Configured for serial subsystem data exchange in CENTUM and ProSafe-RS control platforms, the YOKOGAWA ALR121 (ALR121 Communication Module) provides direct physical/electrical execution. This hardware component serves as a dual-port serial gateway utilized to execute Modbus (RTU/ASCII) and general subsystem communication across distributed control system platforms.

Hardware Specifications

PLC/DCS Integration and Communication Characteristics

The ALR121 module is engineered to provide deterministic serial data bridging between the field control station (FCS) or safety control station (SCS) and external subsystems. It supports both point-to-point (RS-422) and multipoint (RS-485) configurations, allowing for integration with diverse industrial devices, including PLCs and third-party instrumentation. The module manages frame timing with a fixed 1 ms lag after transmission to ensure bus stability, and it supports dual-redundant communication configurations when paired with an adjacent module in the I/O chassis to maintain high availability in critical process loops.

Frequently Asked Questions

Q: Can the two ports on the ALR121 module be configured with different communication functions?

A: No. The two serial ports on a single ALR121 module must be configured with identical communication functions and parameters.

Q: Is this module capable of performing hot-swaps during system operation?

A: Yes, hot-swap replacement is supported when the module is installed in a redundant configuration; however, standard safety protocols should be followed to isolate the communication link before physical removal.

Field Installation Guidelines

• Ensure the control station is powered down before seating the ALR121 into the base plate to prevent electrical short-circuits on the backplane bus.
• Use shielded, twisted-pair cabling for all serial runs; terminate cable shields only at the specified system grounding points to avoid ground loops.
• For RS-485 multipoint networks, ensure that 120 ohm termination resistors are installed at both physical ends of the transmission line to suppress signal reflections.
• Verify that the transmission distance does not exceed 1200 m for RS-485 segments to maintain signal integrity and meet data throughput specifications.
• Confirm that the module locking mechanism is fully engaged after installation to ensure low-resistance contact with the backplane connectors.