Product Overview

The Yokogawa ALR121-S51 S1 is a high-reliability Serial Communication Module designed for the CENTUM VP and CS 3000 Distributed Control Systems (DCS). This module serves as a critical bridge between the Yokogawa Field Control Station (FCS) and external subsystem devices, such as PLCs, motor control centers (MCC), and analytical instruments. By supporting RS-422 and RS-485 interfaces, the ALR121-S51 S1 enables seamless data integration across various industrial protocols.

A core feature of the ALR121-S51 S1 is its support for dual-redundancy. When two modules are installed in a paired configuration, the system maintains a "Hot Standby" state. In the event of a primary module failure or a detected communication error, the system executes a millisecond-level failover to the standby unit, ensuring uninterrupted process visibility and control.

Technical Specifications

• Manufacturer: Yokogawa

• Model Number: ALR121-S51 S1

• Module Type: Serial Communication Module

• Interface: RS-422 / RS-485 (2 ports)

• Transmission Speed: 300 bps to 115.2 kbps

• Connection Method: D-sub 9-pin (female)

• Max. Transmission Distance: 1200 meters (Total extended length)

• Redundancy: Supports Dual-Redundant configuration (hot-swappable)

• Current Consumption: Max. 0.5 A (at 5V DC)

• Operating Temperature: -20°C to +70°C

• Dimensions: 14 cm x 13 cm x 3.2 cm

• Weight: 0.3 kg

• Origin: Japan

Key Technical Characteristics

• Advanced Redundancy Management: Features synchronized data memory between active and standby modules. This ensures that the control station always has access to the most recent data set immediately following a failover transition.

• Multi-Protocol Support: Designed to handle complex communication tasks including Modbus RTU (Master/Slave) and other general-purpose serial communication through customized software drivers.

• Fault-Tolerant Architecture: Each of the two ports operates independently, providing versatile wiring options and preventing a single port failure from disabling the entire module's communication capability.

• Intelligent Self-Diagnostics: Integrated hardware watchdog timers and communication health monitoring allow the module to self-identify internal errors or line faults, triggering automatic recovery or system alerts.

• Industrial Hardening: Certified for use in harsh petrochemical and energy environments, with ISA G3 compliant protection against corrosive gases and a wide thermal operating envelope.

• Hot-Swap Capability: Modules can be replaced online without shutting down the Field Control Unit (when used in a redundant pair), minimizing downtime during maintenance or hardware upgrades.