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Chapter 5: Digital Data Acquisitionby John Cimbala ( edited by Lou Cattafesta)

5.1 Analog to Digital Conversion (A/D conversion) Digital data acquisition is used in digital multimeters, digital oscilloscopes, computer-

controlled data acquisition systems, and many other modern instruments. In all these examples, the conversion of an analog signal into a digital signal is

accomplished with an electronic device called an analog-to-digital converter , which willbe abbreviated as an " A/D converter " or " A/D ". The goal of an A/D is to change an analog signal (usually a voltage) into a digital

number (usually in binary form). A/D converters are typically 8-bit, 12-bit, 14-bit, 16-bit, or 24- bit. The number of bits N

represents how many ones and zeroes (bits) are available for the digital output of the A/Dconverter. For example, an 8-bit converter has 8 bits available. For simplicity, consider a 2-bit A/D converter (N = 2) with a range of -5 to 5 volts. The

voltage range is divided into bins as follows:

Analog voltage(volts) Bin number Digital output(binary number) Assigned voltage,V (volts) 5 2.5V < 0 00 -3.752.5 0V < 1 01 -1.25

0 2.5V < 2 10 1.25

2.5 5V