Spectrum Controls 1762sc-IF8U - Manual (Page 10)

1-4 MicroLogix™ 1200 IO Universal Input Module
User's Manual Pub. 0300243‐02 Rev. B
Section 1.6
System
Overview
The module communicates to the controller through the bus interface. The module also
receives 5 and 24V dc power through the bus interface.
Note: An external power supply is required for all 2-wire transmitters.
1.6.1 Module Power-up
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, it continuously converts the input
data 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 open-circuit, or “input data not valid” condition. If such a condition is detected the
channel data value will fail to a user defined state defined in the module configuration
settings. For more details, refer to Chapter 3.
Using the module image table, the controller reads the two’s complement 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.
1.6.2 Module Operation
When the module receives the input from an analog device, the module’s circuitry
multiplexes the input into an A/D converter. The converter reads the signal and converts
it as required for the type of input. If thermocouples are being utilized, the module
continuously samples the CJC sensor and compensates for temperature changes at the
terminal block cold junction, between the thermocouple wire and the terminal connector.
See the block diagram below.
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