An Overview of Feedback Control
Hoofdmodule
Industrial Control Systems
Amin Mannani
Copyright Notice
This work has been made using the text, formulas and figures from the
following book.
Feedback Control of Dynamic Systems,
8th edition (Global Edition)
By Franklin, Powell, Emami-Naeini
ISBN 10: 1-292-27452-2
All parts of this work are under the copyright of the above book.
Language & Concept
⚫
Manual vs. Automatic Control
⚫
Automatic Controllers: control goals
⚫
⚫
–
Regulators: reaching a constant final value
–
Servo or tracking systems: tracking a reference signal
Automatic Controllers: architecture
–
Open loop controller: no measurement of the output is used
–
Closed-loop or feedback controllers: output measured and used
Feedback System Fundamentals
–
Stability
–
Tracking
–
Disturbance rejection
–
Robustness
A Simple Feedback System
⚫
A household furnace controlled by a thermostat
–
Diagram shows the direction of information flow
Figure 1.1:
Feedback control:
(a) component block
diagram of a room
temperature control
system
(b) plot of room
temperature and
furnace action
A Simple Feedback System
⚫
Components of a feedback control loop:
–
Controller
–
Process
–
Actuator (power, speed, reliability)
–
Sensor (low noise, reliability, linearity)
–
Input filter (if required) to convert reference to the (electrical) signal accepted by
controller
Figure 1.2: Component block diagram of an elementary feedback control
A First Analysis of Feedback
⚫
Automobile cruise control (no-dynamics version)
–
A 1° change in throttle angle causes a 10 mph change in speed
–
A 1% change in the road grade changes the speed by 5 mph
Figure 1.3:
Component block diagram of automobile cruise control
A First Analysis of Feedback
⚫
Automobile cruise control (no-dynamics version)
–
A 1° change in throttle angle causes a 10 mph change in speed
–
A 1% change in the road grade changes the speed by 5 mph
Figure 1.4:
Block diagram of the cruise control plant
A First Analysis of Feedback
⚫
Automobile cruise control (no-dynamics version)
–
Open-loop cruise control
Figure 1.5: Open-loop cruise control
A First Analysis of Feedback
⚫
Automobile cruise control (no-dynamics version)
–
Closed-loop cruise control
Figure 1.6: Closed-loop cruise control
Prob. 1.3: Papermaking Machine
⚫
⚫
⚫
To control:
–
Density of the fibers (or, of the thick stock)
–
Moisture content of the final product
How does it work?
–
Stock from machine chest is diluted by the white water out of the CV valve
–
A meter supplies reading of the consistency
–
At the dry end there is a moisture sensor
Identify the following by drawing the block diagram of the system:
–
Process, process desired output signal,
–
Sensor and actuator; actuator output signal
–
Controller; controller output signal
–
Reference signal and error signal
Figure 1.12: Closed-loop cruise control
Prob. 1.3: Pap. Machine (Cont.)
Control of paper machine consistency
Control of paper machine moisture
Prob. 1.6: Transducers
with Electrical Output
⚫
Temperature sensor: Thermistor
–
⚫
Resistance changes with temperature
Pressure sensor: Strain gage
–
Resistance changes with strain,
⚫
Liquid level sensor: Float connected to a potentiometer
⚫
Flow meter:
–
a turbine actuated by the flow with a magnet to trigger an external circuit
Prob. 1.6: Transducers
with Electrical Output
⚫
Linear position: direct mechanical interaction
–
For precise cases LVDT, etc.
⚫
Rotational position sensor: potentiometer, encoder
⚫
Linear velocity:
–
⚫
Rotational velocity: Rate gyro, tachometer
–
⚫
⚫
RADAR, rack-and-pinion, tachometer
use of Hall effect (magnetic to electrical)
Acceleration:
–
Mass movement restrained by a spring measured by a potentiometer
–
A piezoelectric material (current proportional to acceleration)
Force, torque: dynamometer
–
Based on spring/beam deflection measured by a potentiometer