外文翻譯--正確選擇數據采集系統(tǒng)

1、.外文資料Selecting the Right Data Acquisition SystemEngineers often must monitor a handful of signals over extended periods of time, and then graph and analyze the resulting data. The need to monitor, record and analyze data arises in a wide range of applications, including the design-verification stage

2、 of product development, environmental chamber monitoring, component inspection, bench top testing and process trouble-shooting.This application note describes the various methods and devices you can use to acquire it, record and analyze data, from the simple pen-and-paper method to using today'

3、s sophisticated data acquisition systems. It discusses the advantages and disadvantages of each method and provides a list of questions that will guide you in selecting the approach that best suits your needs.1. IntroductionIn geotechnical engineering, we sometime encounter some difficulties such as

4、 monitoring instruments distributed in a large area, dangerous environment of working site that cause some difficulty for easy access. In this case, operators may adopt remote control, by which a large amount of measured data will be transmitted to a observation room where the data are to be collect

5、ed, stored and processed. The automatic data acquisition control system is able to complete the tasks as regular automatic data monitoring, acquisition and store, featuring high automation, large data store capacity and reliable performance. The system is composed of acquisition control system and d

6、isplay system, with the following features: 1. No. of Channels: 32 (it can be increased or decreased according to user's real needs.)2. Scanning duration: decided by user, fastest 32 points/second3. Store capacity: 20G ( it may be increased or decreased)4. Display: (a) Table of parameter (b) His

7、tory tendency (c) Column graphics.5. Function: real time monitoring control, warning 6. Overall dimension: 50cm×50cm×72cmData acquisition systems, as the name implies, are products and/or processes used to collect information to document or analyze some phenomenon. In the simplest form, a

8、technician logging the temperature of an oven on a piece of paper is performing data acquisition. As technology has progressed, this type of process has been simplified and made more accurate, versatile, and reliable through electronic equipment. Equipment ranges from simple recorders to sophisticat

9、ed computer systems. Data acquisition products serve as a focal point in a system, tying together a wide variety of products, such as sensors that indicate temperature, flow, level, or pressure. Some common data acquisition terms are shown below:Data acquisition technology has taken giant leaps forw

10、ard over the last 30 to 40 years. For example, 40 years ago, in a typical college lab, apparatus for tracking the temperature rise in a crucible of sodiumtungsten- bronze consisted of a thermocouple, a bridge, a lookup table, a pad of paper and a pencil. Today's college students are much more li

11、kely to use an automated process and analyze the data on a PC today, numerous options are available for gathering data. The optimal choice depends on several factors, including the complexity of the task, the speed and accuracy you require, and the documentation you want. Data acquisition systems ra

12、nge from the simple to the complex, with a range of performance and functionality.2. Pencil and paperThe old pencil and paper approach is still viable for some situations, and it is inexpensive, readily available, quick and easy to get started. All you need to do is hook up a digital multimeter (DMM

13、) and begin recording data by hand.Unfortunately, this method is error-prone, tends to be slow and requires extensive manual analysis. In addition, it works only for a single channel of data; while you can use multiple DMMs, the system will quickly becomes bulky and awkward. Accuracy is dependent on

14、 the transcriber's level of fastidiousness and you may need to scale input manually. For example, if the DMM is not set up to handle temperature sensors, manual scaling will be required. Taking these limitations into account, this is often an acceptableMethod when you need to perform a quick exp

15、eriment.3. Strip chart recorderModern versions of the venerable strip chart recorder allow you to capture data from several inputs. They provide a permanent paper record of the data, and because this data is in graphical format, they allow you to easily spot trends. Once set up, most recorders have

16、sufficient internal intelligence to run unattended without the aid of either an operator or a computer. Drawbacks include a lack of flexibility and relatively low accuracy, which is often constrained to a few percentage points. You can typically perceive only small changes in the pen plots. While re

