Digital Control Systems

Introduction

A digital control system provides real-time control of a dynamic system. "Smart" systems usually incorporate one or more sensors to provide feedback on the current state of the system and direction for the next action. One situation that lends itself well to a digital control system is indoor air temperature. Air temperature can be controlled either actively or passively through heating, ventilation, and air conditioning (HVAC) methods. Greenhouses, food production chambers, libraries, etc all require a climate-controlled environment to ensure comfort, safety, and performance. Good HVAC systems provide thermal comfort, acceptable air quality, and reasonable operating and maintenance costs. Simple on-off control systems are an inexpensive option, but they tend to shorten the life of the equipment due to excessive activation of control valves when only a single set point is used. A more practical, long-term alternative is to provide a small amount of hysteresis, or a deadband region, around the set point in which no change to the current action occurs. The width of this deadband can be adjusted to save wear and tear on parts without compromising the overall integrity of the system.

Objectives