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Chapter 1
Overview of FLEX I/O and Your Thermocouple, RTD, and Millivolt Input Module
What the FLEX I/O Input
Module Does
The FLEX I/O Module in a
Logix Control System
FLEX Adapters:
1794-ACN15
1794-ACNR15
1794-ACNR15K
1794-ADN
1794-AENT
1794-APBDPV1
1794-ASB
Adapter
1794-AENT
shown
8
The module is a high-speed, high-accuracy temperature and millivolt measuring module that
accepts thermocouple inputs, 2-, 3-, and 4-wire RTD inputs, and mV source inputs.
It offers the following:
•
Wire-off, overrange, and underrange detection
•
Good common mode rejection
•
Usage with long thermocouple wiring
•
Usage with grounded or ungrounded thermocouples
The Series B version of 1794-IRT8 provides capability to work with grounded thermocouples.
Use cold junction compensators (catalog number 1794-CJC2) in thermocouple mode. Two cold
junction compensators are shipped with the 1794-IRT8.
The FLEX I/O Thermocouple, RTD, and Millivolt modules are intelligent modules that interface analog
signals with Allen-Bradley® programmable controllers through a FLEX I/O adapter.
The adapter transfers data to and from the module. These transfers allow:
•
The adapter to obtain input or output values and status from the module.
•
Establishing the mode of operation through a process called configuration.
Figure 1
shows the flow of communication between the adapter and the I/O module.
Figure 1 - Typical Communication Between the Adapter and a Module
1
The adapter transfers your configuration data.
Flexbus
4
The adapter receives data from the
modules and stores it in the data table.
5
The adapter determines that the transfer was made
without error and input values are within specified
range.
6
Your ladder program can use "and/or" to move the
data (if valid) before it is overwritten by the transfer
of new data in a subsequent transfer.
7
New configuration data can be sent to the module
anytime during operation.
Rockwell Automation Publication 1794-UM012D-EN-P - March 2023
1794-IRT8
TC RTD INPUT 8 CHANNEL
IN 0
IN 1
IN 2
IN 3
IN 4
IN 5
IN 6
IN 7
F
F
F
F
F
F
F
The module converts analog
signals into binary format and
stores these values until the
adapter requests their transfer.
2
External devices transmit
analog signals to the module.
3
PWR
F
3
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