Yokogawa ALR121-S51 RS-422 RS-485 Communication Card

Product Overview

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Industrial automation environments demand robust data exchange across distributed control nodes. Engineers deploy the ALR121-S51 serial communication module to bridge legacy controllers with modern serial field devices. This dual-port hardware card manages half-duplex communication protocols smoothly across extended plant floors. Operators rely on its deterministic start-stop synchronization to prevent packet collision in harsh manufacturing environments. Global PLC Spare HUB's Insight notes that proper serial termination prevents high-frequency signal reflections on long cable runs.

Technical Specifications

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• Brand: Yokogawa
• Model Number: ALR121-S51
• Series: ALR121 Serial Communication Module
• Interface Type: RS-422 / RS-485 (4-wire system)
• Connection Topology: Point-to-point for RS-422, Multipoint for RS-485
• Transmission Speed: 1200, 2400, 4800, 9600, 19200, or 38400 bps
• Communication Function: Half-duplex
• Synchronization Method: Start-stop synchronization
• Transmission Code: ASCII or Binary
• Character Length: 7 or 8 bits
• Stop Bit Length: 1 or 2 bits
• Parity Check Mode: None, Even, or Odd
• Lag Time After Data Transmission: 1 ms wait time before receiving data
• Maximum Transmission Distance: 1200 meters total extended length
• Signal Frequency Response: Baseband serial pulse train up to 38.4 kbps
• Linearity and Resolution: Digital bit-stream translation with zero analog conversion error
• Current Consumption: 0.5 A
• Module Weight: 0.34 kg

Installation Guide

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• Mount the ALR121-S51 directly onto compatible base plates like ANB10☐, ANB11☐, ANR10☐, AFF50☐, AFV10☐, AFV30☐, or AFV40☐.
• Verify rack power isolation before inserting the circuit board into the designated slot.
• Secure field wires using 3-pair shielded cables such as AKB161 or AKB162.
• Fasten stripped wire ends securely to the terminal block using M4 screws across the 5-pole dual rows.
• Ground the cable shield properly at one end to minimize electromagnetic induction from nearby power inverters.

Compatibility and Environmental Tolerance

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• System Compatibility: Integrates seamlessly into Centum CS 3000 and Centum VP distributed control architectures.
• Environmental Tolerance: Built with standard G3 ISA conformal coating to withstand corrosive gases in chemical plants.
• Operating Temperature Range: Designed for standard industrial control room thresholds.
• Interference Resistance: Built-in optical isolation protects internal system buses from external voltage surges.

Maintenance, Diagnostics, and Operational Experience

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Technicians monitor onboard LED indicators to verify active transmit and receive data traffic instantly. Field engineers note that intermittent CRC framing errors usually stem from missing terminating resistors on long RS-485 multi-drop lines. Clean terminal blocks periodically to prevent oxidation dropouts in high-humidity facilities.

Certifications, Shipping, and Warranty

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• Certification Standards: Complies with ISA Standard G3 harsh environment specifications.
• Shipping Logistics: Dispatched within 24 to 48 hours using reliable carriers including FedEx, UPS, and DHL.
• Warranty Terms: Backed by a comprehensive 12-month operational warranty.
• Package Contents: One ALR121-S51 communication module and factory compliance documentation.

Typical Application Scenarios

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• Connecting multi-vendor variable frequency drives to a central CENTUM controller.
• Integrating legacy barcode scanners and weighing scales into automated batching systems.
• Managing SCADA telemetry data across remote terminal units in water treatment plants.

Frequently Asked Questions

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Can I connect an RS-422 device directly to an RS-485 multi-drop network using this card?

No, the physical layer wiring topology differs between point-to-point RS-422 and multipoint RS-485 architectures.

What causes frame framing errors on the ALR121-S51 serial port?

Baud rate mismatches or electromagnetic interference on unshielded cable runs typically trigger data framing errors.

How do I select the correct transmission speed for my field instrument?

Match the baud rate setting of the connected peripheral device exactly within the system engineering software configuration.

Selection Guide

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Verify your controller rack model before ordering to ensure physical slot alignment matches the ALR121-S51 specification. Choose standard G3 coated variants when deploying hardware in pulp mills, refineries, or coastal wastewater facilities. Match your cable shielding requirements to plant layout distances to maintain signal integrity.