ICS Regent
®
PD-6031
Monitored Digital Input Modules
24 VDC
(T3411)
Issue 1,
Monitored digital input modules provide input sensing for 16
field input devices. 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. Input
and line status are reported back to the controller for use in
application program logic.
Features
March, 06
·
Sixteen input points.
·
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 module show the
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.
The input module circuits are completely and automatically
tested, providing a fail-safe interface for safety-critical inputs.
Two or three monitored digital input modules can be
connected in parallel to obtain fault tolerant input sensing.
In these fault tolerant configurations, a failed module can be
removed and replaced without interrupting the input signals.
Industrial Control Services
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Monitored Digital Input Modules
(T3411)
The module requires connection to a f
voltage, ranging from 15 to 80 VDC. This field power is
internally regulated by the module to 24 VDC to power the
field inputs — providing safe, low-voltage inputs signals
common in safety system applications.
Module Operation
A block diagram of a typical monitored digital input module is
shown in Figure 1.
ield power supply
2
Figure 1. Block Diagram of the Monitored Digital Input Module.
A field power supply is connected to the monitored input
module. The field power is internally regulated to 24 Vdc to
power the input module’s field interface circuits. For each
input circuit, the regulated power passes through an internal
dropping resistor to the input screw terminal which is wired to
the field input switch. The other side of the field switch is
Industrial Control Services
Monitored Digital Input Modules
(T3411)
wired back to the field power supply return. Optionally a line
monitor device can be connected across the input switch in the
field (as shown in Figure 1).
The input module monitors the voltage of the input circuit
after the internal dropping resistor, comparing it to a
reference voltage generated by the D/A converter inside the
module. The comparator generates an on or off state
depending on which voltage signal is greater than the other.
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 LEDs.
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 module’s three bus
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.
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 l
egs 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.
PD-6031
Mar-06
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Monitored Digital Input Modules
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 the type of module installed matches
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.
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.
(T3411)
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.
On a background basis, the I/O processors test the input
circuit comparators and logic circuits for stuck-on and stuck
off failure modes. During testing the D/A conver
ter 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.
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Monitored Digital Input Modules
Note:
(T3411)
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.
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 Uni
ts 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-6031
Mar-06
Due to I/O processor fault filtering algorithms, it may take up
to four test intervals to report a failed input module as a
permanent fault
Front Panel Indicators
Figure 2 shows the physical features of the monitored digital
input module. 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/F
ault Status Indicator
This green and red LED pair indicates the overall health of
the module and its field circuits. During normal operation the
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Monitored Digital Input Modules
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.
(T3411)
Power Status Indicator
The POWER GOOD 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 on when the
contact is closed or the line has shorted.
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 20 for more details).
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Monitored Digital Input Modules
(T3411)
PD-6031
Mar-06
Figure 2. Monitored Digital Input M
7
odule.
Monitored Digital Input Modules
(T3411)
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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Industrial Control Services
Monitored Digital Input Modules
(T3411)
Figure 4. Fault Tolerant Monitored Digital Input Modules
Connected to a Single Sensor.
PD-6031
Mar-06
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Monitored Digital Input Modules
(T3411)
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Figure 5. Fault Tolerant
Connected to Redundant Sensors.
Field Wiring
Monitored Digital Input Modules
Field wiring terminal blocks on the I/O chassis are used to
connect the field power supply and field input wiring to the
monitored input 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.
Industrial Control Services
Monitored Digital Input Modules
(T3411)
The field power supply voltage is regulated to 24 Vdc inside
the module. This power is used to source the power to the field
input switches. The return side of the field switches is wired
back to the field power supply return.
Figure 6 shows the wiring connections for a single monitored
input module.
When redundant field sensors are installed, each input
module is wired as shown in Figure 6. In a fault tolerant
configuration the input signals are connected in parallel
across both input modules as shown in Figure 7.
PD-6031
Mar-06
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Monitored Digital Input Modules
(T3411)
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Figure 6. Module Wiring, Single Sensors to a Single
Monitored Digital Input Module.
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Monitored Digital Input Modules
(T3411)
PD-6031
Mar-06
Figure 7. Module Wiring, Single Sensors to Redundant
Monitored Digital Input Modules.
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Monitored Digital Input Modules
(T3411)
Line Monitoring
The Monitored digital input module can perform line
monitoring of the field wiring when a suitable line monitor
device is installed across the field input switch. Two types of
line monitor devices are available to match the type of module
configuration used in the application.
