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1Northampton Community College
Control System Basics
2Northampton Community College
Control
To cause a machine or process to function
in a predetermined manner.
To energize ...
3Northampton Community College
What is a Controller?
A circuit that excepts inputs:
One input is the action (command sig...
4Northampton Community College
Controller
A unit that controls a machine or process. It
can be, but not limited to a:
PL...
5Northampton Community College
What is a Control System?
An interconnection of components forming a system
configuration w...
6Northampton Community College
What is Process?
Any operation to be controlled.
(A natural, progressively continuing opera...
7Northampton Community College
Main Categories of Control
Open loop control system
Closed loop control system
8Northampton Community College
Open Loop Control System
A control system that has no means of
comparing the output with t...
9Northampton Community College
Open Loop Control System
Motor
Controller
Motor
Conveyor
Did the Conveyor start, and if it ...
10Northampton Community College
Closed Loop Control System
A closed loop control system utilizes an additional signal
tha...
11Northampton Community College
Closed Loop Control System
Motor
Controller
Motor
Conveyor
Rotary Encoder
Feedback speed a...
12Northampton Community College
Classroom Discussion
Is a pop-up toaster and example of an Open
Loop or Closed Loop contro...
13Northampton Community College
Feedback
Feedback
The signal or signals returned from a controlled
machine or process to...
14Northampton Community College
Feedback
Feedback Loop
A closed signal path in which feedback is compared
with the comma...
15Northampton Community College
Feedback
Input
Output
Float feedback
H
16Northampton Community College
Feedforward (bias)
Control action in which information concerning upstream
conditions is ...
17Northampton Community College
Feedforward (bias)
Controller
Control
Output
Setpoint +
-
Error
+
+
Kf
Process Variable (P...
18Northampton Community College
Feedforward Example
Motor+
-
+
-
Colored
soda pop out
Flow
Sensor
Valve
Amount
of colorant...
19Northampton Community College
Ratio Control
Ratio control is another common type of feedback control
system. This contr...
20Northampton Community College
Ratio Control
Motor
Motor+
-
x
+
-
x
Setpoint:
amount of
soda water
required
Setpoint:
amo...
21Northampton Community College
What is a System?
A combination of controller(s),
actuators and sensors that act together...
22Northampton Community College
Control Hierarchy
Local Control
 Control is located at the device to be controlled.
Dis...
23Northampton Community College
Control Classifications
Nonlinear
 The control is either ON or OFF. Most physical contro...
24Northampton Community College
Control Classifications
Servo System
 A feedback control system in which the output is s...
25Northampton Community College
Basic Servo Control System
Encoder Digital
Signal
Command Signal
to motor
Controller
D/A C...
26Northampton Community College
Adaptive Control System
An automatic control scheme in which the
controller is programmed...
27Northampton Community College
Affects on Control Systems
28Northampton Community College
Disturbance
An undesirable signal that tends to adversely affect
the value of the output o...
29Northampton Community College
Examples of Disturbance
Power Line
Externally Conducted
Noise
Transmitted Noise
Ground...
30Northampton Community College
Control Response Characteristics
Steady State Performance
 The ability of a system outpu...
31Northampton Community College
Bibliography
Morriss, S. B. (1995). Automated manufacturing systems:
actuators, controller...
32Northampton Community College
Bibliography
Industrial automation glossary: a helpful guide to allen-bradley
technical te...
33Northampton Community College
Bibliography
Patrick, Dale & Fardo, Stephen. Industrial Process Control
Systems. Delmar P...
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Control Systems Basics

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Control Systems Basics

  1. 1. 1Northampton Community College Control System Basics
  2. 2. 2Northampton Community College Control To cause a machine or process to function in a predetermined manner. To energize or de-energize an output, or to set a data table bit or bits to on or off, by means of a user program.
  3. 3. 3Northampton Community College What is a Controller? A circuit that excepts inputs: One input is the action (command signal) The other is the measurement signal (feedback/feed forward) compares these inputs and determines the output reaction.
  4. 4. 4Northampton Community College Controller A unit that controls a machine or process. It can be, but not limited to a: PLC – Programmable Logic Controller PAC – Programmable Automation Controller Robot controller with digital I/O Relay panel Computer data acquisition (DAQ)
  5. 5. 5Northampton Community College What is a Control System? An interconnection of components forming a system configuration which will provide a desired system response. ProcessInput Output
  6. 6. 6Northampton Community College What is Process? Any operation to be controlled. (A natural, progressively continuing operation of development, marked by a series of gradual changes that succeed one another in a relatively fixed way and lead to a particular result or end).
  7. 7. 7Northampton Community College Main Categories of Control Open loop control system Closed loop control system
  8. 8. 8Northampton Community College Open Loop Control System A control system that has no means of comparing the output with the input for control purposes. Controller Process Input Output
  9. 9. 9Northampton Community College Open Loop Control System Motor Controller Motor Conveyor Did the Conveyor start, and if it did, is it running at the right speed?
  10. 10. 10Northampton Community College Closed Loop Control System A closed loop control system utilizes an additional signal that measures the actual output. It then compares the actual output with the desired setpoint, which in turn adjusted the controller to produce the desired output response. Controller Process Output Command Signal, Setpoint Measurement + - Error
  11. 11. 11Northampton Community College Closed Loop Control System Motor Controller Motor Conveyor Rotary Encoder Feedback speed an position
  12. 12. 12Northampton Community College Classroom Discussion Is a pop-up toaster and example of an Open Loop or Closed Loop control system?
