21.1 INTRODUCTION
An analog value is continuous, not discrete, as shown in figure 17.1. In the previous chapters, techniques were discussed for designing logical control systems that had inputs and outputs that could only be on or off. These systems are less common than the logical control systems, but they are very important. In this chapter we will examine analog inputs and outputs so that we may design continuous control systems in a later chapter.
Figure 17.1 - Logical and Continuous Values
Typical analog inputs and outputs for PLCs are listed below. Actuators and sensors that can be used with analog inputs and outputs will be discussed in later chapters.
This chapter will focus on the general principles behind digital-to-analog (D/A) and analog-to-digital (A/D) conversion. The chapter will show how to output and input analog values with a PLC.
