Rockwell Automation T3431-CA ICS Regent Thermo Couple Input Assembly - Manual (Page 2)

Thermocouple Input Assembly (T3431)
2
Industrial Control Services
multiplexing, and analog-to-digital conversion. The
termination panel can be located as far as 50 cable feet from
the I/O chassis.
Each module’s triplicated I/O Safetybus interface ensures that
no failure in the module can affect the operation of the Regent
system or other I/O modules in the system. Extensive fault
detection and annunciation of critical redundant circuits help
prevent the controllers from receiving erroneous data from a
faulty input module. The fault tolerant boundary may be
extended by using three input modules and three termination
panels. A single thermocouple is wired to three different
termination panels for fault tolerance. The fault tolerant
boundary may be further extended into the process by wiring
three separate thermocouples, all measuring the same process
parameter, to three separate termination panels. In either
triplicated configuration, a failed module or multiplexer can
be removed and replaced without interrupting the input
signals.
Module Operation
A simplified block diagram of the thermocouple input
assembly is shown in Figure 1.
Thermocouples are terminated at the termination panel. The
termination panel routes the thermocouple signals to the Mux
for multiplexing, signal conditioning, and A to D conversion.
The Mux also senses the cold junction sensor voltages. Cold
junction sensors are mounted on the termination panel near
the screw terminations.
The termination cable connects the termination panel to the
input module. A DC-to-DC converter on the input module
shares three power legs from the I/O backplane power and
provides isolated power to the Mux over the termination cable.
The Mux transmits digitized serial thermocouple data back to
the input module. The maximum allowable cable length is 50
feet.