HOUSEHOLD POWER MONITORING SYSTEM

DESIGN REPORT

May 02-04

December 17, 2001

Client:Herb Harmison

Advisors:John Lamont

Ralph Patterson

Team:Stephen Woerdehoff

Paul Jonak

Yohan Blount

Jason Muehlmeier

Table of Contents

  1. Abstract……………………………………………………………...1
  2. Acknowledgement………………………………………………...…1
  3. Definition of Terms………………………………………………….1
  4. Introduction………………………………………………………….1-3
  5. General Background…………………….……………….……….1
  6. Technical Problem…………………………….………………….1
  7. Operating Environment……………………….………………….2
  8. Intended Users and Uses……………………….…………………2
  9. Assumptions…………………………………..………………….2
  10. Limitations…………………………………….………………….3
  11. Design Requirements………………………………………………..3-5
  12. Design Objectives………………………………..……………….3
  13. Functional Requirements………………………..…………….….3
  14. Design Constraints…………………………………..……………4
  15. Measurable Milestones………………………………..………….4
  16. End-Product Description…………………………………………...5
  17. Approach and Design……………………………………………….5-14
  18. Approach and Design of Total Power Consumption Meter….…...5

7.1.1 Technical Approach…………………………………………5

7.1.2 Technical Design……………………………………………6

7.1.3 Testing Description.………………………………………...7

7.2Approach and Design of Roaming Meter……...……..……….….7

7.2.1 Technical Approach…………………………………………8

7.2.2 Technical Design……………………………………………8

7.2.3 Testing Description.………………………………………...9

7.3Approach and Design of A/D………………………….…………10

7.3.1 Technical Approach…………………………………………10

7.3.2 Technical Design……………………………………………10

7.3.3 Testing Description.………………………………………...11

7.4Approach and Design of Computer Recording System.………….11

7.4.1 Technical Approach…………………………………………11

7.4.2 Technical Design……………………………………………12

7.4.3 Testing Description.………………………………………...12

7.5 Overall System Testing…………………………………………...13

7.6 Risk and Risk Management………………………………………13

7.7 Recommendation for Continued Work…………………………...14

  1. Financial Budget…………………………………………………….14
  2. Personal Effort Budget……………………………………………..15-16
  3. Project Schedule…………………………………………………….17
  4. Project Team Information…………………………………………. 18
  5. Summary…………………………………………………………….18
  6. References……………………………………………………………19

Appendices…………………………………………………………..20-24

Appendix A………………………………………………………..20

Appendix B………………………………………………………..21

Appendix C………………………………………………………..22

Appendix D………………………………………………………..23

Appendix E………………………………………………………..24

List of Figures

Figure 7.1.1 D’Arsonval Movement………………………………………….6

Figure 7.1.2 Total Power Consumption Meter Connection…………………..7

Figure 7.2.1 Roaming Power Meter Connection……………………………..9

Figure 7.2.2 Wattmeter Needle Deflection…………………………………...9

Figure 7.3.1 Operational Amplifier…………………………………………..11

Figure 10.1: Project Schedule for 1st Semester……………………………….17

Figure 10.2: Project Schedule for 2nd Semester………………………………17

List of Tables

Table 8.1 Financial Budget…………………………………………………..14

Table 9.1 Original Personal Effort Budget…………………………………...15

Table 9.2 Revised Personal Effort Budget……………………………………15

Table 9.3 Personal Effort to Date…………………………………………….16

- 1 -

1. Abstract

With increasing power consumption and costs in the home, many homeowners would like to monitor their energy usage. The Household Power Monitoring System will allow the homeowner to monitor the individual and total power used by household devices. With this information, the user can find ways to reduce their power costs. The system will also allow the user to identify devices that are becoming inefficient or those that are likely to malfunction in the near future.

2. Acknowledgement

We would like to thank Mr. Herb Harmison and Dr. Glenn Hillesland for their input and donations to the project.

3. Definition of Terms

A/D – Analog to digital converter.

RF – Radio frequency.

X-10 – A protocol for communication over household wiring.

RS-232 – Serial port

4. Introduction

4.1 General Background

The purpose of this project is to give the user information about their power usage so they can make educated decisions according to their goals. The system will record the total usage of the home as well as selected individual loads as a function of time. This data will then be available for easy analysis utilizing a PC.

