Yokogawa ALR121 Modules – ALR121-S50 S1

Technical Dossier

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 launched in the late 1990s as a successor to the CENTUM-XL and CENTUM CS systems. The original ALR121 modules provided RS-232C serial communication capability for integration with analyzers, weighing systems, and barcode readers. Subsequent hardware revisions introduced RS-422/RS-485 multi-drop support, expanding the addressable device count per module and reducing wiring infrastructure costs in large-panel installations.

With the transition to CENTUM VP (introduced circa 2008), Yokogawa maintained backward hardware compatibility for the ALR121 form factor, allowing existing CS 3000 installations to migrate software environments without replacing communication hardware. The suffix designations (e.g., -S50, -S1) encode hardware revision levels and firmware compatibility bands. S50 denotes a specific hardware generation with defined firmware compatibility for CENTUM VP R5.x and R6.x environments. S1 indicates the first sub-revision of that hardware generation.

As CENTUM VP has itself matured into a stable/late-lifecycle platform, the ALR121 series is no longer in active production at Yokogawa. Replacement pathways include the ALR111 (for reduced-channel applications) and software-based OPC-UA gateway solutions for greenfield installations. However, the installed base remains extensive, and spare module procurement is the dominant support strategy for brownfield sites with 10–25 year remaining plant lifecycles.

ALR121 Full Catalog & Functionalities (SKU List)

The following SKUs represent the documented ALR121 series range across CENTUM CS 3000 and CENTUM VP platforms. Each module occupies a single slot in the Yokogawa node unit (NU) or field control unit (FCU) chassis.

ALR121-S50 S1: RS-232C/RS-422/485 serial communication module, CENTUM VP R5/R6 compatible, hardware rev S50.
ALR121-S50: Base hardware generation S50 serial communication module for CENTUM VP environments.
ALR121-S10: Earlier hardware revision serial comm module, CENTUM CS 3000 R3.x primary compatibility.
ALR121-S20: Mid-generation hardware revision, bridging CS 3000 R3.x and early VP firmware bands.
ALR121-S30: Hardware revision S30, extended temperature tolerance variant for harsh-environment cabinets.
ALR121-S40: Pre-S50 generation with updated ASIC for improved RS-485 multi-drop noise immunity.
ALR121-E: Export-market variant with modified firmware region lock for non-Japanese plant configurations.
ALR121-S50 S2: Second sub-revision of S50 hardware, minor PCB revision for improved EMC compliance.
ALR121-S50 S3: Third sub-revision, updated conformal coating specification for high-humidity environments.
ALR121-R: Redundant-pair communication module variant for safety-critical serial device integration.
ALR121-S10 S1: First sub-revision of S10 hardware generation, CS 3000 R3.02 and above.
ALR121-S20 S1: Sub-revision 1 of S20, corrected baud rate register behavior at 19200 bps.
ALR121-S30 S1: Sub-revision 1 of S30, updated watchdog timer firmware for long-idle-line recovery.
ALR121-S40 S1: Sub-revision 1 of S40, revised RS-422 line termination resistor network.
ALR121-S40 S2: Sub-revision 2 of S40, final production revision before S50 generation introduction.
ALR121-S50 S4: Latest documented sub-revision of S50, current procurement standard for VP R6.09 and above.

Quality Control for the ALR121 Range

ALR121 modules present specific test challenges due to their dual-protocol serial interface hardware and tight firmware-to-hardware revision binding. DriveKNMS applies the following test protocol to all ALR121 units prior to shipment:

Visual & Physical Inspection: PCB surface examination under 10× magnification for corrosion, cold solder joints, and capacitor bulge. Connector pin integrity check on the backplane edge connector (96-pin DIN 41612 format). Conformal coating continuity assessment.

Power-On Functional Test: Module inserted into a live CENTUM VP R6 test node. Firmware version readback via engineering console to confirm hardware-firmware revision match. LED status verification (RUN, ERR, COM indicators).

Communication Protocol Test: RS-232C loopback test at 9600, 19200, and 38400 bps. RS-485 multi-drop bus test with 4-device chain at 19200 bps. Parity, stop-bit, and framing error injection test to verify error-detection register behavior.

Burn-In: 24-hour continuous operation at 50°C ambient in climate chamber. Post burn-in re-test of all communication channels.