Rockwell Automation T3408 User Manual

ICS Regent

®

PD-6011

DC Digital Input Modules

24 VDC, 48 VDC and 120 VDC

(T3401, T3402 and T3408)

Issue 1,

DC digital input modules provide input sensing for 16 field
input switches. Three types of modules are available for
interfacing to inputs powered from 24, 48, or 120 VDC field
power supplies. Each module's triplicated I/O Safetybus
interface ensures that no failure in the module can affect the
operation of the Regent system or other I/O modules in the
system. Extensive fault detection and annunciation of critical
redundant circuits help prevent the controllers from receiving
erroneous data from a faulty input module.

March, 06

Features

·

Sixteen input circuits, configured as two isolated groups of
eight circuits

·

Fault tolerant operation when connected in parallel with
redundant modules of the same type.

·

Hot-replaceable.

·

Automatic self-testing of triplicated I/O Safetybus circuits and
many simplex logic circuits.

·

Individual front panel indicators on each module show active
and fault status and logic-side input on/off status.

·

2500 volt minimum
circuits.

·

TÜV certified, Risk Class 5.

Three DC digital input modules can be connected in parallel
to obtain fault tolerant input sensing. In this triple module
configuration, a failed module can be removed and replaced
without interrupting the input signals.

each.

electrical isolation between field and logic

Industrial Control Services

1

DC Digital Input Modules

(T3401, 02, and 08)

Module Operation

A block diagram of a typical DC digital input module is shown
in Figure 1.

Optical isolation between field wiring and the module
circuitry provides field-to-logic isolation —
modules’ logic circuits from field signal over-voltages,
transients, and other electrical disturbances. It also provides
a safety barrier between the primary field voltages and user
accessible circuits.

s’ logic

protecting the

2

Figure 1. Block Diagram of DC Digital Input Module.

When the field switch is closed, the input to the module is on.
When the field switch opens, the input to the module turns off.

Data f
the I/O bus interface logic.

The processor modules send triplicated read data requests to
the input module over the I/O Safetybus. The processors’
addressing data and data read requests are voted by the

rom the logic side of the optical isolators are bused to

Industrial Control Services

(T3401, 02, and 08)

module (preventing I/O Safetybus failures upstream from the
module from affecting its ability to be read). The voted result
is then passed to the I/O bus interface logic.

After receiving the voted data read request, the I/O bus
interface logic sends its input data to the module’s three bus
drivers. Each of the three bus drivers is independently
powered and controlled by the I/O transceiver modules—
preventing failures in a single driver from propagating to the
other two busses.

The bus drivers transmit the data across the backplane I/O
Safetybus to the I/O transceivers which, in turn, transmit the
data to the processors.

DC Digital Input Modules

Testing and Diagnostics

Each module’s voter circuits are periodically tested by the
processor modules. Discrepant data are sent through one of
three legs of the I/O Safetybus to determine whether the
module’s voter is able to outvote the incorrect data. A failure
to return the correct majority-voted result to the processors
produces an I/O module error indication at the processor
modules and a module fault indication at the I/O module.

Each type of module has a unique identification code that is
read by the controller. This code lets the controller know
which type of module is installed in each I/O chassis slot and
how to address tha
module is removed, or is replaced with a module of a different
type, the processor modules will indicate I/O module errors.

Loopback logic tests periodically write data to the module and
then read it back to determine whether the module’s I/O bus
interface logic is functioning correctly.

t module and its points specifically. If a

Front Panel Indicators

PD-6011

Mar-06

Figure 2 shows the physical features of the DC digital input
modules. The front panel of each module contains active and
fault status indicators and field signal status indicators for
each circuit.

3

DC Digital Input Modules

(T3401, 02, and 08)

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Figure 2. DC Digital Input Module.

Industrial Control Services

(T3401, 02, and 08)

DC Digital Input Modules

Application

Active and Fault Status Indicators

These green and red LEDs indicate the overall health of the
module. During normal operation the green ACTIVE
indicator flashes at the controller's scan rate. If a module
fault is detected the red FAULT indicator turns on and the
green indicator turns off.

Field Status Indicators

Input status indicators are located on the logic-side (after the
signal conditioning and isolation). The field status indicators
are lit when current is flowing through the input.

Simplex Configuration

Digital input modules provide a suitable interface to non
critical input signals. Although many of the circuits in the
digital input modules are automatically tested and
annunciated, some logic circuits and all of the field-side
sensing circuits are simplex and non-tested. This simplex
input configuration is illustrated in Fi

-

gure 3.

PD-6011

Mar-06

Figure 3. Simplex Digital Input Configuration.

Fault Tolerant Connection

For critical inputs, redundant input modules are used in a
2oo3 or 1oo2 fault tolerant configuration. In these
configurations the redundant input modules are connected to
single or multiple sensors. If redundant sensors are installed

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