inputs and outputs from the field; analog inputs are subject to a mid-value
selection process.
Because each channel is isolated from the others, no single-point failure in any
channel can pass to another. If a hardware failure occurs in one channel, the faulty
channel is overridden by the other channels. Repair consists of removing and
replacing the failed module in the faulty channel while the controller is online and
without process interruption.
Extensive diagnostics on each channel, module, and functional circuit immediately
detect and report operational faults by means of indicators or alarms. All diagnostic
fault information is accessible by the application and the operator. The operator can
use the diagnostic information to modify control actions or direct maintenance
procedures.