Explanation about Hart

Abstract: Interpretation information about Hart is provided by excellent flowmeter and flowmeter production and quotation manufacturers. The open communication protocol of the addressable remote sensor high-speed channel is a communication protocol between the field intelligent instrument and the control room equipment introduced by the American Rosement company in 1985. HART devices provide a pass with relatively low bandwidth and moderate response time. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the details of Hart's explanation article. The open communication protocol of the addressable remote sensor high-speed channel is a communication protocol between the field intelligent instrument and the control room equipment introduced by the American Rosement company in 1985. HART devices provide communication with relatively low bandwidth and moderate response time. After more than 10 years of development, HART technology has matured abroad and has become the industry standard for global smart meters. The HART protocol adopts the FSK frequency shift keying signal based on the Bell202 standard, superimposes the audio digital signal with the amplitude of 0.5mA on the low-frequency 4-20mA analog signal for two-way digital communication, and the data transmission rate is 1.2Mbps. Since the average value of the FSK signal is 0, it does not affect the size of the analog signal transmitted to the control system, ensuring compatibility with the existing analog system. In the HART protocol communication, the main variables and control information are transmitted by 4-20mA. In the case of need, additional measurement, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. HART communication adopts a half-duplex communication method, which is characterized by realizing digital signal communication on the existing analog signal transmission line, which is a transitional product in the process of converting the analog system to the digital system, so it has a strong ability in the current transition period. Market competitiveness has developed rapidly. HART specifies a series of commands that work as commands. It has three classes of commands, the * class is called general commands, which are commands that all devices understand and execute; the second class is called general behavior commands, which provide functions that can be implemented in many field devices (though not all), This type of command includes the function library of the most commonly used field devices; the third type is called special device commands, so as to facilitate the implementation of special functions in some devices. Exclusive to the company that developed this order. These three types of commands are usually found in one field device. HART is not a real fieldbus, but a stepping stone in the transition from analog control systems to fieldbuses. HART is a hybrid protocol that combines analog and data signals to represent the information of the control system. By using HART, traditional 4-20 mA (analog) signals are used to represent process variables or control output signals. Secondary variables, device status and device configuration data are transmitted on this 4-20 mA signal using the HART data protocol. HART devices directly connect to HART using the unified device description language DDL. Field device developers use this standard language to describe device characteristics. The HART Foundation is responsible for registering and managing these device descriptions and compiling them into a device description dictionary. The master device uses DDL technology to understand the characteristics of these devices. Develop a dedicated interface. However, due to this analog-digital mixed-signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can use bus power supply, can meet the requirements of intrinsically safe explosion-proof, and can form a dual-master equipment system with a handheld programmer and a management system host as the main equipment. An example of a practical application: command analysis of the communication between the HART/RS232 converter (SM100-A of Songmao Electronics) and the pressure transmitter Step 1: The connection between the HART/RS232 converter and the pressure transmitter Connect according to the wiring diagram, and confirm that the connection is correct. Step 2: Open the HART/RS232 converter test software, open the serial port and connect it, and test the serial port. The HART/RS232 converter and the PC can communicate normally. Step 3: Press start detection, the test software starts to automatically test the test instrument, the ID and other parameters of the instrument are displayed on the test software, and the command analysis: The command format is explained as follows: start bit sequence delimiter address command data The length check digit terminator is to ensure that the command to be sent is completely sent.We deliberately added a start bit '23' before the standard command format preamble and a terminator '40' after the check digit. 1) For example: Send read device serial number command 23 FF FF FF FF FF 02 80 00 00 82 40 The command comment is shown in the following table: Start bit 23 Preamble FF FF FF FF FF Delimiter 02 Address 80 Command 00 Data length 00 Check bit 82 Terminator 40 The returned command format is shown in the following table: Preamble delimiter address Command data length Data check bit Returned data is: FF FF FF FF FF 06 80 00 0E 00 00 FE 11 0E 05 05 01 0C 08 00 5E EE 09 D5 Return data command comments are shown in the following table: Preamble ff ff ff ff ff Delimiter 06 Address 80 Command 00 Data length 0E Data 00 00 FE 11 0E 05 05 01 0C 08 00 5E EE 09 D5 here according to the manual

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