外文翻譯---正確選擇數(shù)據(jù)采集系統(tǒng)(原文）

1、Selecting the Right Data Acquisition SystemApplication Note 1412Engineers 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

2、and analyze data arises in a wide range of applications, including the design-verification stage of product development, environmental chamber monitoring, component inspection, benchtop testing and process trouble-shooti

3、ng. This application note describes the various methods and devices you can use to acquire, record and analyze data, from the simple pen-and-paper method to using today's sophisticated data acquisition systems. It di

4、scusses 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.IntroductionOn the downside, PC plug-in cards often have o

5、nly 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 radiated throughout

6、. 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 voltag

7、e, temperature or resistance, you may need some sort of external signal conditioning. Additional concerns include problematic calibration and overall system cost, especially if you need to purchase additional signal cond

8、itioning accessories or a PC to accommodate the cards. Taking that into consideration, PC plug-in cards offer an attractive approach to data acquisition if your requirements fall within the capabilities and limitations o

9、f the card. 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 so

10、me 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

11、against user-defined limits, and output signals for control. One advantage of using data loggers is their built-in signal conditioning. Most are able to directly measure a number of different inputs without the need for

12、additional signal conditioning accessories. One channel could be monitoring a thermocouple, another a resistive temperature device (RTD) and still another could be looking at voltage. Thermocouple reference compensation

13、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 com

14、pleted the setup, data 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 dat

15、a to your computer for in-depth analysis. Most data loggers are designed for flexibility and simple configuration and operation, and many provide the option of remote site operation via battery packs or other methods.Dep

16、ending 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 of 250 readings/second are not uncommon. Keep

17、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 acc

18、uracy, multiple readings and averaging are not necessary, as they often are in PC plug-in solutions. Data acquisition front endsData acquisition front ends are often modular and are typically connected to a PC or control

19、ler. They are used in automated test applications for gathering data and for controlling and routing signals in other parts of the test setup. Front end performance can be very high, with speed and accuracy rivaling the

20、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, and proprietary card ca

21、ges.. 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 of