Product Overview
The Allen-Bradley 1791-24A8 is a compact block I/O module engineered for remote I/O architectures in industrial control systems. This self-contained unit integrates a power supply, PLC interface, I/O connections, and signal processing circuitry into a single assembly, simplifying installation and reducing panel space. With 24 inputs and 8 outputs, the 1791-24A8 delivers dependable discrete I/O performance for demanding applications.
Technical Specifications
| Parameter |
Value |
| Manufacturer |
Allen-Bradley |
| Product Type |
Block I/O |
| Part Number |
1791-24A8 |
| UPC |
612598124770 |
| Weight |
1.88 lbs (0.85 kg) |
| Output Voltage Range |
20-123VAC |
| No. of Inputs |
24 |
| No. of Groups |
3 groups of 8 |
| On-state Voltage Range |
79-132VAC |
| No. of Outputs |
8 |
| No. of Output Groups |
1 group of 8 |
| External Power, Voltage |
85-132VAC |
| External Power, Current |
150 mA |
| Mounting |
Vertical / Horizontal |
| Power Dissipation, max |
18.76 Watts |
| Thermal Dissipation, max |
63.97 BTU/Hr |
| Input On-state Voltage Range |
79-132V ac |
| Input On-state Current |
12.3mA @ 132V max. |
| Input Off-state Voltage |
35V max. |
| Input Off-state Current |
2.3mA min. |
| Outputs per Block |
8 |
| External Power |
85-132V ac |
Key Features & Benefits
- 24 isolated 120VAC input channels with on-state voltage range of 79-132VAC ensure reliable signal detection.
- 8 120VAC output channels with output voltage range of 20-123VAC provide flexible switching capability.
- Built-in Remote I/O interface in adapter mode supports seamless integration with PLC2, PLC3, PLC5, and SLC500 controllers via compatible scanner modules.
- Compact, self-contained design with vertical or horizontal mounting options simplifies installation in tight spaces.
- Low power dissipation of 18.76 Watts minimizes heat buildup, contributing to system reliability.
Industry Applications
The 1791-24A8 excels in applications requiring distributed I/O over long distances. For example, in a material handling system, you can place the 1791-24A8 near conveyors to monitor limit switches and control motor starters, reducing wiring costs. In a water treatment plant, this module can handle valve position feedback and actuation commands across a wide area. The module supports standard Remote I/O baud rates of 57.6K, 115.2K, and 230.4K, with maximum cable lengths of 10,000, 5,000, and 2,500 cable-feet respectively, enabling flexible network topology.
Installation & Setup Guidance
Mount the 1791-24A8 vertically or horizontally on a DIN rail or panel using the integral mounting holes. Ensure adequate clearance for ventilation and wiring. Connect the external power supply (85-132VAC, 150 mA) to the designated terminals. For Remote I/O communication, use Belden 9463 cable, a three-wire cable with blue, clear, and shield conductors. When using a daisy-chain topology, install a terminating resistor (82 Ohm or 150 Ohm) at the last node to close the loop and prevent intermittent communication issues. Configure the scanner module in the controller to match the baud rate and node address.
Maintenance & Reliability
Routine inspection every 6-12 months is recommended to check for loose connections, dust accumulation, and signs of overheating. The module's low thermal dissipation (63.97 BTU/Hr) reduces stress on surrounding components. Ensure the ambient temperature stays within the specified operating range and that airflow is not obstructed. Periodically verify input and output signal integrity using a multimeter to catch early signs of wear.
Compatibility & Integration
The 1791-24A8 connects to PLC2, PLC3, and PLC5 controllers via the embedded Remote I/O interface when configured as a scanner. It also works with SLC500 controllers using the 1747-SN Remote I/O scanner module. This compatibility makes it a versatile upgrade or replacement option for existing Remote I/O networks.
Selection Guide & Purchasing Advice
Before purchasing, verify that your controller supports Remote I/O and that the baud rate and cable length requirements match your network layout. Confirm the voltage rating of your I/O devices falls within the module's ranges. PLC Source PRO offers genuine Allen-Bradley 1791-24A8 modules with reliable availability and fast shipping.