Rockwell Automation T3464 User Manual
ICS Regent
®
PD-6021
AC Guarded Digital Output Module
110 VAC
(T3464)
Issue 1,
AC Guarded digital output modules provide guarded
switching of user-supplied 110 AC voltages to a maximum of
sixteen field loads. These modules are called Guarded
because no single fault within a module will inadvertently
apply power to an output. Extensive fault detection and
critical redundant circuits ensure that the module operates in
a fail-safe manner.
Features
March, 06
·
Sixteen Guarded output circuits configured as two separately
powered groups of eight circuits each.
·
Fault tolerant operation when connected in parallel with
another module of the same type.
·
Hot-replace
·
100% self-test of all critical circuits.
·
Zero-cross load switching.
·
Individual front panel indicators on each module show
active/fault and output on/off status (field side). A diagnostic
message display provides additional status indicators.
·
Fuses accessible from front panel.
·
2500 volt minimum electrical isolation between field and l
circuits.
·
TÜV certified, Risk Class 5, see Safety Considerations.
Two Guarded output modules can be connected in parallel to
obtain fault tolerant control of power to loads. In this parallel
module configuration, either module can be removed and
able.
ogic
Industrial Control Services
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AC Guarded Digital Output Module
replaced while the other Guarded module continues to control
the loads without interruption.
(T3464)
Module Operation
A block diagram of a typical AC Guarded digital output
module is shown in Figure 1.
The processor modules send triplicated write data commands
over the I/O Safetybus to the Guarded output module.
Onboard the Guarded output modules the triplicated data are
routed to two independent voter and microcomputer sections.
Each section independently votes the triplicated data to
generate a logic output drive signal. The two logic drive
signals are ANDed to control the output TRIAC.
2
Figure 1. Block Diagram of the AC Guarded Output Module.
The TRIAC will normally be energized only when both
microcomputer sections command the output to be on. If
either microcomputer section commands the output to be off,
Industrial Control Services
(T3464)
AC Guarded Digital Output Module
the TRIAC will be de-energized. If the TRIAC itself fails
shorted when commanded off, either microcomputer section
can trigger an internal crowbar switch that disables the
output by blowing the fuse for that circuit.
The combination of dual independent drive signals, a TRIAC,
and a crowbar circuit provides fail-safe activation of the load
devices. No s
ingle failure can prevent the output from being
turned off when commanded. Single failures result in either
continued correct control or a fail-safe output as shown in
Table 1.
To achieve fault tolerance, two Guarded output modules are
used with their outputs connected in parallel. This
configuration provides for continued correct control even
when an output TRIAC fails open (class 2 and 5 in Table 1).
The module failure is automatically detected and th
e failed
module can be removed and replaced without interrupting
output control.
PD-6021
Mar-06
3
Case
Commanded
Output State
Single
Failure
Actual
Output
to Load
Remarks
1 On
TRIAC
short
On
Continued correct control.
Automatic testing of crowbar
circuit ensures that output will be
able to switch off. If output is
subsequently commanded off,
crowbar switch is energized to
blow fuse and turn off output
(fuse blows 200 msec after
output is commanded off).
2 On
TRIAC
open
Off
Fail-safe output. Automatic
testing detects failed TRIAC.
3 On
Crowbar
fault
On
Continued correct control.
Automatic testing detects failed
crowbar circuit. If output is
subsequently commanded off,
TRIAC will turn off.
4
Off
TRIAC
short
200
msec
bump
A one-time, 200 msec maximum
on-state bump occurs when the
TRIAC shorts. Automatic testing
detects shorted TRIAC and
crowbar switch is activated to
blow fuse. This one-time bump
may not be suitable for certain
energize-to-trip applicatio
ns.
5
Off
TRIAC
open
Off
Fail-safe output. Automatic
testing detects failed TRIAC. If
output is subsequently
commanded on, output will
remain off.
6
Off
Crowbar
fault
Off
Continued correct control.
Automatic testing detects failed
crowbar circuit. If output is
subsequently commanded on,
TRIAC will turn on.
AC Guarded Digital Output Module
(T3464)
Table 1. Output States After Switch Failure.
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Testing and Diagnostics
The voter and I/O bus interface logic of the Guarded output
modules is automatically 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 voters are able
to outvote the incorrect data. A failure to return the correct
majority-voted result to the processors produces an I/O
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(T3464)
AC Guarded Digital Output Module
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. If a
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.
Fuses are periodically checked for continuity. Blown fuse
detection is independent of load connection or output circuit’s
on/off state.
Incoming AC field power is checked for proper frequency,
stabili
ty, and phase. Tests that depend on AC power timing
information, such as turn-on testing, will not execute if the AC
power is unacceptable. However, crowbar switch activation is
not dependent on these power conditions.
Approximately every 2 seconds, output circuits commanded to
be off are tested for their ability to turn on. Three test pulses
are applied on successive AC voltage phase zero crossings to
verify the output switch's ability to conduct bi-directional
current flow. The pulses are limited to 5
0 volts with a
maximum duration of 1 millisecond. This energy is
insufficient to drive most field loads.
Output TRIACs commanded to be on (output switch closed)
are not tested for their ability to turn off. Instead, the crowbar
circuit is periodically tested for its ability to turn on. If a
TRIAC fails to tuns off when commanded, either
microcomputer can energize the crowbar switch and remove
power from the load by blowing the fuse for that circuit. In
this way, an output’s inability to turn off is not discovered
until the switch is commanded to turn off. The result is a
maximum time to switch off a shorted output (blow the fuse) of
200 milliseconds.
Outputs commanded to be on are occasionally tested for open
load and open circuit (faulty output switch) conditions. If load
current is below the minimum requirements, the module tests
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5
AC Guarded Digital Output Module
the output switch's ability to conduct current (through an
internal dummy load). If current is conducted, the fault is in
the load. If no current is conducted, the fault is
switch circuit. Healthy outputs commanded to be on but not
wired to an external load will always cause an open load
condition to be displayed.
(T3464)
in the output
Front Panel
Figure 2 shows the physical features of the AC Guarded
output modules. The front panel contains an active and fault
status indicator, a diagnostic message display, as well as
status indicators and fuses for each output circuit.
Active/Fault Status Indicator
These green and red LEDs indicate the overall health o
f 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 ACTIVE indicator turns off.
Output Status Indicators
The output status indicators are yellow LEDs, located on the
field side of the output circuit, in parallel with the load. These
indicators are on when the load is energized.
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Industrial Control Services
(T3464)
AC Guarded Digital Output Module
PD-6021
Mar-06
Figure 2. AC Guarded Output Mod
7
ule.
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