Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001
· A Continuous signal is sampled by the computer
· The computer uses approximation techniques to estimate the analog value during the sampling window.
· An example of an A/D, D/A control of a process is shown below
· Multiplexers are used when a number of signals are to be input to a single A/D converter. This allows each of a number of channels to be sampled, one at a time
· Signal conditioners are often to amplify, or filter signals coming from transducers, before they are read by the A/D converter.
· Output drivers and amplifiers are often required to drive output devices when using D/A
· Sampling problems occur with A/D conversion. Because readings are taken periodically (not continually), the Nyquist criterion specifies that sampling frequencies should be twice the frequency of the signal being measured, otherwise aliasing will occur.
· Since the sampling window for a signal is short, noise will have added effect on the signal read. For example, a momentary voltage spike might result in a higher than normal reading.
· When an analog value is converted to or from digital values, a quantization error is involved. The digital numbering scheme means that for an 8 bit A/D converter, there is a resolution of 256 values between maximum and minimum. This means that there is a round off error of approximately 0.4%.
