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Total House Power Monitoring System
Design Report
Client:
Herb Harmison
Advisor:
James Triska
Glenn Hillesland
Team:
Sunil Varghese
Ying Chiu Luk
Adam Wheeler
Matthew Gordon
May 03-18
December 10, 2002
Table of Contents
1.
2.
3.
Introductory Materials
Abstract
Acknowledgement
Definition of Terms
Project Design
Introduction
General Background
Technical Problem
Operating Environment
Intended Users
Assumptions
Design Requirements
Design Objectives
Functional Requirements
Design Constraints
Measurable Milestones
End-Product Description
Approach and Design
Technical Approaches
Technical Design
Testing Description
Risks and Risk Management
Recommendation for Continued Work
Financial Budget
Personal Effort Budget
Project Schedule
Closure Material
Project Team Information
Summary
References
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List of Figures
Figure 1: Hardware design block diagram
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Hardware design block diagram
Analog watt meter
Power triangle
Wattmeter schematic on incoming line
Diagram of final system design
Voltage measurement diagram
Diagram of current measuring circuit
The pin assignments for the 25-pin (left) and
9-pin (right) serial ports
Pin assignments for the National Semiconductor
RS-232 driver chip
Circuit schematic of the RS-232 driver chip
Connected to the 25-pin and 9-pin serial port
cables. Also shown are the external capacitors
required for the chip.
Diagram of the 5V power supply
Block diagram of system
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List of Tables
Table 1: Power dissipation of resistors
p. 13
Table 2: Financial Budget Estimate
p. 19
Table 3: Financial Budget Actual
p. 19
Table 4: Personal Effort Estimate
p. 19
Table 5: Personal Effort Revised
p. 19
Table 6: Gantt Chart
p. 20
Introductory Material
Abstract
Homeowners are currently unable to tell how total power consumption is distributed in
the home. They also only get feedback of their consumption on a monthly basis. The
Total House Powering Monitor System will allow users to monitor power consumption of
one’s home in real-time. Hardware will be developed, using a wattmeter to measure the
total power consumption. The data will be collected and sent to a user interface and a
database for long-term trend analysis. The interface will give the user the option of
setting alarms and monitoring total consumption.
Acknowledgements
Mr. Herb Harmison and Mr. Glenn Hillesland have provided the team with guidance and
great technical advice. Their contributions are greatly appreciated by the whole team.
Definition of Terms
CT - Current transformer
PT – Power transformer
VA – Volt-Ampere
W – Watts
PC – Personal computer
A/D – Analog digital converter
Project Design
Introduction
General Background
The total house power monitoring system will allow a homeowner to monitor
total power consumption within his or her home. A read out of real-time power
consumption measured in Watts will be displayed on an interface similar to a
thermostat. The same information will have the capability of loading onto a
spreadsheet where it can be graphed.
Technical Problem
Current monitored using a CT and voltage will be monitored using a PT. A
microcontroller will collect the data and send it to the user interface for display
and to the database for records. Through the combination of current and voltage,
a power triangle can be calculated to determine the power factor. The user
interface will have a numeric readout of power consumed and lights that will
warn the user of high energy usage.
The hardware portion of the project will consist of a metering device that will
plug in between an appliance and an electrical outlet. It will be connected to the
PC via serial cable. The software will perform necessary calculations and record
data to a file on the hard drive. The data will be useable on any compatible
computer and can be analyzed by any graphing software.
Pow e r Cord
Wall Socke t
Pow e r Cord
Prototype
RS232 Cable
Appliance
Com puter
Figure 1: Hardware design block diagram
Operating Environment
Shielding and protection from the elements is a non-issue because the intended
location of the device will be indoors. The unit will possibly be in a fairly dirty
environment with dust and other contaminants. The unit components will need an
operating range between 40 and 115 degrees Fahrenheit.
Intended User(s) and Use(s)
The system will be used by homeowners for the purpose of monitoring power
consumption of appliances and other electronic devices within the home. The
system will not automatically control power consumption, only monitor it.
