The Research Of Multi-Channel Data Acquisition And Processing System Based On ARM Embedded System

The petroleum is one kind of precious underground mineral, and is applied every walk of life widespread. The oil field is based by petroleum gathering. The stability of the oil field production system will affect the stability of other industry. So the oil field will need a perfect data acquisition system.The multi-channel data acquisition supervisory system can input the much kind of signal. These signal will be carried on formal processing, automatic sampling, transformation and storage. The information processed by microprocessor will send to computer. Its meaning is to check different signal by the same system. The system will realize the interface of many sensors and computer, and will complete the processing and checking of much kind of signal. The sensor is usually unstable and the measuring accuracy is also low because of the overlapping sensitivity, So it is using the two-dimensional linear method to process the signal. In the article it uses the two-dimensional regression equation to establish the relation between the goal parameter and the sensor output, and calculate the coefficient of regression equation by the least squares method principle under the condition of mean error smallest. Moreover, this is the multi-channel gathering installment, the system gathering quantity is very large, in order to reduce the memory pressure, in the article it has used the data compression method, and it improves the system memory property.The entire data acquisition system divides into the two major parts of the main terminal and the substation. The main terminal is a central control place. Its responsibility is directing and compiling the data of each substation. It receives the data real time from every local computer and forms the total database. Finally it will display entire union station real time by the way of data, flow and curve. The substation is the scene post. It is responsible for the local data acquisition, the data display, and give an alarm and so on. The gathering data of the local computer can display the data by the way of by the data, the flow and the tendency chart. It can set up,operate and inquire the home station according to the right. The communication, carry on the information and acquisition data is completed by LAN or RS485 between the main terminal and the substation.This article primary completes the scene machine. The scene machine actually is the data acquisition system which is composed by a motherboard and each kinds of circuit board. Its responsibility is to transform the multi-channel delivering signal. It can transmitted to the main terminal or the substation, and can also receive the information from the higher authority.1,The Motherboard CircuitThe motherboard is mainly composed of the embedded system of ARM, and it controlled the display module and the memory module (SD card). This system chooses the LPC2132 of PHILIPS as the core processor. LPC2132 is a micro-controller computer of 16/32 bit ARM7TDMI-STM CPU which is supported real-time simulation and embedded track. 16 Thumb model will be used to reduce code size and performance of over 30% of small losses. Its maximum operating frequency can be achieved to 60 MHz. The ARM system which can be used to provide hardware, and which is also low cost, small size, electricity consumption, handling ability, good stability and hardware expansion is easy. The following brief introduction is to the various parts of the motherboard.(1) In power modules, it uses SPI1117 as the main power supply system chip. The chip can provide stable output current 0.8A, 1A stability peak current, Flow and temperature protection, to provide an effective system of stability and security.(2) Because of oil acquisition channel for more data, there is a specialized storage module for data storage. The design of the SD card used as a data storage module from the main control panel directly control, This will not only reduce costs, and also reduce the size of the system.(3) To meet the design requirements of independent tasks completed acquisition, the system designs the show circuit. It can display temperature-depth curves. This system uses the LCM240128ZK of Beijing Qingyun Company as a display screen. In terms of software it usesμC/OS- II which get across the Federal Aviation Administration (FAA) Commercial Vehicle Certification as the main operation system. The operating system has good real-time and stability, and it can fully meet the design requirements.2,The A/D Collection CircuitThe A/D circuit uses the MSC1210 for the MCU core. It will realize the acquisition of the digital signal after the conversion of sensor, and turn the digital signal to the analog signal. It will also process the data (simple computation, etc). It uses the SPI communication between the A/D circuit and ARM. The output of MSC1210 is 5.0V, and the SPI communication of ARM is 3.0V, so it uses the SPI communication board for the voltage conversion.It requests two A/D boards are in a acquisition state of place when I design the A/D circuit. When the main computer needs the sampling results, other computers give the results to the main computer thought the external interruption. And other computers need to make the calculation of the data.3,The Counting CircuitThe counting board also adopts MSC1210 modules to control. And it will count the output of the four channels of the sensor through the three counters of programmable counter/timer of 8253 and the TI of CPU. It will produce the precision timing of the real -time clock, and get the flow testing after the calculation in period of time. And it will finish the sampling. To facilitate the preservation and retrieval of measured results, the FM25040 is used to store acquisition results. In addition, it is also through the SPI communication between the main board and the counting board. The modal of communication is as the same as the A/D board. It is to decide whether to address the transmission of data.4,Data CompressionAs this data acquisition system has been applied to oil fields, the wells, and it needs enormous capacity. It also needs to work long hours in acquisition scene, so the system is very high demands on memory, and it needs for a large capacity storage devices. To alleviate pressure on memory storage in the system it uses the data compression technology. According to the accuracy of system acquisition, the compression technology must not be undermined. As the characteristic of this paper, this design uses predictive coding method combined with LZ77 dictionary, get a new compression method. The compression ratio can reach 34% more after comparative test data. Therefore we can see the compression ratio can be greatly improved after comparing this lossless data compression method with the traditional method.