毕业设计（论文）-基于嵌入式ARM平台的远程IO数据采集系统的研究和开发.doc

苏州大学本科生毕业设计（论文）Research and Development of the Remote I/O Data Acquisition System Based on Embedded ARM PlatformINTRODUCTION With the wide use of the networked, intelligent and digital distributed control system, the data acquisition system based on the single-chip is not only limited in processing capacity, but also the problem of poor real-time and reliability. In recent years, with the rapid development of the field of industrial process control and the fast popularization of embedded ARM processor, it has been a trend that ARM processor can substitute the single-chip to realize data acquisition and control. Embedded ARM system can adapt to the strict requirements of the data acquisition system, such as the function, reliability, cost, size, power consumption, and so on. In this paper, a new kind of remote I/O data acquisition system based on ARM embedded platform has been researched and developed, which can measure all kinds of electrical and thermal parameters such as voltage, current, thermocouple, RTD, and so on. The measured data can be displayed on LCD of the system, and at the same time can be transmitted through RS485 or Ethernet network to remote DAS or DCS monitoring system by using Modbus/RTU or Modbus/TCP protocol. The system has the dual redundant network and long-distance communication function, which can ensure the disturb rejection capability and reliability of the communication network. The new generation remote data acquisition and moni- toring system based on the high-performance embedded ARM microprocessor has important application significance. STRUCTRUE DESIGN OF THE WHOLE SYSTEM The whole structure chart of the remote data acquisition and monitoring system based on embedded ARM platform is shown in Figure 1. In the scheme of the system, the remote I/O data acquisition modules are developed by embedded ARM processor, which can be widely used to diversified industries such as electric power, petroleum, chemical, metallurgy, steel, transportation and so on. This system is mainly used for the concentrative acquisition and digital conversion of a variety of electrical and thermal signals such as voltage, current, thermal resistance, thermo- couple in the production process. Then the converted data can be displayed on the LCD directly, and also can be sent to the embedded controller through RS485 or Ethernet network communication interface by using Modbus/RTU or Modbus/TCP protocol. The data in the embedded controller platform is transmitted to the work- stations of remote monitoring center by Ethernet after further analyzed and pro- cessed. At the same time, these data can be stored in the real time database of the database server in remote monitoring center. The system has the dual redun- dant network and long-distance communication function, which can ensure the disturb rejection capability and reliability of the communication network. The hardware platform of the Remote I/O data acquisition system based on emb- edded ARM uses 32-bit ARM embedded microprocessor, and the software plat- form uses the real-time multi-task operating system uC/OS-II, which is open- source and can be grafted, cut out and solidified. The real time operating system (RTOS) makes the design and expansion of the application becomes very easy, and without more changes when add new functions. Through the division of the appli- cation into several independent tasks, RTOS makes the design process of the application greatly simple.Figure 1 Structure of the whole systemTHE HARDWARE DESIGN OF THE SYSTEM The remote I/O data acquisition system based on embedded ARM platform has high universality, each acquisition device equipped with 24-way acquisition I/O channels and isolated from each other. Each I/O channel can select a variety of voltage and current signals, as well as temperature signals such as thermal resis- tance, thermocouple and so on. The voltage signals in