Assumptions
- The unit will monitor U.S. Power (60 Hz, 120V lines).
- The user will be familiar with operating a computer.
- The user will have a basic knowledge of electricity and the concept of power.
- The user will need an understanding of the utility rates in their respective area.
Limitations
- The unit will have a single line read out.
- The unit will limited in the max amps it is able to monitor. The small
equipment needed for this project is the limiting factor.
- The environment will be within the limits specified above.
Design Requirements
Design Objective
- Read current using a current transformer and a resistor network connected to
an A/D to measure and digitize the voltage waveform..
- The interface should receive the data from the microcontroller and display it
in a way that is easy for the user to understand.
- The interface will have the ability to signal the user of a period of high power
consumption. This can be done both visually and audibly.
- A spreadsheet in Microsoft Excel will help the user see trends in power
consumption.
Functional Requirements
- Measure the total amount of power that is being consumed.
- Display the power consumption to the user.
- Allow the user to set alarms to warn them of high power consumption with
lights and sounds.
- Store the data collected to a database for analysis. This will be done by
method of graphs and charts.
- Have a reliable source of power. This is to reduce the risk of losing data when
the unit is unplugged.
Design Constraints
- Protecting the system from an over-current by having a fuse.
- The monitoring system must fit easily behind appliances; the microcontroller
must be small enough to mount near the unit.
- The entire system needs to remain within a $100 budget.
Measurable Milestones
- Check the resistor network to ensure accurate voltage measurement. (7.5 %)
- Check the current transformer to ensure accurate current measurement. (7.5%)
- Using a microcontroller, calculate the power consumption and send to the
interface. (40%)
- The interface is able to display the power consumption both with lights or a
visual indicator along with the actual read out of consumed power in Watts.
(25 %)
- Communication via serial cable will be needed to transfer the measured values
from the unit to a PC. (20 %)
End-Product Description
The total house power monitor is a device that can monitor total power in a single home
appliance as a function of time. Any number of portable units can be installed within the
house. There will be a visual and audible method the unit uses to alert the user of high
consumption situations. There is also the serial cable connection capable of loading
information retrieved by the device into a spreadsheet for further analysis and recovery of
data.
Approach and Design
The measuring device can be done with one of
two methods. It can be measured using analog
devices or digital circuits.
One method is to have three analog devices.
Voltage can be measured of the incoming
power line. Current can be measured through
the use of a current transformer. Watts can be
measure utilizing a watt-meter.
The method that we are considering to
implement is the digital circuit. The digital
approach is chosen because we can create a
smaller unit by building a circuit to measure
current and voltage.
Technical Approaches
- Monitor current with the use of a
CT. The CT will reduce the actual
current value to a corresponding
value between 0 and 5 amps.
- Monitor voltage through a network of
Figure 2: Analog Wattmeter
resistors.
- Place the product between the wall socket and the appliance.
- Use similar A/D converters to digitize the current and voltage measurements.
- The A/D converters will then send the digital signal to a RS232 Driver. The
driver is needed to send the data through the serial communication cable to the
PC.
Technical Design:
Analog Meter Approach
- The use of CT’s and PT’s is a cheap and easy way to calculate current and
voltage.
- A wattmeter will be used to record the wattage for calculating a power
triangle. The hypotenuse of this triangle can be calculated from multiplying
the RMS voltage and the RMS current values together. The height of the
triangle will need be calculated. The height of the triangle will represent the
reactive power the appliance is using/causing.
Figure 3: Power Triangle
-
The display might be analog composition of all three devices, as shown in
Figure 4. The interface will be made simple to start and add features
dependent on time and money. More featured will add more interest.
Figure 4: Wattmeter schematic on incoming line..
Digital Circuit Approach
- This approach is chosen because of its simplicity in hardware and software
design.
