具备HART主站功能的模拟量采集模块设计

Design of an Analog Acquisition Module with HART Master Function

摘要:

设计基于CPU+FPGA架构的具备快速HART主站功能的多通道模拟量采集模块；采集模块的CPU与FPGA通过PCIe总线通信；FPGA通过隔离的SPI总线控制8路模拟量采集通道，并与两路协议转换芯片通信；单个协议转换芯片实现一路SPI与四路UART的转换，与四路HART MODEM通过UART接口通信；HART信号通道与模拟量采集通道一一对应，HART信号通过耦合模块与模拟量信号在滤波模块和保护电路之间叠加；模拟量输入信号，经过通道保护电路和滤波模块后到达模拟量转换模块，进行模数转换；通过使用FPGA和协议转换芯片，实现了8个模拟量采集通道的并行采集处理，实现了HART通道串行通信的并行工作；在CPU中运行两个独立线程，各自负责一片协议转换芯片下的四路HART通信，四路HART通信以循环发送和循环接收的方式工作；并行工作的方式提高了模拟量采集的速率，减少了HART通信的等待时间，提高了HART通信的效率；模块通道之间相互隔离，降低了通道间故障相互影响的概率，提高了模块的可靠性；模块支持4~20mA电流信号和±5V、±10V电压信号采集，采集精度0.1%，电流采样电阻250欧姆，通道间隔离电压可达1000VDC。

Abstract:

A multi-channel analog acquisition module which can work as a HART master is designed based on the CPU+FPGA architecture. The CPU and the FPGA of the acquisition module communicates with each other through the PCIe bus. The FPGA controls eight analog acquisition channels through the isolated SPI bus and communicates with two protocol conversation chips. The chip converts one-channel SPI to four-channel UART and communicates with four-channel HART MODEMs through the UART interface. One HART channel corresponds with one analog acquisition channel. HART signals are superimposed with the analog signals between the filtration module and the protection circuit through the coupling module. The analog input signals pass through the channel protective circuit and the filtration module and reach the analog conversion module where analog signals are converted into digital signals. The FPGA and the protocol conversion chips help realize the parallel processing of eight analog acquisition channels and the concurrent working of HART channel serial communication. There are two separated threads in the CPU, each responsible for four channel HART communication which sends and receives signals periodically. The concurrent working method improves the speed of analog acquisition, reduces the delay time and increases the efficiency of the HART communication. The isolated-channel design reduces the impact of fault channels on others, and enhances the reliability of the module. The module can measure 4~20ma current signal and ±5V, ±10V voltage signal, with acquisition accuracy of 0.1%. The module has 250ohms sampling resistance under current mode, and isolation voltage between channels up to 1000VDC.