TABLE OF CONTENTS Modern electronic controllers are digital. But while some transmitters and the majority of systems communicate in digital format, the measurements found in industry operate in a continuous world. This is the analog world of measurement. In order for the digital device to communicate (and control), analog-to-digital (A-to-D) and digital-to-analog (D-to-A) conversions are required. There are different methods for performing both types of conversion, and this chapter will outline some of the more prevalent ones.
Before we can perform conversions of any type, however, we must have some way to represent values as binary numbers. These representations are called binary codes. The first part of this chapter concerns number systems, primarily the binary number system. Though this subject was introduced in Chapter 17, this chapter will focus more on conversion and values than on binary logic.
All number systems follow the same rules. You are familiar with the decimal system. Decimal means that the number system is based on ten digits. Its base is ten. The only numbers allowed in the decimal system are 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. All the numbers that we can use to describe numerical quantities in decimal are made up of those ten numbers and no others.
Figure 18-1 illustrates the powers of ten. Notice that a number, such as 4,302.63, is really 4000 + 300 + 2 +.6 + .03, or more correctly, 4 1000 (10 to the third power) + 3 ...
