Triconex Trident, Planning And Installation Manual

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86 Input/Output Modules
Trident Planning and Installation Guide
Digital Output Module
The following digital output components are available.
The Digital Output (DO) Module contains the circuitry for three identical, isolated
channels. Each channel includes a proprietary ASIC which receives its output table
from the I
⁄
O communication processor on its corresponding main processor. DO
Modules use special quad output circuitry to vote on the individual output signals
just before they are applied to the load. This voter circuitry is based on parallel-
series paths which pass power if the drivers for channels A and B, or channels B
and C, or channels A and C command them to close; in other words, two out of
three drivers are voted on. The quad output circuitry provides multiple redundancy
for all critical signal paths, guaranteeing safety and maximum availability.
The DO Module periodically executes an output voter diagnostic (OVD) routine
on each point. This safety feature allows unrestricted operation under a variety of
multiple-fault scenarios.
OVD detects and provides alarms for the following:
• Points— all stuck-on and stuck-off points are detected in less than 500
milliseconds
• Switches—all stuck-on or stuck-off switches or their associated drive
circuitry are detected
During OVD execution, the commanded state of each point is momentarily
reversed sequentially on one of the output drivers. Loop-back on the module allows
each ASIC to read the output value for the point to determine whether a latent fault
exists within the output circuit. The output signal transition is guaranteed to be less
than two milliseconds (500 microseconds is typical) and is transparent to most field
devices. For devices that cannot tolerate a signal transition of any length, OVD can
be disabled.
The DO Module supports hot sparing for online replacement of a faulty module or
continuous back-up to an active module. The DO Module is mechanically keyed to
prevent improper installation in a configured baseplate.
Model Description Voltage Type
3401 Digital Output Module 24 V DC Commoned
2401 Digital Output Baseplate Direct Termination
2402 Digital Output Baseplate Current Limited