The 1756-RM ControlLogix Redundancy Module from Rockwell Automation is a core system module used to implement controller redundancy (hot backup) in ControlLogix architectures.
It synchronizes two identical ControlLogix processors so that a secondary controller can immediately take over if the primary controller fails. This ensures continuous operation with minimal or zero downtime, which is critical for high-availability industrial automation systems.
The 1756-RM is widely used in oil & gas, power generation, chemical processing, water treatment, and continuous manufacturing systems, where PLC failure is not acceptable.
Key Function
The 1756-RM is not an I/O or power module. Its primary role is:
- Synchronizing two ControlLogix CPUs (primary + secondary)
- Maintaining real-time data consistency between both controllers
- Managing redundancy status and switchover logic
- Enabling automatic failover in case of controller fault
- Working with redundancy firmware and configuration tools (Studio 5000)
It connects two chassis using fiber optic redundancy communication cables (1756-RMCx series).
Technical Specifications (Including Size & Weight)
| Parameter | Specification |
|---|---|
| Model | 1756-RM |
| Series | ControlLogix Redundancy Modules |
| Module Type | Controller Redundancy Synchronization Module |
| Slot Requirement | 1 slot in ControlLogix chassis |
| Function | CPU redundancy synchronization |
| Communication | Fiber optic (LC connector) |
| Redundancy Cable | 1756-RMC1 / RMC3 / RMC5 |
| Backplane Current (5.1V DC) | ~1.2 A |
| Backplane Current (1.2V DC) | ~4 mA |
| Backplane Current (24V DC) | ~120 mA |
| Power Dissipation | ~9 W |
| Thermal Dissipation | ~31 BTU/hr |
| Isolation Voltage | 250V continuous |
| Mounting Position | Any slot in chassis |
| Compatible Controllers | 1756-L6x / L7x / L8x series (depending on system design) |
| Compatible Power Supplies | 1756-PA75R, 1756-PB75R, 1756-PSCA2 |
| Operating Temperature | 0°C to 60°C |
| Storage Temperature | -40°C to 85°C |
| Relative Humidity | 5%–95% non-condensing |
| Weight | ~0.29 kg |
(Technical values compiled from ControlLogix redundancy module specifications. )
Physical Dimensions
- Size (H × W × D): 145 × 58 × 28 mm (approx.)
(Compact single-slot module form factor used in ControlLogix chassis redundancy systems. )
System Architecture Role
In a redundant ControlLogix system:
- Two identical PLC chassis are built (Primary + Secondary)
- Each chassis contains a 1756-RM module
- Fiber optic cable links both RM modules
- Both controllers continuously synchronize memory and state
- If primary fails → secondary takes over instantly
- Process continues without interruption
This is known as hot standby redundancy architecture.
Recommended Related Models
The 1756-RM is typically used with:
- 1756-L71 / L73 / L75 ControlLogix CPUs
- 1756-PA75R / 1756-PB75R redundant power supplies
- 1756-PSCA2 redundancy power chassis adapter
- 1756-RMCx fiber optic redundancy cables
- 1756-EN2T / EN2TR communication modules
- 1756-A7 / A10 chassis systems
