YOKOGAWA ALR121-S00

Technical Specifications Communication Ports: 2 independent RS-422 / RS-485 ports (4-wire) Physical Layer: RS-422 (full-duplex) / RS-485 (half-duplex), selectable Protocol: Modbus RTU (master or slave), subsystem communication, general-purpose serial Transmission Rate: 1200 / 2400 / 4800 / 9600 / 19200 / 38400 bps Data Bits: 8 Stop Bits: 1 or 2 Parity: None, Even, Odd Synchronization: Asynchronous start-stop Connection: Point-to-point or multi-drop (up to 32 nodes per port without repeater) Transmission Distance: Up to 1200 m (shielded twisted pair, low capacitance) Isolation: Port-to-port and port-to-system, 500 V AC Power Supply: 24 V DC from rack backplane Power Consumption: Approximately 3 W Operating Temperature: 0 °C to 55 °C Storage Temperature: -40 °C to +70 °C Humidity: 5 % to 95 % RH, non-condensing EMC: IEC 61000-6-2 / IEC 61000-6-4 Mounting: Plug-in card for SSC50D / SSC60D / SSC10D safety control unit or SNB10D node unit

Functional Features Dual independent serial ports with separate configuration Modbus RTU master for polling field instruments and analyzers Modbus RTU slave for data exchange with external DCS or SCADA Subsystem communication function for reading/writing PLC data Communication status and error counters accessible to controller Watchdog timeout and link-failure detection per port Hot-swap capability in redundant configurations

Application Scenarios Integration of Modbus analyzers (gas chromatographs, pH/conductivity transmitters) into SIS Data exchange between ProSafe-RS and third-party PLCs or RTUs Connection of intelligent motor control centers and VFDs via Modbus RTU Remote terminal unit (RTU) interfaces in pipeline and water treatment SCADA

Material Composition Housing: Steel card frame with aluminum front panel PCB: FR-4 with conformal coating Transceivers: Isolated RS-422/485 transceivers with ESD protection Connectors: Card-edge backplane connector + 10-pin terminal block Terminal Block: Pluggable screw-type, nickel-plated copper

Structural Features Single-width plug-in card for ProSafe-RS rack Front panel with two port status LEDs (TX/RX), module health LED, and captive retaining screw Rear card-edge connector for backplane Terminal block with RDA/RDB/SDA/SDB/SG signals per port Keying mechanism prevents wrong-slot insertion

Working Principle The module’s embedded communication controller serializes data from the controller into Modbus RTU frames, transmits them over the RS-422/485 physical layer, receives responses, validates CRC, and maps register data into controller memory. Each port operates independently, and the module maintains isolation so communication faults cannot propagate into safety logic.

Installation Requirements Install in any available communication slot of ProSafe-RS rack Use shielded twisted-pair cable (Belden 3105A or equivalent), 120 Ω characteristic impedance Install 120 Ω termination resistors at first and last nodes only Ground cable shield at one end (typically the module side) Set node addresses and baud rate to match all connected devices before power-up

Usage Precautions Do not mix RS-422 and RS-485 devices on the same port Do not exceed 32 nodes per port without active repeaters Verify Modbus register map and byte order with third-party device manual Configure communication timeout to match slowest device on the bus Isolate communication port from safety loops; do not use this module for SIL-rated I/O Replace module only with identical revision to preserve system certification