【正文】 Selecting the Right Data Acquisition System Engineers 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 designverification stage of product development, environmental chamber monitoring, ponent inspection, benchtop testing and process troubleshooting. This application note describes the various methods and devices you can use to acquire, record and analyze data, from the simple penandpaper method to using today39。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. Introduction In geotechnical engineering, we sometime encounter some difficulties such as 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 collected, stored and processed. The automatic data acquisition control system is able to plete the tasks as regular automatic data monitoring, acquisition and store, featuring high automation, large data store capacity and reliable performance. The system is posed of acquisition control system and display system, with the following features: 1. No. of Channels: 32 ( can be increased or decreased according to user39。s real needs.) 2. Scanning duration: decided by user, fastest 32 points/second 3. Store capacity: 20G( may be increased or decreased) 4. Display: (a) Table of parameter (b) History tendency (c) Column graphics. 5. Function: real time monitoring control, warning 6. Overall dimension: 50cm50cm72cm 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 acquistion 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 sodiumtungsten bronze consisted of a thermocouple, a bridge, a lookup table, a pad of paper and a pencil. Today39。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. Pencil and paper 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 multimeter (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 transcriber39。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 acceptable method when you need to perform a quick experiment. Strip chart recorder 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 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. Scanning digital multimeter Some benchtop 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 instrument39。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 external PC usually handles data acquisition and analysis. PC plugin cards PC plugin cards are singleboard measurement systems that take advantage of the ISA or PCIbus expansion slots in a PC. They ofte