TABLE OF CONTENTS The measurement signal appearing at the output of a measurement converter is an analog quantity, described by a continuous function x( y), usually a time-dependent variable x( t). In order to process measurement signals in computer systems, analog signals must be converted into digital signals, which are recorded as binary words. This conversion is performed by analog-to-digital converters (ADCs). The reverse operation, that is the digital-to-analog (D/A) conversion, is very often necessary as well. This operation is performed by digital-to-analog converters (DACs).
Analog-to-digital (A/D) conversion of a variable signal x( t) involves two processes:
Sampling: the drawing of samples of the signal at specific time moments,
Quantizing: assigning to every sample a value X from a finite set of N values, into which the conversion (measurement) range is divided.
After sampling the analog signal becomes a discrete signal, and after quantizing, it becomes a digital signal. In the sampling process the sampling period T s, which is the time between drawing successive samples, is usually constant. This kind of sampling is called uniform sampling. In advanced measurement systems, a variable sampling period is sometimes used. The period is then dependent on the dynamics of the measured quantity x( t). Henceforth, only conversion with uniform sampling will be considered.
The reverse of the sampling period is the sampling frequency, f s = 1/ T s. Sampling consists of digitizing...
