A-B Allen-Bradley

Model: 1786-RPFRXL/B

Full Name: ControlNet Fiber Ring Medium Repeater Module

Brand: Allen‑Bradley (Rockwell Automation)

Applicable System: ControlNet fieldbus network for PLC-5 and ControlLogix PLC platforms

The 1786-RPFRXL/B is a dedicated media repeater module designed for Rockwell ControlNet 5 Mbps fieldbus, which realizes mutual conversion between ControlNet coaxial electrical signals and fiber optical signals and supports redundant fiber ring topology. Its core functions are as follows:

1. Bidirectional Conversion Between ControlNet Coaxial and Fiber Signals Standard ControlNet bus relies on coaxial cable for 5 Mbps electrical communication. This module integrates optoelectronic conversion circuits to convert electrical bus signals to optical signals and vice versa. Its coaxial port connects legacy ControlNet coaxial segments, while ST fiber ports enable long-distance optical transmission to overcome the short transmission limit and anti-interference defects of coaxial cables.
2. Build Self-Recovering Redundant ControlNet Fiber Ring Topology Equipped with two independent fiber transmit/receive channels (CH1 & CH2), the module supports closed-loop fiber ring networking. If a fiber cable breaks or a module fails, the bus communication automatically switches to the reverse transmission path within milliseconds without network interruption, realizing ring self-healing redundancy and improving network stability in workshops with welders and high-power motors.
3. Signal Regeneration & Distance Extension for ControlNet Bus Coaxial ControlNet cables have a short maximum single-segment transmission distance. Optical fiber delivers signal transmission over several kilometers without electromagnetic attenuation. The module reshapes and amplifies degraded bus signals to eliminate distortion caused by long-distance transmission, meeting cross-workshop and cross-floor long-range ControlNet networking requirements.
4. Complete Electrical Isolation to Suppress Severe Industrial EMI Data is transmitted via light instead of electrical conductors, achieving full electrical isolation between field segments. It blocks high-voltage harmonics and surge interference generated by inverters, large motors and welding machines, preventing bus communication errors, offline nodes and disordered PLC control logic in harsh electromagnetic industrial environments.
5. Mixed Networking Compatibility for New & Legacy ControlNet Devices Multiple 1786-RPFRXL/B modules can be deployed in daisy-chain or ring layout. Multiple coaxial branches can be derived from the fiber backbone, so legacy coaxial stations, remote I/O blocks, servo drives and PLC controllers can access the same ControlNet network simultaneously. There is no need to replace all original coaxial wiring, which significantly reduces renovation costs.
6. Real-Time Network Diagnostics & Link Fault Indication Front panel LEDs display operating status of two fiber channels and coaxial link separately. The module can upload diagnostic fault codes to the ControlNet master PLC, including fiber breakage, coaxial short circuit, signal loss and ring breakpoints, allowing maintenance staff to locate fault points rapidly and minimize production downtime.
7. Standard OEM Spare Part for Legacy ControlNet System Retrofit This module is the exclusive fiber repeater matching PLC-5 and 1756-ENBTA ControlNet communication modules. It is widely adopted for equipment upgrading, hazardous area wiring and long-distance plant networking without full replacement of the original bus hardware.

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