  13. 13. 13Northampton Community College Feedback Feedback The signal or signals returned from a controlled machine or process to denote its response to the command signal. Feedback Element (feedback device) An element that converts motion, position, pressure, flow or temperature to and electrical signal for comparison to the command signal.
  14. 14. 14Northampton Community College Feedback Feedback Loop A closed signal path in which feedback is compared with the commanded value to obtain a corrective error signal. Feedback Signal The measurement signal indicating the value of a directly controlled variable, which is compared to the commanded value to obtain the corrective error signal
  15. 15. 15Northampton Community College Feedback Input Output Float feedback H
  16. 16. 16Northampton Community College Feedforward (bias) Control action in which information concerning upstream conditions is converted into corrective commands to minimize the deviations of the controlled variable. Feedforward is predominantly used to enhance PID control to improve system response. A feedforward control system sends information about a disturbance to the control before it affects the process. This type of control system can also be referred to as predictive control. Systems where the setpoints come from, or are modified by, sensed conditions upstream of the process being controlled. Sometimes called cascade controllers. Cascade suggests that a change in an upstream variable will affect, or cascade down to, later control systems.
  17. 17. 17Northampton Community College Feedforward (bias) Controller Control Output Setpoint + - Error + + Kf Process Variable (PV) Feedforward Path
  18. 18. 18Northampton Community College Feedforward Example Motor+ - + - Colored soda pop out Flow Sensor Valve Amount of colorant required Setpoint: Color sensorColorant In Uncolored soda pop in Setpoint: Final mix color
  19. 19. 19Northampton Community College Ratio Control Ratio control is another common type of feedback control system. This control scheme is often confused with cascade and/or feedforward control but they are quit different. Ratio control is most often used with processes that have two or more streams of material that need to be continually mixed together to form a composition of materials in the final mixture. An example could be that if the blending of two ingredient is 10 to 1 (10:1), then for every liter per minute of one material that is flowing, 10 liters per minute of the second material needs to flow.
  20. 20. 20Northampton Community College Ratio Control Motor Motor+ - x + - x Setpoint: amount of soda water required Setpoint: amount of flavor required Color to flavor ratio setting Color to soda water ratio setting Colorant in Fully mixed soda pop out Flow sensor Flow sensor Flavoring in Soda water in Color sensor Valve Valve
  21. 21. 21Northampton Community College What is a System? A combination of controller(s), actuators and sensors that act together to perform a desired objective.
  22. 22. 22Northampton Community College Control Hierarchy Local Control  Control is located at the device to be controlled. Distributed Control  A control system organization in which factory or machine control is divided into several subsystems, each managed by a separate controller, yet all interconnected to form a single entity.
  23. 23. 23Northampton Community College Control Classifications Nonlinear  The control is either ON or OFF. Most physical control systems are nonlinear. Linear  The control is variable. It is not completely ON or completely OFF but can be.
  24. 24. 24Northampton Community College Control Classifications Servo System  A feedback control system in which the output is some mechanical position, velocity or acceleration. The terms servo system and position, velocity or acceleration controls are used synonymously.
  25. 25. 25Northampton Community College Basic Servo Control System Encoder Digital Signal Command Signal to motor Controller D/A Converter Encoder Analog Servo Amp PWM Motor
  26. 26. 26Northampton Community College Adaptive Control System An automatic control scheme in which the controller is programmed to evaluate its own effectiveness and modify its own control parameters to respond to dynamic conditions occurring in or to the process which affect the controlled variables.
  27. 27. 27Northampton Community College Affects on Control Systems
  28. 28. 28Northampton Community College Disturbance An undesirable signal that tends to adversely affect the value of the output of a system. Types of disturbances:  Internal  External
  29. 29. 29Northampton Community College Examples of Disturbance Power Line Externally Conducted Noise Transmitted Noise Ground Loops Inductive Driven Devices SCR’s Firing Motor Drives Welders
  30. 30. 30Northampton Community College Control Response Characteristics Steady State Performance  The ability of a system output to maintain SP following a disturbance. Transient Performance  The response of a system to maintain SP with abrupt changes to inputs or following an abrupt disturbance. Response Time (Settling Time)  The time required for a system to achieve steady state after an input change or following a disturbance. This time should be as short as possible. Overshoot  The condition when the output temporarily exceeds the desired SP. Oscillatory Behavior  A system that is not at steady state but is continuously varying above and below the SP.
  31. 31. 31Northampton Community College Bibliography Morriss, S. B. (1995). Automated manufacturing systems: actuators, controllers, sensors, and robotics. New York, NY: Glencoe/McGraw-Hill. Hunter, R. P. (1978). Automated process control systems concepts and hardware. Englewood Cliffs, NJ: Prentice-Hall, Inc. Rexford, K.B. (1997). Electrical control for machines. Albany, NY: Delmar Publishing.
  32. 32. 32Northampton Community College Bibliography Industrial automation glossary: a helpful guide to allen-bradley technical terms. (1993). Milwaukee, WI: Allen Bradley. Patrick, D, & Stephen, F. (1997). Industrial process control systems. Albany, NY: Delmar Publishers. Maloney, T. (2001). Modern industrial electronics. Upper Saddle River, NJ: Prentice-Hall. Hughes, T. (2007). Measurement and control basics. Research Triangle Park, NC: International Society of Automation.
  33. 33. 33Northampton Community College Bibliography Patrick, Dale & Fardo, Stephen. Industrial Process Control Systems. Delmar Publishers 1997. ISBN 0-8273-6386-9 Maloney, Timothy, J. Modern Industrial Electronics 4th Edition. Prentice Hall 2001 ISBN 0-13-015676-0
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