基于HART协议的智能多段式电容汽包液位计设计

Design of Intelligent Multi-segment Capacitive Level Meter for Boilers Based on HART Protocol

多段式电容液位计采用基于电容数字转换技术的专用电容测量芯片PCap01进行多段电容高精度同时测量。测量结果通过SPI通信接口传送给单片机,经过数据处理之后,通过D/A转换芯片AD421输出两线制标准的4~20m A信号,同时应用HART调制解调芯片DS8500在4~20m A模拟信号的基础上叠加数字音频信号进行双向数字通信。通过HART协议访问传感器的测量过程参数、设备组态及校准等信息,实验结果表明:该液位计精度等级可以达到0.5级。

An intelligent multi-segment capacitive level meter was designed,which has the capacitive to digital conversion technology-supported PCap01 special chip based to measure each segment's capacitance accurately and then has the measurement results transmitted to the MCU via a SPI communication interface and to output 4 ~ 20 m A current signal through a AD421 D / A chip. Through making use of HART DS8500 modem chip and adding FSK signal to the 4 ~ 20 m A current signal,a two-way digital communication can be realized.Basing on the HART protocol,the information like the process parameters,device configuration and calibration can be accessed. Experimental results show that this level meter's accuracy grade can reach 0. 5.