Data acquisition systems either perform an analysis

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from a process or piece of equipment. Data acquisition systems either perform an analysis of the data or transmit the data to another computer for processing and analysis. A microcomputer is used as the controller/ processor for a current technology DAS. Other possible controller/processor include minicomputers, microprocessor and single-board computers. The function of the controller/ processor includes synchronizing the data sampling and storage, tabulating the data for presentation, and statistical and other analysis. Other components of the DAS include analog transducers, analog- to –digital converters (ADCs), digital transducers, and digital input interfaces. A standard microcomputer can be converted to use as a DAS by adding the necessary ADCs, multiplexers, and other circuitry either as a separate front-end unit or in the form of I/O cards installed in the computer. The means of sampling the data can be either synchronous or asynchronous [6]. Synchronous sampling involves the use of software to drive the sampling process. In this case, the frequency of the sampling rate is determined by the computer processor timer, and sampling must be performed synchronously with the timer. Asynchronous involves the use of hardware to perform the sampling task; this is faster and more accurate, but more expensive. The hardware based system cannot be reprogrammed, thus reducing its flexibility to meet changing application requirements. (2)Multilevel scanning In computer process monitoring, it is possible for the number of monitored to become quite large. Although it is technically feasible to monitor all of the variables, it may result in inefficient use of the computer since some of the variables would not be needed under normal operating condition. In this kind of situation, it is appropriate to utilize a computer process monitoring configuration referred to as multilevel scanning. The configuration is illustrated in figure. In multilevel scanning, there are two (or more) level scan and low-level scan. During normal operation of the process, only the key variables and status data are scanned. When these variables indicate that the process is operating abnormally, the computer switches to low-level scan. For the affected operations and equipment, this low- level scan involves a more complete data logging and analysis procedure to ascertain the source of malfunction. A low –level can be initiated on request of the operator. Figure : Multilevel scanning in computer process monitoring. Low - level scan More complete data Key variables Key variables More complete data High- level scan Process monitoring computer system
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