Rockwell Automation 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module User Manual - Manual (Page 14)

Publication 1746-UM022B-EN-P - January 2005
1-4 Module Overview
Each module channel can receive input signals from a thermocouple
or a mV analog input device. You configure each channel to accept
either one. When configured for thermocouple input types, the
module converts analog input voltages into cold-junction
compensated and linearized, digital temperature readings. The
module uses National Institute of Standards and Technology (NIST)
ITS-90 for thermocouple linearization.
When configured for millivolt analog inputs, the module converts
analog values directly into digital counts. The module assumes that
the mV input signal is linear.
System Operation
At power-up, the module checks its internal circuits, memory, and
basic functions. During this time the module status LED remains off. If
the module finds no faults, it turns on its module status LED.
After completing power-up checks, the module waits for valid channel
configuration data from your SLC ladder logic program (channel status
LEDs are off). After channel configuration data is transferred and
channel enable bits are set, the enabled channel status LEDs turn on.
Then the channel continuously converts the thermocouple or millivolt
input to a value within the range you selected for the channel.
Each time the module reads an input channel, the module tests that
data for a fault, i.e. over-range or under-range condition. If open
circuit detection is enabled, the module tests for an open-circuit
condition. If it detects an open-circuit, over-range, or under-range
condition, the module sets a unique bit in the channel status word
and causes the channel status LED to flash.
The SLC processor reads the converted thermocouple or millivolt data
from the module at the end of the program scan, or when
commanded by the ladder program. After the processor and module
determine that the data transfer was made without error, the data can
be used in your ladder program.
SL C 5 00
P rocessor
Thermocouple
Input
Module
Thermocouple or mV
Analog Signals
Channel Data Word
C hannel Status Word
C hannel Co nfiguration Word