Rockwell Automation T3431-CA User Manual
ICS Regent
®
PD-6024
Thermocouple Input Assembly
Input Module, Mux, Termination Panel and Cable
(T3431-IM, T3431-Mux, T3431-TP and T3431-CA)
Is
sue 1,
March, 06
The thermocouple input assembly consists of a thermocouple
input module (T3431-IM), a thermocouple input multiplexer
(T3431-MUX), a thermocouple termination panel (T3431-TP),
and a thermocouple termination cable (T3431-CA). This
equipment provides terminations and temperature conversion
for as many as 24 thermocouple inputs, arranged in 3 groups
of eight inputs.
Features
·
Twenty-four thermocouple inputs.
·
Configuration options:
Thermocouple type:
Units:
Resolution:
Filter response:
·
Complete linearization, cold junction compensation and
automatic calibration.
·
Remote terminations up to 50 cable feet from I/O chas
·
2500 volt isolation between Input Module and Mux.
·
High speed acquisition.
·
Hot-replaceable input module and Mux.
·
Extensive fault diagnostics.
·
Thermocouple burnout detection (downscale).
·
TÜV certified, Risk Class 5, non-interfering.
The input module plugs into an I/O chassis slot and receives
data from the thermocouple input multiplexer (or Mux). The
thermocouple input multiplexer plugs into the termination
panel and provides low level signal conditioning,
J, K, S, T (in groups of eight)
Degrees F or degrees C
Units or tenths
50 Hz, 60Hz rejection
sis.
Industrial Control Services
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Thermocouple Input Assembly
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 inpu
signals.
(T3431)
t
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.
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Industrial Control Services
Thermocouple Input Assembly
(T3431)
Figure 1. Block Diagram of the Thermocouple Input Assembly.
The Serial data received from the Mux is optically coupled at
the input m
odule to provide electrical isolation. The input
module's 68000-based microcomputer processes the
thermocouple data. This microcomputer’s functions include:
·
Digital filtering
·
Automatic calibration
·
Cold junction compensation
·
Temperature conversion and linearization
·
Diagnostics
The processor modules send triplicated read data req
the thermocouple 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 module operations). The voted
result is then passed to the I/O bus interface logic.
uests to
PD-6024
Mar-06
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Thermocouple Input Assembly
After receiving the voted data read request, the
microcomputer transmits the conditioned temperature data to
the Safetybus interface. This interface places the voted
temperature data onto the triplicated Saf
Each of the three bus drivers is independently powered and
controlled (by the I/O transceiver modules) — preventing
failures in a single driver from propagating to the other two
I/O busses. The bus drivers then transmit the data via the
backplane I/O Safetybus to the I/O transceiver modules which,
in turn, transmit the data to the processors.
The thermocouple input data is packaged as a 16-bit word for
each input. The format of each word is shown in Figure 2.
The most significant bit in the word is used as an alarm bit to
indicate an out-of-range thermocouple input signal. The
remaining 15 bits contain signed 15-bit integer data
representing the temperature in degrees C or F and in units
or tenths of degrees, as configured by jumper settings on the
Mux.
(T3431)
etybus bus drivers.
Figure 2. Thermocouple Input Data Format.
Testing and Diagnostics
Input Module Testing
Each module’s voter circuits are periodically tested by the
p
rocessor modules. Discrepant data are sent through one of
three legs 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.
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Industrial Control Services
Thermocouple Input Assembly
(T3431)
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.
Multiplexer Testing
The serial communications link to the thermocouple Mux is
continuously monitored. Additionally the data r
eceived from
the Mux is checked for proper data format, parity and numeric
range reasonableness. The cold junction sensor values are
monitored and compared to detect a failed cold junction
sensor. The precision voltage references on the multiplexer
are also checked to verify that the power to the Mux is present
and that the voltage references are within tolerance.
Input Module Front Panel Indicators
Figure 3 shows the physical features of the thermocouple
input module. The front panel of each module contains status
indicators to display the operational status of the input
module, multiplexer and cold junction sensors.
Active and Fault Status Indicators
These green and red LEDs indicate the overall health of the
module. 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.
PD-6024
Mar-06
MUX Fault Indicator
The red MUX FAULT indicator turns on when any
following fault conditions are detected:
·
No data received from the Mux.
·
Corrupted data from the Mux.
·
Unreasonable data values from the Mux.
5
of the
Thermocouple Input Assembly
Failure of the DC-to-DC converter supplying power to the
termination panel or the receiver circuitry can also result in a
MUX fault. Both of these faults are input module faults.
(T3431)
CJ Fault Indicator
There are two cold junction sensors located on the termination
panel. The red CJ FAULT indicator turns on when any of the
following fault conditions are detected:
·
Either CJ sensor temperature is < -5°
·
Either CJ sensor temperature is > 65° C (149° F)
·
The CJ sensors differ by more than 2.8° C (5° F)
C (23° F)
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Thermocouple Input Assembly
(T3431)
PD-6024
Mar-06
Figure 3. Thermocouple Input Module.
Termination Panel and Multiplexer
Figure 4 shows the physical features of the Termination Panel
and Multiplexer. The multiplexer plugs into the termination
panel and is secured in place with two thumb screws located at
each end of the multiplexer.
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Thermocouple Input Assembly
The termination cable plugs into the DB-9 connector located
at the upper right corner of the termination panel.
Thermocouple inputs are ter
located along the bottom of the termination panel. These
terminals are arranged in three groups of eight inputs. Two
screw terminals are provided for each thermocouple input.
Two additional ground terminals within each group are
provided to connect thermocouple cable shield wires if desired.
(T3431)
minated at the screw terminals
Termination Panel Indicators
The termination panel has status indicators for power supply
voltages, and transmit data. When positive and negative
supply voltages are present at the termination panel, the
POWER + and POWER -
indicators are on. The TX DATA
indicator is on when the Mux is transmitting data to the input
module. Normally, all these green indicators should be on.
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Industrial Control Services
Thermocouple Input Assembly
(T3431)
PD-6024
Figure 4. Thermocouple Termination Panel and Multiplexer.
Mar-06
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