Allen-Bradley 1771-A1B 4-Slot IO Chassis Base

The Allen-Bradley 1771-A1B four-slot universal I/O chassis base is the back-panel-mounted foundation for 1771 I/O modules in PLC-5 era automation, providing a compact four-slot backplane to house digital and analog I/O modules in a single enclosure. It measures 298 x 70 x 187 mm (11.75 x 2.75 x 7.375 in) and weighs about 1.4 kg (3.0 lb), designed for secure attachment in panel or cabinet installations. The chassis accepts four 1771 I/O modules, forming a modular expansion backplane that supports the 1771 Universal I/O family and complements PLC-5 control configurations with remote or centralized I/O points. As a member of the 1771 Universal I/O ecosystem, it enables compatibility with a wide range of 1771 modules and backplane architectures designed for data exchange within 1771 I/O systems. This base is typically used in older installations or retrofits where PLC-5 systems require additional plug-in I/O capacity without replacing the controller.