17、corders perform well when monitoring a few channels over a long period of time, their value can be limited. For example, they are unable to turn another device on or off. Other concerns include pen and paper maintenance, paper supply and data storage, all of which translate into paper overuse and wa

18、ste. Still, recorders are fairly easy to set up and operate, and offer a permanent record of the data for quick and simple analysis.4. Scanning digital multimeterSome bench top DMMs offer an optional scanning capability. A slot in the rear of the instrument accepts a scanner card that can multiplex

19、between multiple inputs, with 8 to 10 channels of mux being fairly common. DMM accuracy and the functionality inherent in the instrument's front panel are retained. Flexibility is limited in that it is not possible to expand beyond the number of channels available in the expansion slot. An exter

20、nal PC usually handles data acquisition and analysis.5. PC plug-in cardsPC plug-in cards are single-board measurement systems that take advantage of the ISA or PCI-bus expansion slots in a PC. They often have reading rates as high as 100,000 readings per second. Counts of 8 to 16 channels are common

21、, and acquired data is stored directly into the computer, where it can then be analyzed. Because the card is essentially part of the computer, it is easy to set up tests. PC cards also are relatively inexpensive, in part, because they rely on the host PC to provide power, the mechanical enclosure an

22、d the user interface. 6. Data acquisition optionsIn the downside, PC plug-in cards often have only 12 bits of resolution, so you can't perceive small variations with the input signal. Furthermore, the electrical environment inside a PC tends to be noisy, with high-speed clocks and bus noise radi

23、ated throughout. Often, this electrical interference limits the accuracy of the PC plug-in card to that of a handheld DMM .These cards also measure a fairly limited range of dc voltage. To measure other input signals, such as ac voltage, temperature or resistance, you may need some sort of external

24、signal conditioning. Additional concerns include problematic calibration and overall system cost, especially if you need to purchase additional signal conditioning accessories or a PC to accommodate the cards. Taking that into consideration, PC plug-in cards offer an attractive approach to data acqu

25、isition if your requirements fall within the capabilities and limitations of the card.7. Data loggersData loggers are typically stand-alone instruments that, once they are setup, can measure, record and display data without operator or computer intervention. They can handle multiple inputs, in some

26、instances up to 120 channels. Accuracy rivals that found in standalone bench DMMs, with performance in the 22-bit, 0.004-percent accuracy range. Some data loggers have the ability to scale measurements, check results against user-defined limits, and output signals for control. One advantage of using

27、 data loggers is their built-in signal conditioning. Most are able to directly measure a number of different inputs without the need for additional signal conditioning accessories. One channel could be monitoring a thermocouple, another a resistive temperature device (RTD) and still another could be

28、 looking at voltage. Thermocouple reference compensation for accurate temperature measurement is typically built into the multiplexer cards. A data logger's built-in intelligence helps you set up the test routine and specify the parameters of each channel. Once you have completed the setup, data

29、 loggers can run as standalone devices, much like a recorder. They store data locally in internal memory, which can accommodate 50,000 readings or more.PC connectivity makes it easy to transfer data to your computer for in-depth analysis.   Most data loggers are designed for flexibility and sim

30、ple configuration and operation, and many provide the option of remote site operation via battery packs or other methods. Depending on the A/D converter technique used, certain data loggers take readings at a relatively slow rate, especially compared to many PC plug-in cards. Still, reading speeds o

31、f 250 readings/second are not uncommon. Keep in mind that many of the phenomena being monitored are physical in nature such as temperature, pressure and flow and change at a fairly slow rate. Additionally, because of a data logger's superior measurement accuracy, multiple readings and averaging

32、are not necessary, as they often are in PC plug-in solutions. 8. Data acquisition front endsData acquisition front ends are often modular and are typically connected to a PC or controller. They are used in automated test applications for gathering data and for controlling and routing signals in othe

33、r parts of the test setup. Front end performance can be very high, with speed and accuracy rivaling the best standalone instruments. Data acquisition front ends are implemented in a number of formats, including VXI versions, such as the Agilent E1419A multifunction measurement and control VXI module

34、, and proprietary card cages. Although front-end cost has been decreasing, these systems can be fairly expensive, and unless you require the high performance they provide, you may find their price to be prohibitive. On the plus side, they do offer considerable flexibility and measurement capability.