Figure 8 shows a single switch connected to a single monitored
input module. This type of configuration uses the T0412 line
monitor device which contains two resistors, one in series with
the field switch and one in parallel with the field switch.
Figure 8 also applies to fault tolerant input configurations
that include redundant sensors connected to redundant input
modu
les.
14
Figure 8. Line Monitoring, Single Switch Connected to
Single Module.
For fault tolerant configurations using single sensors
connected to redundant input modules, the T0413 line
monitor device is used as shown in Figure 9. This line
monitor device includes two zener diodes, one in series with
the field switch and one in parallel with the field switch.
Industrial Control Services
Monitored Digital Input Modules
V
ref
Threshold
Voltage
Vin with Line
Monitor
Vin with
out
Line Monitor
Stuck-on Test
32 Vdc
24 Vdc
Wire Open
Switch Open
Open Circuit
20 Vdc
16 Vdc
Switch Open
NA
On/Off
12 Vdc
8 Vdc
Switch Closed
NA
Short Circuit
4 Vdc
0 Vdc
Wire Short
Switch Closed
Stuck-Off Test
-
5 Vdc
(T3411)
Figure 9. Line Moni
toring, Single Switch Connected to
Redundant Modules.
With the line monitor device installed, the input voltage, Vin,
has four possible states as represented in Table 1. When the
input module reads the input, the reference voltage, V
ref
, is
set to the values shown in Table 1 to detect the state of the
field input and wiring.
Table 1. Input States and Reference Voltage Thresholds.
PD-6031
Mar-06
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Monitored Digital Input Modules
(T3411)
Keying
The I/O chassis can be physically keyed to prevent accidental
damage caused by inserting a module into a slot wired for a
different module type. Figure 10 illustrates how the slot keys
are installed on the I/O chassis slot field wiring connectors.
The slot key positions for the monitored digital input module
are listed in Table 2.
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Figure 10. Installing Slot Keys.
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Monitored Digital Input Modules
Module
Upper
Connector
Lower
Connector
T3411
4
7
(T3411)
Table 2. Slot Key Positions.
Configuration
Each monitored input module is configured using the
W
INTERPRET I/O Configuration Editor. In the editor, you will
perform the steps d
module.
1) Set the Module Type:
escribed below to configure the input
Position the cursor on the module slot you wish to define.
Choose Set Module Type from the Edit Menu and select
the T3411, 24 Vdc Monitored Digital Input Module from
the list.
2) Edit the Module Definition:
Choose Edit Module Definition from the Edit Menu. A
dialog box will open where you can define the input module
and point definitions.
Figure 11. Monitored Digital Input Module Definition.
PD-6031
Mar-06
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Monitored Digital Input Modules
(T3411)
3) Define the Input Module Fields and Thresholds:
With the cursor at the top of the list in the Module
Definition dialog shown in Figure 11, open the Line
Monitored Input Module dialog by pressing Enter or
double clicking on the “(Module)” selection. The dialog box
shown in Figure 12 will open.
Figure 12. Defining the Input Module Fields and Thresholds.
In the module definition dialog you can define a tag names
representing all sixteen input point
s as a 16-bit word. The
Name field represents the On/Off status of all sixteen
inputs and the Fault Name represents the Line Fault
status of all sixteen inputs.
The module tag names represents the 16 inputs as a
signed, 16-bit integer. In this format, input point one is
the least significant bit (LSB) and input point 16 is the
most significant bit (MSB). Enter tag names up to 12
characters long and descriptions up to 40 characters long.
In the module definition dialog you can also set the
threshold values used to determine the Open Circuit,
On/Off, and Short Circuit input status. Normally these
should be left at the default values of 20, 12 and 4 Vdc
shown in Figure 12. These values are applicable to field
inputs with no line monitor device installed and also for
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Monitored Digital Input Modules
(T3411)
inputs with the standard (T0412 and T0413) line monitor
devices installed. If non-standard line monitor devices are
installed, then the threshold values may need to be
adjusted.
3) Edit each point:
Choose Edit from the Module Definition dialog box to
define a name and description for each input point. In the
Line Monitored Input Point dialog, enter names and
values for the configuration fields as described below.
PD-6031
Mar-06
Figure 13. Defining a Monitored Digital Input Point.
Name
Also called the tag name, this is the name used in the
application program to reference the field input switch’s
On/Off state. The name can be up to 12 characters long.
