Analog-to-Digital Conversion of Measurement Data

Physical processes are continuous functions of time and space and manual approaches to measurements of these parameters are cumbersome. In applications such as atmospheric flow patterns, turbulence and combustion, a large volume of data has to be collected in a short span of time. In yet another class of problems, nuclear power plants, process industries and material processing and metal forming operations, for example, process variables must be continuously monitored with the help of a centralized control room to ensure product quality, high efficiency and to prevent accidents. These requirements have necessitated the development of Data Acquisition Systems (DAS) .

A variety of general-purpose as well as special-purpose, stand-alone DAS units are commercially available. However, such units are costly and may not be flexible in their configuration. Their primary use pertains to situations wherein a large number of sensors and hence process variables are employed. For typical laboratory-scale applications, the number of sensors is limited (to say 8 or 16) and low cost DAS can be configured. With rapid advances in the technology of microprocessors, desk-top (personal) computers (PC) and associated peripherals and interfaces, such units have become attractive alternatives to a stand-alone system. The flexibility in configuration is very high for these PC-based DAS and hence a host of options and expansion possibilities are available.

With a properly configured DAS, a variety of tasks can be accomplished through software alone. These include, a collection of probe data as a function time, (b) collection of data simultaneously from a set of probes, (c) post processing of sensor data to extract meaningful information, and (d) generation of control action that would alter the state of the process itself. Step (c) requires that the DAS additionally posses adequate computing power and memory.