Allen-Bradley 1791-24A8 Block I/O Module | 24 Input 8 Output RIO

Product Insight – 1791-24A8 Block I/O

1791-24A8 is a compact block I/O module from Allen‑Bradley. It packs 24 discrete 120VAC inputs and 8 120VAC outputs. The built‑in Remote I/O adapter simplifies integration with PLC‑2, PLC‑3, PLC‑5, and SLC 500 via 1747‑SN scanner. This self‑contained unit includes power supply, signal conditioning, and RIO interface – ideal for distributed control architectures.

Oiltech Controls’s Insight

For plants running legacy RIO networks, the 1791‑24A8 offers a drop‑in solution. Its three input groups (8 points each) and single output group reduce wiring complexity. We often see this module used in conveyor systems, packaging lines, and material handling – where 120VAC discrete control remains standard. The built‑in RIO adapter eliminates separate communication cards, saving rack space.

Key Specifications – 1791-24A8

• Manufacturer: Allen‑Bradley (Rockwell Automation)
• Product Type: Block I/O – Remote I/O compatible
• Inputs: 24 channels, 120VAC (79‑132V on‑state)
• Outputs: 8 channels, 120VAC (20‑123V range)
• Input current: 12.3 mA @ 132V max; off‑state ≤2.3 mA
• External power: 85‑132VAC, 150 mA
• Power dissipation: 18.76 W (max) / 63.97 BTU/hr
• Mounting: Vertical or horizontal orientation
• Weight: 1.88 lbs (0.85 kg)

Communication & Cabling

• Supports RIO baud rates: 57.6K, 115.2K, 230.4K
• Cable distance: 10,000 ft (57.6K), 5,000 ft (115.2K), 2,500 ft (230.4K)
• Recommended cable: Belden 9463 (Blue Hose) – 3‑wire with shield
• Daisy‑chain topology: install 82Ω or 150Ω terminating resistor at last node
• Missing terminator may cause intermittent communication – verify during setup

Compatible Controllers & Systems

• PLC‑2, PLC‑3, PLC‑5 (via embedded RIO interface)
• SLC 500 with 1747‑SN Remote I/O scanner
• Any controller supporting standard RIO protocol at 57.6/115.2/230.4 K
• Ideal for legacy system upgrades or expansions

Installation & Maintenance Notes

• • Mount on DIN rail or panel – vertical/horizontal orientation acceptable.
• • Use Belden 9463 cable for reliable RIO communication.
• • Check terminating resistor (82Ω or 150Ω) at the last node.
• • No field calibration required – factory set.
• • Status LEDs assist with fast troubleshooting.

Typical Applications

• Conveyor motor control (start/stop, feedback)
• Packaging machine discrete I/O
• Material handling systems
• Remote I/O drops in large factories
• Replacement for obsolete 1771 or 1746 I/O

Professional FAQ – 5 Experience‑Based Answers

• Q1: Can I mix input groups with different voltages?
  No. All 24 inputs are 120VAC only. Do not apply DC or higher AC – it may damage the input circuitry.
• Q2: How do I choose between 82Ω and 150Ω terminator?
  Use 82Ω for baud rates 57.6K and 115.2K (most common). Use 150Ω only for 230.4K. When in doubt, start with 82Ω – it works for most legacy RIO networks.
• Q3: My SLC 500 scanner can’t see the module. What to check?
  Verify baud rate matches the scanner. Check node address (set via dip switches). Ensure the terminating resistor is present if it’s the last node. Also confirm external power (85‑132VAC) is applied to the module.
• Q4: Can I use this with ControlLogix via RIO?
  Yes, with a 1756‑DHRIO or 1756‑RIO module. The 1791‑24A8 acts as a standard RIO adapter – the CLX scanner must be configured for block transfer.
• Q5: What’s the typical lifespan and spare parts availability?
  These modules are robust – average field life >10 years. However, input optocouplers and output relays may age. We recommend keeping one spare unit for critical lines.

Selection Guide – Quick Tips

• ✔ Need 24 AC inputs and 8 AC outputs? – This is your module.
• ✔ Using RIO at 115.2K over 5000 ft? – Yes, with Belden 9463.
• ✔ Replacing a 1771‑IBN / 1771‑OBN? – Direct drop‑in with adapter cable.
• ✔ For new projects, consider 1794 Flex I/O – but for legacy, 1791 is the practical choice.

Why Buy From Oiltech Controls?

We bring 15+ years of hands‑on industrial automation experience. Every 1791‑24A8 is tested before shipment – we verify RIO communication, input/output functionality, and terminator matching. Our global shipping (FedEx, UPS, DHL) ensures delivery in 24‑28 hours (stock permitting). We support obsolete systems with reliable surplus and refurbished options – all covered by a 12‑month warranty. Technical support is just a call away.

Contact: info@oiltechcontrols.com  |  +86 158 8020 0923 (WhatsApp)

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