Rockwell Automation T3470A User Manual

ICS Regent

®

PD-6025

Analog Output Modules

4 to 20 mA

(T3470A)

Issue 1,

Analog output modules provide 4 to 20 mA current outputs for
a maximum of eight user loads per module. The module's
triplicated I/O Safetybus interface ensures that no R
system failure will inadvertently affect the output signal, and
that no failure in the module can affect the operation of the
Regent system or other I/O modules in the system.

Features

March, 06

egent

·

Eight 4 to 20 mA output circuits.

·

High resolution 12-bit D/A converter per output.

·

Hot-replaceable.

·

Automatic testing of triplicate I/O Safetybus circuits and many
simplex logic circuits.

·

Front panel indicators on each module show active/fault and
shutdown status.

·

2500 volt minimum electrical isolation between field and logic
circuits.

·

TÜV certified, Risk Class 5, non-interfering.

Module Operation

A block diagram of the analog output module is shown in
Figure 1.

The processor modules send triplicated write data commands
to the output module over the I/O Safet
addressing data and data write commands are voted by the
module (preventing I/O Safetybus failures upstream from the

ybus. The processors’

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Analog Output Modules

module from affecting module operation). The voted result is
then passed to the I/O bus interface logic.

The voted output data from the I/O bus interface logic is then
used to drive individual digital-to-analog (D/A) converters per
output channel. The field-side D/A output circuits are
optically isolated from the I/O bus interface logic circuits and
receive power from the external power supply.

Each D/A output circuit provides a 4 to 20 mA output current
corresponding to analog output values ranging from 0 to

4095. The analog output circuits are capable of driving
external load devices up to 500 Ohms.

(T3470A)

2

Figure 1. Block Diagram of Analog Output Module.

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 Safety

bus to determine whether the

module’s voter is able to outvote the incorrect data. A failure

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Analog Output Modules

Note:

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 that module and its points specifically. I
module is removed, or is replaced with a module of a different
type, the processor modules will indicate an I/O module error.

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.

Whenever a module fault is detected, there will be an I/O
module fault indication at the controller, the controller's fault
relay contacts are actuated, and fault indication will appear
on the module.

(T3470A)

f a

Front Panel Indi

The analog output module is shown in Figure 2. The front
panel contains active, fault, and shutdown indicators.

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 occurs the red FAULT indicator turns on and the green
ACTIVE indicator turns off.

The module will indicate a FAULT if the field power is not
applied.

cators

PD-6025

Mar-06

3

Analog Output Modules

(T3470A)

4

Figure 2. Analog Output Module.

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Analog Output Modules

Note:

(T3470A)

Application

Shutdown Indicator

Upon loss of communications with the controller, output
modules enter either a shutdown or hold fault mode. If the I/O
unit is set to shutdown, the red SHUTDOWN indicator will
turn on when communications with the controller are lost. If
the I/O unit is set to hold, the SHUTDOWN indicator will
always be off (see page 8, Fault Mode Jumper).

When the module is installed in the I/O

power (from the I/O power supply modules) is first applied to
the module, it will be in the shutdown mode until the first
output scan, regardless of the fault mode jumper settings.
Also, removing two I/O transceiver modules, two I/O power
supply modules, or two power legs will cause the module to be
in the shutdown mode.

chassis or when logic

Simplex Configuration

Analog output modules provide a suitable interface to non
critical load devices. These non-critical devices typically
include analog display meters, valve positioners and analog
signal repeats to other electronic equipment. Although much
of the circuitry of the analog output module is automatically
tested, some of the logic circuits and the field-side D/A circuits
are simplex and non-tested. This simplex configuration is
shown in Figure 3.

Figure 3. Simplex Analog Output Configuration.

-

PD-6025

Mar-06

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Analog Output Modules

For high integrity applications requiring fail-safe or fault
tolerant analog outputs, guarded analog outputs should be
used.

(T3470A)

Field Wiring

Field wiring terminal blocks on the I/O chassis are used to
connect an external 24 VDC power source and analog loads to
the module. The terminal blocks are located directly above
and below the slot where the module is installed. Each
terminal block consists of ten #6 wire clamp screw terminals
capable of holding two 12 AWG wires. Figure 4 shows the
proper field wiring connections for the analog output module.

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