4-20mA vs. HART

Attribute	4-20mA	HART
Signal Type	Analog	Digital
Communication	One-way	Two-way
Range	4-20mA	Varies
Accuracy	Depends on sensor	High
Cost	Low	Higher

Introduction

When it comes to industrial automation and process control, communication protocols play a crucial role in ensuring seamless data transmission between devices. Two widely used communication protocols in the industry are 4-20mA and HART (Highway Addressable Remote Transducer). Both protocols have their own set of attributes and advantages, making them suitable for different applications.

4-20mA Communication Protocol

The 4-20mA communication protocol is one of the oldest and most widely used analog signals in industrial automation. In this protocol, the current signal ranges from 4mA to 20mA, representing the range of values being measured. One of the key advantages of the 4-20mA protocol is its simplicity and robustness. Since it is an analog signal, it is less susceptible to noise and interference compared to digital signals.

Another advantage of the 4-20mA protocol is its ability to transmit signals over long distances without significant signal degradation. This makes it ideal for applications where devices are located far apart from each other. Additionally, the 4-20mA protocol is easy to implement and does not require complex programming or configuration, making it a cost-effective solution for many industrial applications.

• Simple and robust
• Less susceptible to noise
• Can transmit signals over long distances
• Easy to implement

HART Communication Protocol

HART (Highway Addressable Remote Transducer) is a hybrid communication protocol that combines analog and digital signals. It allows for digital communication over the existing 4-20mA analog signal, providing additional information and functionality. One of the key advantages of the HART protocol is its ability to transmit both process variables and additional data such as device diagnostics and configuration parameters.

Another advantage of the HART protocol is its bi-directional communication capability, allowing for remote configuration and monitoring of devices. This feature enables operators to access real-time data and make adjustments to devices without the need for physical access. Additionally, the HART protocol is backward compatible with existing 4-20mA systems, making it easy to upgrade to HART-enabled devices without replacing the entire infrastructure.

• Combines analog and digital signals
• Transmits process variables and additional data
• Bi-directional communication capability
• Backward compatible with 4-20mA systems

Comparison of Attributes

When comparing the attributes of the 4-20mA and HART communication protocols, several key differences emerge. The 4-20mA protocol is known for its simplicity and robustness, making it a reliable choice for applications where noise and interference are a concern. On the other hand, the HART protocol offers additional functionality and data transmission capabilities, making it a more versatile option for applications that require advanced monitoring and control.

One of the main differences between the two protocols is their communication capabilities. While the 4-20mA protocol can only transmit analog signals, the HART protocol allows for digital communication over the same analog signal. This enables operators to access a wealth of additional data and functionality that is not available with the 4-20mA protocol.

Another key difference between the two protocols is their ease of implementation. The 4-20mA protocol is known for its simplicity and ease of use, making it a popular choice for many industrial applications. In contrast, the HART protocol requires more complex programming and configuration, which may be a barrier for some users.

Overall, the choice between the 4-20mA and HART communication protocols depends on the specific requirements of the application. For simple applications that require reliable and robust communication, the 4-20mA protocol may be the best choice. However, for applications that require advanced monitoring and control capabilities, the HART protocol offers a more versatile solution.