Product Overview

The Allen-Bradley 1746-BAS​ is the fundamental hardware chassis, or “basic module,” that forms the physical and electrical backbone of the Allen-Bradley SLC 500 modular programmable controller system. This module, commonly referenced as the 1746-BAS-A​ denoting a specific hardware revision, is not an intelligent controller or I/O module itself, but rather the passive, metal enclosure and printed circuit board backplane that houses and interconnects all other active components. Its primary function is to provide the mechanical mounting structure, the internal data/address bus, and the power distribution pathways for a central processing unit (CPU) module, I/O modules, and special function modules. A standard Allen-Bradley 1746-BAS​ unit comes in various slot configurations, with the 4-slot version being one of the most common, providing a compact and cost-effective platform for small to medium-sized control applications.The value of the 1746-BAS-A​ lies in its role as the enabling infrastructure for a highly flexible and scalable control system. It establishes a standardized, modular architecture where users can select and mix the exact CPU performance and I/O point mix (digital, analog, special communication) required for their application. The chassis manages the critical communication between the processor in slot 0 and the I/O modules in subsequent slots via its internal backplane, ensuring reliable, high-speed data exchange. It also distributes the 5V DC logic power and 24V DC field sensor power (if provided by a power supply) to all installed modules. The robust metal construction of the Allen-Bradley 1746-BAS​ provides EMI/RFI shielding, protects sensitive electronics, and allows for secure DIN-rail or panel mounting in industrial environments. As the foundational “rack” of the SLC 500 system, the proper selection and installation of the 1746-BAS​ basic module is the first and most critical step in building a reliable, maintainable, and expandable PLC-based control solution.

Technical Specifications