Allen-Bradley SLC 500 1746-A4 4-Slot Chassis

Technical Dossier

Product Details And Specifications

Allen-Bradley SLC 500 Series Technical Notes

The Allen-Bradley SLC 500 (Small Logic Controller 500) series, manufactured by Rockwell Automation, is one of the most widely deployed modular PLC platforms in global heavy industry. Installed across petrochemical refineries, nuclear auxiliary systems, pulp and paper mills, water treatment facilities, and automotive assembly lines, the SLC 500 platform established a benchmark for mid-range programmable logic control from its introduction in the late 1980s through its peak deployment era of the 1990s–2000s. The 1746-A4 is a 4-slot chassis within this series, providing the physical backplane and power distribution infrastructure for up to 4 I/O or specialty modules. Its compact form factor made it the preferred chassis for distributed control panel installations where rack space is constrained.

The Evolution of SLC 500 Architecture

The SLC 500 platform was introduced by Allen-Bradley (acquired by Rockwell Automation in 1985) as a successor to the SLC 100 and SLC 150 fixed-format controllers. The architecture is built around the 1746 backplane bus, a proprietary parallel communication bus that connects the processor module to I/O and specialty modules within the same chassis. Key architectural milestones include:

Generation 1 (1987–1993): Fixed and modular chassis introduced. Processors: SLC 5/01 (1747-L511, 1747-L514). Limited memory, no DH+ native support. Chassis: 1746-A4, 1746-A7, 1746-A10, 1746-A13.

Generation 2 (1993–1999): SLC 5/02, 5/03, 5/04 processors introduced. DH+ and RS-232 DF1 communication added. Expanded I/O density with 32-point digital modules. Enhanced analog resolution (12-bit).

Generation 3 (1999–2012): SLC 5/05 processor with native Ethernet/IP support. Integration with RSLogix 500 programming environment. Compatibility with DeviceNet via 1747-SDN scanner. This generation represents the platform's technological peak.

End-of-Life / Lifecycle Status: Rockwell Automation announced the SLC 500 series as end-of-life (EOL) with last-time-buy notices issued between 2012 and 2017. The recommended migration path is to the Allen-Bradley MicroLogix 1400 or CompactLogix 5370/5380 platforms. However, due to the massive installed base — estimated at several million units globally — demand for SLC 500 spare parts and chassis remains active in the industrial MRO (Maintenance, Repair & Operations) market. The 1746-A4 chassis, as a passive backplane component, has an extended service life and remains critical for panel-level replacements.

SLC 500 Full Catalog & Functionalities (SKU List)

Chassis (1746-A Series):

1746-A4: 4-slot modular chassis; backplane for up to 4 I/O modules; compact panel mount.

1746-A7: 7-slot modular chassis; standard mid-size rack for mixed I/O configurations.

1746-A10: 10-slot modular chassis; high-density I/O expansion rack.

1746-A13: 13-slot modular chassis; maximum capacity SLC 500 rack.

Processors (1747-L Series):

1747-L511: SLC 5/01 processor; 1K memory; DH-485 port; entry-level fixed control.

1747-L514: SLC 5/01 processor; 4K memory; DH-485; expanded program capacity.

1747-L524: SLC 5/02 processor; 4K memory; DH-485; improved scan time performance.

1747-L531: SLC 5/03 processor; 8K memory; RS-232 DF1 + DH-485 dual port.

1747-L541: SLC 5/04 processor; 16K memory; DH+ network port; high-speed comms.

1747-L551: SLC 5/05 processor; 64K memory; Ethernet/IP + DH-485; network-ready.

Digital Input Modules (DI):

1746-IB16: 16-point 24VDC sink digital input module; standard field device interface.

1746-IB32: 32-point 24VDC sink digital input; high-density panel wiring reduction.

1746-IA16: 16-point 120VAC digital input; legacy AC field device compatibility.

Digital Output Modules (DO):

1746-OB16: 16-point 24VDC source digital output; solid-state switching, 0.5A per point.

1746-OW16: 16-point relay output; isolated contacts; AC/DC mixed load switching.

Analog Modules (AI/AO):

1746-NI4: 4-channel analog input; 4–20mA / 0–10V; 12-bit resolution; process instrumentation.

1746-NO4I: 4-channel analog output; 4–20mA isolated; precision process control loops.

Communication & Specialty:

1747-SDN: DeviceNet scanner module; master node for DeviceNet field device networks.

1747-SCNR: Remote I/O scanner; links remote chassis to main SLC 500 rack via RIO cable.

Power Supplies (1746-P Series):

1746-P1: 2A @ 5VDC power supply; for 4- and 7-slot chassis; 120/240VAC input.

1746-P2: 5A @ 5VDC power supply; for 10- and 13-slot chassis; high-current backplane.

Quality Control for the SLC 500 Range

The SLC 500 backplane architecture presents specific testing challenges due to its parallel bus design and the interdependency between the processor module and I/O modules during initialization. DriveKNMS applies the following test procedures to all SLC 500 components prior to shipment:

Chassis (1746-A Series): Physical inspection of backplane connector pins (50-pin edge connectors); continuity test across all backplane bus lines; power rail isolation test (5VDC, 24VDC).

Processor Modules: Full power-on test with RSLogix 500 communication verification; memory integrity check; DH+/DH-485/Ethernet port functional test; firmware version documentation.

I/O Modules: Point-by-point functional test using dedicated SLC 500 test rack; input threshold verification; output load switching test at rated current; LED status indicator verification.

Analog Modules: Calibration verification against NIST-traceable reference instruments; linearity test across full input/output range; channel isolation test.