1794-OF4I | FLEX I/O 4-Channel Isolated Analog Output Module | Allen-Bradley

Functional Performance and System Integration

The 1794-OF4I is a high-performance analog expansion module designed for the Allen-Bradley FLEX I/O platform. It provides four fully isolated channels for precise control of field devices such as actuators, valves, and motor drives. By utilizing channel-to-channel isolation, this module effectively eliminates ground loop interference and protects the internal FlexBus logic from field-side electrical noise. Its modular design allows it to interface with a variety of terminal bases, providing flexibility in wiring and grounding strategies for complex industrial control architectures.

Detailed Technical Specifications

The 1794-OF4I is engineered for precision signal reproduction and robust thermal management in demanding environments.

• Output Configuration: 4 individually isolated analog channels.

• FlexBus Parameters: 5V DC supply voltage at a 50 mA current draw.

• External Power Requirements: 24V DC nominal (Acceptable range 19.2 to 31.2V DC, including 5% AC ripple).

• Power Consumption: 210 mA @ 24V DC.

• Energy Dissipation: Maximum power dissipation of 4.7 W; Thermal dissipation rated at 16 BTU/hr @ 31.2V DC.

• Isolation Capabilities:

• 120V continuous (Basic Insulation) with 1794-TB2, TB3, TB3S, TB3T, TB3TS.

• 250V continuous (Basic Insulation) when paired with 1794-TBN base.

• Dielectric withstand type-tested at 1000V AC for 60 seconds.

• Digital Data Formats: 2’s Complement, 2’s Complement %, Binary, and Offset Binary.

• Physical Interface: Module installs into keyswitch position 4 on the terminal base.

• Dimensions: 94.0 x 94.0 x 66.0 mm (3.7 x 3.7 x 2.6 in) when fully seated.

• Environmental Ratings: North American T4A and IEC T4 temperature codes.

Wiring and Terminal Base Compatibility

To ensure signal integrity, the 1794-OF4I requires shielded cabling on all signal ports (Category 2). It is compatible with a wide array of FLEX I/O terminal bases including the 1794-TB2, 1794-TB3, and the high-isolation 1794-TBN. The choice of terminal base directly dictates the maximum continuous isolation voltage and the permissible wire gauge for field connections.

Engineering FAQ

What are the status indicators on the front panel?

The module features a bi-color LED (Red/Green) that provides immediate diagnostic feedback on power status and internal module health.

Does this module support current and voltage outputs?

Yes, the 1794-OF4I is typically used for both 0–20mA/4–20mA current loops and ±10V voltage signals, depending on the software configuration and data format selected in the controller's I/O tree.

Why is the 1794-TBN base recommended for certain applications?

The 1794-TBN provides a higher continuous isolation rating (250V), which is essential for applications where field devices are powered by separate circuits with significant potential differences relative to the system ground.

Module Comparison: 1794-OF4I vs. 1794-OF4

Unlike the standard 1794-OF4, the 1794-OF4I features complete galvanic isolation between channels. This makes the "I" variant superior for applications where field sensors share a common environment but require separate, non-interfering signal paths to prevent cross-talk.