Product Overview

The Allen-Bradley 1756-OA8D is a high-performance, diagnostic-enabled digital AC output module designed for the ControlLogix® platform. This 8-point module provides sophisticated circuit monitoring capabilities, allowing the controller to detect and report field-side faults such as blown fuses, no-load conditions, and output device failures. By integrating these diagnostic features directly into the I/O layer, the 1756-OA8D significantly reduces troubleshooting time and enhances system availability in critical industrial processes.

Operating within a voltage range of 74V to 132V AC, this module is engineered for the precise control of solenoids, motor starters, and indicators. Each channel is electronically protected and isolated from the backplane to ensure that transient noise from the field does not interfere with the logic circuitry. The module resides in a single slot of the 1756 chassis and interfaces seamlessly with the Logix5000™ controller family via the Producer/Consumer communication model.

Advanced Diagnostic and Operational Features

The 1756-OA8D distinguishes itself through its ability to provide real-time feedback on the health of the output circuit, which is essential for predictive maintenance and safety monitoring.

• Comprehensive Diagnostics: Detects and reports "No Load," "Output Short," and "Field Power Loss" conditions per point, sending unique status bits to the controller tags.

• Electronic Fusing: Each output point is protected against overcurrent conditions, eliminating the need for external individual fuses in many applications.

• Configurable States: Users can program specific "Fault Mode" and "Program Mode" behaviors, ensuring outputs transition to a safe state (On, Off, or Hold Last State) during a communication loss.

• High Surge Handling: Capable of managing an 8A peak surge current for 43ms, making it ideal for high-inductive loads that require a high inrush current upon activation.

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Model Number: 1756-OA8D

• Output Type: 120V AC Diagnostic Digital Output

• Number of Outputs: 8 Points (Group of 8)

• Operating Voltage Range: 74–132V AC @ 47–63 Hz

• Backplane Current (5.1V DC): 175 mA

• Backplane Current (24V DC): 250 mA

• Maximum Output Current: 1A per point @ 30°C (derated to 0.5A @ 60°C)

• Surge Current: 8A for 43ms per point

• Maximum On-State Voltage Drop: 3V AC @ 1A

• Isolation Voltage: 125V (continuous), Basic Insulation Type

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Dimensions: 21.5 x 17.5 x 5.0 cm

• Weight: 0.44 kg (0.97 lbs)

Integration and Hardware Requirements

• Removable Terminal Block: Requires a 1756-TBNH or 1756-TBSH RTB for field wiring. The RTB keying is user-configurable to prevent the insertion of the wrong module type into a wired slot.

• Chassis Compatibility: Fully compatible with all 1756 ControlLogix chassis (4, 7, 10, 13, and 17-slot) and can be used in local or remote I/O racks via EtherNet/IP or ControlNet.

• Software Configuration: Managed within the Studio 5000 Logix Designer® environment, providing a graphical interface for setting diagnostic thresholds and latching features.

• Thermal Management: Efficient design with a thermal dissipation of 18.0 BTU/hr, ensuring stable operation even in densely packed control cabinets.