Comprehensive Guide to ControlLogix Redundancy Systems for Increased Reliability
ControlLogix Redundancy Systems
In applications where uninterrupted operation is critical, ControlLogix redundancy systems provide increased system availability and reliability. This article provides an overview of ControlLogix redundancy systems, their components, procedures to build them, and considerations for both ControlNet and EtherNet/IP networks in such systems.
Introduction to ControlLogix Redundancy
ControlLogix redundancy systems enhance system availability by switching control to a secondary controller chassis in case of a fault in the primary chassis. This switchover can occur due to several reasons such as power loss, hardware or firmware failures, major faults in the user program, or loss of communication between the primary chassis and remote modules.
The redundancy system is designed to be transparent to devices connected over EtherNet/IP or ControlNet networks, requiring no additional programming.
System Requirements
To establish a redundant system, at least the following components are required:
| Quantity | Item | Notes |
|---|---|---|
| 2 | ControlLogix chassis | Both chassis must be the same size |
| 2 | ControlLogix power supply | Must be the same in each chassis |
| 2 | ControlLogix controllers | Use 1756-L6x or 1756-L7x controllers. The controllers in each chassis must have the same catalog number, series, firmware revision, and memory size |
| 2 | ControlLogix ControlNet communication modules | Examples include 1756-CN2/B, 1756-CN2R/B, or 1756-CN2RXT modules. Communication modules in each chassis must be identical in firmware revision, series, slot placement, and module type |
| 2 | ControlLogix EtherNet/IP communication modules | Examples include 1756-EN2T, 1756-EN2TXT, or 1756-EN2TR modules. These modules must also be identical in firmware revision, slot placement, and module type |
| 2 | Redundancy module | Use 1756-RM2 or 1756-RM2XT modules |
Note: It is crucial to ensure that components in the redundant chassis pair are identical in terms of module configuration.
Building a Redundant System
Follow these steps to set up a ControlLogix redundant system:
- Install a ControlLogix chassis and power supply.
- In the primary chassis, add 1756-L6x or 1756-L7x controllers. Note that you cannot mix 1756-L6x and 1756-L7x controllers in the same chassis.
- Add one or more ControlNet or EtherNet/IP communication modules.
- Add one redundancy module.
- Configure a secondary chassis that is identical to the primary chassis.
- Connect the redundancy modules in the chassis.
- Add I/O modules to ControlNet or EtherNet/IP networks.
- Add operator interfaces to ControlNet or EtherNet/IP networks【18:2†source】【18:4†source】.
ControlNet Considerations in Redundant Systems
You can have up to seven ControlNet communication modules in a redundant chassis. Redundancy modules placed in each chassis maintain communication between the redundant chassis. Depending on the priority of tasks, outputs can experience either a bumpless switchover or a change in state during a switchover.
EtherNet/IP Considerations in Redundant Systems
ControlLogix redundancy supports up to seven EtherNet/IP modules in the redundant chassis. These modules can be used for the following purposes:
- I/O control
- Producing and consuming data
- HMI connections to the primary controller
- Remote I/O modules
In systems with firmware revision 13 or later, IP address swapping is supported. This involves configuring primary and secondary EtherNet/IP modules with the same IP address, with the secondary module taking an IP address that is one unit higher. During a switchover, these IP addresses are swapped, allowing HMI devices to continue to communicate with the new primary controller without interruption. However, communication may halt for several seconds, typically less than a minute.
Redundancy and Scan Time
At the end of each program, the primary controller synchronizes and crossloads fresh data to the secondary controller. This process, which keeps the secondary controller up-to-date, increases scan time compared to nonredundant systems.
The amount of time spent in crossloading depends on the amount of data modified since the last crossload. Optimizing these synchronization points can reduce the overall impact on task scan time and save overhead time.
Conclusion
Redundant systems in ControlLogix controllers offer a robust solution for applications requiring high availability. By following proper installation and configuration guidelines, users can effectively leverage redundancy to ensure system reliability and minimize downtime.