TABLE OF CONTENTS The last chapter concluded with the development of the standard (also called the "textbook," "classical," or "ideal") form of the PID controller. Equation 4-5 presented it as:
Although it is desirable to have a thorough understanding of both the rationale and the behavior of this standard form, in real applications one often finds the need for subtle deviations from the standard form. Indeed, if one attempted to purchase exactly that form, or choose it from a microprocessor-based system vendor's library of control algorithms, frustration would be the likely result. The reason: few manufacturers offer the standard form of the PID; most offer one or more variations of it, called "configuration options."
Some of the modifications are offered by only a few manufacturers, or even only one. After all, each manufacturer claims to have features that will be an advantage to users of that product. On the other hand, all manufacturers offer many of the modifications in forms that are at least similar to each other. In this chapter we describe some of the more common modifications available, as well as their application or purpose. Several manufacturers' software control forms are reviewed at the end of the chapter. These particular manufacturers were selected to illustrate a range of features; their inclusion here should not be interpreted as an endorsement of their products.
Because of the power and flexibility of the microprocessor, users will encounter most of the modifications, or optional features, to standard PID control in a digital-based system rather...
