Allen-Bradley 1794-OF8IH HART Output Module

Allen-Bradley 1794-OF8IH Flex I/O HART Analog Output Module

Product Introduction

The Allen-Bradley 1794-OF8IH is a sophisticated output module from the Flex I/O family, specifically designed for applications requiring both analog control and HART communication. This module features eight isolated, single-ended current outputs that you can configure individually for 0-20 mA or 4-20 mA signal ranges. Its integrated HART capability allows for bi-directional communication with smart field devices, enabling you to access diagnostic data and configure parameters remotely. Consequently, the 1794-OF8IH module significantly enhances your system's intelligence and control capabilities.

Key Technical Specifications

The 1794-OF8IH module delivers high precision and fast performance. It utilizes a 16-bit digital-to-analog converter for each channel, providing a unipolar resolution of 16 bits. This results in a fine current resolution of 0.305 µA per count. The module features a fast data conversion rate of just 10 milliseconds, ensuring responsive and accurate output control. Additionally, each channel has a settling time of 70 ms, which is the time required for the output to stabilize after a change.

Output Configuration and Data Formats

This output module offers flexibility not only in signal ranges but also in data representation. You can program each of the eight channels independently. The 1794-OF8IH supports multiple data formats, including Engineering Units, Percent of Full Scale, and RAW/Proportional Count. This versatility simplifies programming and integration with various control strategies. Importantly, the module can detect lead breakages and features alarms for overrange and underrange current conditions, providing valuable diagnostic feedback.

HART Communication and Pass-Through Messaging

A standout feature of the 1794-OF8IH is its support for HART (Highway Addressable Remote Transducer) communication. It achieves this through pass-through messaging support. The module can handle 1 or 2 pass-through connections, each supporting up to 8 queues per connection. This functionality allows the module to send HART messages directly to field devices, enabling you to access the primary variable in IEEE 754-1985 single-precision 32-bit floating-point format, along with other device-specific data. A dedicated 6-WORD register holds this HART data, including the Field Device status, HART Communication status, Loop Status, and the primary value.

Power, Environmental, and Mechanical Parameters

The 1794-OF8IH is designed for efficient and reliable operation. Unlike some other modules, it does not require an external power supply; it derives its power directly from the FlexBus. It draws a FlexBus current of 80 mA at 5V DC. Its maximum power dissipation is rated at 5.0 W at 24V DC, with a corresponding maximum thermal dissipation of 17.06 BTU/hr. The module operates reliably within a temperature range of 32 to 131 °F (0 to 55 °C). For physical installation, it is designed to be mounted on a DIN rail and locks securely to the terminal base when you rotate the keyswitch to position 4.

Installation and Compatibility

Proper installation is straightforward. The 1794-OF8IH is compatible with specific Flex I/O terminal bases, namely the 1794-TB3 and 1794-TB3S. The module is factory calibrated, eliminating the need for manual calibration during initial setup. However, the design provides options for calibration if required later. The wire type you should use depends on the terminal base you select. You can use this module with any available Flex I/O communication adapter, making it a flexible component for a wide range of systems.

Packaging List

Your shipment for the 1794-OF8IH module will include the following items:

• (1) Allen-Bradley 1794-OF8IH Flex I/O HART Analog Output Module

• (1) Product Installation Instructions Manual

Note: The terminal base unit (e.g., 1794-TB3, 1794-TB3S) and configuration software are sold separately.
All products are shipped via FedEx, UPS, or DHL.

Frequently Asked Questions (FAQ)

1. What is the primary function of the Allen-Bradley 1794-OF8IH?
The 1794-OF8IH is a Flex I/O output module. It provides eight isolated analog current outputs for controlling field devices. Its integrated HART capability also enables digital communication with smart instruments.

2. What terminal bases are compatible with the 1794-OF8IH?
This module is specifically compatible with the 1794-TB3 and 1794-TB3S terminal bases. You must use one of these bases for proper installation and operation.

3. Does the 1794-OF8IH require an external 24V DC power supply?
No, the 1794-OF8IH does not require an external power supply. It receives all necessary power from the FlexBus backplane, drawing 80 mA at 5V DC.

4. What data formats does the 1794-OF8IH support for its outputs?
The 1794-OF8IH supports three data formats: Engineering Units, Percent of Full Scale, and RAW/Proportional Count. You can select the format that best fits your control system's programming.

5. How does the 1794-OF8IH communicate with HART devices?
The 1794-OF8IH uses pass-through messaging to communicate with HART devices. This method allows the module to send and receive HART messages through a dedicated register to access device data and diagnostics.