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The ALR121-S51 S1 is an industrial-grade serial communication module designed for Yokogawa's high-performance field control stations to enhance data exchange and system integration capabilities. It is typically used in Centum VP or Centum CS 3000 distributed control systems and is a core component for achieving stable and efficient serial communication with various subsystems.
ISA Class G3 corrosion-resistant conformal coating
Features two physically isolated onboard serial ports per module
Supports dual-redundant configuration when installed in adjacent slots
Modbus communication is adopted as the subsystem communication function for ProSafe-RS that allows an SCS to act as a Modbus master to communicate with the subsystem as a Modbus slave.ALR121 supports ProSafe-SLS communication function which is to extend the Modbus communication function. The serial communication module communicates with subsystems at the specified intervals and stores the subsystem data in the communication modules’ I/O image. The subsystem communication function of SCS accesses the communication module asynchronously from them, and refers to or sets the I/O image. The application logic of SCS reads data from the communication I/O data areawhen the communication input FB is executed, and writes the calculation data to the communication I/O data area when the communication output FB is executed.ALR121 acquires ProSafe-SLS events and data by the ProSafe-SLS communication function, which enables SCS to use those events and data in the same way as general analog and digital I/O signals. ProSafe-SLS’s system time has to be synchronized with ProSafe-RS by digital input and output modules to match the event time stamp. A bleeder resistor has to be connected on the ProSafe-SLS side to match the I/O specification of ProSafe-SLS and ProSafe-RS
Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description.
Yokogawa ALR121-S51 S1 Serial Communication Module Manuals, Datasheets, Drivers, Link
Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description.
Oil & Gas Refining
Connects to field gas chromatographs and analyzer houses via Modbus to upload real-time crude oil composition data to the CENTUM DCS for distillation monitoring.
Liquefied Natural Gas
Communicates with multi-run flow computers to acquire accurate custody transfer and cryogenic gas storage tank level metrics asynchronously.
Thermal Power Plants
Interfaces with the balance-of-plant (BOP) programmable logic controllers (PLCs) governing coal handling and ash removal sub-loops to achieve centralized supervision.
Pharmaceutical
Retrieves batch formulation weight measurements from field industrial weigh scales, reading data seamlessly into the SCS application logic via communication FBs.
Nuclear Power
Deploys in dual-redundant configuration within FIO node units to reliably transmit peripheral radiation monitoring and cooling loop parameters.
To ensure optimal field operation of the ALR121-S51 S1 module, rigorous signal and parameter management is mandatory. Engineers must integrate a side-terminal bleeder resistor for ProSafe-SLS interfacing, while establishing a dual-redundant configuration across adjacent slots. Furthermore, field loop reliability relies heavily on strict signal impedance management—including secure terminal tightening, shield grounding, and line-terminators—alongside precise baud rate and polling interval calibration within System View to completely eliminate communication timeout alarms.
What is the ALR121-S51 S1 Serial Communication Module?
It is a 2-port RS-422/RS-485 serial communication module manufactured by Yokogawa.
Which automation systems are compatible with ALR121-S51 S1?
It is primarily compatible with Yokogawa's CENTUM CS 3000, CENTUM VP Distributed Control Systems (DCS), and ProSafe-RS Safety Instrumented Systems (SIS), acting as a field I/O (FIO) subsystem gateway.
How do you install and insert the ALR121-S51 S1 module?
It is plugged directly into a Yokogawa Field Control Unit (FCU, such as AFV30/AFV40) or an ESB/ER Bus Node Unit (such as ANB10/ANR10). It supports hot-swapping under a dual-redundant configuration.
What serial protocols does ALR121-S51 S1 natively support?
It natively supports industry-standard Modbus RTU/ASCII (as a Master or Slave) and Yokogawa's proprietary or user-defined custom subsystem communication protocols.
What is the physical connection interface of ALR121-S51 S1?
It features two isolated communication ports utilizing standard RS-422 or RS-485 interfaces (4-wire system) with terminal block connections for field wiring.
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