基于嵌入式ARM平台的远程IO数据采集系统的研究和开发.docx

1、基于嵌入式ARM平台的远程IO数据采集系统的研究和开发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

2、 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

3、 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

4、 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

5、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- torin

6、g 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 sys

7、tem, 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

8、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 communicat

9、ion 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 data

10、base 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-

11、 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 ve

12、ry 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

13、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, thermoco

14、uple 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.F

15、igure2. 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, E2P

16、ROM, 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 embedd

17、ed 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

18、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 mo

19、dule 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 pret

20、reatment 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 si

21、gnal 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 t

22、he 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 i

23、nput, 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 contr

24、ol 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

25、REALIZATION OF THE SYSTEMThe 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

26、 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 syst

27、em 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 re

28、alize 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 tas

29、k 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 o

30、rder 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

31、 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 priorit

32、y, 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/O

33、S-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 a