Honeywell 900RSM-0101 Redundant Switch Module – HC900 Redundant CPU Failover Controller
Product Overview
The Honeywell 900RSM-0101 is a redundant switch module (RSM) engineered specifically for the ControlEdge HC900 hybrid control system, serving as the critical arbitration component between dual Control Processor Modules (CPMs) in high-availability configurations. The Honeywell 900RSM-0101 sits physically between the primary and backup CPUs within a dedicated redundant controller rack, continuously monitoring the health and heartbeat signals of both processors to enable seamless automatic failover when the active controller experiences a fault . This module is not an I/O device or a power supply—it is the dedicated redundancy management component that transforms two standalone processors into a fault-tolerant control pair.
The Honeywell 900RSM-0101 performs three essential functions within the HC900 redundant architecture. First, it provides real-time visual indication of which CPU is currently operating as the Lead (active) controller and which is in Reserve (standby) mode through green arrow LEDs on the front panel . Second, it employs a key-operated mode switch that locks both processors into matched operating modes, preventing the destabilizing condition where both CPUs attempt to act as primary or both fall into standby simultaneously . Third, the Honeywell 900RSM-0101 facilitates manual switchover tests through a momentary transfer position on the key switch, allowing maintenance personnel to verify redundancy functionality without pulling cables or restarting the system .
When a CPU fault is detected, the Honeywell 900RSM-0101 arbitrates the transfer of control to the standby processor in under 100 milliseconds, enabling the reserve CPU to resume output with its fully synchronized memory image . Operators monitoring SCADA screens typically observe only a status indicator change, while process variables, valve positions, and control outputs remain undisturbed—a level of continuity essential for mission-critical applications in chemical processing, power generation, and oil refining . The module supports hot-swap capability, allowing replacement without de-energizing the controllers or interrupting the running process .
