TC-HAI081 HONEYWELL HART模拟输入模块

这个问题先要弄明白什么是HART， HART协议采用基于Bell202标准的FSK频移键控信号，在低频的4-20mA模拟信号上叠加幅度为0.5mA的音频数字信号进行双向数字通讯，数据传输率为1.2Mbps。由于FSK信号的平均值为0，不影响传送给控制系统模拟信号的大小，保证了与现有模拟系统的兼容性。在HART协议通信中主要的变量和控制信息由4-20mA传送，在需要的情况下，另外的测量、过程参数、设备组态、校准、诊断信息通过HART协议访问。HART通信采用的是半双工的通信方式，其特点是在现有模拟信号传输线上实现数字信号通信，属于模拟系统向数字系统转变过程中过渡性产品，因而在当前的过渡时期具有较强的市场竞争能力，得到了较快发展。HART 规定了一系列命令，按命令方式工作。它有三类命令，第一类称为通用命令，这是所有设备都理解、都执行的命令；第二类称为一般行为命令，所提供的功能可以在许多现场设备（尽管不是全部）中实现，这类命令包括最常用的的现场设备的功能库；第三类称为特殊设备命令，以便于工作在某些设备中实现特殊功能，这类命令既可以在基金会中开放使用，又可以为开发此命令的公司所独有。在一个现场设备中通常可发现同时存在这三类命令。

TC-HAI081

HART protocol uses FSK frequency shift keying signal based on Bell202 standard to superposition audio digital signal with amplitude of 0.5mA on 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, the size of the analog signal transmitted to the control system is not affected, and the compatibility with the existing analog system is guaranteed. In HART communication, the main variables and control information are transmitted by 4-20mA, and additional measurement, process parameters, equipment configuration, calibration, and diagnostic information are accessed through HART if needed. HART communication adopts the half-duplex communication mode, which is characterized by the realization of digital signal communication on the existing analog signal transmission line, and belongs to the transitional product in the transformation process from analog system to digital system, so it has strong market competitiveness in the current transition period, and has been developed rapidly. HART prescribes a series of commands that work as ordered. It has three types of commands. The first type is called general commands, which are the commands that all devices understand and execute. The second category, called general behavior commands, provides functions that can be implemented in many (though not all) field devices, including the most commonly used field device libraries; The third category is called special equipment commands, which make it easier to work on implementing special functions in certain devices, and which are either open to use in the foundation or unique to the company that developed the command. It is common to find these three types of commands in a field device.