Rockwell Automation T743x-xx ICS Regent+Plus RTD Input Equipment - Manual (Page 2)

RTD Input Equipment (T7432)
2
Industrial Control Services
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
multiplexers. A single RTD can be wired to a single RTD
termination panel which contains three RTD multiplexers for
fault tolerance. The fault tolerant boundary may be further
extended into the process by wiring three separate RTDs, all
measuring the same process parameter, to separate
termination panels, multiplexers and input modules. 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 RTD input equipment is
shown in Figure 1.
Two, three, or four-wire RTDs are terminated at the
termination panel. The termination panel routes the RTD
signals to the Mux for multiplexing, signal conditioning, and
A to D conversion. Up to three Mux’s can be installed in the
termination panel for fault tolerance.
The termination cable connects to the termination panel to
carry RTD data between the input Mux’s and RTD input
modules. 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 RTD data back to the input
module. The maximum allowable cable length is 50 feet.
Sixteen, replaceable current sources on the term panel
provide power to the individual RTDs. These current sources
receive and share power from the one, two or three Mux’s
installed in the termination panel.