Yokogawa ALR121-S51 S1 Communication Modules

Name: Yokogawa ALR121-S51 S1 Communication Modules
Brand: Yokogawa

Model: ALR121-S51 S1

Brand Yokogawa

Series ALR121-S51 S1

Model ALR121-S51 S1

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Product Details And Specifications

Yokogawa ALR121 Series Technical Notes

The Evolution of ALR121 Architecture

The ALR121 series was introduced as part of Yokogawa's CENTUM CS 3000 platform, which succeeded the earlier CENTUM CS and CENTUM-XL generations. The architectural shift from CENTUM-XL to CS 3000 introduced a Windows-based HIS (Human Interface Station) and a standardized V-net/IP communication backbone, replacing proprietary bus structures. Within this evolution, the ALR121 modules were designed to bridge legacy RS-232C and RS-422/485 serial protocols with the CS 3000 control bus, ensuring backward compatibility with existing field instrumentation during plant upgrades. Early ALR121 revisions (S1 suffix) established the baseline hardware specification. Subsequent suffix variants (S2, S3) introduced firmware enhancements and improved EMI tolerance for high-noise industrial environments. As CENTUM CS 3000 itself has entered its extended support phase — with Yokogawa's CENTUM VP now positioned as the current-generation successor — ALR121 modules are no longer in active production. Plants operating CS 3000 systems must source ALR121 spares from certified secondary market suppliers to maintain system integrity without full DCS migration.

ALR121 Full Catalog & Functionalities (SKU List)

The following SKUs represent verified components within the Yokogawa ALR121 and associated CENTUM CS 3000 communication module range. Each entry reflects a distinct hardware configuration or suffix revision:

ALR121-S51 S1: Serial communication interface module, RS-232C/RS-422 compatible, CENTUM CS 3000 bus
ALR121-S51 S2: Revised serial comm module with enhanced EMI shielding and firmware update
ALR121-S51 S3: Third-generation serial interface, extended temperature tolerance variant
ALR111-S51 S1: Analog input communication relay module, 4-channel, CS 3000 compatible
ALR111-S51 S2: Updated analog relay module with improved signal isolation
ALR131-S51 S1: Digital input communication interface, 16-point, CS 3000 V-net bus
ALR131-S51 S2: Enhanced DI communication module, surge protection revision
ALR141-S51 S1: Digital output communication relay, 16-point, CS 3000 field bus interface
ALR141-S51 S2: DO relay module, updated contact rating specification
ALR161-S51 S1: Pulse input communication module, frequency measurement, CS 3000
ALR171-S51 S1: HART communication interface module for CS 3000 field device integration
ALR181-S51 S1: Foundation Fieldbus H1 communication module, CS 3000 platform
ALR191-S51 S1: PROFIBUS DP communication interface module, CS 3000 compatible
ALR201-S51 S1: Modbus RTU/TCP communication gateway module, CS 3000
ALR211-S51 S1: DeviceNet communication interface module, CS 3000 I/O bus
ALR221-S51 S1: AS-Interface (AS-i) communication module, CS 3000 field network
ALR231-S51 S1: CC-Link communication interface module, CS 3000 compatible

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