Description
This 40-character field provides a place
to describe the input
point definition. The description is used to help document
your system (it does not affect application program operation).
Fault Name
This is the name used in the application program to reference
the input point line fault status. The name can be up to 12
characters long.
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Note:
Monitored Digital Input Modules
During operations the input circuit is monitored for open
circuit and short circuit wiring faults. This bit is normally on
and turns off if either an open circuit or short circuit is
detected.
Line fault status is only reported through the Fault Name
variables. Line faults are not reported as a permanent I/O
module fault and do not turn on the associated system control
relay fault bit for the module. Line faults are not latched. If a
line fault condition returns to normal, the Fault Name
variable status also returns to normal.
(T3411)
Fault Name Description
This 40-character field provides a place to describe the input
point fault name definition. The description is used to help
document your system (it does not affect application program
operation).
Disable Fault LED
Marking the Disable Fault LED check box disables the fault
LED for this input point on the face of the input module.
Marking this box does not stop the module from line
monitoring the input circuit and updating the state of the
Fault Name variable, it only stops the module from displaying
line faults on the face of the input module. Line faults are still
reported to the Regent and are available to the application
program through the fault name variable.
This box can be checked for those input points that do not
have LMDs installed, or that are spare and have no field
switches connected. In this configuration the line fault LED
will always be off. If you do not check this box for input points
without LMDs installed or unconnected spare input points,
the line fault LED will always be on.
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Programming
Inputs are referenced in the application program through the
tag names defined in the I/O Configuration Editor. When
current flows through the
input (field switch closed) the input
is said to be on, or have a value of one. In ladder logic, the on
state would produce power flow in a normally open (N.O.)
contact.
Industrial Control Services
Monitored Digital Input Modules
With Line Monitor Device
Installed
Without Line Monitor
Device Installed
Field Input
Condition
Name
Fault Name
Name
Fault Name
Switch Open
OFF ON OFF
OFF
Switch Closed
ON ON ON OFF
Open Circuit
OFF OFF
Same as Switch Open
Short Circuit
ON
OFF
Same as Switch Closed
(T3411)
Field wiring open circuit or short circuit conditions are
referenced in the application program using the Fault Name
tag names defined in the I/O configuration Editor. When a
line monitor device is installed across the field switch and the
wiring is healthy, the Fault Name status is on. If there is a
short or open circuit (or there is no line monitor device
installed) the Fault Name status is off.
The status of the Name and Fault Name input variables are
summarized in Table 3 for the various field input conditions.
Table 3. Input Status for Field Input Conditions.
Programming Dual Fault Tolerant Monitored Inputs
To program fault tolerant configurations using dual
monitored input modules, ladder logic is used to check the
status of the inputs and the system control relays (that report
a faulted I/O module) and provide a voted input value. Two
examples are shown below.
PD-6031
Mar-06
Normally Energized Inputs
Figure 14 shows a ladder logic rung that would be suited for
normally energized inputs that de-energize to trip.
Figure 14. Dual Voting for Normally Energized Inputs.
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Monitored Digital Input Modules
In this example, IN1A and IN1B represent the input
variables from two redundant monitored input modules.
IO01U01 and IO01U02 are the system control relays that
report a fault for the monitored input modules (one installed
in slot 1 of chassis 1 and the other in slot 1 of chassis 2). The
variable IN1VOTE is a shared control relay that will
represent the voted value of the two inputs. This variable
would be used elsewhere in the application program to
represent the status of the field input in the associated safety
interlock logic.
When both input modules are healthy, both inputs must turn
off to turn off the voted result and initiate a trip. Because the
inputs are normally energized, the voted result is normally
on. If a fault occurs on one of the input modules, the voted
result will remain on, eliminating a nuisance trip. Automatic
testing of the input
associated fault bit will be turned on, leaving the voted result
under the control of the remaining healthy input module.
The faulted module can be removed and replaced. After
replacing the input module and performing a voted reset, the
fault bit is turned off, restoring the input configuration to the
dual mode.
(T3411)
module will detect the fault and the
Normally De-Energized Inputs
Figure 15 shows a ladder logic rung that would be suited for
normally de-energized inputs that energi
ze to trip.
Figure 15. Dual Voting for Normally De-Energized Inputs.
In this example the variables represent the same status
information as described above for normally energized inputs.