the range of 0-75 mV ,1- 5V ,0-5V, and so on, the current signals in the range of 0-10mA and 4-20 mA, the thermal resistance measurement components including Cu50, Cu100, Pt50, Pt100, and the thermocouple measurement components including K, E, S, T, and so on.Figure2. Structure of the remote I/O data acquisition system based on ARM processorThe structural design of the embedded remote I/O data acquisition system is shown in Figure 2. The system equipped with some peripherals such as power, keyboard, reset, LCD display, ADC, RS485, Ethernet, JTAG, I2C, E2PROM, and so on. The A/D interface circuit is independent with the embedded system, which is independent with the embedded system, which is system has setting buttons and 128*64 LCD, which makes the debugging and modification of the parameters easy. The collected data can be sent to the remote embedded controller or DAS, DCS system by using Modbus/RTU or Modbus/TCP protocol through RS485 or Eth- ernet communication interface also, and then be used for monitoring and control after farther disposal. The system of RS485 has a dual redundant network and long-distance communication function. As the embedded Ethernet interface makes the remote data exchange of the applications become very easy, the system can choose RS485 or Ethernet interface through jumper to communicate with host computer. Ethernet interface use independent ZNE-100TL intelligent embedded Ethernet to serial port conversion module in order to facilitate the system maintenance and upgrade. The ZNE-100TL module has an adaptive 10/100M Ethernet interface, which has a lot of working modes such as TCP Server, TCP Client, UDP, Real COM, and so on, and it can support four connections at most. Figure3. Diagram of the signal pretreatment circuitFigure 3 shows the signal pretreatment circuit diagram. The signals of thermo- couple such as K,E,S,T etc and 0-500mV voltage signal can connect to the positive end INPx and the negative end INNx of the simulate multiplexers(MUX) directly. The 4-20mA current signal and 1-5V voltage signal must be transformed by resis- tance before connecting to the positive end INPx and the negative end INNx of the MUX of certain channel. The RTD thermal resistance signals such as Cu50, Cu100, Pt50 and Pt100 should connect one 1mA constant current before connecting to the positive end INPx and the negative end INNx of the MUX of certain channel.Figure4. Diagram of ADC signal circuitFigure 4 shows the ADC signal circuit, which using the 16-bit ADC chip AD7715. The connection of the chip and the system is simple and only need five lines which are CS(chip select), SCLK(system clock), DIN(data input), DOUT (data output) and DRDY(data ready). As the ARM microprocessor has the characteristics of high speed, low power, low voltage and so on, which make its capacity of low-noise, the ripple of power, the transient response performance, the stability of clock source, the reliability of power control and many other aspects should be have higher request. The system reset circuit use special microprocessor power monitoring chip of MAX708S, in order to improve the reliability of the system. The system reset circuit is shown in Figure 5.Figure5. Diagram of system reset circuitSOFTWARE DESIGN AND REALIZATION OF THE SYSTEM The system software of the remote I/O data acquisition system based on embedded ARM platform use the real-time operating system (RTOS) uC/OS-II, which is open-source and can be grafted, cut out and solidified. The key part of RTOS is the real-time multi-task core, whose basic functions including task management, resource management, system management, timer management, memory management, information management, queue management and so on. These functions are used though API service functions of the core. The system software platform use uC/OS-II real-time operating system core simplified the design of application system and made the whole structure of the system simple