Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 14)

14 Rockwell Automation Publication 1769-UM004B-EN-P - March 2010
Chapter 1 Overview
General Diagnostic Features
The module contains a diagnostic status indicator that helps you identify the
source of anomalies that may occur during powerup or during normal channel
operation. The status indicator indicates both status and power. Power-up and
channel diagnostics are explained in
Chapter 5, Diagnostics and
Troubleshooting .
System Overview The modules communicate to the controller through the bus interface.
The modules also receive 5 and 24V DC power through the bus interface.
System Operation
At powerup, the module performs a check of its internal circuits, memory, and
basic functions. During this time, the module status indicator remains off. If no
faults are found during power-up diagnostics, the module status indicator is
turned on.
After power-up checks are complete, the module waits for valid channel
configuration data. If an invalid configuration is detected, the module generates a
configuration error. Once a channel is properly configured and enabled, it
continuously converts the thermocouple or millivolt input to a value within the
range selected for that channel.
Each time a channel is read by the input module, that data value is tested by the
module for an over-range, under-range, open-circuit, or ‘input data not valid’
condition. If such a condition is detected, a unique bit is set in the channel status
word. The channel status word is described in
Input Data File on page 38 .
By using the module image table, the controller reads the two’s complement
binary converted thermocouple or millivolt data from the module. This typically
occurs at the end of the program scan or when commanded by the control
program. If the controller and the module determine that the data transfer has
been made without error, the data is used in the control program.