When both input modules are healthy, both inputs must turn
on to turn on the voted result and initiate a trip. Because the
inputs are normally de-energized, the voted result is normally
off. If a fault occurs on one of the input modules, the voted
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Monitored Digital Input Modules
(T3411)
Maintenance
result will remain off
testing of the input module will detect the fault and the
associated fault bit will be turned on, allowing the voted result
to be controlled by the remaining healthy input module. The
faulted module can be removed and replaced. After replacing
the input module and performing a voted reset, the fault bit is
turned off, restoring the input configuration to the dual mode.
Programming Triple Fault Tolerant Monitored Inputs
Fault tolerant applications that include triplicated monitored
input modules should use the Voter instruction in ladder
logic. The voter instruction performs two-out-of-three voting
of triplicated inputs, storing the voted result in the defined
shared variable. Refer to the Regent User’s Guide section 5,
Working with Programs and Function Blocks for more details
on using the ladder logic Voter instruction.
, eliminating a nuisance trip. Automatic
No periodic maintenance or calibration is required for the
monitored digital input modules. There are no user
replaceable parts inside these modules.
Safety Considerations
The monitored digital input modules are TÜV certified for
Risk Class 5 safety critical inputs. Safety critical
configurations include dual and triple redundant input
modules and associated application voting methods.
In safety critical input applications using a single sensor, it is
important that the sensor failure modes be predictable and
well understood, so there is little probability of a failed sensor
not responding to a critical process condition. In such a
configuration, it is important that the sensor be tested
regularly, either by dynamic process conditions that are
verified in the Regent, or by manual intervention testing.
Redundant sensors can be used with redundant input
modules to eliminate any single points of failure and extend
fault tolerance to include the sensors.
PD-6031
Mar-06
23
Safetybus Power
0.85 load units
Number of Inputs
16, common power return
Field Power
Voltage:
Current:
15 to 80 VDC
450 mA, maximum
Turn-On Voltage
(default)
> 12 Vdc
Turn-Off Voltage
(default)
< 12 Vdc
Input Current
5.0 mA, maximum
Turn-On Delay
10 msec, maximum
Turn-Off Delay
10 msec, maximum
Over Voltage Protection
Field Power Terminals:
Input Terminals:
100 Vdc continuous
27 Vdc continuous
Heat Dissipation
8.5 Watts, 29 BTUs/hour
Fusing
None required, internal
resistor limits current to
5
mA if input short circuit.
Isolation
2500 volts minimum (field
wiring to
control logic)
Input Circuit Test Interval
Function of application
program scan time and size
of I/O configuration.
Typically less than 2 seconds
(see page 5 for details).
Monitored Digital Input Modules
If energize-to-trip inputs are used in safety critical
applications, line monitor devices
field switches. The Fault Name
and line fault status must be alarmed to plant operations
personnel.
For de-energize-to-trip inputs, line monitor devices are
recommended in order to detect the difference between a
normally closed input and a shorted field wire.
For additional safety considerations, please refer to the Safety
Considerations section of the Regent User’s Guide.
(T3411)
must be installed at the
variables must be configured
Specifications
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Monitored Digital Input Modules
Intrinsic Safety
External barrier, if required.
(requires threshold
adjustment, see page 18).
Operating Temperature
0°
to 60° C
(32° to 140° F)
Storage Temperature
-40°
to 85° C
(-40°
to 185° F)
Operating Humidity
0 to 95% relative humidity,
non-condensing
Vibration
10 to 55 Hz:
±0.15mm
Shock
Operating:
15 g, ½ sine wave, 11 msec
Electromagnetic
Interference
•
IEC 801 Part 2 - Electrostatic
Discharges
•
IEC 801 Part 3 - Radiated
Electromagnetic Fields
•
IEC 801 Part 4 - Transients
and Bursts
•
ANSI/IEEE C37.90 - Surge
Withstand Capability
Level 3: Contact discharge of
6 kV
Level 3: 10 V/M, 27 MHz 500 MHz
Level 4: 2 kV, 2.5 kHz for t =
60 seconds
2.5 kV damped 1 MHz sine
wave
4 kV bi-directional impulse,
10 nsec rise time, fast
transient
Safety
Certified to DIN V VDE
0801 for Risk Class 5. Also
designed to meet UL 508 and
CSA 22.2, No. 142-M1981
Dimensions
Height:
Width:
D
epth:
12.6" (320 mm)
1.27" (32 mm)
10.12" (257 mm)
Weight
3.3 lbs (1.5 kg)
(T3411)
PD-6031
Mar-06
25
Monitored Digital Input Modules
(T3411)
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