【正文】 uracy, multiple readings and averaging are not necessary, as they often are in PC plugin solutions. 31外文翻譯Data 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 other 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, and proprietary card cages.. Although frontend 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.A good, lowcost 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 monly face. Some key applications include: Data 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 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 sophisticated puter 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 mon data acquisition terms are shown below.Data acquisition technology has taken giant leaps forward 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 sodium tungsten bronze consisted of a thermocouple, a bridge, a lookup table, a pad of paper and a pencil. Today’s college students are much more likely 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 plexity of the task, the speed and accuracy you require, and the documentation you want. Data acquisition systems range from the simple to the plex, with a range of performance and functionality.The 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 multiple meters (DMM) and begin recording data by hand.Unfortunately, this method is errorprone, 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 bees bulky and awkward. Accuracy is dependent on the transcribers 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 acceptable method when you need to perform a quick experiment.Modern 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 sufficient internal intelligence to run unattended — without the aid of either an operator or a puter. 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 recorders perform well when monitoring a few channels over a long period of time, their value can be limited. For 35西安交通大學(xué)城市學(xué)院本科生畢業(yè)設(shè)計(jì)（論文）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 waste. Still, recorders are fairly easy to set up and operate, and offer a permanent record of the data for quick and simple analysis.Some bench top DMMs offer an optional scanning capability. A slot in the rear of the instrument accepts a scanner card that can multiplex between multiple inputs, with 8 to 10 channels of mux being fairly mon. DMM accuracy and the functionality inherent in the instruments 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 external PC usually handles data acquisition and analysis.PC plugin cards are singleboard measurement systems that take advantage of the ISA or PCIbus 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 mon, and acquired data is stored directly into the puter, where it can then be analyzed. Because the card is essentially part of the puter, 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 and the user interface. In the downside, PC plugin 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 highspeed clocks and bus noise radiated throughout. Often, this electrical interference limits the accuracy of the PC plugin 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 o