Allen-Bradley 1794-OB16D Flex I/O Diagnostic Output

Allen-Bradley 1794-OB16D 16-Channel 24VDC Diagnostic Output Module

Product Introduction

The Allen-Bradley 1794-OB16D is a high-performance digital output module that includes advanced diagnostic capabilities. This unit offers sixteen non-isolated, sourcing outputs with a nominal voltage of 24V DC. Its diagnostic features allow it to detect, indicate, and report open or shorted field devices and wiring. Consequently, this module significantly reduces troubleshooting time and improves system uptime. The 1794-OB16D is a smart choice for critical applications where fault detection is essential.

Diagnostic Features and Benefits

What sets the 1794-OB16D apart is its integrated diagnostic functionality. This module actively monitors the output circuit status.

• Open-Wire Detection: The module can identify when a wire breaks or disconnects from a field device. This feature helps you quickly pinpoint wiring failures.

• Shorted-Load Detection: It also detects short-circuit conditions in the field wiring or the connected load. Early detection prevents potential damage to the system.

• Status Indication: Sixteen yellow LED indicators on the front panel show the status of each output channel. These indicators are logic-driven and provide immediate visual feedback.

• Fault Reporting: The diagnostic data is communicated back to the controller via the FlexBus. You can then use this data in your control program for alarm generation or automatic shutdown sequences.

Technical Specifications

This output module delivers robust electrical performance for demanding automation tasks. Its specifications ensure compatibility with a wide array of standard 24V DC field devices.

Output Characteristics

• Number of Outputs: The 1794-OB16D provides 16 sourcing outputs in a single, non-isolated group.

• Voltage Range: The on-state voltage range is from 10V DC minimum to 31.2V DC maximum, with a nominal voltage of 24V DC.

• Current Ratings: Each channel supports a maximum on-state current of 500mA. The total output current rating for all 16 channels is 8.0A.

• Signal Delay: This module offers an extremely fast output signal delay of just 0.1ms. This rapid response makes it suitable for high-speed control processes.

• Off-State Leakage: The maximum off-state leakage current is a low 0.5mA, which minimizes unwanted current flow when the output is off.

Power and Isolation

• FlexBus Current: The maximum FlexBus current drawn by the 1794-OB16D is 60mA at 5V DC.

• Power Dissipation: Under maximum load at 31.2V DC, the module dissipates up to 4.8W of power.

• Thermal Dissipation: Its thermal dissipation is rated at 16.4 BTU/hr under maximum load conditions.

• Isolation Voltage: The module provides an isolation voltage of 50V (continuous) between the user and the system.

Mechanical and Environmental Parameters

Understanding the physical and environmental limits is essential for a successful installation. The 1794-OB16D is built to perform reliably in demanding industrial environments.

Physical Dimensions

• Dimensions (HxWxD): The module follows the standard Flex I/O form factor. Please refer to the terminal base documentation for exact overall dimensions.

• Weight: This unit weighs approximately 78 grams (2.75 oz), consistent with other modules in the Flex I/O line.

• Installation: You can install the module by snapping it onto a DIN rail. It is inserted into a compatible terminal base unit.

Environmental Limits

• Operational Temperature: You can operate this unit in environments from 0 to 55°C (32 to 131°F). For extreme environments, XT-rated versions are also available.

• Relative Humidity: The module functions correctly in conditions with 5 to 95% non-condensing relative humidity.

• Hot Swapping: A key advantage of the Flex I/O system is that you can insert or remove the 1794-OB16D under power. Since the module has no direct wiring, this saves time and eliminates system restart inefficiencies.

Installation and Compatibility

Proper installation ensures the longevity and reliability of the Allen-Bradley 1794-OB16D.

Terminal Base Requirements
This module must be mounted on a compatible terminal base unit. Specifically, it is designed for use with the 1794-TB3, 1794-TB3S, and 1794-TBKD base units. The wiring size you use will depend on the specific terminal base you select.

Communication Options
The Flex I/O platform supports various communication adapters. Therefore, the 1794-OB16D can be used in systems with ControlNet, DeviceNet, EtherNet/IP, and Universal Remote I/O networks.

System Integration
You can install multiple instances of the 1794-OB16D in a single Flex I/O rack. It works seamlessly with any 1794 Flex I/O adapter to implement distributed I/O applications.

Packaging List

Your shipment for the Allen-Bradley 1794-OB16D will include the following item:

• (1) Allen-Bradley 1794-OB16D Flex I/O Digital Output Module with Diagnostics

Frequently Asked Questions (FAQ)

1. What is the main difference between the 1794-OB16 and the 1794-OB16D?
The 1794-OB16D includes advanced diagnostic features that detect open or shorted field wiring. The standard 1794-OB16 does not offer this diagnostic capability.

2. What terminal bases are compatible with the 1794-OB16D?
This module is compatible with the 1794-TB3, 1794-TB3S, and 1794-TBKD terminal base units.

3. Can I remove the 1794-OB16D while the system is powered on?
Yes, you can safely insert or remove the 1794-OB16D under power because it has no direct wiring connections. This feature prevents unnecessary system downtime.

4. What is the output signal delay for the 1794-OB16D?
The output signal delay is only 0.1ms for both on-to-off and off-to-on transitions. This fast switching speed is ideal for time-critical applications.

5. What do the 16 yellow LEDs on the module indicate?
Each of the 16 yellow LED indicators corresponds to a specific output channel. They show the current status of the output signal, helping with quick visual troubleshooting.