Yokogawa | ALR121-S50 RS-422/RS-485 2-Port Serial Communication Module

Long-Distance Subsystem Integration for DCS Architectures

In large-scale continuous process facilities, such as petrochemical plants, power stations, and water treatment utilities, field smart instruments and subsystem controllers are frequently located hundreds of meters away from main control rooms. The Yokogawa ALR121-S50 RS-422/RS-485 Serial Communication Module serves as a specialized gateway within Yokogawa CENTUM VP Field Control Stations (FCS) and remote I/O node units. By providing differential serial signal transmission over extended distances, the module enables seamless multi-drop networking with programmable logic controllers, YS series instruments, and field analyzers without signal loss.

Dual RS-422/RS-485 Ports and Extensive Protocol Compatibility

The ALR121-S50 module is equipped with two independent serial communication channels utilizing standard D-sub 9-pin female connectors. Operating on half-duplex start-stop synchronization, each port supports configurable transmission speeds of 1200, 2400, 4800, 9600, 19200, and 38400 bps over segment distances up to 1200 meters.

According to official specification GS 33K50G10-50E, the ALR121-S50 offers exceptional protocol versatility. In addition to standard Modbus (RTU/ASCII), FA-M3, MELSEC-A, and SLC500 protocols, it natively supports Yokogawa YS Communication (both direct connection and via SCIU interface units). This allows system engineers to map up to 128 communication definitions per module, integrating field subsystem data directly into CENTUM VP regulatory and sequence control function blocks.

Dual-Redundancy and Rugged Industrial Design

Engineered to maintain continuous 24/7 process uptime, the ALR121-S50 module supports dual-redundant communication configurations when two identical modules are paired in adjacent even and odd slots of a node unit. Front-panel status indicators provide real-time diagnostic visibility for module health and individual port transmission activity. With a compact physical footprint, a net weight of approximately 0.3 kg, and a low current consumption of 0.5 A, the module integrates smoothly into standard Field Control Units (including AFV30, AFV40, AFV10, AFF50) and ESB bus node racks (ANB10, ANB11, ANR10 series).

Applications

• Distributed Control Systems (DCS): Multi-drop serial network expansion for Yokogawa CENTUM VP process control stations.

• Oil & Gas Processing: Long-distance serial data acquisition from tank farm gauging systems, flow skids, and chromatographs.

• Chemical & Petrochemical Operations: Subsystem integration with packaged PLC skids, weighing controllers, and YS100/YS1000 instruments.

• Power Generation Facilities: Remote monitoring of turbine auxiliary control skids, electrical protection relays, and excitation panels.

• Water & Wastewater Utilities: Centralized telemetry communication with remote pump stations and analytical transmitter panels.

Technical Specifications

• Manufacturer: Yokogawa

• Product Model: ALR121-S50

• Product Type: Serial Communication Module (RS-422 / RS-485)

• Interface Standard: EIA RS-422 / RS-485 compliant

• Number of Ports: 2 ports (D-sub 9-pin female x 2)

• Communication Function: Half-duplex, start-stop synchronization

• Transmission Speed: 1200 / 2400 / 4800 / 9600 / 19200 / 38400 bps

• Transmission Distance: Maximum 1200 meters

• Connection Topology: Point-to-point, Multi-drop

• Supported Protocols: YS Communication, Modbus (RTU/ASCII), FA-M3, MELSEC-A, SLC500, PLC-S

• Dual-Redundancy: Supported (paired in adjacent even/odd slots)

• Current Consumption: 0.5 A

• Module Net Weight: 0.3 kg

• Compatible Control Units: AFV30, AFV40, AFV10, AFF50, ANB10, ANB11, ANR10 series

FAQ

Q1: What is the primary difference between Yokogawa ALR111 and ALR121 modules? A: The ALR111 utilizes an RS-232C interface for short-range communication (up to 15 m), whereas the ALR121-S50 provides RS-422/RS-485 interfaces for long-distance multi-drop communication up to 1200 meters.

Q2: Does the ALR121-S50 support Yokogawa YS Series controller communication? A: Yes. According to Yokogawa specification sheet GS 33K50G10-50E, the ALR121 exclusively supports YS Communication (both direct connection and via SCIU units).

Q3: Can the ALR121-S50 module be configured for dual-redundant operation? A: Yes. Dual-redundant communication is supported by installing two identical ALR121 modules in adjacent even and odd-numbered slots on the same node unit.

Q4: How can I confirm pricing and availability for this model? A: Simply submit your required part number and quantity through our website inquiry form to receive a prompt quotation.

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