Allen-Bradley FLEX I/O 1794-TB3 Master Relay Module

Technical Dossier

Product Details And Specifications

Allen-Bradley FLEX I/O 1794 Series Technical Notes

The 1794-TB3 is a terminal base unit within this series, providing the mechanical and electrical interface between the backplane bus and field wiring. It functions as a Master Relay Module terminal base, supporting relay-output modules in safety-critical switching applications.

The Evolution of FLEX I/O 1794 Architecture

The 1794 FLEX I/O platform was introduced by Allen-Bradley in the mid-1990s as a response to the industry demand for compact, rail-mounted distributed I/O that could operate over standard industrial networks (DeviceNet, ControlNet, EtherNet/IP, PROFIBUS). The architecture is built around a passive backplane (terminal base) and active I/O modules that snap onto it, with the adapter module providing network communication at the left end of the node.

Early generations (circa 1995–2002) supported DeviceNet and ControlNet adapters exclusively. The introduction of EtherNet/IP adapters (1794-AENT, 1794-AENTR) in the 2000s extended the platform's lifecycle significantly, enabling integration into modern Ethernet-based plant networks without hardware replacement of the I/O modules themselves. The 1794-TB3 terminal base is compatible across all adapter generations, making it a long-lifecycle component that remains in active use even as network-layer hardware is upgraded.

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

Terminal Bases

• 1794-TB3: Master relay module terminal base; 3-wire field wiring; backplane bus interface for relay output modules.
• 1794-TB3S: Terminal base with screw-clamp wiring; 3-wire; safety-rated variant for SIL applications.
• 1794-TB3T: Terminal base with cage-clamp (spring-clamp) wiring termination; 3-wire field side.
• 1794-TB32: 32-point terminal base; supports high-density digital I/O modules.
• 1794-TB32S: 32-point terminal base, screw-clamp; safety-rated variant.

Digital Output Modules

• 1794-OB16: 16-point 24VDC source output module; 0.5A per point; solid-state.
• 1794-OB16P: 16-point 24VDC protected output; short-circuit and overload protection per point.
• 1794-OW8: 8-point relay output module; 2A per point; AC/DC load switching.
• 1794-OW8I: 8-point isolated relay output; individual common per output; 2A per point.

Digital Input Modules

• 1794-IB16: 16-point 24VDC sink input module; standard digital field input.
• 1794-IB16D: 16-point 24VDC input with diagnostics; open-wire and short detection.
• 1794-IM8: 8-point 120VAC input module; for legacy AC field devices.
• 1794-IV16: 16-point 10–30VDC input; wide voltage range for mixed field environments.

Analog Modules

• 1794-IE8: 8-channel analog input; 4–20mA / 0–10V selectable; 12-bit resolution.
• 1794-OE4: 4-channel analog output; 4–20mA / 0–10V; 12-bit resolution.
• 1794-IE4XOE2: Combination 4-input / 2-output analog module; reduces node count in mixed-signal applications.

Communication Adapters

• 1794-ADN: DeviceNet adapter; original network interface for 1794 nodes.
• 1794-ACN15: ControlNet adapter; coax-based; 1.5Mbps network rate.
• 1794-AENT: EtherNet/IP adapter; single-port; standard plant Ethernet integration.
• 1794-AENTR: EtherNet/IP adapter with DLR (Device Level Ring) redundancy; for high-availability network topologies.

Quality Control for the 1794 FLEX I/O Range

All 1794-series modules processed by DriveKNMS undergo a structured inspection and functional verification protocol:

• Visual inspection: Backplane connector pin integrity, housing crack assessment, label legibility, and date code verification.
• Backplane bus continuity test: Verification of the 1794 backplane data and power bus contacts using calibrated test fixtures that simulate the 1794-TB3 mechanical interface.
• Functional power-up test: Each module is installed in a live 1794 test node (EtherNet/IP adapter, 24VDC power supply) and scanned by a ControlLogix controller. I/O point status, diagnostic bits, and module identity data are verified against factory specifications.
• Relay output modules (1794-OW8, 1794-OW8I): Contact resistance measurement per output point; coil actuation voltage verification; isolation resistance test between output commons.
• Analog modules (1794-IE8, 1794-OE4): Full-scale linearity test at 0%, 25%, 50%, 75%, and 100% of input/output range; offset and gain error recorded against Rockwell Automation published specifications.