The Allen-Bradley 1756-RM2 is a ControlLogix Redundancy Module. It has enhanced features with speeds of up to 1000 Mbps. When paired with 1756-L7x controllers in both chassis, it gives the best scan performance. For cross loading, the 1756-RM2 uses redundant fiber ports with no single point of failure. During channel switchover, the processing chassis remains synched while the scan time may encounter a delay of around 10 ms. It has enhanced safety features with interference-free diagnostics.

The 1756-RM2 redundancy module draws 1.16 A current at 5.1V DC and 3.4 mA at 24V DC. It has a maximum power dissipation of 6W and a thermal dissipation of 21 BTU/hr. It can be installed in any slot in a ControlLogix chassis. The 1756-RM2 weighs 0.64 lbs. and it has an open enclosure. For communication, it supports up to seven enhanced ControlNet and EtherNet/IP communication modules. For wiring, the 1756-RM2 supports 1756-RMC1, 1756-RMC3 and 1756-RMC10 cable with 1m, 3m and 10m lengths respectively.

The ControlLogix 5560 and ControlLogix 5570 series of controllers support the 1756-RM2 module. The Redundancy Module Configuration tool, RSLinx 2.59.

A variety of synchronization speed may be enabled depending on the combination of redundancy module used. Particularly, if used with the same 1756-RM2 module, speed may reach up to 1000 Mbps. If both series A or series B 1756-RM2 are used, speed may reach up to 100 Mbps. Up to 20 ms controller switchover may be achieved with the use of the 1756-RM2 redundancy module.

Unlike the first versions of the redundancy module, the 1756-RM2 only occupies a single slot of any ControlLogix chassis. When implementing redundancy, A pair of redundant racks must be installed with each rack installed with the same controller type and revision. I/O modules, intelligent modules and encompass partner modules cannot be installed in any of the redundant chassis pair. These modules must be installed on a 3rd or higher order chassis, depending on the supported number of node of the communication module used.

The Redundancy module has integrated fiber optic connector where the controller synchronization is actively happening. This Fiber cable has LC-Type connector with cable type of 8.5/125 micron single-mode fiber-optic cable. Up to 10 km (10,000 m, 10936.13 yd) of distance can be established between each redundancy module however, it is ideal that the redundant chassis pair is near each other.