Control Systems

Table of Contents

Chapter 1: Introduction to Control Systems

Topics: Automatic control; Control system basics; Two-position, floating, and proportional control; Open- and closed-loop control; Operating power

Learning Objectives:

• Explain why control systems are needed and name devices used to control environmental conditions.
• Define the terms used to describe control systems-controlled variable, controller, controlled device, setpoint, control point, and controlled medium-and name the basic elements of a control system.
• Describe the action of two-position, floating, and proportional control.
• Explain how anticipators work.
• Compare open-loop and closed-loop control.
• Compare the basic requirements of pneumatic/hydraulic control systems to those of electric/electronic control systems.

Chapter 2: Sensors and Controlled Devices

Topics: Temperature, humidity, and pressure sensors; Dampers; Valves; Variable-speed drives

Learning Objectives:

• Explain the need for a sensor in a control system.
• Name and explain the operation of three kinds of temperature sensors.
• Define relative humidity, state the range required for human comfort, and describe common humidity sensors.
• Name three common pressure sensors and explain their operation.
• Explain the operation of two-position dampers and valves in shutoff and throttling applications.
• List the advantages of variable-speed drives over older methods of speed control.

Chapter 3: Automatic Control Systems

Topics: Two-position, floating, and proportional electric control; Pneumatic systems, controllers, actuators, relays, and switches; Electronic systems; Proportional band, gain, and PID control

Learning Objectives:

• Describe the operation of two-position, floating, and proportional electric controllers.
• List the equipment needed for a pneumatic control system.
• Name several pneumatic relays and switches, and explain why each is used.
• Discuss the advantages and basic operation of electronic controls.
• Define resolution, sensitivity, proportional band, and gain, and explain how they are related.
• Distinguish between integral and derivative action, and explain how each can improve system performance.

Chapter 4: Control of Refrigeration and Air-Conditioning Processes

Topics: Primary control; Low-pressure, high-pressure, and high-temperature controls; Anti-recycle timers; Pressure regulators; Oil-level controls; Overload protection; Capacity control

Learning Objectives:

• Explain how pumpdown control operates and why pumpdown is often preferred over other methods of primary control.
• Describe the location, function, and operation of a high-pressure control.
• Name three ways to control condenser pressure and at least three ways to control system capacity.
• Explain how a differential oil pressure safety control works.
• Compare the two methods of modulating the flow of water to hydronic terminals.

Chapter 5: Maintaining and Troubleshooting Controls

Topics: Maintaining pressure controls, thermostats, switches, valves, timers, controllers, relays, and power supplies; Troubleshooting the system

Learning Objectives:

• List the four basic steps involved in setting up a PM program.
• Explain the importance of high-pressure controls as safety devices and explain their testing procedures.
• Explain how oil pressure is maintained in various kinds of compressors.
• Describe the testing and maintenance required for condenser water regulating valves and compressor capacity controls.
• Explain how to check for oil and water contamination in control air and what measures to take to minimize them.
• Explain the major maintenance requirements of a pneumatic control system.
• Describe the maintenance required by electric and electronic controllers.
• Explain how to use a troubleshooting chart.

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