Triconex Trident - Digital Input Module; Digital Output Module

Controller Architecture 13
Chapter 1 Theory of Operation
Digital Input Module
A Digital Input Module contains the circuitry for three identical channels (A, B,
and C). Although the channels reside on the same module, they are completely
isolated from each other and operate independently. Each channel conditions
signals independently and provides optical isolation between the field and the
controller. A fault on one channel cannot pass to another. In addition, each channel
contains a proprietary ASIC which handles communication with its corresponding
MP, and supports run-time diagnostics.
Each of the three input channels measures the input signals from each point on the
baseplate asynchronously, determines the respective states of the input signals, and
places the values into input tables A, B, and C, respectively. Each input table is
interrogated at regular intervals over the I⁄O bus by the I⁄O communication
processor located on the corresponding MP. For example, MP A interrogates Input
Table A over I⁄O Bus A.
Special self-test circuitry is provided to detect and alarm all stuck-at and accuracy
fault conditions in less than 500 milliseconds, typically. This safety feature allows
unrestricted operation under a variety of multiple-fault scenarios.
The input diagnostics are specifically designed to monitor devices which hold
points in one state for long periods of time. The diagnostics ensure complete fault
coverage of each input circuit even if the actual state of the input points never
changes.
Digital Output Module
A 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. All 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, 2-out-of-3 drivers are
voted on. The quad output circuitry provides multiple redundancy for all critical
signal paths, guaranteeing safety and maximum availability.
A 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.