Overview
The Allen-Bradley 1771-IAD/C is a 16-point digital AC/DC input module designed for PLC-5 programmable logic controllers. As part of the 1771 Universal I/O family, it accepts discrete ON/OFF signals from field devices operating at 120V AC (50/60 Hz) or 125V DC. The Series C module includes optoelectric isolation to protect system logic circuits from electrical transients and input filtering to reduce noise—essential features for stable operation in harsh industrial environments.
Key Features
- 16 Discrete Input Channels – Accommodates up to 16 separate input devices per module
- 120V AC/DC Rated – Operates across 79–138V AC and 79–138V DC supply range
- Optoelectric Isolation – Protects CPU and rack power supply from electrical transients and noise
- Adjustable Input Delays – Selectable 5ms or 20ms delay via jumper to filter false signals
- Front-Panel Status Indicators – One green module-active LED and 16 red input-status LEDs for troubleshooting
- Modular Field Wiring – Uses 1771-WH terminal arm for quick installation and maintenance without breaking connections
Technical Specifications
- Input Voltage Rating: 120V AC (79–138V AC @ 50/60 Hz) or 125V DC (79–138V DC)
- Input Channels: 16 discrete inputs
- Nominal Input Current: 9.9 mA @ 120V AC 60 Hz; 8.7 mA @ 120V AC 50 Hz; 2.56 mA @ 125V DC
- Signal Delay: 5 (±3) ms or 20 (±5) ms on AC; 3 (±0.1) ms or 10 (±1) ms on DC (selectable)
- Backplane Current Load: 195 mA
- Power Dissipation: 1.0–8.8 W (typical 3.5 W)
- Thermal Dissipation: 3.42–30.1 BTU/hr
- Compatible Chassis: 1771-A1B, A2B, A3B, A3B1, A4B, AM1, AM2
- Keying Positions: Slots 10–12 or 14–16 on backplane connector
- Field Wiring Arm: 1771-WH (included)
Typical Applications
The 1771-IAD excels in monitoring discrete field devices throughout industrial automation systems:
- Limit switches and proximity switches on machinery
- Pushbuttons and selector switches for operator control
- Auxiliary relay and contactor contacts for status feedback
- Motor starter interlock signals and safety devices
- Pilot lights and annunciator feedback loops
- General discrete process monitoring in assembly lines, packaging, and material handling
Compatibility & Replacements
The 1771-IAD/C is a legacy module designed for PLC-5 systems and is no longer manufactured as of March 2020. It integrates with all 1771-series I/O chassis (A1B through A4B and later universal models, as well as AM1 and AM2) and is compatible with the 1771-WH field wiring arm. Engineers modernizing systems may consider migration to current Rockwell Automation CompactLogix, ControlLogix, or Stratix I/O modules, though this module remains widely available as surplus stock and parts. The 1771-IA and 1771-IM modules offer similar 120V AC/DC input functionality for alternative configurations.
