Allen-Bradley 1794 FLEX I/O Modules – 1794-TB3/A Terminal Base Unit

Technical Dossier

Product Details And Specifications

Allen-Bradley 1794 FLEX I/O Series Technical Notes

The Evolution of 1794 FLEX I/O Architecture

The 1794 FLEX I/O platform was introduced in the mid-1990s as Rockwell Automation's response to the growing demand for distributed, rail-mounted I/O that could operate independently of the main controller chassis. Early iterations supported DeviceNet and Remote I/O (RIO) communication adapters, enabling integration with legacy Allen-Bradley PLC-5 and SLC 500 controllers. As fieldbus standards evolved, the platform expanded to include EtherNet/IP (1794-AENT, 1794-AENTR), ControlNet (1794-ACN15), and PROFIBUS DP (1794-APB) adapters, extending the series' operational lifespan well into the 2010s and 2020s.

The terminal base architecture — exemplified by the 1794-TB3/A — remained mechanically consistent across generations, allowing facilities to upgrade communication adapters or I/O modules without rewiring field devices. This backward compatibility is a primary reason the 1794 series remains active in maintenance and spare parts procurement even as Rockwell Automation positions the 5069 Compact I/O and 1734 POINT I/O as successor platforms for new installations. Sites with existing 1794 infrastructure typically maintain the platform through its full lifecycle rather than undertaking costly migration projects.

1794 FLEX I/O Full Catalog & Functionalities (SKU List)

Terminal Bases

1794-TB3/A: 3-wire terminal base unit for FLEX I/O modules, screw-type field wiring termination, DIN rail mount.
1794-TB3S: 3-wire terminal base with spring-clamp termination, tool-free field wiring connection.
1794-TB3T: 3-wire terminal base with cage-clamp termination, vibration-resistant for harsh environments.
1794-TB32: 32-point terminal base for high-density I/O modules, dual-row screw termination.
1794-TB32S: 32-point terminal base with spring-clamp termination, compact footprint.

Digital Input Modules (DI)

1794-IB16: 16-point 24VDC digital input module, sink/source compatible, 3ms input filter.
1794-IB32: 32-point 24VDC digital input module, high-density, requires 1794-TB32 base.
1794-IA16: 16-point 120VAC digital input module, optically isolated, 8.3ms filter.
1794-IV16: 16-point 10–30VDC digital input module, NAMUR sensor compatible.

Digital Output Modules (DO)

1794-OB16: 16-point 24VDC digital output module, 0.5A per point, short-circuit protected.
1794-OB32: 32-point 24VDC digital output module, high-density, 0.25A per point.
1794-OA16: 16-point 120/240VAC digital output module, triac output, 0.5A per point.
1794-OW8: 8-point relay output module, Form A contacts, 2A per point, 240VAC rated.

Analog Input/Output Modules (AI/AO)

1794-IE8: 8-channel analog input module, 4–20mA or 0–10VDC, 12-bit resolution.
1794-OE4: 4-channel analog output module, 4–20mA or 0–10VDC, 12-bit resolution.
1794-IE4XOE2: Combination 4-input / 2-output analog module, 4–20mA, 12-bit.

Communication Adapters

1794-AENT: EtherNet/IP adapter, single-port, supports up to 8 FLEX I/O modules per node.
1794-AENTR: EtherNet/IP adapter with dual-port ring topology (DLR), redundant network support.
1794-ACN15: ControlNet adapter, coax media, 1.5Mbps, supports up to 8 modules.
1794-ADN: DeviceNet adapter, supports up to 8 FLEX I/O modules, 125/250/500Kbps.
1794-APB: PROFIBUS DP adapter, 12Mbps, GSD file configuration.

Sourcing Hard-to-Find & Obsolete 1794 FLEX I/O Parts

DriveKNMS maintains a dedicated inventory of both active and discontinued 1794 series components sourced through verified industrial surplus and refurbishment channels. All units are inspected against original Rockwell Automation specifications prior to shipment. For facilities operating 1794 FLEX I/O infrastructure beyond its published lifecycle, DriveKNMS provides long-term maintenance support including cross-reference identification, functional equivalency assessment, and multi-unit procurement for critical spare parts programs.

Quality Control for the 1794 FLEX I/O Range

The 1794 series presents specific quality verification requirements due to its backplane communication architecture and the interdependency between terminal base and I/O module. DriveKNMS applies the following test protocol to all 1794 series units:

Backplane Continuity Test: Each terminal base (including 1794-TB3/A) is verified for backplane connector integrity using a dedicated FLEX I/O test fixture that simulates module insertion load and signal path continuity across all 26 backplane pins.

Communication Adapter Functional Test: Adapter modules (AENT, AENTR, ACN15, ADN, APB) are powered and connected to a live network segment. Node address assignment, I/O tree enumeration, and cyclic data exchange are verified against the module's published EDS or GSD file.

I/O Module Channel-Level Verification: Digital modules are tested point-by-point at rated voltage and current. Analog modules undergo full-scale calibration verification at 0%, 50%, and 100% of input/output range, with linearity error recorded against the 12-bit specification.

Thermal Burn-In: Refurbished units undergo a minimum 24-hour powered burn-in at ambient temperature to screen for latent component failures prior to shipment.