- In Figure 5 is a block diagram of the final hardware approach that is being
implemented. The hardware has four main parts, the voltage measurement,
current measurement, power supply, and the computer interface devices. The
job of the hardware is to provide the computer with a scaled replica of the
current and voltage waveforms that are feeding the load. This is done by
scaling the current and voltage waves down to a 0 to 5V scale first. They are
both then digitized by the A/D and sent to the computer by the RS232 driver.
Neutral
Load
Hot
CT
Voltage
Measurment
Serial
Communication
A/D
Wall Plug
Hot
Neutral
5V
Gnd
Input
5V
Supply
5V
AD7823
Computer
Driver
A/D
Current
Measurment
RS 232
DS14C232
AD7823
LP2954
Figure 5: Diagram of final system design.
Voltage Measurement
- The voltage measurement section consists of a voltage divider and an analog
to digital converter. The voltage waveform that is feeding the load cannot
exceed utility tolerances of 5% shown in equation (1). The voltage divider is
able to scale 0 to 180Vpeak down to 0 to 5Vpeak, which is the input range of
the A/D.
120VRMS *1.05
 178VPeak
0.707
178VPeak
 126VRMS
2
-
(Equation 1)
(Equation 2)
The large resistor of the voltage divider was chosen to be 1M for two
reasons. The first is so power dissipation can be minimized which a large
resistor helps. But in order to keep the noise from the operating environment
out of the system a small resistor is needed. The 1M resistor value
optimizes this trade off according to Prof. Patterson. Below in Figure 6 the
schematic of the voltage measurement device is shown.
Wall Plug
Neutral
Hot
Hot
Neutral
Gnd
Gnd
0
Pins
10K
AD7823
Vin-
A/D
Vin+
Neutral
20K
Load Being
1M
Hot
Gnd
Measured
Figure 6: Voltage measuring circuit.
-
In the table that follows the value, tolerance, and expected power dissipation
of each resistor is shown. Since a variable resistor has been included in the
design loose tolerances can be used for the resistance values because they will
be measured and any compensation can be done with the trim pot. Also since
large resistance values were chosen the power dissipation is low and standard
¼ watt resistors can be used. It should also be noted that the internal
resistance of the A/D is on the order of several M’s so it does not need to be
included as part of the voltage divider.
Table 1: Power dissipation of resistors.
Resistor Tolerance Current Power Dissipation
1 M Ohm
10%
0.175 mA
30 mW
20 K Ohm
10%
0.175 mA
0.612 mW
10 K Ohm
10%
0.175 mA
0.175 mW
Current Measurement
- The current measurement part of the hardware system is very simple, the heart
of the design is a current transformer. The CR Magnetics split core current
transformer 3110 was chosen because it was said to have a large linear
operating range and relatively high accuracy while keeping costs low. A
diagram of the current measurement hardware can be seen below in Figure 7.
Wall Plug
Neutral
Hot
Hot
Neutral
Gnd
Gnd
Pins
AD7823
Vin-
1K
A/D
Vin+
Neutral
Gnd
Hot
Load Being
Measured
Figure 7: Diagram of current measuring circuit.
-
The 1K resistor was chosen in accordance with the datasheet for the current
transformer. It should dissipate .025 Watts of power so a ¼ watt resistor will
work well. There will be a 5V drop across the resistors terminals at full scale
which is 15A.
A/D Chip
- The A/D chips should communicate to the RS232 driver, speed of
communication should not be a problem since the A/D only run at 133,000
samples per second. The A/D was chosen for its cheap cost and adequate
accuracy, 8-bit. This will allow 256 digital output values, which will provide
adequate precision since they cover a 0-5V range.
RS 232 Driver
- The interface between the hardware and software is done using the serial port
of the computer. This communication protocol is called RS232 and is a very
common way to communicate with the computer. The pin assignments for
both the 9-pin and 25-pin serial port are shown in Figure 8 below.
Figure 8: The pin assignments for the 25-pin (left) and 9-pin (right) serial ports.
