DeviceNet: Applications, Advantages, and Disadvantages

Introduction

DeviceNet, built upon the Controller Area Network (CAN) protocol, simplifies communication between industrial devices such as sensors and actuators. It provides cost-effective and reliable solutions for small to medium-scale automation systems. This guide highlights DeviceNet’s applications, advantages, and disadvantages to aid your decision-making process.

What is DeviceNet?

DeviceNet is an industrial network protocol designed for communication between industrial devices like sensors, actuators, and controllers within automation systems. It’s based on the Controller Area Network (CAN) protocol and was developed by Allen-Bradley (now Rockwell Automation) in the 1990s. The protocol is now maintained and standardized by ODVA (Open DeviceNet Vendors Association).

Key Features of DeviceNet

• CAN-Based Protocol: DeviceNet utilizes the robust CAN protocol as its transport layer, ensuring high reliability in noisy industrial environments.
• Master-Slave Architecture: Supports hierarchical communication with master devices (e.g., PLCs) managing communication with slave devices (e.g., sensors or actuators).
• Supports Multiple Data Types: Enables efficient transmission of I/O data, configuration parameters, and diagnostic information.
• Power and Data on a Single Cable: Combines power supply and communication lines into a single cable, simplifying wiring and reducing costs.
• Automatic Address Assignment: Features plug-and-play capability with automatic node address assignment, reducing setup time.
• Scalability: Can support networks with up to 64 nodes.
• Error Handling: Incorporates robust error detection and handling mechanisms inherent in the CAN protocol.

How DeviceNet Works

DeviceNet enables communication using a producer-consumer model, where:

• Producers (devices that generate data) send messages.
• Consumers (devices that receive data) process these messages as needed.

It uses three key communication mechanisms:

1. Polled Communication: The master polls devices for data at regular intervals.
2. Change of State (COS): Devices send data only when a state change occurs, reducing network traffic.
3. Explicit Messaging: Used for non-time-critical communication, such as device configuration and diagnostics.

Advantages of DeviceNet

Here are some of the benefits of DeviceNet:

1. Combines power and data on a single cable, reducing installation complexity.
2. Built on the low-cost CAN protocol, making it economical for small to medium-sized networks.
3. CAN-based error detection ensures reliable operation in harsh industrial environments.
4. Open standard supported by multiple vendors, ensuring device compatibility.
5. Simplifies network setup with automatic node addressing and easy device replacement.

Disadvantages of DeviceNet

Here are some of the drawbacks of DeviceNet:

1. Supports a maximum of 64 nodes, making it unsuitable for large-scale applications.
2. Maximum data rate of 500 kbps, which is slower than Ethernet-based protocols.
3. Cable length decreases with higher data rates, requiring repeaters for long distances.
4. Gradual replacement by Ethernet-based protocols like EtherNet/IP, which offer higher performance.
5. Requires specialized tools and expertise for diagnosing and resolving network issues.

Applications of DeviceNet

• Factory Automation: Connecting sensors, actuators, and controllers in manufacturing plants.
• Material Handling: Integrating conveyors, robotic arms, and packaging systems.
• Automotive Industry: Commonly used in assembly lines for communication between PLCs and devices.
• Energy Monitoring: Monitoring and controlling energy distribution within industrial facilities.

Conclusion

DeviceNet provides a cost-effective, simple solution for industrial automation, particularly for smaller networks. While it has limitations in scalability and speed, its benefits make it a reliable choice for many applications.