Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 17)

Publication 1762-UM003A-EN-P - February 2003
Overview 1-7
System Overview The modules communicate to the local controller or communication
adapter through the 1762 bus interface. The modules also receive 5
and 24V dc power through the bus interface.
System Operation
At power-up, the module performs a check of its internal circuits,
memory, and basic functions. During this time, the module status LED
remains off. If no faults are found during power-up diagnostics, the
module status LED 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, the module continuously converts the RTD
or resistance input to a value within the range selected for that
channel.
Each time the module reads an input channel, it tests the data for a
fault (over- or under-range, short-circuit, or open-circuit condition). If
it detects a fault, the module sets a unique bit in the channel status
word. See Input Data File on page 3-3.
Using the module image table, the controller reads the two’s
compliment binary converted input 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.