Description

The Allen-Bradley 1771-IA is a legacy discrete input module designed for operation within the PLC-5 and 1771 I/O platform architectures. This standard AC/DC input module provides reliable sensing for industrial control applications, featuring built-in input filtering to minimize the effects of voltage transients caused by contact bounce and radiated electrical noise. It interfaces directly with field devices such as pushbuttons, limit switches, and AC proximity sensors.

The module receives operational power directly through the 1771 I/O chassis backplane from the system power supply, drawing 75 mA of backplane current. Mechanical keying bands on the backplane connector align with slotted cutouts on the module circuit board to prevent improper insertion into unauthorized chassis slots, protecting connected hardware from configuration errors.

Features

• Compatible with standard Allen-Bradley 1771 I/O chassis and PLC-5 control systems
• Supports nominal input voltages of 120 VAC (47 to 63 Hz) and 125 VDC
• Built-in input filtering with nominal filtering delays for enhanced noise immunity
• Optical isolation between field input and backplane logic circuitry
• Mechanical keying slots to prevent incorrect module placement in the chassis
• Compatible with AC proximity switches and low leakage current field devices

Applications

The Allen-Bradley 1771-IA module is deployed in industrial automation systems utilizing the PLC-5 platform. Typical applications include monitoring status signals from limit switches, pushbuttons, selector switches, electronic proximity sensors, and auxiliary relay contacts in discrete manufacturing, material handling, and process control environments.

Technical Specifications

Connections / Interfaces

The 1771-IA module connects to field wiring via a removable terminal block or swing-arm connected to the front of the 1771 I/O chassis wiring arm. The rear edge features physical slots designed to match keying bands on the backplane connector, ensuring the module can only be inserted into compatible I/O chassis slots.

Installation Guidelines

Ensure all power to the 1771 I/O chassis is removed before installing or removing the module. Verify that the backplane keying bands correspond exactly to the slots on the rear edge of the module circuit board. Calculate total backplane current requirements across all installed modules in the chassis to prevent power supply overload.