Rockwell Automation T8472 Trusted TMR 120V ac Isolated Output Module - Manual (Page 8)

Trusted
TM
Module T8472
Issue 13 Sep 11 PD-T8472 8
The switch commands from each HIU slice are voted by each FIU switch interface circuit and
conversely, each FIU slice relays diagnostic information back to the three HIU slices for further
processing. The overall functions of the FIU are summarised below:
Control function – The FIU receives and decodes ON/OFF commands from the HIU for each of the
switch elements and forwards the commands to the appropriate switches.
Monitoring function – The FIU receives and processes measurement data from each of the switch
elements and forwards the results to the HIU.
Isolation – The FIU provides galvanic isolation between logic and field.
The majority voting carried out in the FIU ensures that any single slice failure in the HIU does not
degrade the output switch operation. Under those circumstances, all output switches would continue to
function correctly so long as two out of the three control circuits were operational. A second slice failure
would therefore ensure the quad output switches degraded to a known (‘OFF’ or ‘Normally – Open’)
state.
1.3. Host Interface Unit (HIU)
The HIU is the point of access to the Inter-Module Bus (IMB) for the module, it is the only section of the
I/O module to directly connect to the IMB backplane. The HIU also provides power distribution and
local programmable processing power. The HIU is common to most high integrity I/O types and has
type dependent and product range common functions. Each HIU contains three independent sections,
known as ‘slices’, commonly referred to as A, B, and C. All interconnections between the three slices
incorporate isolation to prevent any fault interaction between the slices. Each slice is considered a
Fault Containment Region (FCR), as a fault on one slice has no effect on the operation of the other
slices.
The HIU provides the following services common to the modules in the family:
1.4. Front Panel Unit (FPU)
The Front Panel Unit (FPU) contains the necessary connectors, switches, logic, and LED indicators for
the front panel. For every module, the FPU contains the Slice Healthy, Active/Standby, the Educated
indicators (LED’s), and the module removal switches. Additional bi-colour LED’s provide status
indication for the individual I/O signals. Serial data interfaces connect the FPU to each of the HIU
slices to control the LED status indicators and monitor the module removal switches
• High Speed Fault-Tolerant Communications with the TMR Processor via the IMB interface.
• FCR Interconnect Bus between slices to vote incoming IMB data and distribute outgoing I/O
module data to IMB.
• Optically isolated serial data interface to the FIU slices.
• Redundant power sharing of dual 24V dc chassis supply voltage and power regulation for logic
power to HIU circuitry.
• Serial data interface to the FPU for module status LED’s.
• Digital Signal Processing to perform local data reduction and self-diagnostics.
• Local memory resources for storing module operation, configuration, and field I/O data.
• On-board housekeeping, which monitors reference voltages, current consumption and board
temperature.
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