Allen-Bradley 1791-8AR Block I/O Module: Flexible Relay-Based Remote I/O

Technical Specifications

• Brand: Allen-Bradley
• Model: 1791-8AR
• Product Line: 1791 Block I/O
• Input Channels: 8 isolated channels.
• Input On-State Voltage: 79 to 132 VAC.
• Output Channels: 8 relay contacts.
• Output Ratings: 125 VDC/1A, 30 VDC/1A, 125 VAC/0.2A (resistive).
• External Supply: 85-132 VAC, 150 mA.
• Power Dissipation: Max 12.9 Watts.
• Thermal Dissipation: Max 56.1 BTU/hour.
• Communication: Allen-Bradley RIO Protocol (57.6K, 115.2K, 230.4K baud).
• Module Weight: Approx. 1.00 lbs (0.45 kg).

Performance & Network Details

• Relay outputs offer excellent load flexibility for both AC and DC control circuits.
• The RIO network supports distances up to 10,000 feet at 57.6K baud with proper termination.
• Input circuits feature a low off-state voltage maximum of 35V for clear signal definition.
• Network requires 82 or 150-ohm terminating resistors at each end of the daisy chain.
• The module provides robust isolation between I/O groups and control logic for stable operation.

Frequently Asked Questions (FAQ)

• Q: What types of loads can the 1791-8AR relay outputs control?
  A: They can control various loads: resistive (lamps, heaters), inductive (solenoid coils, contactors), and both AC or DC voltages within ratings.
• Q: What PLCs are compatible with this module?
  A: It is compatible with Allen-Bradley PLC2, PLC3, PLC5, and SLC500 systems using a 1747-SN Remote I/O scanner module.
• Q: What is the maximum cable length for the RIO network?
  A: Maximum length depends on baud rate: 10,000 ft at 57.6K, 5,000 ft at 115.2K, and 2,500 ft at 230.4K baud.
• Q: Does the module need external relays?
  A: No, the 1791-8AR has built-in electromechanical relays, eliminating the need for external interposing relays in most cases.
• Q: How do I terminate the RIO network?
  A: Install an 82-ohm or 150-ohm terminating resistor at the first and last physical device on the daisy chain.

© 2025 Ubest Automation Limited. https://www.ubestplc.com/ All rights reserved.
Contact: sales@ubestplc.com Phone: +86 180 3000 5825