Allen-Bradley 1794-OF8IH HART Analog Output Module Overview

The Allen-Bradley 1794-OF8IH is a Flex I/O isolated analog output HART module. This module has eight isolated output channels for current signals. The Allen-Bradley 1794-OF8IH is configurable for 0-20 mA and 4-20 mA output ranges. It features 16-bit unipolar resolution for precise analog control. The Allen-Bradley 1794-OF8IH can be used without jumpers and switches. Multiple data ranges can be programmed independently on each channel. This output module detects lead breakages and provides overrange and underrange alarms. It supports pass-through messages for sending HART commands to field devices.

Technical Specifications

General Specifications

• Manufacturer: Rockwell Automation.

• Brand: Allen-Bradley.

• Series: Flex I/O 1794.

• Part Number: 1794-OF8IH.

• Product Description: Flex IO Isolated Analog Output HART Module.

• Product Type: Output module.

• Number of Outputs: 8 isolated outputs.

• Pass-through Message Support: Yes.

Output Specifications

• Output Signals: 0-20 mA and 4-20 mA (configurable).

• Module Resolution: 16-bit unipolar.

• Actual Resolution: 0.305 μA per count.

• Conversion Method: 16-bit digital to analog converter.

• Conversion Rate: 10 ms (internal).

• Data Conversion Rate: 10 milliseconds.

• Channel Settling Time: 70 ms.

Data Formats Supported

The Allen-Bradley 1794-OF8IH supports multiple data formats:

• Engineering Units

• Percent of Full Scale

• RAW/Proportional Count

HART Communication

• Dedicated HART Register: 6 WORD register containing:

  • Fields Device data

  • HART Communication status

  • Loop Status

  • Primary value in IEEE 754-1985 Single-Precision 32-bit floating point

• Pass-through connections: 1 or 2 connections supporting 8 queues per connection.

Power Specifications

• Flexbus Current: 80 mA at 5V DC.

• External Power Supply: Not required (receives power from FlexBus).

• Maximum Power Dissipation: 5.0 W at 24V DC.

• Maximum Thermal Dissipation: 17.06 BTU/hr at 24V DC.

Compatible Terminal Bases

The Allen-Bradley 1794-OF8IH requires keyswitch position 4 for:

• 1794-TB3

• 1794-TB3S

Calibration

• Calibration Type: Factory calibrated (no field calibration required).

Environmental Specifications

• Operating Temperature: 32°F to 131°F (0°C to 55°C).

• Wire Type: Depends on the terminal base used.

Alarm and Detection Features

• Lead breakage detection

• Overrange current alarms

• Underrange current alarms

Physical Specifications

• Product Net Weight: 0.35 kg.

• Gross Weight: 0.55 kg (with packaging).

Installation Guide

Follow these steps to install the Allen-Bradley 1794-OF8IH correctly:

1. Turn off all power to the Flex I/O system before installation.

2. Insert the Allen-Bradley 1794-OF8IH into a compatible terminal base (1794-TB3 or 1794-TB3S).

3. Rotate the keyswitch to Position 4 to lock the module to the terminal base.

4. Connect output devices to the 8 isolated analog output channels.

5. Configure each channel for 0-20 mA or 4-20 mA output range.

6. Select the desired data format (Engineering Units, Percent of Full Scale, or RAW).

7. Set up HART pass-through messaging if communicating with HART devices.

8. Test the Allen-Bradley 1794-OF8IH by commanding output values and verifying current signals.

Packaging List

• Allen-Bradley 1794-OF8IH HART analog output module (1 unit)

• Anti-static protective bag (1 piece)

• Installation instructions manual (1 copy)

• Product label with catalog number

Frequently Asked Questions (FAQ)

1. How many output channels does the 1794-OF8IH provide?
The Allen-Bradley 1794-OF8IH provides 8 isolated analog output channels.

2. What output signal ranges are available on this module?
This module is configurable for 0-20 mA and 4-20 mA output signals.

3. Does the 1794-OF8IH support HART communication?
Yes, this module supports HART pass-through messages for communication with HART field devices.

4. What is the resolution of the 1794-OF8IH?
The module provides 16-bit unipolar resolution with actual resolution of 0.305 μA per count.

5. What terminal bases are compatible with the 1794-OF8IH?
Compatible terminal bases are 1794-TB3 and 1794-TB3S with keyswitch position 4.