Control Function Block Diagrams EGR 386 8/26/2011
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Control
Function Block Diagrams
EGR 386
8/26/2011
Block diagram: terminology
Feedback Basic Terminology• Process: system or central component whose output is to be
controlled
• Actuator: Device that can influence the process and change the process output
• Plant: Combination of Plant and Actuator
• Controller (or compensator): Device that computes the control signal/variable : Combination of Comparator and Compensator
• Senor: Provides an electrical output proportional to variable to be measuredmeasured
• Reference: the desired value for the output of a system, sometimes called Reference Input or Input or Set point
• Output: the process variable of a system to be controlled
• Comparator: Computes the difference between Reference and Output
• Transfer Function: function when multiplied by an Input provides an Output for the component or system being modeled (usually thought of in terms of Laplace transforms for continuous systems)
Temperature Control Function Block
Diagram: Open Loop System
Desired
Input T
Disturbance
Heat flow
in/out QDist
Compensator
TActual
OutputQIn Plant
dV/dt
Actuator
RoomInput
TemperatureFuel
Flow Control
TSET
TActualFurnace
dV/dt
Fuel
Rate
Reference
Input
TempTSET
Error
Disturbance
Heat flow
in/out QDist
TActual
Temperature Control Function Block
Diagram: Closed-Loop Continuous System
OutputQIndV/dt
Compensator Actuator
RoomTSET
TMeasured
+_
ErrorTActual
Temperature
Sensor
Fuel
Flow Control
Furnace
dV/dt
Fuel
Rate
Function block diagram of a room temperature control system, digital output
Room temperature and furnace output vs. time
Plant and Controller• Plant ~= Actuator + Process
• Controller ~= Comparator + Compensator
Disturbance
Plant Controller
Room
Reference
Input
TempTSET
TMeasured
+_
Error
Disturbance
Heat flow
in/out QDist
TActual
Temperature
Sensor
Output
Fuel
Flow Control
QIn
Furnace
dV/dt
Fuel
Rate
Compensator Actuator
Why is feedback needed?
• Disturbances ( weather changes for example)
• Unmodeled plant or actuator characteristics
• Changes plant or actuator
What is required to control a system
Open Loop? • Compensator + Actuator
• Model of system response to control input
What additional is required to control
a system via feedback control? a system via feedback control?
• Output sensor
• Comparator
Modeling of Systems
• Needed to design an appropriate compensator
(whether feedback is used or not)
• Characterize the system performance or best
possible performancepossible performance
Modeling: Dynamic Models
Mechanical Systems: Car Suspension
Electro/Mech. Systems : Disk Drive
Segway
Electronic circuits
DC Motor
DC motor
• (a) electric circuit of the armature;
• (b) free-body diagram of the rotor
Fluid systems
Thermal Systems (heat transfer)
Steam Engine + Control
Operating parts of a fly-ball governor
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