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Engineering and Process Control
You know more than you realize
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Introduction
• Feedback control is found everywhere
• Can be natural or anthropic
• Examples:– Electric kettle– Cruise control– Insulin levels
Image Sources
1. http://www.stashtea.com/mocat.htm
2. http://www.in.gr/auto/dokimes/pr_dokimes_in/Mazda_6_1800/in_Mazda_6_1800_05.htm
3. http://www.fda.gov/fdac/features/2002/102_diab.html
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How does it work?
ProcessActuator
Control (PDI)
Error(compared to
set point)
Controlled Variable
(temp, conc., height, speed)
Measurement
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Problem Description
• To create cola, a company is continuously mixing water and syrup together
• Each component comes from a hold tank
• These tanks must remain full or else the production process will be interrupted
• Design a control system that will maintain the liquid levels
Image Source1. http://www.zanesville.ohiou.edu/emedia/Advertising%20archive/
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Design Criteria
• Tank• Constant liquid level• Draw from a reservoir to the
hold tank• Detect low level• Detect full level• Fill tank if required
MeasureLevel
FillTank
MeasureLevel
NoAction
Full Low
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Solution
Height Sensor
Fill tank
Stop/start
Float
Pump
Reed switch
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+
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Start/Stop – Reed Switch
• When a magnet comes close to a reed switch the two paramagnetic contacts become magnetized and attracted to each other (closes the circuit)
• This allows an electrical current to pass through
• When the magnet is moved away from the reed switch the contacts demagnetize, separate, and move to their original position (opens the circuit)
Glass
Tube
Contacts
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Filling the Tank - Basic centrifugal pump
• Transfer angular momentum of impeller into kinetic energy of discharged fluid
• Faster impeller speed = higher discharge velocity = higher pressure
• Bigger housing = larger impeller = higher volumetric flow rate
Image Source
http://www.yourdictionary.com/ahd/p/p0657700.html
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Final Schematic
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+
-
+
Low tank
•Primary magnet keeps circuit closed
•Pump operational
Full tank
•Secondary magnet on float counteracts primary magnet
•Circuit opens
•Pump deactivated
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Final Schematic
Photo courtesy of Paul Jowlabar, Lab Manager, Department of Chemical Engineering. Reproduced with permission.
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Materials
1. 3V DC motor2. Two AA batteries
(each 1.5 V)3. 500 mL clear water
bottle4. AA Battery holder5. Electrical wire6. Electrical wire clips7. 0.5 m of ¼”clear,
flexible tubing8. Straws
9. Wooden skewers10. Plastic core bard11. High density
Styrofoam12. Two magnets with
centre holes13. Glue14. Reed switch15. Small plastic dish16. Multimeter
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Calculations
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Energy Input
• Power input (Win) = AV where:
• A = current (A)
V = voltage across load (V)
A
V
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Energy Output• Power output (Wout) = Qgh
where:
• Q = vol flow rate (m3/s)
g = acc. Gravity (m/s2)
h = height between pump inlet and outlet (m)
= fluid density (kg/m3)
* Q may also be expressed as A(dh/dt) where A is the cross section area of the tank (assuming the tank has uniform A along h.)
h
Q
Fluid input ( )
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Efficiency
• Overall pump efficiency = Wout/Win
• Pump efficiency is always less than 1
• Source of energy lost:– Electrical resistance– Friction (fluid viscosity,
piping, motor)– Impeller (inherent pump
efficiency)
A
V
h
Q
Fluid in ( )
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Customize the Project
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Expandability
• Alter flexible tube diameter
• Adjust size of pump
• Change height of inlet and/or outlet
• Use other fluids – corn syrup, (thicker than water)
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Questions?