Allen-Bradley 1771-IG USNT Digital Input Module

The Allen-Bradley 1771-IG USNT Digital Input Module is a 16-point TTL input module in the 1771 Universal I/O family, designed for PLC-5 backplanes to translate 16 discrete field signals into digital data for the controller. Each channel accepts 5 V DC TTL signals with a HIGH threshold of 2.0–5.25 V and a LOW threshold of -0.2–0.8 V, delivering typical input delay around 1 ms and drawing backplane current of about 122 mA on the 1771 bus. The module is compatible with Universal I/O chassis such as 1771-A1B, A2B, A3B, and A4B, and it uses a 1771-WH wiring arm for field connections. In practical PLC-5 installations, it provides 16 discrete data points that map to the controller’s I/O data table for monitoring field devices like limit switches, sensors, and simple push-buttons in automation systems.