Allen-Bradley 1791-IOBX 1791 Block I/O High-Density Digital Combo Module

Product Overview

The Allen-Bradley 1791-IOBX operates as a high-density, centralized remote I/O interface within the Bulletin 1791 Block I/O product line. This digital combo module condenses massive channel counts into a standalone field-mounted assembly, deploying 64 sinking inputs and 64 sourcing outputs down to decentralized machinery zones.

While the original manufacturer classifies this specific hardware series as discontinued and obsolete, we source and distribute this critical component strictly as a 100% brand new, original factory-sealed unit. This ensures pristine internal solid-state traces, uncompromised signal isolation barriers, and flawless optocoupler responses for engineers maintaining or restoring legacy industrial control networks.

Technical Specifications

The table below logs the precise electrical parameters, logic thresholds, and load tolerances of this high-density block module:

Engineering Advantages

• Drastically Compresses Control Enclosure Footprint: Integrating 128 total digital I/O points (64 In / 64 Out) onto a single block eliminates the physical space requirements of a traditional multi-slot PLC chassis, remote backplanes, and separate input/output cards. This massive concentration allows machine builders to mount extensive interface blocks directly into shallow machine junction boxes.

• Eliminates Inter-Channel Wiring Cross-Talk: Despite processing 128 simultaneous lines, the multi-layer internal PCB traces isolate internal logic signals from the adjacent high-current output lanes. This structural shielding stops electromagnetic cross-talk from generating false logical triggers on the sensitive 1.56mA minimum sinking input channels.

• Simplifies Legacy System Restoration Projects: This brand new unit matches the mounting footprint and physical terminal positions of existing field-installed 1791 systems. This engineering cross-compatibility allows technicians to execute a direct drop-in replacement, skipping costly and time-consuming controller migrations, panel metal modifications, or control logic rewrites.

FAQs

• Can the 64 sourcing outputs handle inductive loads like large AC contactors directly?

  No. The 64 sourcing output transistors handle up to 300mA of continuous resistive current per channel under standard 24V DC external power. When switching inductive loads like heavy solenoid valves or magnetic contactor coils, the collapsing magnetic field creates severe reverse voltage spikes. You must install external flyback diodes across the inductive load terminals to shield the internal sourcing transistors from overvoltage puncture.

• How do technicians prevent voltage drops from destabilizing the input logic states on long cable runs?

  Ensure that the external 24V DC power supply maintains a steady voltage output between 18V DC and 26.4V DC at the module terminals. Because the sinking inputs switch state when the incoming potential hits a minimum of 12V DC, engineers must specify appropriately sized copper wire gauges to counteract line resistance over extended runs, keeping the voltage safely above the 7V DC maximum off-state threshold.

• Does this module require a separate network communication card to bridge data back to a master PLC-5 or SLC 500 processor?

  The 1791-IOBX functions as an integrated network block that connects directly to the legacy Allen-Bradley Remote I/O (RIO) blue-hose network scanner architecture. You do not need an auxiliary chassis adapter; simply configure the hardware dip switches on the block body to assign the correct rack address and baud rate before connecting the communication trunk line.