and the complex application hierarchical. The design of the whole system includes the tasks of the operating system and a series of user applications. The main function of the system is mainly to realize the initialization of the system hardware and the operating system. The initialization of hardware includes interr- upt、keyboard、LCD and so on. The initialization of operating system includes the control blocks and events control blocks, and before the start of multi-task schedu- ling, one task must be started at least. A start task has been created in this system, which is mainly responsible for the initialization and startup of clock, the start-up of interruption, the initialization of communication task module, as well as the division of tasks and so on. The tasks must be divided in order to complete various functions of the real-time multi-task system. Figure6. Functional tasks of the system softwareFigure6 shows the functional tasks of the system software. According to importance of the tasks and the demands of real-time, the system applications are divided into six tasks with different priority, which including the tasks of A/D data acquisition, system monitoring, receive queue, data send, keyboard input, LCD display. The A/D data acquisition task demands the highest real-time requirements and the LCD display task is the lowest. Because each task has a different priority, the higher-priority task can access the ready one by calling the system hang up function or delay function. Figure7. Chart of AD7715 data transfer flowFigure 7 shows the data conversion flow of AD7715. The application A/D conversion is an important part of the data acquisition system. In the uC/OS-II real-time operating system core, the realization process of A/D driver depends mainly on the conversion time of A/D converter, the analog frequency of the conversion value, the number of input channels, the conversion frequency and so on. The typical A/D conversion circuit is made up of analog multiplexer (MUX), amplifier and analog to digital converter (ADC). Figure8. Diagram of the application transfer driverFigure8 shows the application procedure transfer driver. The driver chooses the analog channel to read by MUX, then delay a few microseconds in order to make the signal pass through the MUX, and stabilize it. Then the ADC was triggered to start the conversion and the driver in the circle waiting for the ADC until its completion of the conversion. When waiting is in progress, the driver is detecting the ADC state signal. If the waiting time is longer than the set time, the cycle should be end. During waiting time of the cycle, if the conversion completed signal by ADC has been detected, the driver should read the results of the conversion and then return the result to the application. Figure9. Diagram of serial receiveFigure9 shows the serial receive diagram with the buffer and signal quantity. Due to the existence of serial peripheral equipment does not match the speed of CPU, a buffer zone is needed, and when the data is sending to the serial, it need to be written to the buffer, and then be sent out through serial one by one. When the data is received from the serial port, it will not be processed until several bytes have been received, so the advance data can be stored in buffer. In practice, two buffer zones, the receiving buffer and the sending buffer, are needed to be opened from the memory. Here the buffer zone is defined as loop queue data structure.As the signal of uC/OS-II provides the overtime waiting mechanism, the serial also have the overtime reading and writing ability. If the initialization of the received data signal is 0, it expresses the loop buffer is empty. After the interrupt received, ISR read the received bytes from the UART receiving buffer, and put into receiving buffer region, at last wake the user task to execute read operation with the help of received signal. During the entire process, the variable