35、9. Data Logger ApplicationsA good, low-cost data logger with moderate channel count (20 - 60 channels) and a relatively slow scan rate is more than sufficient for many of the applications engineers commonly face. Some key applications include: Product characterization Thermal profiling of electronic

36、 products Environmental testing; environmental monitoring Component characterization Battery testing Building and computer room monitoring Process monitoring, evaluation and troubleshooting No single data acquisition system works for all applications. Answering the following questions may help you d

37、ecide which will best meet your needs:1. Does the system match my application?What is the measurement resolution, accuracy and noise performance? How fast does it scan? What transducers and measurement functions are supported? Is it upgradeable or expandable to meet future needs? How portable is it?

38、 Can it operate as a standalone instrument?2. How much does it cost?Is software included, or is it extra? Does it require signal conditioning add-ons? What is the warranty period? How easy and inexpensive is it to calibrate? 3. How easy is it to use?Can the specifications be understood? What is the

39、user interface like? How difficult is it to reconfigure for new applications? Can data be transferred easily to new applications? Which application packages are supported? 10. ConclusionData acquisition can range from pencil, paper and a measuring device, to a highly sophisticated system of hardware

40、 instrumentation and software analysis tools. The first step for users contemplating the purchase of a data acquisition device or system is to determine the tasks at hand and the desired output, and then select the type and scope of equipment that meets their criteria. All of the sophisticated equip

41、ment and analysis tools that are available are designed to help users understand the phenomena they are monitoring. The tools are merely a means to an end.譯文正確選擇數據采集系統(tǒng)工程師經常要對很長時間內的很多信號進行監(jiān)測、畫圖和分析產生的數據。監(jiān)測、記錄和分析數據在大范圍內的應用趨勢上升，包括設計-檢定產品發(fā)展狀態(tài)、環(huán)境的監(jiān)測、組成物的檢驗、臺式測試和處理故障檢查。從簡單的紙筆記錄方法到現(xiàn)在所使用的復雜的數據采集系統(tǒng)這些應用筆記描述了你能獲

42、得、記錄和分析數據的很多種不同方法和裝置。討論每一種方法的缺點和優(yōu)點，然后列出一張能夠指引你選擇適合你實際需要的問題單。1前言在工程上，我們有時遇到一些困難，諸如監(jiān)控設備分散在大范圍內，危險的工作環(huán)境很容易引發(fā)一些困難。在這種情況下，操作者可能采用視訊遙控，通過大量檢測數據傳輸到檢測室，在那里收集、存儲和處理數據。自動數據采集的控制系統(tǒng)能夠完成很多任務，像自動定時數據監(jiān)測，數據采集和存儲，高度自動化為特色，大量數據存儲能力和可靠功能。自動數據采集的控制系統(tǒng)和顯示系統(tǒng)優(yōu)如下特點：1）多通路數：32（根據使用者的需要增長或減少）2）掃描持續(xù)時間：由使用者決定，最快一秒種掃描32點3）存儲容量：20

43、G（可能增加或減少）4）顯示：（a）參數表 （b）歷史趨勢 （c）專欄圖表5）功能：實時監(jiān)測、控制和報警6）大體尺寸：50cm×50cm×72cm數據采集系統(tǒng)，正如名字所暗示的，是一種用來采集信息成文件或分析一些現(xiàn)象的產品或過程。在最簡單的形式中，技術人員將烤箱的溫度記錄在一張紙上就是數據采集。隨著技術的發(fā)展，通過電子設備，這個過程已經得到簡化和變得比較精確、多用途和可靠。設備從簡單的存儲器發(fā)展到復雜的電腦系統(tǒng)。數據采集產品像聚焦點一樣為系統(tǒng)服務，和一系列產品一起，諸如傳感器顯示溫度、水流、程度或者過程。數據采集技術在過去30到40年以來已經取得了很大的飛躍。舉例來說,在

