Mitsubishi MELSEC-SD Series Modules SD2DYE-A / SD-2DYE-05

Technical Dossier

Product Details And Specifications

Mitsubishi Electric MELSEC-SD Series Technical Notes

The Mitsubishi Electric MELSEC-SD series represents a compact, high-density programmable logic controller platform deployed across global heavy industry sectors including petrochemical refineries, nuclear power auxiliary systems, steel processing lines, and continuous chemical manufacturing. The SD series occupies the mid-tier of Mitsubishi's MELSEC architecture, positioned between the entry-level FX family and the high-availability Q/iQ-R platforms. Its modular backplane design, deterministic scan cycle performance, and broad I/O density made it a standard specification in plant-floor automation projects throughout the 1990s and early 2000s. Installed base remains significant across Asia-Pacific, the Middle East, and Eastern Europe, where long-lifecycle plant assets continue to operate on original control hardware.

The Evolution of MELSEC-SD Architecture

The MELSEC-SD series was introduced as part of Mitsubishi Electric's second-generation modular PLC strategy, succeeding the MELSEC-A series and running in parallel with the MELSEC-AnS compact line. The SD platform standardized on a 5V DC backplane bus with a proprietary high-speed serial link (MELSECNET/MINI-S3) for distributed I/O expansion. Early revisions used mask ROM-based CPU firmware, limiting field upgradability; later revisions introduced EEPROM-based parameter storage and battery-backed SRAM for program retention.

Compatibility constraints are a primary maintenance concern for SD-series installations. The SD CPU modules are not pin-compatible with MELSEC-Q or iQ-R base units. I/O modules from the AnS series share physical form factor but differ in bus signaling voltage tolerances, requiring verification before cross-substitution. Communication adapter modules (e.g., SD-A1SJ71UC24-R2) use RS-232C/RS-422 interfaces that predate modern Ethernet-based SCADA integration, necessitating protocol converters in retrofit projects. As of 2026, the MELSEC-SD series is classified as End-of-Life (EOL) by Mitsubishi Electric, with no new production. Spare parts availability depends entirely on secondary market inventory and authorized refurbishment channels.

MELSEC-SD Full Catalog & Functionalities (SKU List)

CPU / Controller Modules

• SD2DYE-A / SD-2DYE-05: Transistor output CPU module, 24VDC sink type, 32-point integrated I/O, EEPROM program storage, battery-backed SRAM, RS-422 programming port.
• SD1: Base CPU module, 20-point I/O, relay output, single-slot base unit, entry-level SD platform controller.
• SD2: Enhanced CPU, 32-point I/O, supports up to 8 extension modules, 8K step program capacity.
• SD2-CPU: Standalone CPU card for SD2 base, no integrated I/O, designed for high I/O count configurations via expansion.
• SD3: High-capacity CPU, 64-point I/O, 16K step program memory, supports MELSECNET/MINI-S3 master function.

Digital Input (DI) Modules

• SD-X8: 8-point DC input module, 24VDC, sink/source compatible, LED status per channel.
• SD-X16: 16-point DC input module, 24VDC, high-density terminal block, 4ms input filter.
• SD-X32: 32-point DC input module, 24VDC, dual 16-point connector, compact footprint.
• SD-XA8: 8-point AC input module, 100-240VAC, optocoupler isolated, surge protected.

Digital Output (DO) Modules

• SD-Y8R: 8-point relay output module, 2A per point, 250VAC/30VDC rated, independent commons.
• SD-Y16T: 16-point transistor output, 0.5A per point, 24VDC sink type, short-circuit protected.
• SD-Y32T: 32-point transistor output, high-density, dual connector, 0.1A per point.

Analog I/O (AI/AO) Modules

• SD-AD4: 4-channel analog input, 12-bit resolution, 0–10VDC / 4–20mA selectable per channel, conversion time 2.5ms/ch.
• SD-DA2: 2-channel analog output, 12-bit resolution, 0–10VDC / 4–20mA, simultaneous output update.
• SD-AD8: 8-channel analog input, 12-bit, high-density process signal acquisition module.

Communication & Network Modules

• SD-A1SJ71UC24-R2: RS-232C/RS-422 serial communication module, supports MELSEC communication protocol and Modbus RTU.
• SD-NET/MINI: MELSECNET/MINI-S3 master module, supports up to 64 remote I/O stations, coaxial or twisted-pair media.

Power Supply Modules

• SD-PA3: 24VDC input power supply module, 3A output, built-in overcurrent and overvoltage protection, DIN rail mount.
• SD-PA6: 24VDC input, 6A output, for high I/O density configurations with multiple expansion modules.

Quality Control for the MELSEC-SD Range

MELSEC-SD modules present specific test challenges due to their proprietary backplane bus protocol and battery-dependent program retention. DriveKNMS applies the following verification procedures to all SD-series units prior to shipment:

• Backplane bus continuity test: Each module is seated in a reference SD base unit and polled via GX Developer or GX Works2 to confirm bus address recognition and data integrity.
• I/O point-level verification: All digital input and output channels are individually exercised using a calibrated signal generator and load bank. Analog modules are verified against NIST-traceable reference instruments at 0%, 25%, 50%, 75%, and 100% of rated range.
• Battery and SRAM retention test: CPU modules with battery-backed SRAM are loaded with a test program, powered down for a minimum of 4 hours, and re-powered to confirm program retention without corruption.
• Communication port test: RS-232C and RS-422 ports are loopback-tested at 9600, 19200, and 38400 baud to confirm UART integrity.
• Thermal cycling: Modules destined for high-ambient environments are subjected to a 0°C to 55°C thermal cycle prior to final inspection.
• Visual and mechanical inspection: Connector pins, backplane edge connectors, and PCB surfaces are inspected under magnification for corrosion, cold solder joints, and mechanical damage.