4.2 Technical Problem

The system will consist of four subsystems that will be integrated to give the final product. They are: total consumption wattmeter, roaming wattmeter, A/D, and computer interface and recording system. The two wattmeters will have a small analog output that will be sent to the A/D before being recorded by the computer.

Total Consumption Meter: The purpose of this device is to measure the total watts consumed by the home over the single-phase 240-Volt wiring. This will be done using current transformers to step down and measure current before entering the wattmeters. The wattmeters will be older analog meters that can be obtained inexpensively. The small analog output they produce will be turned into a digital signal for the computer using the A/D.

Roaming Wattmeter: This device measures the total watts consumed by the single-phase 120-Volt appliance being monitored. This will be done using an older wattmeter directly. The small analog output it produces will be turned into a digital signal for the computer using the A/D.

A/D: Outputs from the analog wattmeters will be converted to digital values and interfaced with the computer. The voltage output from the analog wattmeter will be small in magnitude and must be amplified before it is converted to a digital signal. An A/D chip will be used for the digital conversion and will have a sufficient sampling rate to accommodate the desired data collection speed. The chip will have a built in serial communication interface to connect directly to the computer via a serial port.

Computer Interface and Recording System: The computer system will receive data from the A/D via the serial port. This will be done using a program created with Visual Basic. The data will then be recorded prior to analysis using Microsoft Excel.

4.3 Operating Environment

This system will be located in a residential household, this environment is not very demanding however the system should be able to function despite the following. Possibly a fairly dirty environment with dust and other contaminants such as pet hair may be present. The system should be resistant to any electrical interference caused by operating appliances and other devices. Some resistance to both high and low temperatures would be needed, with an operating range between 30 and 110 degrees Fahrenheit. The roaming wattmeter should be somewhat robust and able to survive a drop in shipping or around the house.

4.4 Intended Users and Uses

The system is intended to be used in a residential setting. Home residents conscientious about their utility costs can track power usage and learn what devices cost the most to operate and how to save money. The system could be used to monitor larger appliances to determine if they need servicing or replacement.

4.5 Assumptions

What follows is a list of assumptions that are being made under the current plan. These assumptions may change as the project develops.

 The user will be familiar with operating a computer.

 The user will know basic spreadsheet operations.

 The user will have a computer capable of analyzing the collected data.

 The user will have a basic knowledge of electricity and the concept of power.

 The house will comply with the operating environment described above.

 The user will have access to average power consumption rates of appliances.

 The user will know the current utility rate for their location.

 The user will be able to operate a simple GUI.

 The home has reasonably balanced load legs in the breaker box.

4.6 Limitations

What follows is a list of limitations that are evident under the current plan. These limitations may change as the project develops.

 Wattmeters will be compatible with a maximum of a 200A service.

 Due to complexity, only one roaming meter will be produced.

 The house will have a modern, grounded electrical wiring system.

5. Design Requirements

5.1 Design Objectives

The following are design objectives that should be reached to realize the intended system.

Total consumption meter will consist of two current transformers and two analog wattmeters wired in a 1-phase 240V manner. They will measure the total power consumed in the home. Their output will be sent to the A/D over hard wiring. There will also be voltage, current, and VARS measurement capability.

Roaming wattmeter will be a portable device consisting of an analog wattmeter wired in a 1-phase 120V manor. It will measure the power consumption of a single household device and the voltage, current, and VARS. Its output will be communicated to the A/D over hard wiring.

The A/D will consist of an operational amplifier and an A/D chip. It will receive input from the wattmeters. It will output a serial communication signal to the serial port.

The computer interface system will be a Windows 95 compatible computer running a Visual Basic program that will access the serial port, scale the data, and record the data to a file.

These subsystems will be integrated into an accurate, user-friendly system.

5.2 Functional Requirements

These functional requirements should make the end product useful and reliable in the intended operating environment.

The system will be easy to use.

The total consumption meter’s measured results should be within 5% of the actual power consumed as measured by the power utility’s meter.

The wattmeters must have outputs suitable for the A/D subsystem to convert to serial data.

The wattmeters will utilize older inexpensive devices.

The roaming wattmeter will be able to measure the real power consumed by any 120V appliance.

The computer interface system must collect data into a file that can be placed on a disk and can be imported into Excel.

The roaming meter will communicate to the A/D via a hardwire link of sufficient length to make it useful.

The A/D will communicate in RS 232 format with the computer.

The system will not lose data if supply power to it is interrupted.