value of the current bytes in recording buffer can be inquired, which is able to shows whether the receive buffer is full. The size of the buffer zone should be set reasonable to reduce the possibility of data loss, and to avoid the waste of storage space.CONCLUSIONS With the rapid development of the field of industrial process control and the wide range of applications of network, intelligence, digital distributed control System, it is necessary to make a higher demand of the data accuracy and reliability of the control system. Data acquisition system based on single-chip has been gradually eliminated because the problem of the poor real-time and reliability. With the fast popularization of embedded ARM processor, there has been a trend that ARM processor can alternate to single-chip to realize data acquisition and control. The embedded ARM system can adapt to the strict requirements of the data acquisition system, such as the function, reliability, cost, size, power consum- ption, and so on. In this paper, A kind of ARM-based embedded remote I/O data acquisition system has been researched and developed, whose hardware platform use 32-bit embedded ARM processor, and software platform use open-source RTOS uC/OS-II core. The system can be widely applied to electric power, petroleum, chemical, metallurgy, steel, transportation and so on. And it is mainly used in the collection and monitoring of all kinds of electrical and thermal signals such as voltage, current, thermal resistance, thermocouple data of the production process. Then these data can be sent to the remote DAS, DCS monitoring system through RS485 or Ethernet interface. The system has the dual redundant network and long- distance communication function, which can ensure the disturb rejection capability and reliability of the communication network.基于嵌入式ARM平台的远程I / O数据采集系统的研究和开发导言 随着网络化，智能化，数字化分布式控制系统的广泛使用，基于单芯片的数据采集系统不仅在处理能力上受限制，并且在实时性和可靠性方面也出现了问题。近几年来，随着工业过程控制领域的迅速发展和嵌入式ARM处理器的迅速普及，ARM处理器代替单芯片实现数据的采集和控制成为了趋势。嵌入式ARM系统能适应数据采集系统的严格要求，如功能性，可靠性，成本，体积，功耗等等。 在本文中提出一种新型的基于ARM嵌入式平台的远程I / O数据采集系统已被研制开发，它可以衡量各种电气和热参数，如电压，电流，热电偶，热电阻等等。那个测量数据可以显示在液晶显示器的系统中，同时可通过使用Modbus / RTU或的Modbus / TCP协议从RS485或以太网网络传送到DAS或DCS远程监控系统。该系统具有双冗余网络和长途电通信功能，它可以确保通信网络的干扰抑制能力和可靠性。基于高性能嵌入式ARM微处理器的新一代远程数据采集和监控系统具有重要的应用意义。整个系统的结构设计 基于嵌入式ARM的平台的远程数据采集和监控系统的整个结构图在以下的图1中展示。在这系统的计划中，通过使用广泛用于多种行业如电气电力，石油，化工，冶金，钢铁，运输等的嵌入式ARM处理器来开发远程I / O数据采集模块。该系统主要用于的集中采购和将各种电和热信号如电压，热电阻，热电偶在生产过程中进行数字转换。转换的数据可直接在液晶显示器上显示，也可以通过使用的Modbus / RTU或的Modbus / TCP协议的RS485总线或以太网网络通信接口被发送到嵌入式控制器。嵌入控制器平台的数据通过进一步以太网的分析和处理被传送至远程监控中心的工作站。与此同时，这些数据可以存储在远程监控中心数据库服务器的实时数据库中。该系统具有双冗余网络和远程通讯功能，它可以确保通信网络的干扰抑制能力和可靠性。基于嵌入式ARM远程I / O数据采集系统的硬件平台使用32位ARM嵌入式微处理器和软件平台使用的是开源的并且可移植，削减和巩固的实时多任务操作系统的第二代UC / OS核心。实时操作系统（ RTOS ）使设计和应用的扩大变得非常容易，增加新的功能时也没多大变化。通过几个独立的任务的应用，实时操作系统使得应用的设计过程极为简单。系统的硬件设计 基于嵌入式ARM平台的远程I / O数据采集系统具有很高的普遍性，每个购置设备配备24收购方式的I / O渠道且彼此孤立。每个I / O通道可以选择不同的电压和电流信号，以及温度信号如热电阻，热电偶等。在0 - 75mV ,1 - 5V的,0 - 5V范围的电压信号，在0 - 10毫安和4 - 20毫安范围的电流信号，热阻测量元件包括Cu50 ， Cu100 ， Pt50 ，Pt100和热电偶测量元件包括K ，E，S，T等等。嵌入式远程I / O数据采集系统的结构设计如图2所示。该系统配备了一些外围设备，如电源，键盘，复位， LCD显示器，模拟数字转换器， RS485总线，以太网的JTAG ， I2C接口，串行E2PROM等等。该A / D转换接口电路独立于有利于系统维护和升级的嵌入式系统。那个系统有设置按钮和128 * 64液晶显示器，这使得调试和修改参数变得容易。使用通过485或以太网通信接口的Modbus / RTU或的Modbus / TCP协议将收集的数据传送到远端嵌入式控制器或DAS ， DCS系统，然后经过进一步处理将它用于监测和控制。ARM processorRS485系统具有双冗余网络和长途通信功能。正如嵌入式以太网接口使应用的远程数据交流变得非常容易，系统可以通过跳投沟通主机电脑选择485或以太网接口。为了便于系统维护和升级以太网接口使用独立ZNE - 100TL智能嵌入式以太网串口转换模块。该ZNE - 100TL模块具有一个自适应的有很多的工作模式如TCP服务器，客户端的TCP ，UDP连接，实时的COM 10/100M以太网接口，而且它可以最多可支持四个连接。图 3 表示信号预先处理线路图表。热电偶如K，E，S，T等的信号和0 - 500mV的电压信号可以直接接到模拟多路复用器（复用器）的INPx正极和INNx负极。4 - 20mA电流信号和1 - 5V的电压信号必须用阻抗转换。热电阻的电阻信号如Cu50，Cu100，Pt50和Pt100应在接到某些频道的复用器INPx正极和INNx负极前连接一1毫安的恒流源。图4显示了使用16位ADC芯片AD7715的ADC信号电路 。芯片与系统的连接非常简单，只需要CS（芯片选择），SLCK（系统时钟），DIN（数据输入），DOUT （数据输出）和DRDY（数据准备）5根线 。由于ARM微处理器具有高速，低功耗，低电压等优点，这使它在低噪音，纹波权力，瞬态响应性能，时钟来源的稳定，功率控制和许多其他方面需要有更高的要求。为了改善系统的可靠性该系统复位电路中使用特殊的微处理器电源监测芯片MAX708S ，。图5展示了该系统复位电路。系统软件的设计与实现 基于嵌入式ARM平台的远程I / O数据采集系统的软