How Control Loops Operate

Table of Contents

Chapter 1: Fundamentals of Control Loops

Topics: Definitions; Process sensors; Sensor characteristics; Controllers; Recorders; Signal conditioners; Final control elements

Learning Objectives:

• Explain the difference between an open loop and a closed loop.
• Define error, feedback, disturbance, and feedforward control.
• List several kinds of process sensors and describe the operation of each.
• Explain how accuracy, resolution, sensitivity, linearity, and step response affect sensor operation.
• Describe the functions of process controllers, recorders, signal conditioners, and final control elements.
• Explain the basic operation of a typical control loop.

Chapter 2: Control Loop Characteristics

Topics: Two-position and floating control; Proportional, integral, derivative, and PID mode; Supervisory control; DDC; DCS

Learning Objectives:

• Describe the difference between continuous and discontinuous control modes and give an example of each.
• Describe the action of the various continuous control modes.
• Define proportional band, reset time, and rate time.
• Discuss the advantages of each of the combination control modes.
• Name several advantages of digital controllers.
• Discuss the differences between supervisory control, direct digital control, and distributed control systems.

Chapter 3: Advanced Control Methods

Topics: Cascade and ratio control system; Feedforward control; Ratio control in a secondary loop; Multivariable control systems

Learning Objectives:

• Describe how a cascade control system works.
• Identify the primary and secondary variables in a cascade loop.
• Compare feedforward and feedback control.
• Identify dependent and independent variables in ratio control.
• Explain the advantage of having a secondary control loop in ratio control.
• Describe how a multivariable control system works and define interaction.

Chapter 4: Loop Dynamics

Topics: Effects of process time lag; Dead time compensation; System stability; Transient response; Gain; Phase shift

Learning Objectives:

• Describe two kinds of process time lags and give an example of each.
• Discuss the effects of capacitance and resistance on loop dynamics.
• State the three main objectives of a well-designed process control system.
• Describe how PI, PD, and PID controllers are adjusted to achieve optimum response.
• Discuss the effects of system gain and phase shift on system stability.

Chapter 5: Loop Protection

Topics: Explosion-proof enclosures; Intrinsically safe instrument systems; Fail-safe mechanisms; Hard and soft constraints; Alarms

Learning Objectives:

• Discuss the classification of hazardous locations as identified in the NEC Handbook.
• Define volatility and flash point, and explain the purpose of a purged enclosure.
• Describe two kinds of explosion-proof enclosures.
• Discuss ways of making a system intrinsically safe.
• Describe examples of fail-safe mechanisms, and differentiate between hard and soft constraints.
• Compare latching and nonlatching alarm systems, and explain the function of annunciators.
• Discuss the purpose and operation of interlocked and sequential control.

Chapter 6: Process Control Symbols and Drawings

Topics: Symbol recognition; Piping and instrument drawing; Location and installation drawing; Loop and wiring diagram

Learning Objectives:

• Recognize standard symbols used in process control diagrams.
• Describe a process control system through the use of instrument symbols.
• Recognize and use four kinds of process control diagrams.

Chapter 7: Flowcharts and Electrical Diagrams

Topics: Sequence of operation; Flowchart; Switches; Relays; Electrical elementary diagram; Pump system schematic; PLC diagram; Symbols

Learning Objectives:

• Convert sequence-of-operation text to a flowchart.
• Read electrical and electronic control diagrams and drawings. 
• Recognize symbols used on electrical and electronic diagrams, including those for PLCs and SAMA logic.
• Convert electrical diagrams to PLC diagrams. 

Request Exam Copies