An introduction to Allen Bradley's high-performance ControlLogix PLC system
The ControlLogix PLC system is designed for large, demanding applications. Typically, a ControlLogix system is used for distributed or supervisory control.
In this post, I'll talk you through the features of the ControlLogix system and the ControlLogix modules that are available to use.
Let's start by looking at the structure of a ControlLogix system.
A ControlLogix system is made up of a power supply, chassis, controller(s), I/O modules, and communication modules. Modules can be arranged in any order in the chassis and a single chassis can contain multiple controllers.
All ControlLogix module numbers begin with 1756.
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A power supply is mounted outside of the chassis. It provides power to energize the modules in the chassis.
Power supplies are available with 120V AC, 230V AC, and 24V DC input.
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ControlLogix modules are installed in a physical chassis. The chassis is available with 4, 7, 10, 13, and 17 slots. Slots are numbered from left to right, starting at 0. Empty slots can be filled with a 1756-N2 slot filler module.
A ControlBus backplane runs along the back of the chassis. This backplane supplies power to the modules and allows them to communicate with each other.
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ControlLogix controllers are available with different combinations of memory and capabilities. Each ControlLogix controller is capable of addressing a large number of I/O points and communicating with many devices on a network.
The latest series of ControlLogix controllers are the L7 and L8 series. Some of the most important features of ControlLogix controllers include;
Both L7 and L8 controllers have a scrolling display that shows the project name, fault information, firmware revision, and other data
ControlLogix controllers have an SD card that provides nonvolatile memory for project storage.
The SD card is located inside the front cover of the L8 controllers. Before you can open the cover, you must remove the key from the key switch
ControlLogix controllers have an embedded USB port. This is used to create a temporary point-to-point connection with a computer
ControlLogix controllers use an Energy Storage Module, or ESM, for project retrieval from non-volatile memory after power loss and to keep a wall clock running without power for up to 5 days.
This ESM replaces the lithium batters that were used in older ControlLogix controllers. This reduces environmental issues and safety concerns that come from using lithium batteries
The ESM is embedded in L8 controllers and removable in L7 controllers.
L8 controllers deliver up to 20 times faster performance and 45% more memory than equivalent L7 controllers.
They also have an embedded Ethernet port which enables high-speed communication without an additional communication module.
Finally, security for the L8 controller has been enhanced through controller-based changed detection and logging, digitally signed controller firmware, and role-based access controller (RBAC).
RBAC is a method of controller access to a computer or network resource based on the roles of individual users within an enterprise. Only specific users are allowed to perform a specific task such as view, create, or modify a file
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ControlLogix I/O modules add input and output points to a ControlLogix system. There is a wide range of modules available including digital and analog input and output modules.
ControlLogix I/O modules feature status indicating LEDs.
These LEDs indicate the health of the module and the status of the I/O points. These LEDs can be ver helpful when troubleshooting a system.
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ControlLogix input and output modules use a Removable Terminal Block, or RTB, to connect the module to field wiring. These modules use a locking tab to secure the RTB to the module to ensure a good connection between the RTB and the module.
To prevent someone from connecting the wrong RTB to a module, RTBs feature slots for mechanical keying.
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Communication modules allow a ControlLogix controller to communicate on an industrial network.
The most common types of ControlLogix communication modules allow a ControlLogix system to communicate on an EtherNet/IP network.
Communication modules like the 1756-EN4TR have a scrolling display and status indicators that display the status of the module.
The LINK 1 and LINK 2 indicators show if data is being transmitted over the network.
The NET indicator shows the state of the device’s EtherNet/IP ports. The indicator is solid when the controller has an IP address and at least one active connection.
The OK indicator indicates the module’s health.
Third-party communication modules are available that allow a ControlLogix system to communicate on other industrial networks like Modbus TCP, Modbus RTU, and even PROFINET.
The ControlLogix system is a multi-controller system. This means that a chassis can contain multiple controllers which communicate with each other across the backplane.
This capability is useful for high-speed applications since the load can be shared across controllers.
ControlLogix modules support Removal and Insertion Under Power (RIUP).
This is a feature that allows a ControlLogix system to continue running while a module is being changed.
There is a high potential for an accident to occur when changing a module in a running system. It is your responsibility to make sure that it is safe to remove and insert modules in a running system.
In this post, I have introduced the ControlLogix PLC system.
For more details on this system and the modules that are available for it, check the ControlLogix Selection Guide published by Rockwell Automation.