Engineering and Process Control You know more than you realize

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?