Measurement of Primary Data

Abstract

The primary data in any experiment consists of the raw basic measurements before any manipulation or data reduction processes have been carried out. In acquiring the primary data, transducers of one sort or another will have been used. The transducer may be considered as a device which converts a measured physical variable, or measurand, into some convenient form of signal. For a microcomputer-based data-acquisition system the transducer signal must ultimately be in the form of an electrical voltage. A Bourdon-tube pressure gauge, for example, is a common enough instrument for measuring pressure, but it cannot be linked to a microcomputer unless the graduated scale indicator can be related in some manner to an applied voltage. While this could actually be done, the availability and range of relatively low-cost pressure transducers would not warrant the practice. The requirement that the output is in voltage form is a consequence of the nature of the analogue interface, see section 6.3, which performs the translation of the analogue voltage level into a digitally encoded number.