Rockwell Automation T7411F User Manual

ICS Regent+PLUS

®

PD-7027

Monitored Digital Input Modules, Field

Powered (Type F)

24 to 48 VDC, 120 VAC/DC

(T7411F, T7418F)

Issue 1,

Monitored digital input modules provide input sensing for 16
field input devices. The field powered (Type F) mod
suitable for inputs that are directly powered from an external
field power supply. Two types of modules are available for
inputs powered from 24 to 48 VDC and 120 VAC/DC. With a
line monitor device installed at the field switch, monitored
digital input modules detect input switch status and field
wiring open and short circuits (VDC powered inputs only).
Input and line status are reported back to the controller for
use in application program logic.

March, 06

ules are

Features

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The input module circuits are completely and automatically
tested, providing a fail-safe interface for safety-critical inputs.

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Sixte

en input points, powered from external field supply.

Fault tolerant operation when connected in parallel with
another module of the same type.

Hot-replaceable.
Complete, automatic testing of all input circuits.
Automatic line monitoring detects open and short field wiring

faults.
Individual front panel indicators on each m

module’s active/fault and power status, as well as input status
and line fault status for each point.

2500 volt minimum electrical isolation between field and logic
circuits.

TÜV certified, Risk Class 5.

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odule show the

Monitored Digital Input Modules

Two or three monitored digital input modules can be
connected in parallel to obtain fault tolera
In these fault tolerant configurations, a failed module can be
removed and replaced without interrupting the input signals.

The module requires connection to the same field power
supply that powers the field switches. This field power is
internally regulated by the module to power the module’s
input interface circuits.

, Type F (T7411F, T7418F)

nt input sensing.

Module Operation

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

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Figure 1. Block Diagram of the Type F, Monitored Digital Input Modules.

An external field power supply provides power directly to field
switches. This power supply is also connected to the

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Monitored Digital Input Modules

Important:

monitored input module. The field power is internally
regulated to power the input module’s field interface circuits.
The switched side of each input is wired back to the input
module terminal screws. Inside the input module the signal
passes through an internal dropping resistor and back to the
field power supp
can be connected across the input switch in the field (as shown
in Figure 1).

Line monitoring only applies to inputs powered by a well
regulated (± 5%) DC voltage power supply. Line monitoring is
not supported for inputs powered from 120 VAC power
sources.

The input module monitors the voltage of the input circuit at
the internal dropping resistor, comparing it to a reference
voltage generated by the D/A converter inside th
The T7418F input module rectifies the input signal for
120 VAC applications. The comparator generates an on or off
state depending on which voltage signal is greater than the
other.

ly return. Optionally a line monitor device

, Type F (T7411F, T7418F)

e module.

The field-side FPGA controls and monitors the reference
voltage signal and reads the status of all 16 input
comparators. This information is stored and sent through
optical isolation to the logic-side FPGA. The logic-side FPGA
interfaces the input data to the I/O Safetybus and drives the
module’s front panel status

Testing and Diagnostics

Standard I/O Module Testing

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
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 modul
drivers. Each of the three bus drivers is independently
controlled — preventing failures in a single driver from being
propagated into the rest of the system.

LEDs.

e’s three bus

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Mar-06

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Monitored Digital Input Modules

The bus drivers then move the data onto the I/O Safetybus
which, in turn, passes it to the processors.

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
address that module and its points specifically. The processor
modules periodically check each module’s identification code
to determine whether
type of module indicated in the I/O configuration that was
loaded when the system was started. If a module is removed,
or is replaced with a module of a different type, the processor
modules will indicate I/O module errors.

, Type F (T7411F, T7418F)

the type of module installed matches

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.

Input Circuit Testing

The field interface circuits of the monitored input module are
completely tested to detect stuck-on or stuck-off input circuit
faults and optionally identify input wiring open and short
circuits. The automatic execution and evaluation of the input
testing is controlled by the triplicated Regent processor
modules.

