System Of Data Acquisition And Application Design

With the rapid development of the digital electronic technology, the computer has been widely applied in the fields of automatic control, self-examination, and signal process etc. In order to realize that gathers and analyses to a large amount of multi-date information and parameter of working site in industrial production in scientific research, people have adopted data gathering and transmission system. "Data collection" refers to the process, that converting the temperature, pressure, flow, displacement, analog into digital acquisition, and then dealing with by the computer storage, processing, display or print. That system is known as the Data Acquisition System. Data Acquisition System is the task of the measured object from the sensor to obtain useful information, and output signals into a computer recognizing the digital signals and then sent to the appropriate computer processing to get the required data.Data acquisition system is generally formed by five parts: data input channels, data storage and management, data processing, output data and showing. The main task of Data Acquisition System is to collect analog signals which sensors output and to convert them into digital signals which the computer can recognize, and then put into the computer processing to get the required data. General micro-computer data acquisition and processing system is operated by sensors, multi-channel analog switches, program-controlled amplifier, sample / holder, A / D converter, computer peripherals and components. Through the task of data acquisition system, we can see that in addition to data collection, the system should process the collected data according to the actual needs. Data processing has a variety of types. According to the methods of processing, it has real-time (online) and after dealing with (offline) processing; according to the nature of processing, it has processing and secondary processing. The major task of Data processing is collecting the signals to do physical explanation, the elimination of data in the signal interference and data analysis of the inherent characteristics. Data acquisition system is mainly composed of hardware and software. From the hardware point of view, there are three forms in the structure of the current data collection system: first is the general micro-computer data acquisition system; second is the direct data controlled computer data acquisition system; three is the Distributed Data Acquisition System.The sensor can be defined as the device which can feel the provisions of the measure and can be used to convert into useful output signals in accordance with certain laws. The sensor is usually composed of the measured sensitive components and conversion components. The sensitive components refer to the part which can feel directly or be responded to measured. The conversion components refer to the part which can convert measurement of sensitive components into electrical signals available for transmission or measurement. The sensors commonly inculde used resistance strain sensors, thermocouple sensors, inductive sensors, capacitive sensors, and piezoelectric sensors. An interface circuit is a circuit who buffer, convert and match between a computer and peripherals. Interface circuit is responsible for the coordination between the CPU and peripheral data. As the host and the peripherals are different in information formats, data bus was not allowed to take up a long-term facilities. Because the speed between the CPU and peripherals does not match, and other reasons, there needing an interface circuit between the host and peripheral. There are usually three transmission ways for CPU and peripherals to input and output data: the delivery of process control, interruption of transmission, and DMA (direct memory access) mode. Data Acquisition System is generally used in the production process. Due to internal or external interference, the measured signals will be superimposed on the interference signal. Commonly, such interference signal is called noise, and the noise is a serious interference to the signal measured. When the measured signal is weak, the noise will be "swamped" out, resulting in a lot of data collection errors. In order to collect accurate data, we need eliminate and suppress the noise in the system. Hardware commonly used measures to interfere with the long-term transfer: begin-way match, end-way match. The anti-jamming methods of power system inculde: the power transformer initial screening, the primary use of the balanced legal system around the power transformers, power transformers used mine to reduce power leakage-flux, the use of noise isolation transformers, power supply using filters, use of good performance Power supply and choice of power supply lines into the relatively stable power supply. When the strong magnetic lines of the electric equipment or power lines would interfere with the instrumentation system' s working, we can adopt the shield technology, which is fully used of low resistance of the conductive material or high permeability of the vessel made of ferromagnetic materials, to shield the parts of vulnerable to be interferred, in order to prevent or suppress a variety of field disruption. The noise suppression measures can be used to resist the noise source, for the elimination of direct interference. This is the first adopted measure. Or we can eliminate the noise or the source of disturbance and noise coupling between the device and radiation, to cut off all kinds of interference pathway, or increase the role of transmission decay, or strengthen the resistance ability of interferred devices to resist and reduce its sensitivity to noise.With the rapid development of electronic technology, due to its high-reliability, high-performance, low-cost, flexible application, single-chip is extensively used in industrial control systems, data acquisition systems, smart instrumentation, office automation and many other fields. By virtue of a single-chip and display, we desinged a system, which make data acquisition technology for data collection and transmission, and data processing and display control into reality. This system is of simple structure, of terrific usage, and easy to master. In this design, we used the AT89C51 to gather 8 paths analog signal (four paths signal of voltage and four current signal respectively ) and then input them in ADC0809 chip separately. AT89C51 offers the frequency of the clock and various kinds of controlling voltage signal for ADC0809 and 8155. After conversion, it will output the form of TTL digital voltage, and then it will pass the MAX485 and convert the digital voltage to the differential voltage. We adopted the international standard RS-485 differential interfaces between sending terminate and the receiving terminate and can be assured the valid transmission in the case of decaying or interfering. In order to monitor voltage or current signals expediently at the local, display the corresponding values and alarm fault signals, it is very important to design a low-cost system with convenient observation and disposal operation. This article brings forward an idea based on a system of digital data collection, transmitting and processing, and introduces the interfaces between the A / D converter and the single chip microcomputer, and analyzes the principal of the transmitting system based on MAX485 serial ports, and describes the method of driving LED by parallel ports in details, and designs a complete circuit architecture and implemented software under this foundation. In addition of clock circuit, the chip can provide the operating frequency; manually reset circuit allow for the system to work more reliablly; frequency circuit, as the additional frequencies that clock circuit provide can not meet all of the chip operating frequency, when necessary to achieve the frequency of changes through sub-frequency circuit to in the design, I used a falling edge trigger D effective to realize the frequency band 2. The system has a small, simple-structure, strong actural effect, high reliability and strong anti-interference ability and so on. As a long-distant transmission data acquisition and processing device, the staff in control room can easily observe the monitoring of voltage or current signals at site. To program facilitatively and debug efortlessly, C language is adopted as the programminglanguage and the developed environment is Keil software...