Product Overview
The Allen-Bradley 1791-8BR is a compact Block I/O module designed for distributed industrial automation. This combination module integrates eight 24VDC inputs and eight normally open relay outputs into a single rackless unit. It supports Remote I/O (RIO) protocol, enabling seamless connection to RIO scanners and controllers. With its built-in power supply, communication interface, and signal conditioning circuitry, the 1791-8BR operates as a stand-alone I/O station, reducing long cable runs by mounting near field devices.
Key Features & Benefits
-
8 inputs / 8 outputs – Combines discrete input and output capability in one module.
-
24VDC input rating – Matches standard industrial sensor voltages.
-
Dry contact relay outputs – Compatible with AC or DC loads, offering flexibility.
-
RIO protocol support – Interfaces directly with Allen-Bradley PLC and SLC families.
-
Rackless design – Mounts on standard DIN rail or panel, saving cabinet space.
-
Built-in diagnostics – Integrated circuitry simplifies troubleshooting.
Technical Specifications
| Parameter |
Value |
| Manufacturer |
Allen Bradley |
| Category |
PLCs |
| Product Line |
1791 Block I/O |
| Part Number |
1791-8BR |
| UPC |
612598126224 |
| Weight |
1.00 lbs (0.45 kg) |
| Module Type |
Block I/O combination module |
| Module Power |
24VDC |
| No. of Inputs |
Eight (8) |
| Input On-state Voltage |
10-30VDC |
| Input Off-state Voltage |
5V dc max. |
| Input On-state Current |
11mA @ 30V max. |
| Input Off-state Current |
1.5mA min. |
| No. of Outputs |
Eight (8) |
| Output Voltage Range |
20-30V dc @ 1A resistive max. |
| External Power |
19.2-30V dc |
| Mounting Orientation |
Vertical and Horizontal |
Industry Applications
The 1791-8BR excels in applications requiring distributed I/O near sensors and actuators. Typical uses include:
-
Material handling systems – Monitor limit switches and control solenoid valves.
-
Packaging machinery – Interface with proximity sensors and motor starters.
-
Process control skids – Connect float switches and pilot lights.
Its compact form factor and RIO connectivity make it ideal for retrofitting older PLC-2/PLC-3 systems, reducing wiring costs and downtime.
Installation & Setup Guidance
Mount the 1791-8BR on a standard DIN rail or directly to a panel using the integral mounting holes. Ensure the module is oriented vertically or horizontally as per the application layout. Connect incoming power to terminals +24 (1), RET +24 (3), and GND (2). For RIO communication, use terminals BLU (6), CLR (8), and SHD (7). Use 14-gauge stranded wire with a maximum insulation thickness of 3/64 inches for signal termination. Avoid parallel output connections, as this lowers circuit resistance and can lead to malfunction.
Maintenance & Reliability
The 1791-8BR requires minimal routine maintenance. Periodically inspect terminal connections for tightness and check for signs of corrosion or overheating. Because the module lacks internal fusing, install appropriate external fuses to protect both the module and connected devices. Pay special attention to surge currents – the module does not have surge limiting, so external protection is essential for long-term reliability. Regular cleaning of the enclosure and ensuring proper ventilation will extend service life.
Compatibility & Integration
The 1791-8BR integrates with a wide range of Allen-Bradley controllers, including PLC-2, PLC-3, PLC-5/20, and PLC-5. It supports RIO protocol and pairs with scanner modules such as 1771-SN, 1772-SD/SD2, 1775-S5, 1775-SR5, and PLC-5VME (6008-LTV). This compatibility ensures seamless integration into existing Rockwell Automation architectures.
Buying Guide
When selecting the 1791-8BR, verify your controller's scanner compatibility and confirm the required input/output voltage ranges. Ensure your power supply delivers 24VDC within the 19.2-30V dc range. For genuine Allen-Bradley parts and reliable service, consider PLC Source PRO as your trusted supplier.