Rockwell Automation T3431-CA ICS Regent Thermo Couple Input Assembly - Manual (Page 4)

Thermocouple Input Assembly (T3431)
4
Industrial Control Services
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 Safetybus bus drivers.
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.
Figure 2. Thermocouple Input Data Format.
Testing and Diagnostics
Input Module Testing
Each module’s voter circuits are periodically 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 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.