-
A National Semiconductor RS-232 driver chip, model number DS14C232,
was chosen for the system because it has two channels for digital input. The
two digital inputs to this chip are the outputs from the two A/D converters:
one for current and one for voltage. The RS-232 driver chip converts the 0-5
V digital signal from the A/D to a –10-10 V signal required for the serial port.
One output from the RS 232 driver chip is sent to the computer via a 9-pin
serial port cable. The second output is sent to the computer via a 25-pin serial
port cable. The pin assignments for the RS232 driver chip are shown below in
Figure 9.
Figure 9: Pin assignments for the National Semiconductor RS-232 driver chip.
-
From the figure, pins 11 and 12, called Din1 and Din2, accept the digital input
from the A/Ds. The 9-pin and 25-pin serial port cables are connected to pins
14 and 7, called Dout1 and Dout2. The entire circuit schematic of the RS-232
driver chip and the two serial cables is shown in Figure 10.
+5 V
C1 +
Vcc
V +
Gnd
C1 -
Dout1
5
C2 +
4
3
2
1
Rin1
DS14C232
C2 -
Rout1
V -
Din1
Dout2
Din2
Rin2
Rout2
9
Fr om A/D
Fr om A/D
8
7
6
9 Pin Serial Port
13
12
11
10
9
8
7
6
5
4
3
2
25
24
23
22
21
20
19
18
17
16
15
14
25 Pin Serial Port
Figure 10: Circuit schematic of the RS232 driver chip connected to the 25-pin and 9-pin serial
port cables. Also shown are the external capacitors required for the chip.
-
In the figure pin, C1+, C1-, C2+, and C2- are connected with external
capacitors. The minimum value for the capacitor connected to those pins is 0.1
F.
1
Power Supply
- The power supply is needed because each of the three chips being used
require 5V input and some require a 5V reference as well. The power for the
system is taken off the 120V line that also feeds the load or appliance. The
power that the box uses however is not measured by the system. This way the
user gets an accurate measure of what the appliance in question uses. This is
done by measuring the current leaving the measurement box, which is the
current that goes into the appliance. The power supply consists of a variable
DC power supply that was originally set to 7VDC. This 7V is then passed
through a National Semiconductor voltage regulator LP2954 that will have 5V
1.2% output. The schematic of the power supply can be seen below in
Figure 11.
Neutral
Neutral
7V DC
Vac
Hot
Supply
7V out
Wall Plug
1.5 uF
IN
5V Regulator
GND
OUT
Hot
1.98 uF
Gnd
0
Gnd
0
Figure 11: Diagram of the 5V power supply.
Packaging Design
- The overall design of the system can be seen below in Figure 12. The box
will contain all the hardware and will be connected to the computer by the
serial port cable. It has a cord that connects it to the wall and has a utility plug
on it where the appliance can be plugged into. The prototype box measures
6x3x8” and is made of black plastic. Plastic was chosen over metal because it
will not scratch appliances or the floors it is placed on, it also acts as an
electric insulator, which should make the device safer.
Pow e r Cord
Wall Socke t
Pow e r Cord
Prototype
RS232 Cable
Appliance
Com puter
Figure 12: Block Diagram of system.
Testing Description:
- Check the capability of the system to display the correct information to the
interface and store the data. This can be done with short test cases.
- The A/D will be fed with a constant voltage (analog signal); the chip output
will be connected to the serial port of the PC. The computer program will
then poll the serial port and record the data to the hard drive. Acceptance
criteria: The test is successful if the expected output is received and recorded
in the data file. Since a constant voltage is being used the data file should
have one numerical value repeated throughout the file.
- As functions are added to the interface, check them individually.
- For the final product, run a long test case bringing all the functionalities
together.
Risks & Management:
- Lost member: With 2 EE and 2 CPRE, if a member is lost, then the remaining
EE or CPRE will need to pick up the slack of that member. Loosing two
members would cause the project to fail.
- Failures: Through multiple approaches we should be able to develop a
working model of power consumption.
