4-20mA HART vs. Foundation Fieldbus

Attribute	4-20mA HART	Foundation Fieldbus
Communication Protocol	Analog	Digital
Signal Range	4-20mA	Varies
Power Supply	Loop powered	External power required
Device Addressing	Point-to-point	Multi-drop
Device Integration	Less complex	More complex

Introduction

When it comes to industrial automation and process control, two commonly used communication protocols are 4-20mA HART and Foundation Fieldbus. Both protocols have their own set of attributes and advantages, making them suitable for different applications. In this article, we will compare the attributes of 4-20mA HART and Foundation Fieldbus to help you understand which one may be more suitable for your specific needs.

Physical Layer

4-20mA HART uses a current loop as its physical layer, where the current signal ranges from 4mA to 20mA to represent the process variable being measured. This current loop is simple and robust, making it suitable for long-distance communication and harsh industrial environments. On the other hand, Foundation Fieldbus uses a digital communication protocol over twisted pair cables, allowing for higher data transmission rates and more complex communication capabilities.

Communication Protocol

4-20mA HART is a hybrid protocol that combines analog 4-20mA signal with digital HART communication. This allows for additional information to be transmitted along with the process variable, such as device diagnostics and configuration parameters. Foundation Fieldbus, on the other hand, is a fully digital protocol that supports advanced features like control in the field, device interoperability, and predictive maintenance capabilities.

Device Integration

4-20mA HART devices are typically easier to integrate into existing systems, as they can be connected to standard analog input/output modules. However, the additional digital communication capabilities of HART may require specialized equipment for full functionality. Foundation Fieldbus devices, on the other hand, require specific Fieldbus-compatible hardware and software for integration, but offer more advanced features and capabilities once integrated.

Network Topology

4-20mA HART communication is typically point-to-point, where each device is connected directly to the control system. This makes it simple to implement and troubleshoot, but limits the scalability and flexibility of the network. Foundation Fieldbus, on the other hand, uses a multidrop topology where multiple devices can be connected to a single communication segment. This allows for more complex network configurations and greater flexibility in system design.

Power Requirements

4-20mA HART devices are typically powered by the current loop itself, eliminating the need for separate power supplies. This makes installation simpler and more cost-effective, especially for remote or hard-to-reach locations. Foundation Fieldbus devices, on the other hand, require external power sources, which may add complexity to the installation process but allow for more advanced functionality and features.

Diagnostic Capabilities

4-20mA HART devices offer basic diagnostic capabilities, such as device status and health information, which can be accessed using a handheld communicator or control system. Foundation Fieldbus devices, on the other hand, provide more advanced diagnostic features, such as predictive maintenance alerts, device configuration, and troubleshooting capabilities, all accessible through the Fieldbus network.

Conclusion

Both 4-20mA HART and Foundation Fieldbus have their own set of attributes and advantages, making them suitable for different applications in industrial automation and process control. While 4-20mA HART is simple and robust, Foundation Fieldbus offers more advanced features and capabilities. The choice between the two protocols will depend on the specific requirements of your application, such as network complexity, device integration, and diagnostic capabilities.