Mitsubishi MELSEC-AnS Series Modules: A1SJ71QC24-R2

Technical Dossier

Product Details And Specifications

Mitsubishi MELSEC-AnS Series: Comprehensive Module Range and Technical Overview

The Mitsubishi Electric MELSEC-AnS (A1S) series is a compact, rack-based programmable logic controller platform that has achieved widespread deployment across global heavy industry sectors including petrochemical refineries, nuclear auxiliary systems, steel rolling mills, and continuous-process chemical plants. Introduced as a space-optimized derivative of the full-size MELSEC-A series, the AnS platform shares the same instruction set and I/O bus architecture while occupying a significantly reduced panel footprint. Its modular backplane design — supporting 4-slot (A1S38B), 8-slot (A1S68B), and extension configurations — made it the default choice for distributed control nodes and remote I/O stations throughout the 1990s and into the 2000s. Installed base estimates across Asia-Pacific and EMEA industrial facilities remain in the hundreds of thousands of nodes, making long-term spare parts availability a critical operational concern for plant maintenance engineers.

The Evolution of MELSEC-AnS Architecture

The MELSEC-AnS architecture traces its lineage to the original MELSEC-A series (A2, A3) launched in the early 1980s. Mitsubishi Electric introduced the AnS compact form factor to address panel space constraints in the mid-1980s, retaining full binary/BCD instruction compatibility with the parent A-series. The CPU bus operates at a fixed cycle, with the A1SCPU and A1SHCPU representing the baseline and high-performance CPU variants respectively. The A1SJHCPU introduced an expanded program memory capacity (30K steps) and faster scan times, targeting applications previously requiring the larger A2SHCPU.

Communications architecture evolved through three distinct generations: (1) early RS-232C point-to-point via the A1SJ71C24-R2 and A1SJ71C24-R4; (2) multi-drop RS-422/485 networks via the A1SJ71QC24-R2 and A1SJ71QC24-R4; and (3) open-network integration via MELSECNET/10 (A1SJ71LP21, A1SJ71BR11) and CC-Link (A1SJ61BT11). The Q-series (MELSEC-Q) platform, introduced in 1999, is the designated modern successor. Migration paths from AnS to Q-series are supported via the A1S-to-Q conversion base units, though the majority of installed AnS systems remain in service under lifecycle extension programs due to the cost and complexity of full migration in continuous-process environments.

MELSEC-AnS Full Catalog & Functionalities (SKU List)

CPU Modules

• A1SCPU: Standard CPU, 8K step program memory, basic instruction set, AnS backplane.
• A1SHCPU: High-performance CPU, 14K steps, faster scan, extended I/O addressing.
• A1SJHCPU: Compact high-performance CPU, 30K steps, built-in RS-232C port.
• A1SCPUC24-R2: CPU with integrated RS-232C/RS-422 dual-port communications.

Communications Modules

• A1SJ71QC24-R2: RS-232C + RS-422 dual-channel serial communications module, MELSEC protocol & non-procedure mode, 19.2 kbps max. (Current page SKU)
• A1SJ71QC24-R4: Dual RS-422/RS-485 channel serial module, multi-drop network support, 19.2 kbps.
• A1SJ71C24-R2: Earlier-generation RS-232C/RS-422 serial module, predecessor to QC24 series.
• A1SJ71C24-R4: Earlier-generation dual RS-422 serial module.
• A1SJ71LP21: MELSECNET/10 optical loop master/local station module.
• A1SJ71BR11: MELSECNET/10 coaxial bus master/local station module.
• A1SJ61BT11: CC-Link master/local station module, up to 64 stations.

Digital I/O Modules

• A1SX40: 16-point DC input module, 24 VDC sink/source, isolated commons.
• A1SX80: 32-point DC input module, 24 VDC, high-density terminal block.
• A1SY10: 16-point relay output module, 2A per point, independent commons.
• A1SY40P: 16-point transistor output module, 24 VDC source type, 0.5A per point.
• A1SY80: 32-point transistor output module, 24 VDC sink type.

Analog & Specialty Modules

• A1S62DA: 2-channel analog voltage/current output module, 12-bit resolution.
• A1S64AD: 4-channel analog input module, 12-bit resolution, ±10V / 4–20mA.
• A1SD75P1-S3: 1-axis positioning module, pulse train output, 200 kpps max.

Power Supply Modules

• A1S61P: 100–240 VAC input power supply, 6A DC output for AnS backplane.
• A1S62P: 100–240 VAC input power supply, 8A DC output, extended capacity.

Sourcing Hard-to-Find & Obsolete MELSEC-AnS Parts

Mitsubishi Electric officially discontinued active production of the MELSEC-AnS series. Repair parts, replacement modules, and new-old-stock (NOS) units are no longer available through standard distribution channels. DriveKNMS maintains a dedicated inventory of AnS-series modules — including the A1SJ71QC24-R2 and related communications, I/O, CPU, and power supply modules — sourced from decommissioned plant equipment, certified refurbishers, and bonded warehouse stock.

For facilities operating AnS-based DCS or SCADA nodes where full migration to MELSEC-Q or iQ-R is not feasible within the current maintenance cycle, DriveKNMS provides: verified replacement units with full functional test documentation, cross-reference support for identifying compatible Q-series migration alternatives, and multi-year supply agreements for critical spare parts programs. Procurement teams managing plant turnaround schedules can submit consolidated parts lists for batch quotation.

Quality Control for the MELSEC-AnS Range

All MELSEC-AnS modules processed by DriveKNMS undergo a structured inspection and functional verification protocol specific to the AnS backplane bus architecture. For communications modules such as the A1SJ71QC24-R2, the test procedure includes: physical inspection of the RS-232C (DB9) and RS-422 (terminal block) connectors for pin integrity and corrosion; backplane edge connector cleaning and continuity verification across all bus lines; firmware version identification and comparison against Mitsubishi Electric's published version matrix; live functional test using a reference A1SHCPU with MELSEC protocol loopback on both CH1 and CH2; and isolation resistance measurement between signal commons and chassis ground. CPU modules are tested for program memory integrity, scan cycle stability under simulated I/O load, and battery-backed RAM retention. All units are shipped with a test report and 90-day operational warranty.