The ControlLogix I/O Modules

Learn Logix Part 2.3. This article explains the features of the 1756 I/O modules, the I/O modules used in ControlLogix systems for local and distributed I/O.

Learn Logix is a series of articles designed to teach you everything you need to know to work with Rockwell Automation’s Studio 5000 Logix Designer and the Logix 5000 series of PLCs.

In the last part of the series, we learned about the ControlLogix controllers and the features of the L7x and L8x ControlLogix controllers. You can find that part here or if you’re new to the series, you can find all of the previous parts here.

In this part of the series, we’ll look at 1756 I/O modules, which are the I/O modules for the ControlLogix system.

In a ControlLogix System, I/O modules can be local I/O modules or distributed I/O modules.

A local I/O module is an I/O module that is mounted in the same chassis as the controller that contains the I/O module’s configuration information.

A distributed I/O module is an I/O module that is mounted in a different chassis than the controller that contains its configuration information. Distributed I/O modules help to minimize the amount of wiring needed to connect field devices to a controller.

In the image above, you can see examples of both local and distributed I/O modules.

1756 Input and Output Modules

The ControlLogix system uses 1756 series input and output modules for local and distributed I/O. These I/O modules are mounted in a ControlLogix chassis. Both input and output modules have a very similar design.

Removable Terminal Blocks (RTBs)

1756 I/O Module Removable Terminal Blocks

The 1756 I/O modules are equipped with a Removable Terminal Block, also known as an RTB.

The field devices are connected to the RTB, which is then connected to the I/O module. Connector pins on the I/O module create an electrical connection between the RTB and the I/O module.

When the RTB is connected to an I/O module the locking tab, located on the front of the 1756 I/O module, is used to secure the RTB to the module. This locking tab helps to ensure that the electrical connection between the RTB and the module is secure.

ControlBus Backplane Connector

1756 I/O Module ControlBus Connector

At the rear of 1756 I/O modules is a ControlBus connector. This connector connects the I/O modules to a ControlBus backplane, like the one found in a ControlLogix chassis, and allows the modules to communicate over the backplane.

Status Indicators

1756 I/O Module Features

Each 1756 I/O module has status indicators on the front of the module. These status indicators provide an easy way to understand the health of the I/O module and its communication status.

The status indicators are very useful for troubleshooting issues in a ControlLogix system.

Slots for Mechanical Keying

Finally, to prevent the wrong RTB from being connected to an I/O module, each module is equipped with slots for mechanical keying.

Conclusion

In this article, we learned about the features of 1756 I/O modules, the I/O modules for the ControlLogix system.

In the next part of the series, we will learn about the communication modules available for the ControlLogix system. If you haven’t already, be sure to subscribe to the mailing list below to be notified when the next part is available.

Update: You can find the next part of the Learn Logix series, The ControlLogix Communication Modules, here. This article explains the communication modules available for the ControlLogix system and looks in detail at two commonly used communication modules - the 1756-EN2T and 1756-EN2TR EtherNet/IP communication modules.

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