Allen-Bradley 1791-8BC 16-Point Combination Discrete I/O Module

Product Introduction

When implementing a distributed I/O architecture, the Allen-Bradley 1791-8BC provides a rackless, DIN rail-mountable solution that simplifies wiring and reduces panel space. This 16-point combination discrete I/O module from the Block I/O series integrates eight 24 VDC discrete inputs and eight 24 VDC discrete outputs into a single, compact unit. Designed for use with Allen-Bradley PLC-2, PLC-3, 1785 PLC-5, 1747 SLC 500, and Logix platforms via a Remote I/O (RIO) communication module, the 1791-8BC communicates using the RIO protocol over 1771-CD or Belden 9463 3-wire cable at transmission rates of 57.6K, 115.2K, and 230.4K baud. This module is externally powered by a 19.2–30 VDC supply and draws a maximum of 300 mA.

Technical Specifications

The 1791-8BC operates with an input on-state voltage range of 10–30 VDC and an input signal range of 10–30 VDC. The output voltage range is also 10–30 VDC. The external power supply requirement is 19.2–30 VDC. Output current ratings depend on mounting orientation and ambient temperature: in vertical mounting, the module delivers 500 mA at 60 °C and 1 A at 30 °C; in horizontal mounting, it provides 250 mA at 60 °C and 500 mA at 30 °C. The module includes individual channel LED indicators and an OK LED for status monitoring.

Industry Applications

The 1791-8BC is ideally suited for material handling, packaging, and assembly line applications where distributed I/O reduces cabling complexity. In a conveyor system, for example, the eight inputs can monitor sensor status while the eight outputs control actuators, all over a single RIO network. This configuration lowers installation costs and simplifies troubleshooting.

Installation & Setup Guidance

Mount the 1791-8BC on a standard DIN rail in a vertical or horizontal orientation. Connect the external power supply (19.2–30 VDC) to the module terminals. For RIO communication, use 1771-CD or Belden 9463 3-wire cable connected to terminals 6 (BLU), 7 (SHD), and 8 (CLR). Terminate the first and last nodes on the RIO network with a 150-ohm resistor at 57.6K and 115.2K baud rates, or an 82-ohm resistor at 230.4K baud, connected across terminals 6 and 8. Use 14 AWG stranded wire with a maximum insulation thickness of 3/64 inch for field wiring.

Maintenance & Reliability

Regularly inspect the module for dust accumulation and ensure proper ventilation to maintain thermal performance. Verify that the external power supply remains within the 19.2–30 VDC range to prevent erratic operation. The module's internal current protection safeguards against overloads, but periodic testing of input and output channels is recommended to confirm functionality.

Compatibility & Integration

The 1791-8BC integrates seamlessly with Allen-Bradley PLC-2, PLC-3, 1785 PLC-5, 1747 SLC 500, CompactLogix, and ControlLogix controllers via a Remote I/O (RIO) communication module. The RIO protocol supports transmission rates of 57.6K, 115.2K, and 230.4K baud. This compatibility makes the module a flexible choice for both legacy and modern automation systems.

Selection Guide & Purchasing Advice

Before ordering the 1791-8BC, verify that your controller supports Remote I/O (RIO) communication and that the network topology matches the module's requirements. Confirm the mounting orientation and ambient temperature to ensure the output current rating meets your application needs. For current availability and lifecycle status, please contact BluePLC Industrial. They can also provide information on compatible cables and terminating resistors.

For complete technical specifications for the 1791-8BC, please contact BluePLC Industrial.