addressable

Distant

Transducer) is an open communication protocol for addressing high-speed channels of remote sensors, which was introduced by Rosement Company of the United States in 1985. It is used as a communication protocol between field intelligent instruments and control room equipment. HART devices provide communication with relatively low bandwidth and moderate response time. With the development of 10 years, HART technology has become very mature abroad and has become the global industrial standard of intelligent instruments.

HART protocol adopts FSK frequency shift keying signal based on Bell202 standard, and audio digital signal with amplitude of 0.5mA is superimposed on low-frequency 4-20mA analog signal for two-way digital communication, and the data transmission rate is 1.2Mbps. Because the average value of FSK signal is 0, it does not affect the size of analog signal transmitted to the control system, thus ensuring the compatibility with existing analog systems. In HART protocol communication, main variables and control information are transmitted by 4-20mA. If necessary, other measurement, process parameters, equipment configuration, calibration and diagnostic information can be accessed through HART protocol.

HART communication adopts half-duplex communication mode, which is characterized by realizing digital signal communication on the existing analog signal transmission line. It belongs to the transition product from analog system to digital system, so it has strong market competitiveness and has developed rapidly in the current transition period. Male red deer

A series of commands are specified and work as commands. It has three commands. The first one is called general command, which is understood and executed by all devices. The second category is called general behavior command, which provides functions that can be implemented in many field devices (though not all). These commands include the function library of the most commonly used field devices; The third category is called special equipment command, which is convenient for work and realizes special functions in some equipment. Such orders can be used publicly in foundations and can be unique to the company that developed them. These three types of commands can usually appear in field devices at the same time.

HART adopts a unified device description language DDL. Field equipment developers use this standard language to describe equipment characteristics, and the HART Foundation is responsible for registering and managing these equipment descriptions and compiling them into the equipment description dictionary. The master device uses DDL technology to understand the characteristic parameters of these devices without developing special interfaces for these devices. However, due to this analog-digital mixed signal system, it is difficult to develop communication interface chips that can meet the requirements of various companies. HART can use bus to supply power, which can meet the requirements of intrinsic safety and explosion-proof, and can form a dual-master system with handheld programmer and management system host as the main equipment.