- Lack of communication: There are three methods already in place that are
working effectively: email, telephone, and direct communication
Financial Budget
Table 2: Financial Budget Estimated
Item
Poster
Equipment and Materials
Total
Estimated Cost
$100
$100
$200
Table 3: Financial Budget Actual
Item
Poster
Equipment and Materials
Total
Actual Cost
$40
$100
$140
Personal Effort Budget
Table 4: Personal Effort Budget Estimated
Team Member
Matthew Gordon
Sunil Varghese
Ying Luk
Adam Wheeler
Estimated Effort
102 Hours
120 Hours
118 Hours
94 Hours
Advisor Meetings
Research
Computer Interfacing
Testing
Project plan report
Design report
Poster
Website
Final report
Estimated
Team Members
Group Member Meetings
Fabrication and integration
of system
Table 5: Personal Effort Budget Revised
Matthew Gordon
16
15
9
2
0
0
3
3
4
0
5
57 hours
Sunil Varghese
17
15
6
4
0
0
3
3
4
0
4
56 hours
Ying Luk
17
16
5
5
0
0
3
3
4
0
4
57 hours
Adam Wheeler
17
16
11
2
0
0
4
5
5
0
4
64 hours
Total Effort
67
62
31
23
0
0
13
14
17
0
17
244 hours
Revised
Effort
Project Schedule
Table 6: Gantt Chart
Sep 2002
ID
Task Name
Start
Oct 2002
Nov 2002
Dec 2002
Jan 2003
Feb 2003
Mar 2003
Apr 2003
Finish
9/1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 11/17 11/24 12/1 12/8 12/15 12/22 12/29 1/5 1/12 1/19 1/26 2/2 2/9 2/16 2/23 3/2 3/9 3/16 3/23 3/30 4/6 4/13 4/20
1 Project Definition
9/2/02
9/6/02
2 Technology Selection
9/9/02
11/19/2002
3 Project Design
11/22/02
4/4/03
4 Project Implementation
1/13/03
4/4/03
5 Project Testing
1/20/03
3/28/03
6
Basic Functions
1/20/03
2/21/03
7
Extra Functions
2/24/03
3/28/03
8 Project Revision
9/2/02
9/2/02
9 Project Documentation
9/2/02
4/25/03
10
Project Plan
9/2/02
10/8/02
11
Project Poster
10/14/02
10/22/02
12
Design Report
10/25/02
12/18/02
13
Final Report
1/13/03
4/25/03
4/28/03
5/2/03
14 Project Demonstration
Closure Material
Project Team Information
Matthew Gordon
1100 Pinon Dr. #2
(515) 360-4345
[email protected]
Electrical Engineering
Sunil Varghese
611 Meadow Pl.
(515) 451-9109
[email protected]
Computer Engineering
Ying Chiu Luk
PO Box #9083
(515) 708-1202
[email protected]
Computer Engineering
Adam Wheeler
202 Creekside Dr.
(515) 232-0766
[email protected]
Electrical and Computer Engineering
Herb Harmison
2692 Meadow Glen Rd
Ames , IA
Tel. # (515) 292-7059
James Triska
2218 Coover
(515) 294-4676
[email protected]
Faculty Advisor
Glenn Hillesland
2315 Buchanan Dr.
Ames, IA
Tel. # (515) 232-7661
Summary
This system has resounding possibilities. The need for energy consumption becomes
greater everyday and anyway that we can help will make for a better future. This is a
very attainable project that can be accomplished incrementally, which means a final
product should not be a problem. The solution that has been laid out can be achieved
because similar things have been done successfully. The system is just building upon
those already in existence.
References
smarthouse.com
radioshack.com
http://www.ee.ualberta.ca/~elliott/ee552/studentAppNotes/2000_w/interfacing
http://www.ucfprofessor.com/ucf/eel4767/serial.html
http://www.howstuffworks.com/serial-port2.htm
http://www.rdrop.com/~cary/html/serialportdocs.html