1756-CNB/B | Allen-Bradley ControlNet Bridge Module

Introduction to the 1756-CNB/B

When your ControlLogix system needs reliable communication on a ControlNet network, the 1756-CNB/B from Allen-Bradley is a proven solution. This bridge module interfaces a ControlLogix rack to a ControlNet network, enabling seamless data exchange between controllers and I/O devices.

Part of the ControlLogix series, the 1756-CNB/B is designed for standard, non-redundant configurations. It is an ideal choice for applications requiring 40 to 48 Logix communication connections per module, offering a balance of performance and simplicity.

Key Features and Technical Specifications

The 1756-CNB/B is packed with features that make it a versatile and dependable component in industrial automation. Here are the core specifications:

• Manufacturer: Allen-Bradley / Rockwell Automation
• Module Type: Bridge Module for ControlNet
• Maximum Nodes: 99
• Maximum Connections: 64 bidirectional connections (mix of scheduled and unscheduled)
• ControlNet Communication Rate: 5 megabits per second
• Input Current: 970 milliamps at 5.1 Volts DC; 1.7 milliamps at 24 Volts DC
• Power Dissipation: 5.1 Watts
• Thermal Dissipation: 17.4 BTU per Hour
• Slot Width: 1
• Weight: 0.57 pounds (0.26 kilograms)

One distinctive feature is its support for up to 64 bidirectional connections, which allows flexible network design. This capability is particularly useful in applications where multiple devices need to communicate simultaneously, ensuring efficient data flow.

Applications and Use Cases

The 1756-CNB/B excels in distributed I/O applications where multiple racks of ControlLogix I/O modules are installed. It also bridges across networks of different protocols, exchanging information over ControlNet. Additionally, it interfaces with HMI and SCADA systems, making it a central hub for supervisory control.

For example, in a manufacturing plant with several remote I/O racks, the 1756-CNB/B provides a direct path to the main controller, allowing program modifications and tests to be executed efficiently. This capability reduces downtime and improves overall system responsiveness.

Installation and Setup

Installing the 1756-CNB/B is straightforward. First, set the module's node address switches to a unique address between 01 and 99. Then, insert the module into a single slot in the ControlLogix chassis. The module features two ports: one BNC connector for non-redundant media and one NAP (RJ-45 with shield) for network access.

For redundant control setups, use identical pairs of modules and ensure the node address switches are set to the same address. This configuration enhances reliability without complicating the setup.

Maintenance and Reliability

Regular inspection of the 1756-CNB/B ensures long-term reliability. Check the front panel display for module name, connection status, and node address. The module supports self-diagnostics via the online backplane connection, which displays connection properties and error counters.

By monitoring these indicators, you can detect issues early and prevent unexpected downtime. The module's robust design, with a power dissipation of only 5.1 Watts, contributes to its stable operation in industrial environments.

Compatibility and Integration

The 1756-CNB/B is compatible with a wide range of Allen-Bradley platforms, including Flex I/O, POINT I/O, SLC, and PLC5 ControlNet systems. It also works with ControlNet interface cards and Encompass partner modules. This broad compatibility makes it a flexible choice for mixed-vendor environments.

When integrating, ensure the path information is correctly configured to route messages properly. This step is crucial for seamless communication between the ControlLogix backplane and the ControlNet network.

Troubleshooting Common Issues

If you encounter communication errors, first verify the node address is unique and within the 01-99 range. Check the BNC and RJ45 connections for secure seating. Use the module's self-diagnostic features to view error counters and connection properties.

If the module fails to communicate, confirm that the network configuration supports the number of connections you are using. Adding another 1756-CNB module in the same chassis and network can increase capacity if needed.

FAQ

Q: What is the maximum number of nodes supported by the 1756-CNB/B?

A: The 1756-CNB/B supports up to 99 nodes on a ControlNet network.

Q: How many connections can the 1756-CNB/B handle?

A: It supports up to 64 bidirectional connections, which can be a mix of scheduled and unscheduled connections.

Q: What is the communication rate of the 1756-CNB/B?

A: The ControlNet communication rate is 5 megabits per second.

Q: Can the 1756-CNB/B be used in redundant configurations?

A: Yes, it can be used in redundant control setups by using identical pairs of modules with the same node address.

Q: What is the power dissipation of the 1756-CNB/B?

A: The power dissipation is rated at 5.1 Watts.

Product Support and Availability

The 1756-CNB/B is available from Petro Auto Tech, an industrial automation parts supplier. It is in stock and ready to ship. For detailed technical support, contact Petro Auto Tech to ensure the module meets your application requirements.