1794-OF8IH | Allen-Bradley FLEX I/O | 8-Point Isolated Analog Output Module with HART

Module Overview

The 1794-OF8IH is a high-performance analog output module within the Allen-Bradley FLEX I/O family, specifically engineered for process control environments requiring high density and intelligent field device integration. This module provides eight fully isolated channels capable of delivering both voltage and current signals. A standout feature is its integrated HART (Highway Addressable Remote Transducer) protocol support, which allows the controller to communicate digitally with "smart" field instruments—such as valve positioners and actuators—simultaneously with the 4-20mA analog signal. This dual-layer communication enables advanced asset management, remote calibration, and real-time device diagnostics.

Detailed Engineering Specifications

The 1794-OF8IH utilizes a 16-bit digital-to-analog converter (DAC) to provide the fine granularity required for precise PID loop control.

• Number of Outputs: 8 Isolated Channels

• Resolution: 16-Bit

• Output Signal Ranges: 4 to 20 mA and ±10V DC

• Protocol Support: Integrated HART (Version 5, 6, and 7 compatible)

• Isolation: Channel-to-channel and channel-to-logic isolation (tested at 500V AC)

• External DC Power: 24V DC nominal (19.2 to 31.2V DC range)

• FlexBus Current: 80 mA @ 5V DC

• Thermal Dissipation: 5.1 Watts @ 24V DC

• Accuracy: 0.1% Full Scale @ 25°C

• Mounting Orientation: Horizontal or Vertical (DIN rail or Panel mount)

• Enclosure Rating: IP20 (Open-style)

• Physical Weight: 0.35 lbs (0.16 kg)

HART Communication and Intelligent Control

The 1794-OF8IH eliminates the need for external HART multiplexers by embedding the modem directly into the module hardware. When paired with a HART-compatible communication adapter (such as the 1794-AENTR for EtherNet/IP), the module passes secondary process variables and device status data to the Logix5000 controller. This allows maintenance teams to monitor valve health, stroke counts, and internal temperature of the field device without needing a handheld communicator at the site.

Modular Installation and Termination

As part of the FLEX I/O system, the 1794-OF8IH is a "plug-in" component that requires a separate terminal base for wiring. It is compatible with several 1794 bases, including:

• 1794-TB3G: Recommended for grounded applications and increased noise immunity.

• 1794-TB3GS: Features spring-clamp terminals for high-vibration environments.

  The modular design supports "Removal and Insertion Under Power" (RIUP), allowing for the replacement of a module without shutting down the entire I/O rack or interrupting the communication bus.

Technical FAQ

Can the 1794-OF8IH provide different signal types on the same module?

Yes. Each of the eight channels is independently configurable. You can have a mix of 4-20mA current loops and ±10V voltage outputs on a single module to meet various field device requirements.

Does this module require a specific firmware version for HART functionality?

The HART capabilities are accessible when using the module with an EtherNet/IP adapter (1794-AENT or 1794-AENTR) and Studio 5000 Logix Designer. While it can function as a standard analog module on older protocols, the digital HART data typically requires a modern CIP-based network.

How does channel-to-channel isolation benefit my system?

Isolation prevents ground loops and ensures that a fault or electrical surge on one field device does not propagate to the other seven channels or the main PLC backplane. This significantly increases system uptime in harsh industrial electrical environments.