Allen-Bradley 1771-IAD High Density Input Module

The Allen-Bradley 1771-IAD High Density Input Module is a 16-channel digital input card for the 1771 I/O family, designed to bring 120V AC/DC sensing into PLC-5 era backplanes. Each of its 16 inputs accepts 120V AC or 120V DC signals within a broad supply window, typically 79–138 V, and the module provides electrical isolation between input circuits and the 1771 backplane to help suppress transients and protect the controller. As a Series D device, the 1771-IAD is compatible with 1771 I/O chassis B, enabling high-density input wiring in compact racks. It interfaces with the 1771 backplane using standard 1/2-slot addressing schemes and is intended for discrete, non-analog sensing of field devices such as pushbuttons, limit switches, relays, and other 120V sensors. The 16 discrete inputs collectively enable more inputs per module than older 8-channel options, contributing to more efficient cabinet layouts and easier wiring in automation panels. Typical applications include machine control, process monitoring, safety circuits, and general-purpose digital input acquisition in PLC-5 or related Allen-Bradley control systems. This module is identified by its catalog/part designation 1771-IAD and relates to stock numbers such as 96220674, enabling integration into existing Allen-Bradley 1771 backplanes.