SMART System for Electrical Heater

1
SMART System for Electrical Heater

• Team 13
• Cheng Wong Clement Wee

2
Overview
SMART System for Electrical Heaters

• Objectives
• Design Features
• Comparison with Conventional Heaters
• Design Description Test Analysis
• Challenges
• Recommendations
• Conclusion
• QA

3
Objectives
SMART System for Electrical Heaters

• To develop a control system for an electrical
  household heater
• To provide dynamically stable heating at a preset
  temperature
• To offer extra efficiency and added comfort to
  end-users with reduced room temperature
  fluctuation

4
Design Features
SMART System for Electrical Heaters

• User interface to preset desired room temperature
• Programmed Micro controller to dynamically
  control heat production
• Sensitive temperature sensors to accurately
  detect the slightest change in room temperature

5
Comparison with Conventional Heaters
SMART System for Electrical Heaters

• Conventional Heater
• Thermostat
• Significant temperature fluctuation
• Temperature exceeds desired level
• Consumer discomfort

• SMART Syst Heater
• Feedback/Control System with microprogrammed
  algorithm
• Minimal temperature fluctuation
• Temperature hardly exceeds desired level
• Consumer comfort and convenience

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Design Description Test Analysis
SMART System for Electrical Heaters

• Design Flowchart
• User Interface
• Input/Output Interface
• Code
• Control Circuit
• Heating Component

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Design Description - Flowchart
SMART System for Electrical Heaters
Temperature Sensors
User Interface
Microprocessor
D/A Converter
Control Circuit
Heating Component
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Code Breakdown
SMART System for Electrical Heaters
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Temperature Data Acquisition
SMART System for Electrical Heaters
Block Diagram
Operational Amplifier
Temperature Sensor
A/D Converter
10
LM 35 Precision Centigrade Temperature Sensor
SMART System for Electrical Heaters

• Pros
• /-0.2 oC accuracy at temperature of 25 oC
• Rated for full -55 oC to 150 oC range
• Cons
• Small scale factor of 10 mV/oC
• i.e at 25 oC, only 0.25V
• Accuracy may not be guaranteed when fed into HC12

Temperature Data Acquisition
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Solution
SMART System for Electrical Heaters

• Use an operational amplifier

Temperature Data Acquisition
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LM 747 Operational Amplifier
SMART System for Electrical Heaters

• Purpose
• Amplify temperature sensor inputs by 10 times.
  Output of Op Amp goes to HC12.

R2
R1
-
Vo

Vi
Temperature Data Acquisition
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LM 747 Operational Amplifier
SMART System for Electrical Heaters

• Closed-loop gain Vo/Vi 1R2/R1
• Setting gain10, R2/R19
• Consider effect of open-loop gain A on the gain
  of the following non-inverting configuration
• G Vo/Vi (1R2/R1)/(1 (1R2/R1)/A)
• Note if A gtgt 1R2/R1, G gt 1R2/R1
• Now since A gtgt 10, effect of A is negligent.
• Therefore Op Amp works

Temperature Data Acquisition
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A/D Converter
SMART System for Electrical Heaters

• Uses HC12s internal ADC
• Read analog voltages as 8 bit binary numbers
• 8 independent channels

Temperature Data Acquisition
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ADC Initialization
SMART System for Electrical Heaters

• Has its own power supply and reference voltages
  need to connect
• Set ADPU bit in ATDCTL2 (a control register)
• Power up the chip
• Choose single mode or multi-mode in ATDCTL5

Temperature Data Acquisition
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ADC Single Multi Modes
SMART System for Electrical Heaters

• Single Mode
• When using just single mode, the converted value
  is stored in all 8 result registers
• Average to get temperature
• Multi Mode
• When using multi-mode, can put several sensors in
  different parts of the room
• Might not be as accurate as different parts of
  the room may get different heating

Temperature Data Acquisition
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Experimentation Multi Mode sensors T1, T2, T3,
T4
SMART System for Electrical Heaters
Temperature Data Acquisition
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Experimentation
SMART System for Electrical Heaters
Temperature Data Acquisition
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Experimentation Conclusion
SMART System for Electrical Heaters

• Single or Multi mode gave similar results when
  averaged out
• But Multi mode reflects the overall room
  temperature much better
• Use Multi mode

Temperature Data Acquisition
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User Interface
SMART System for Electrical Heaters
Block Diagram
Keypad
16-Key Encoder
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User Interface Code Flowchart
SMART System for Electrical Heaters
Set Port A as input port
No
Output error message
No
Yes
No
Is Input gt Room Temp?
Print out number
Yes
Yes
User Interface
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Display Code
SMART System for Electrical Heaters

• Initialization
• Print (individual) character
• Print strings

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SMART System for Electrical Heaters
Initialization
Set Baud Rate Control Register to 9600 Clear
Serial Communication Interface Control Register
(SC0CR) 1 Set Transmit Enable bit and Receiver
Enable bit in SC0CR2
Display Code
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Print Character Code
SMART System for Electrical Heaters