During normal operations, the internal reference voltage is
set to three levels and the comparator output is read. These
three reference voltage levels represent thresholds that
determine whether the input signal is on or off and if the field
wiring is open

circuit or short circuit. The logic-side FPGA
determines input status and line fault status based on the
comparator data for the three voltage levels. The FPGA data
is provided to the I/O processors for application processing.

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On a background basis, the I/O processors test the input
circuit comparators and logic circuits for stuck-on and stuck

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Monitored Digital Input Modules

Note:

off failure modes. During testing the D/A converter generates
two reference voltages outside the normal operating range of
the field input voltages to test that the comparator output can
turn-off and turn-on. The I/O processors read the resulting
input status, line fault status, and reference voltage readings
for the test cycle to determine if there are faults in the input
circuits or the common data paths.

If the I/O processors detect a faulted input circuit, an I/O
module fault is indicated at the processor modules and the
Fault LED on the face of the input module is turned on.

, Type F (T7411F, T7418F)

Input Circuit Test Interval

The Regent processor modules schedule testing of the input
circuits on a background basis. The test interval for these
circuits may range from a few seconds to several minutes,
depending on the application program scan time and the size
of the I/O configuration. The equation below can be used to
estimate the test interval for monitored digital inputs.

TI = 172 * IOU

where:

TI

IOU

TSCAN

=

=

QTY

=

* TSCAN + 2

QTY

Test interval, seconds
Quantity of I/O Units in the system (1 to 16)
The application program scan time, seconds

For example, for a system with 8 I/O units and an application
scan time of 60 milliseconds, the test interval would be:

TI = 172 * IOU
TI = 84.6 seconds

* TSCAN + 2 = 172 * 8 * 0.060 + 2

QTY

In this system, all of the monitored input modules would be
tested for stuck-on and stuck-off faults approximately every 85
seconds. This test interval can be used in reliability and
availability calculations to select the fault tolerant input
configuration that meet the application’s safety requirements.

PD-7027

Mar-06

Due to I/O processor fault filtering algor

ithms, it may take up
to four test intervals to report a failed input module as a
permanent fault

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Monitored Digital Input Modules

, Type F (T7411F, T7418F)

Front Panel Indicators

Figure 2 shows the physical features of the type F, monitored
digital input modules. The front panel of each module
contains fault/active and power indicators for the module as
well as input status indicators for each channel.

Active/Fault Status Indicator

This green and red LED pair indicates the overall health of
the module and its field circuits. 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 indicator turns off.

Power Status Indicator

The POWER OK LED indicates the presence of field voltage
at the module’s field power input terminals and the overall
health of the module’s field power regulator circuits.

Input Status Indicators

Input status indicators show contact and line status for each
point.

A yellow contact status indicator is turned
contact is closed or the line has shorted.

on when the

A red line status indicator is turned on when the field wiring
is open circuit or short circuit. If line monitoring is not
desired, this LED can be disabled (see Disable Fault LED,
page 18 for more details).

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Monitored Digital Input Modules

, Type F (T7411F, T7418F)

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Mar-06

Figure 2. Type F, Monitored Digital Input Modules.

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Monitored Digital Input Modules

, Type F (T7411F, T7418F)

Application

Simplex Configuration

Monitored digital input modules provide a suitable interface
to safety-critical input signals. The circuits in the monitored
digital input modules are automatically tested and
annunciated, providing a fail-safe interface to digital inputs.
This simplex input configuration is illustrated in Figure 3.

Figure 3. Single Monitored Digital Input Configuration.

Fault Tolerant Configurations

For fault tolerant applications, redundant monitored input
modules are used in a fault tolerant configuration. In one
configuration the redundant input modules are connected in
parallel to a single field input device as illustrated in Figure
4

. If redundant field sensors are installed in the field, the
modules are connected so that each sensor connects to one of
the modules as illustrated in Figure 5. In these fault tolerant
configurations, each monitored digital input module is hot
replaceable. If a fault occurs on one module, it can be
removed and replaced while the system continues to correctly
sense the inputs from the remaining module(s).

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