Basic features of HART protocol:

• Bidirectional communication: The HART protocol supports bidirectional data exchange between master and slave devices. The master device can be a control system such as PLC and DCS, while the slave device is usually a variety of industrial equipment such as sensors and actuators.
• Based on 4-20mA analog signal: The HART protocol mainly transmits through 4-20mA analog current signal, and uses frequency modulation (FM) technology to superimpose a digital signal on this analog signal. In this way, existing analog control systems can be compatible with HART devices while also providing digital communication capabilities.
• Multiple device connections: The HART protocol can connect multiple devices (up to 15 devices) on a shared cable. This feature is ideal for large-scale field device deployment.
• Supports standard devices: The HART protocol is compatible with traditional analog devices and can also communicate with modern digital devices.
• Standardized communication protocol: HART protocol follows ISO/IEC
• 62591 standard, and it is open, allowing manufacturers to develop products according to the standard.

How the HART protocol works:

• Analog signal: The traditional 4-20mA analog signal transmits the process variables of the device (such as temperature, pressure, etc.). In this signal, the device's measurement typically maps to a current of 4mA to 20mA.
• Digital signal: The HART protocol superimposes a digital signal on an analog signal through frequency modulation (FM) technology. This means that the analog signal transmitted by the device also contains digital data, and additional information (such as device status, diagnostic information, set values, etc.) can be transmitted without affecting the analog signal.
• Master-slave device communication: HART communication uses the master-slave mode. The master device sends query commands and the device responds with corresponding data. These query commands can be to read sensor data, write set values, obtain diagnostic information, etc.

Communication model of HART protocol:

Equipment configuration and diagnosis: HART protocol supports device configuration and diagnosis functions. It can obtain device status, alarm information, setting values, etc. through digital signals, thereby facilitating operation and maintenance personnel to maintain the equipment.

Command set: The HART protocol has a predefined command set, including device information query, data reading and writing, device diagnosis, firmware upgrade, etc.

Data format:

• The master device sends a command: The master device sends a command in a specific format (such as a request to read data or set parameters) and transmits it through an analog signal.
• Slave device response: After receiving the command, the slave device returns the requested data through a modulated signal, usually including process variables (such as temperature, pressure, etc.) and additional information.

Application of HART protocol:

• Process control: HART protocol is widely used in process automation control systems, especially in chemical, petroleum, natural gas and other industries.
• Smart instruments: The HART protocol enables traditional analog instruments (such as flow meters and temperature sensors) to have digital communication capabilities, enabling more efficient monitoring, diagnosis and maintenance.
• Equipment diagnosis: The diagnostic function of the HART protocol is very powerful. It can obtain the status, fault information, alarm information, etc. of the equipment in real time, making it easy to deal with equipment problems in a timely manner.