Interpreting the concept of HART communication protocol

What is the role of HART communication protocol? Recently, many of my friends have been paying attention to this agreement. So here is a detailed introduction to the content of this agreement. This article describes the basic knowledge of this Protocol and analyzes some of its protocol commands and access processes.

HART (Highway Addressable Remote Transducer), an open communication protocol that can address Remote sensor express connect, it is a communication protocol between on-site intelligent instruments and control room equipment launched by Rosement in 1985. The HART device provides communication with relatively low bandwidth and moderate response time, after more than 10 years of development, HART technology has matured abroad and has become an industrial standard for global intelligent instruments ｡

The HART protocol uses the binary Frequency Shift Keying Signal Based on the Bell202 standard, and overlays an audio digital signal with a amplitude of 20mA on the low-frequency 4-5mA analog signal for Bidirectional digital communication, the data transmission rate is 1.2Mbps. Because the average value of the key-1-bit-2 signal is 0, the analog signal sent to the control system is not affected, it ensures compatibility with the existing simulation system. The main variables and control information in the HART protocol communication are transmitted from 4-20mA, in addition, measurement, process parameters, device configuration, calibration, and diagnosis information are accessed through the HART communication protocol ｡

HART communication adopts a half-duplex communication method. It is a transitional product that implements digital signal communication over the existing analog signal transmission line, therefore, it has a strong market competitiveness in the current transitional period and has achieved rapid development. HART has defined a series of commands to work in the form of commands ｡

It has three types of commands. The first type is generic commands, which are understood and executed by all devices. The second type is general behavior commands, the functions provided can be implemented in many field devices (though not all). Such Commands include the function libraries of the most commonly used field devices. The third class is the special device commands, to facilitate work to implement special functions in certain devices, such commands can be made available in the Foundation, it can also be exclusive to the company that developed this command. In a field device, the three types of commands can be found at the same time ｡

HART uses the unified device Description Language DDL. Field Equipment developers use this standard language to describe device features. The HART Foundation is responsible for registering and managing these device descriptions and compiling them into a device description dictionary, the main device uses DDL technology to understand the characteristic parameters of these devices without having to develop special interfaces for these devices, as a result, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can use bus power supply to meet the essential safety and explosion-proof requirements, A dual-master device system consists of a handheld programmer and a management system host ｡

There are a variety of different hosts and Field Equipment in modern industrial production. To use them well, a complete communication protocol is required. The HART protocol was initially developed by Rosemount, USA, it has been used for many years. The HART protocol uses the base-Bell202-Based Frequency Shift Keying Signal, an audio digital signal with a amplitude of 20mA MPa is superimposed on the low-frequency 4-5mA analog signal for mutual digital communication, the data transmission rate is 1.2Mbps. The main variables and control information in the HART protocol communication are transmitted from 4-20mA, in addition, the measurement, process parameters, device configuration, calibration, and diagnosis information are accessed through the HART protocol, the OSI Standard physical layer, data link layer, and application layer are used. The HART Protocol specifies the physical form of transmission, message structure, data format, and a series of operation commands, is a master-slave protocol. When the communication mode is "Q &, one field device only responds to the request. The HART protocol allows two hosts in the system (for example, one for system control and the other for HART communication). If analog signals are not required, up to 15 slave devices can be connected to a single cable line in a multi-point system ｡

HART specifies a series of commands that work in command mode. It has three types of commands:

(1) General commands. This is a command that all devices understand and execute ｡

(2) general behavior commands. The provided functions can be implemented in many field devices. The Commands include the function libraries of the most commonly used field devices ｡

(3) special device commands. In order to facilitate work on certain devices to implement special functions, such commands can be opened for use in the foundation and can be exclusive to the companies that develop this command ｡

The HART communication protocol uses the unified device Description Language DDL. Field Equipment developers use this standard language to describe device features, the HART Foundation registers and manages the device descriptions and compiles them into a device description dictionary, the main device uses DDL technology to understand the characteristic parameters of these devices without having to develop special interfaces for these devices, as a result, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can use bus power supply to meet the essential safety and explosion-proof requirements, A dual-master device system consists of a handheld programmer and a management system host ｡