44、40 年以前,在一個著名的學院實驗室中,為追蹤用青銅做的坩堝中的溫度上升情況的裝置是由熱電偶、繼電器、查詢臺、一捆紙和一支鉛筆。今天的大學學生很可能在PC機上自動處理和分析數據，有很多種可供你選擇的方法去采集數據。至于選擇哪一種方法取決于多種因素，包括任務的復雜度、你所需要的速度和精度、你想要的證據資料等等。無論是簡單的還是復雜的，數據采集系統(tǒng)都能夠運行并發(fā)揮它的作用。2鉛筆和紙用鉛筆和紙的舊方式對于一些情形仍然是可行的，而且它便宜、易獲得、快速和容易開始。而你所需要的就是捕捉到多路數字信息（DMM），然后開始用手記錄數據。不幸的是這種方法容易發(fā)生錯誤、采集數據變慢和需要太多的人工分析。此外，

45、它只能單通道采集數據；但是當你使用多通道DMM時，系統(tǒng)將很快變得非常龐大和笨拙。精度取決于謄寫器的水平，并且你可能需要自己動手依比例輸入。舉例來說, 如果DMM 沒有配備處理溫度的傳感器,就需要動手找比例。考慮到這些限制，只有當你需要實行一個快速實驗時，它才是一個可接受的方法3長條圖表記錄儀現(xiàn)代多種版本的長條圖表記錄儀允許你從多個輸入取得數據。他們提供數據的長備紙記錄,因為數據是圖解的格式,他們易于現(xiàn)場采集數據。一旦建立了長條圖表記錄儀，在沒有操作員或計算機的情況下，大多數記錄儀具有足夠的內部智能運行。缺點是缺乏靈活性和相對的精度低，時常限制在百分點。你能很清楚地感覺到與筆只有小的改變。在多通

46、道內較長時間的監(jiān)控，記錄儀能發(fā)揮很好的作用，除此之外，它們的價值得到限制。舉例來說，他們不能夠與另外的裝置輪流作用。其他的顧慮就是筆和紙的維護,紙的供給和數據的存儲,最重要的是紙的濫用和浪費。然而，記錄儀相當容易建立和操作，為數據快速而簡單的分析提供永久的記錄。4數字掃描傳多用表一些 臺式 DMMs 提供可選擇的掃描能力。儀器的背面有一個槽孔接收一張在較多輸入時能多重發(fā)訊的掃描儀卡片，通常是8到10通道的多路復用器。固有的在儀器的前面嵌板中的受到限制。它的柔韌性也受到限制，因為它不能超過可用通道數。外部的PC機通常處理數據采集和分析。5PC機插件卡片PC機插件卡片是單板測量系統(tǒng)，它利用ISA或PCI總線在PC機內擴大插槽。它們時常具有高達每秒1000的閱讀速率。8到16通道是普遍的，采集的數據直接存儲在電腦里，然后進行分析。因為卡片本質上是計算機的一部分,建立測試是容易的。PC機卡也相對的便宜,一部分地，因為他們以來主機PC去提供能源、機械附件和使用界面。6數據采集的選擇在缺點上，PC機插件卡片時常只有12字的容量,因此你不能察覺輸入信號的小變化。此外,PC機內的電子環(huán)境經常很容易發(fā)出噪聲、產生高速率的時鐘和總線噪聲，電子接觸面限制PC機插件卡片的精度。這些插件卡片也測量一定范圍的電壓。為了測量其他輸入信號，如電壓、溫度