1、 大连交通大学信息工程学院 毕业设计 (论文 )外文翻译 学生姓名 1111 专业班级 自动化 0111 班 指导教师 1111 职 称 11111 所在单位 电气工程系 教研室 主任 完成日期 1111 年 4 月 13 日 大连 交通大学信息工程 学院 2012 届本科生毕业设计（论文）外文翻译 1 Date Acquisition Date acquisition systems are used to acquire process operating data and store it on secondary storage devices for later analysis.
2、Many of the data acquisition systems acquire this data at very high speeds and very little computer time is left to carry out any necessary, or desirable, data manipulations or reduction. All the data are stored on secondary storage devices and manipulated subsequently to derive the variables of int
3、erest. It is very often necessary to design special purpose data acquisition systems and interfaces to acquire the high speed process data. This special purpose design can be an expensive proposition. Powerful mini- and mainframe computers are used to combine the data acquisition with other function
4、s such as comparisons between the actual output and the desirable output values, and to then decide on the control action which must be taken to ensure that the output variables lie within pre-set limits. The computing power required will depend upon the type of process control system implemented .S
5、oftware requirements for carrying out proportional, ratio or three term control of process variables are relatively trivial , and microcomputers can be used to implement such process control systems . It would not be possible to use many of the currently available microcomputers for the implementati
6、on of high speed adaptive control systems which require the use of suitable process models and considerable on-line manipulation of data. Microcomputer based data loggers are used to carry out intermediate functions such as data acquisition at comparatively low speeds, simple mathematical manipulati
7、ons of raw data and some forms of data reduction. The first generation of data loggers, without any programmable computing facilities, were used simply for slow speed data acquisition from up to one hundred channels. All the acquired data could be punched out on paper tape or printed for subsequent
8、analysis. Such hardwired data loggers are being replaced by the new generation of data loggers which incorporate microcomputers and can be programmed by the user. They offer an extremely good method of collecting the process data, using standardized interfaces, and subsequently performing the necess
9、ary manipulations to provide the information of interest to the process operator. The data acquired can be analyzed to establish correlations, if any, between process variables and to develop mathematical models necessary for adaptive and optimal process control. The data acquisition function carrie
10、d out by data loggers varies from one logging system to another. Simple data logging systems acquire data from a few channels while complex systems can receive data from hundreds, or even thousands, of input channels distributed 大连 交通大学信息工程 学院 2012 届本科生毕业设计（论文）外文翻译 2 around one or more processes. Th
11、e rudimentary data loggers scan select number of channels, connected to sensors or transducers, in a sequential manner and the data are recorded in digital format. A data logger can be dedicated in the sense that it can only collect data from particular types of sensors and transducers. It is best t
12、o use a non-dedicated data logger since any transducer or sensor can be connected to the use of appropriate signal conditioning modules. Microcomputer controlled data acquisition facilitates the scanning of a large number of sensors. The scanning rate depends upon the signal dynamics which means tha
13、t some channels must be scanned at very high speeds in order to avoid aliasing errors while here is very little loss of information by scanning other cannels at slower speeds. In some data logging applications the faster channels require sampling at speeds of up to 100 times per second while slow ch
14、annels can be sampled once every five minutes. The conventional hardwired, non-programmable data loggers sample all the channels in a sequential manner and the sampling frequency of all the channels must be the same. This procedure results in the accumulation of very large amounts of data, some of w
15、hich is unnecessary, and also slows down the overall effective sampling frequency. Microcomputer based data loggers can be used to scan some fast channels at a higher frequency than other slow speed channels. The vast majority of the user programmable data loggers can be used to scan up to 1000 anal
16、og and 1000 digital input channels. A small number of data loggers, with a higher degree of sophistication, are suitable for acquiring data from up to 15,000 analog and digital channels. The data from digital channels can be in the form of Transistor-Transistor Logic or contact closure signals. Anal
17、og data must be converted into digital format before it is recorded and requires the use of suitable analog to digital converters (ADC). The characteristics of the ADC will define the resolution that can be achieved and the rate at which the various channels can be sampled. An increase in the number
18、 of bits used in the ADC improves the resolution capability. Successive approximation ADCs are faster than integrating ADCs. Many microcomputer controlled data loggers include a facility to program the channel scanning rates. Typical scanning rates vary from 2channels per second to 10,000 channels p
19、er second. Most data loggers have a resolution capability of 0.001% or better. It is also possible to achieve a resolution of 1 micro-volt. The resolution capability, in absolute terms, also depends upon the range of input signals, Standard input signal ranges are 0-1- volt, 0-50 volt and 0-100 volt. The lowest measurable signal varies form 1 u volt to 50 u volt .A higher degree of recording accuracy can be achieved by using modules which accept data in small, selectable rages. An alternative is the auto ranging facility available on some data loggers.
