Engineering and Process Control
You know more than you realize
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
How does it work?
ProcessActuator
Control (PDI)
Error(compared to
set point)
Controlled Variable
(temp, conc., height, speed)
Measurement
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/
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
Solution
Height Sensor
Fill tank
Stop/start
Float
Pump
Reed switch
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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
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
Final Schematic
-
+
-
+
Low tank
•Primary magnet keeps circuit closed
•Pump operational
Full tank
•Secondary magnet on float counteracts primary magnet
•Circuit opens
•Pump deactivated
Final Schematic
Photo courtesy of Paul Jowlabar, Lab Manager, Department of Chemical Engineering. Reproduced with permission.
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
Calculations
Energy Input
• Power input (Win) = AV where:
• A = current (A)
V = voltage across load (V)
A
V
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 ( )
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 ( )
Customize the Project
Expandability
• Alter flexible tube diameter
• Adjust size of pump
• Change height of inlet and/or outlet
• Use other fluids – corn syrup, (thicker than water)
Questions?