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Yokogawa ALR121-S01 Serial Communication Module

Configured for subsystem data exchange in CENTUM CS 3000 and CENTUM VP platforms, the Yokogawa ALR121-S01 (base model ALR121) provides direct electrical interfacing between the DCS and external serial devices using RS-422/RS-485 physical layers. The module executes deterministic half-duplex transmission without protocol translation overhead.

Hardware Specifications

Parameter	Specification
Brand	Yokogawa
Origin	Japan
Weight	0.34 kg
Dimensions	Not specified in source data
Operating Temp	Standard industrial range (conformal coated)
Power Consumption	0.5 A @ backplane supply
Interface	RS-422 / RS-485
Number of Ports	2 (dual-port, 2-wire/4-wire selectable)
Transmission Speed	1200, 2400, 4800, 9600, 19200, 38400 bps
Max Distance	15 m (RS-422), 1200 m (RS-485)
Supported Protocols	Modbus RTU / ASCII, custom serial protocols

Channel-to-Channel Isolation and CJ Compensation

The ALR121-S01 employs channel-to-channel isolation to prevent ground loop formation across serial links in multi-node configurations. Electrical separation is maintained between each port and the backplane control bus. In installations involving analog subsystems sharing the same rack, cold junction compensation is applied at the connected I/O level to correct thermocouple reference errors, ensuring stable temperature-referenced data transmission through the serial gateway.

Frequently Asked Questions

Q: Does the ALR121-S01 support hot-swapping?

A: Hot-swap replacement is supported only when installed in a redundant pair; single-module operation requires system shutdown before removal.

Q: What is the lag time after data transmission?

A: The module introduces a fixed 1 ms lag after completing each transmission frame.

Q: Can RS-422 and RS-485 be used simultaneously?

A: No. Each port must be configured identically; mixed physical layer operation on a single module is not supported.

Field Installation Guidelines

Install the ALR121-S01 in designated Yokogawa mounting bases with verified backplane engagement. Use shielded twisted-pair cable for all serial runs; terminate shields at the DCS cabinet earth busbar only. For RS-485 multipoint networks, maintain consistent biasing resistors across all nodes to prevent signal reflection. Verify screw terminal torque to 0.5 N·m during commissioning to avoid intermittent contact on clamp terminals. Ensure conformal-coated surfaces remain free from solvent exposure during handling.

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