• Check LOOPS bit in SC0CR1
• When LOOPS0, SCI transmit and receive sections
  operate normally
• When LOOPS1, SCI receive section is disconnected
• Occurs if a character is being sent, etc
• Therefore, when LOOPS1, send the 8-bit ASCII
  value to SC0DRL

Display Code
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Print Character Code Flowchart
SMART System for Electrical Heaters
Is LOOPS bit 1?
No
Yes
Transmit character
Display Code
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Print Strings Code
SMART System for Electrical Heaters

• Load string into Register X
• Put the first byte value pointed to by X, send it
  to Print Char routine
• Go to next byte, and do the same
• Stop when a null character is reached

Display Code
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Algorithm
SMART System for Electrical Heaters

• Empirical based
• Voltage Output vs Temperature Difference (Desired
  Temp Room Temp)
• Use Least Squares Solution

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Least Squares Solutions
SMART System for Electrical Heaters

• Given a table of data
• Wish to find linear function
• Y C0 C1X
• have a system of m equations in two unknowns

 
Algorithm
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SMART System for Electrical Heaters
Least Squares Solutions
(
)
)

• X1
• X2
• . .
• . .
• . .
• 1 Xm

(
)

Co C1
Algorithm
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Least Squares Method
SMART System for Electrical Heaters

• Therefore system becomes
• Acy
• Normal equations
• AT AcATy

 
Algorithm
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Least Squares Solutions
SMART System for Electrical Heaters
 

• Solving using l.s method, Co 0.056, C1 1.102

Algorithm
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Voltage Output
SMART System for Electrical Heaters

• Output to PORT B
• Send to 8-bit DAC

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Control Circuit
SMART System for Electrical Heaters

• Function
• To actively vary voltage output to heating
  component through feedback from Microprocessor
• Components
• AC DC Transformer
• Rectifier
• Voltage Regulator
• Input from Microprocessor
• Output to Heating Element

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Control Circuit Flowchart
SMART System for Electrical Heaters
AC-DC Transformer
Rectifier
Input from DAC
Voltage Regulator
Heater Coil
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Control Circuit Schematic
SMART System for Electrical Heaters
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Control Circuit -Voltage Regulator National
Semiconductor LM317T
SMART System for Electrical Heaters

• Features
• Current Limit - 1.5A
• Output Voltage - 1.2V to 37V
• - varies with
  potentiometer
• - Vout 1.25V(1R2/R1) IadjR2
• Vref R2(I1 Iadj)
• Vref voltage across R2
• Input Voltage - gt28V
• Current limit constant with temperature
• Operating temperature range 0 to 125 deg
  celsius
• Output is short-circuit protected

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Control Circuit Voltage Regulator
National Semiconductor LM317T
SMART System for Electrical Heaters

• Implementation
• Input Voltage - 30V
• Replace potentiometer R2 with voltage output
  (Vdac) from DAC
• Output Voltage - 1.2V to 37V
• - Vout Vref Vdac
• Operating temperature range 20 to 40 deg
  celsius

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Testing Control Circuit / Voltage Regulator
SMART System for Electrical Heaters

• Objectives
• To verify the voltage control and voltage
  stability
• characteristics of the regulator
• Test Parameters
• Vin constant, 30V
• Iload
• Vdac vs Vload
• Stability of Vout with applied load, Vload vs
  Rload

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SMART System for Electrical Heaters

• a) Analysis of Vdac and Vload (with Vin 30V,
  Rload 2500 Ohm)
• Linear relationship between Vload and Vdac
• Positive response

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SMART System for Electrical Heaters

• b) Analysis of Vload Rload (with Vdac 13V,
  Vin 30 V)
• Regulator deviates from expected characteristic
  at low values of Rload (Rload lt 2400 Ohm)
• Vload is not constant with Rload

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Heating Coil
SMART System for Electrical Heaters

• Function
• To produce heat and vary temperature of enclosed
  environment
• Implementation
• Input Voltage 1.2V to 37V
• Power Output 2W to 30W
• Coil Resistance 30 Ohms
• Heating Rate 0.5 deg cel/min to 2.5 deg cel/min
  

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Testing Heating Coil
SMART System for Electrical Heaters

• Objectives
• To select a heating coil that achieves a heating
  rate of 0.5 0C/min to 2.5 0C/min
• Test Parameters
• Rload (varies with different heating coil)
• Vload
• Temperature Difference, Tdiff (0C)
• Heating rate of coil, Trise per min
• Cooling rate of coil, Tfall per min

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SMART System for Electrical Heaters

• a) Analysis of Vload and Trise
• Heating Rate, Trise increases with Vload
• Trise falls below Rload
• Desired Trise is unachievable when Rload gt 30
  Ohm

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Challenges
SMART System for Electrical Heaters

• Limited memory of HC12 have to download program
  into EEPROM for greater capability. But that
  means debugger will not be working
• Heater resistance vs voltage regulation

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Recommendation
SMART System for Electrical Heaters

• Acquire more powerful chips
• Drawback more expensive
• Study feasibility of voltage regulator
  modification

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Conclusion
SMART System for Electrical Heaters

• Valuable experience in engineering applications
• Diagnosis and solution of engineering problems
• Project management

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Question Answer
SMART System for Electrical Heaters