Product Overview

The Allen-Bradley 1794-OB8​ is an 8-channel digital DC sourcing (PNP) output module within the Rockwell Automation 1794 FLEX I/O product family, designed for distributed and remote I/O applications where a compact, DIN-rail-mountable I/O block must be located close to field devices while communicating back to a ControlLogix, CompactLogix, MicroLogix 1500 (with 1769-ADN), SLC-500, or PLC-5 controller via a FLEX I/O communication adapter (such as 1794-AENTR for EtherNet/IP, 1794-ACNR15 for ControlNet, or 1794-AND for DeviceNet). The 1794-OB8​ provides eight (8) individually isolated 24 V DC source-type output points, each capable of switching up to 0.5 A continuous resistive load, with a maximum combined module load of 4.0 A. Each output point is electronically protected against short-circuit and thermal overload, with automatic recovery upon fault removal. Output state is indicated by individual point LEDs on the module face, and the module reports open-wire / blown-fuse status (via the adapter’s electronic keying and diagnostics) to the host controller for alarm generation.The 1794-OB8​ derives its operating power from the FLEX I/O backplane (drawn through the installed terminal base assembly, e.g., 1794-TB3, 1794-TB2, or 1794-TBN) and requires a user-supplied 24 V DC external field power source connected at the terminal base to energize the output loads. It is not a standalone device—it must be paired with a 1794 FLEX Terminal Base and plugged into a 1794 Adapter module (or used in a local FLEX I/O rack with a 1794-IB16/OB16 combination behind an adapter). The 1794-OB8​ occupies one logical slot in the I/O image of the controller and is fully configurable in RSLogix 5000 / Studio 5000 or RSLogix 500 via the Add-On Profile (AOP) associated with the FLEX adapter. With its IP20-rated enclosed design, 500 V DC (type-tested) isolation between field-side outputs and the logic/bus side, and broad agency approvals including Class I Division 2, the 1794-OB8​ is the standard choice for sourcing 24 V DC discrete outputs—pilot lights, solenoid valves, contactor coils, indicator stacks, and small DC relays—in material handling, packaging, process skids, and automotive assembly distributed I/O drops. Its small footprint (12 mm / 0.47 inch module width when used with the narrow terminal base) allows high-density I/O packing in tight enclosures while preserving the diagnostic transparency and tag-based data access of the Logix control platform.

Technical Specifications

Main Features and Advantages

The Allen-Bradley 1794-OB8​ combines the space-efficiency of the FLEX I/O form factor with robust output protection and comprehensive diagnostics that make it the go-to 24 V DC sourcing output module for distributed control applications.High-density 8-point sourcing output in minimal width: When mounted on a standard 1794 terminal base (e.g., 1794-TB3 – 12 mm module width or 1794-TBN – 22 mm wider base), the 1794-OB8​ delivers eight independently controllable 24 V DC source outputs while consuming only one I/O slot and a fraction of the panel width required by rack-based PLC I/O. This allows system designers to closely match I/O point count to application needs—adding only as many 1794-OB8​ modules as required—reducing both initial cost and panel real estate in machines with mixed discrete and analog I/O.Built-in electronic protection with auto-recovery: Each output point on the 1794-OB8​ is current-limited to protect against short-circuit or overload conditions. If a point is shorted, the module limits current, signals a fault to the adapter (visible in controller status tags), and thermally shuts down the affected output. Once the short is cleared, the output automatically recovers—no fuse replacement is needed for typical overload events, though an external fuse may still be specified per machine standards for branch-circuit protection. This reduces nuisance downtime and spare-parts inventory (no mini-fuses to stock for the module itself).Per-point LED diagnostics and controller-visible status: Eight green LEDs—one per output point—provide immediate visual confirmation of which outputs are commanded ON. A separate module-status LED indicates communication with the FLEX adapter and module health (solid green = OK; flashing/red = fault condition). The adapter propagates output fault bits into the controller’s I/O image, enabling the control program to annunciate open-load, shorted-load, or module-communication-loss conditions on the HMI or SCADA, dramatically shortening troubleshooting time during commissioning and maintenance.