Product Overview of the Allen-Bradley 1794-OB8

The Allen-Bradley 1794-OB8 is a Flex I/O 1794 series output module. Specifically, it provides 8 sourcing current type outputs for your automation system. These outputs are non-isolated for efficient DC load control. The 1794-OB8 fits directly inside a terminal base unit. Consequently, it creates a secure connection between field devices and the I/O bus. This module has received approval for safe operation in hazardous locations. Therefore, you can use it in both European and North American classified areas.

Key Technical Specifications of the 1794-OB8

First, let us examine the output characteristics in detail. The 1794-OB8 provides 8 sourcing outputs with a nominal on-state voltage of 24V DC. Each channel delivers a maximum on-state current of 500mA. Furthermore, the total output current rating for the module is 4A. The on-state voltage drop reaches a maximum of only 0.5V DC. Thus, this module provides efficient power delivery to your loads.

The off-state leakage current is just 0.5mA maximum per channel. Therefore, the 1794-OB8 effectively isolates loads when turned off. The output signal delay varies by direction. Off-to-On delay is a fast 0.5ms for quick response. On-to-Off delay takes a maximum of 1ms for reliable switching.

Electrical and Power Specifications

The 1794-OB8 draws a Flexbus current of 60mA at 5V DC. The external power supply requires 10 to 31.2V DC with a 5% AC ripple. External current draw ranges from 10 to 35mA for the module logic. Maximum power dissipation reaches 3.3W at 31.2V DC. Likewise, maximum thermal dissipation is 11.2 BTU/hr. at 31.2V DC. The isolation voltage rating is 50V continuous for basic protection. Consequently, this module operates efficiently without excessive heat generation.

Hazardous Location Approvals

The 1794-OB8 holds important safety certifications for dangerous areas. It is approved for European hazardous locations under Zone 2 standards. Similarly, it is approved for North American hazardous locations as well. Therefore, you can confidently install this module in classified environments. Always verify your specific area classification before installation.

Hot-Swapping Capability for Easy Maintenance

The 1794-OB8 supports module removal and insertion under power. This is possible because the I/O module has no direct wiring. As a result, you save valuable time during system maintenance. Furthermore, there is no need to restart the entire system after module replacement. This feature eliminates system restarting inefficiency completely. Consequently, your production uptime improves significantly with the 1794-OB8.

Fusing Recommendations for Output Protection

The outputs on the 1794-OB8 are not fused at the factory. Therefore, you should add external fusing for each output channel. This protects your field devices and wiring from overcurrent damage. Use fast-acting fuses rated for 24V DC operation. Typically, a 500mA fuse per channel works well for most applications. Thus, you can customize protection based on your specific load requirements.

Compatibility and Mounting Guidelines

The 1794-OB8 is compatible with several terminal base units. These include the 1794-TB3, 1794-TB3S, and the 1794-TBKD. You can insert or remove the module under power easily. The 1794-OB8 installs using a standard DIN rail mounting method. Simply snap the terminal base onto the DIN rail first. Then, push the module into the base until fully seated.

Additionally, this module supports various communication options. For example, it works with ControlNet, DeviceNet, and EtherNet/IP networks. It also supports Universal Remote I/O for legacy systems. Therefore, the 1794-OB8 integrates seamlessly into your existing architecture.

Status Indicators and Diagnostics

The 1794-OB8 features 8 yellow LED status indicators for visual feedback. Each channel has a corresponding LED showing output signal status. These LEDs help you quickly identify which outputs are active. Consequently, troubleshooting becomes much faster and more intuitive.

Environmental Specifications and XT Versions

The operating temperature range is 0 to 55 °C (32 to 131 °F) . The relative humidity range is 5 to 95% noncondensing. Therefore, the 1794-OB8 works reliably in most industrial environments. Additionally, XT versions of standard modules are available. These XT versions operate in extreme environments with wider temperature ranges. Consequently, they reduce panel and maintenance costs for harsh applications.

Installation Guidelines for the 1794-OB8

First, select a compatible terminal base like the 1794-TB3. Mount the terminal base securely on a DIN rail. Then, snap the 1794-OB8 into the terminal base until fully seated. Always verify that external power is within the 10 to 31.2V DC range. Use proper wire gauges for the 500mA per channel current. Additionally, ensure the total module current does not exceed 4A. Install external fuses on each output channel for protection. Finally, check the yellow LED indicators after power-up. These LEDs confirm correct output operation for each channel.

Package Contents

• One Allen-Bradley 1794-OB8 Flex I/O Digital Output Module

• One user manual with installation instructions

• One label sheet for channel identification

• Four dust covers for unused terminal base slots

Frequently Asked Questions (FAQ)

Q1: How many outputs does the 1794-OB8 provide?
A: The 1794-OB8 provides 8 sourcing outputs for DC load control. Each channel delivers up to 500mA of current. Therefore, it suits most small to medium DC loads.

Q2: Can I remove the 1794-OB8 while power is applied?
A: Yes, the 1794-OB8 supports removal under power. The module has no direct wiring to the terminal base. Consequently, you can replace it without system shutdown.

Q3: Does the 1794-OB8 have factory-installed fuses?
A: No, the 1794-OB8 outputs are not fused at the factory. You should add external fuses for each output channel. This protects your loads from overcurrent damage.

Q4: What terminal base units work with the 1794-OB8?
A: The 1794-OB8 works with 1794-TB3, 1794-TB3S, and 1794-TBKD bases. Always choose a base that matches your wiring requirements.

Q5: Is the 1794-OB8 approved for hazardous locations?
A: Yes, the 1794-OB8 has approval for European hazardous locations. It also holds approval for North American hazardous locations. Thus, you can use it safely in classified areas.