Technical Description
The ALR121 is a dual-port serial communication module designed for Yokogawa CENTUM CS 3000 and Centum VP distributed control systems. It enables data exchange between the control system and external serial devices, such as analyzers, PLCs, and variable frequency drives (VFDs).
The module supports both RS-422 (point-to-point) and RS-485 (multipoint) interfaces, offering flexible connectivity for various industrial bus topologies. By providing start-stop synchronization and supporting ASCII and binary data formats, the ALR121 ensures reliable and deterministic communication in complex process environments.
Technical Specifications
| Parameter | Specification |
|---|---|
| Model Designation | ALR121 |
| Communication Ports | 2 independent serial ports |
| Physical Interface | RS-422 (Point-to-Point) / RS-485 (Multipoint) |
| Synchronization | Start-stop |
| Communication Mode | Half-duplex |
| Transmission Baud Rates | 1200, 2400, 4800, 9600, 19200, 38400 bps |
| Data Encoding | ASCII or Binary protocols |
| Power Consumption | 0.5 A @ 5 V DC (internal system bus) |
| Physical Dimensions | 32.8 mm × 142.9 mm × 130 mm |
| Unit Weight | 0.3 kg |
Operational Application
The ALR121 is used to integrate third-party smart field devices into CENTUM networks. Common applications include:
-
Pipeline monitoring systems
-
Chemical process instrumentation
-
Plant-wide telemetry and data acquisition
Its support for both RS-422 and RS-485 allows adaptation to existing plant wiring, minimizing the need for additional communication gateways when upgrading or expanding legacy systems.
Frequently Asked Questions
Can the ALR121 support full-duplex communication?
No. The module operates in half-duplex mode, which is standard for most RS-485 multipoint polling applications.
Does this module support protocol conversion?
The ALR121 serves as a serial interface only. Protocol mapping (e.g., Modbus RTU to system registers) must be configured in the CENTUM engineering station software to ensure proper data interpretation.
What is the maximum cable length for RS-485?
The maximum distance follows RS-485 physical layer specifications, typically up to 1200 meters, depending on cable type and baud rate.
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