Allen-Bradley 1791-32A0 RIO Input Block | 120VAC 32-Channel I/O

1791-32A0 – 32-Channel 120VAC Discrete Input Block (RIO)

The Allen‑Bradley 1791‑32A0 is a fixed I/O block with 32 digital inputs. It operates at 120V AC (79‑132V AC, 47‑63 Hz). Each input sinks 11 mA nominal. The module communicates via Remote I/O (RIO) protocol. It supports PLC‑2, PLC‑3, PLC‑5, and SLC 5/02 controllers. This block suits distributed control architectures.

Key Technical Data

• Brand: Allen‑Bradley
• Model: 1791‑32A0
• Series: 1791 Block I/O
• Inputs: 32 (4 groups × 8 channels)
• Nominal Voltage: 120V AC
• On‑state Range: 79‑132V AC, 47‑63 Hz
• On‑state Current: 5 mA min (@79V) … 12.3 mA max (@132V)
• Off‑state Voltage: 35V max
• Off‑state Current: 2.3 mA min
• Input Impedance: 15 kΩ @ 60 Hz
• Switching Delay: Off→On 1 ms; On→Off 26 ms max
• Isolation: 1250V AC (group‑to‑group & logic); 500V (PS‑to‑RIO)
• Power Dissipation: 13.62 W (46.44 BTU/hr)
• External Supply: 85‑132V AC, 47‑63 Hz, 150 mA
• Temperature (operating): 0…60 °C
• Storage Temp: -40…85 °C
• Humidity: 5‑95 % non‑condensing
• Wiring: 14 AWG stranded, max insulation 3/64″
• Mounting: DIN rail or panel
• Dimensions: 6.95 × 4.35 × 3.85 in
• Weight: 2.00 lbs (0.91 kg)

Hardware Architecture & Integration

• Stand‑alone I/O station with fixed channel count.
• Embedded RIO communication port – 1250V AC isolated.
• Removable terminal strips for RIO, power, and field wiring.
• Two switch assemblies configure: starting I/O group, last chassis, rack number, last state, and baud rate.
• Compatible controllers: PLC‑2, PLC‑3, PLC‑5/250, PLC‑5 family, and SLC 5/02 modular.

Oiltech Controls’s Insight

• ✔ The 1791‑32A0 excels in high‑density AC input applications. Its 4 isolated groups reduce cross‑talk in noisy plants.
• ✔ We recommend using shielded cable for field wiring to maintain signal integrity over long RIO runs.
• ✔ For retrofit projects, this block directly replaces older 1771 I/O racks – saving panel space.
• ✔ Always verify the last‑state switch setting to avoid unexpected outputs during controller fault.

Suitable Equipment & Systems

• PLC‑5 Classic and Enhanced processors (1785‑Lxx).
• SLC 5/02 modular controllers with RIO scanner.
• Legacy 1771 I/O chassis replacement – distributed remote racks.
• Material handling, packaging, and conveyor AC sensor arrays.
• Machine tool monitoring and industrial furnace control.

Professional FAQ – 5 Essential Q&A

• Q1: Can the 1791‑32A0 work with a ControlLogix system?
  A: Not directly. It uses RIO protocol. You need a 1756‑DHRIO or 1756‑RIO scanner to interface with ControlLogix.
• Q2: What is the practical maximum cable length for RIO?
  A: Up to 10,000 ft (3,048 m) with baud rate 57.6k. Use Belden 9463 or equivalent twin‑axial cable.
• Q3: How do I set the starting I/O group?
  A: Use the DIP switches on the top assembly. Refer to the manual – group 0 to 7 setting maps to rack and slot.
• Q4: Is this module suitable for 110V vs 120V systems?
  A: Yes. On‑state range 79‑132V AC covers both. The 11 mA nominal current is stable across the range.
• Q5: What does “last state” switch do?
  A: It defines output behavior if communication fails. Set to “hold last” or “reset” – choose based on safety logic.

Shipping, Warranty & Support

• Warranty: 12 months against defects – repair or replacement.
• Dispatch: 24‑28 hours from order confirmation.
• Carriers: FedEx, UPS, DHL – global tracking provided.

Why Buy From Oiltech Controls?

• 15+ years focused on industrial automation spare parts.
• Worldwide shipping – fast, insured, and reliable.
• All surplus / refurbished units are tested prior to dispatch.
• 12‑month warranty with technical support.
• Pre‑shipment verification of parameters and firmware.
• Specialized in obsolete and legacy control system support.

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