5.3 Design Constraints

These design constraints are intended to minimize interference in normal household activities such as causing static in television reception.

The overall system will be inexpensive to implement.

The system should not gravely disturb the aesthetic qualities or normalcy of life in the household.

The system’s installation and operation will not pose any unreasonable risk to the safety of the user.

The roaming wattmeter will be small enough to be conveniently portable.

5.4 Measurable Milestones

These milestones are deadlines to ensure the project is completed on schedule, they will be used to gauge the ongoing progress, and completion status of the project. The first percentage denotes the progress of that particular task. The second percentage represents the progress of the overall project when that task is complete. These are also listed on the Gantt chart on page 17. Success will be gauged by how much of the project is completed. The project will be considered a success if a final product is implemented and functions properly.

  • Project Plan- The project plan to outline the project’s functionality and implementation will be completed by September 25. (100% Complete) (5% Overall)
  • Revised Project Plan- A revised version of the project plan will be completed by October 9. (100% Complete) (6% Overall)
  • Poster- A poster outlining the project’s design and functions will be completed by October 30. (100% Complete) (10% Overall)
  • Design Report- A report detailing the project’s proposed design will be completed by December 4. (100% Complete) (25% Overall)
  • Design Finalized- After more research is done on the subject, a final design will be decided on in February 2002. (30% Complete) (35% Overall)
  • First Implementation- The separate subsystems are constructed in early March 2002. (5% Complete) (40% Overall)
  • Initial Testing Begins- Individual subsystems will begin testing in late March 2002. (0% Complete) (50% Overall)
  • Revised Design- The initial design will be improved, based on the first implementation and testing. (0% Complete) (60% Overall)
  • Revised Design Testing- A revised design will enter the final testing stage in early April 2002. (0% Complete) (80% Overall)
  • Final Implementation- A finished product will be completed in mid April 2002.

(0% Complete)(90% Overall)

  • Final Report- A final report that summarizes the project design and resulting end product will be completed in late April 2002. (0% Complete) (98% Overall)
  • Presentation- A presentation reporting the project’s final product will be given in late April 2002. (0% Complete) (100% Overall)

6. End-Product Description

The end product will be a system that will record total power used in the home as a function of time. A roaming wattmeter will be capable of measuring the consumption of an individual device. The information will be recorded on an obsolete PC. The user will periodically take data from the recording PC to a modern machine for display and analysis possibly using software developed specifically for this system.

7. Approach and Design

This system has four major components and will thus be designed in four parts. The four main parts to be designed and implemented are; the total consumption wattmeter, the roaming consumption wattmeter, the analog to digital converter, and the recording system. What follows is the design approach that will be followed to implement each of these four main parts and how they will be integrated.

7.1 Approach and Design of Total Power Consumption Meter

7.1.1 Technical Approach

The total consumption meter could be designed in many different ways. The possible design ideas are listed and discussed below.

A digital wattmeter could be used that would measure the watts and interface directly to a computer recorder, thus eliminating the need to design an A/D and increasing system accuracy and decreasing complexity.

A data logging watt-hour meter with recording ability could also be used, this system would require the user to periodically download the information that had been recorded into a PC for analysis. This would increase accuracy and cost while decreasing complexity.

A watt-hour meter could be used and the user could monitor it and hand record values. These values could be then entered in a computer for analysis. This is by far the simplest approach and would work, however, the system would not be automated and wouldn’t be as helpful as it should be.

A computer could be used to read in the current and voltage information. The computer would then calculate the phase angle between E and I, and use this to calculate watts being used. This would also give the user recorded values for voltage, current, and VARS as well. This information could be useful to the user if they chose to monitor the health of their loads, or to satisfy some curiosity that they may have about their power usage. This would be accurate if accurate enough instrument current and voltage transformers were obtained.

An analog wattmeter could be used to indirectly measure the power consumption by measuring the true voltage and using a current transformer to measure a scaled down version of the current entering the home. This measurement can then be converted to a digital signal and put into the recording device. This system could be implemented relatively cheaply by utilizing older analog meters that can be obtained cheaply and current transformers that are also relatively cheap and within our budget.

7.1.2 Technical Design

Using a digital wattmeter would be ideal and simplify the system however the cost of such a device is outside the project budget. A data logging watt-hour meter would greatly simplify the system but this device too is outside our budget. A standard watt-hour meter would work and is obtainable, but would not be automated enough to be practical given the project goals. Implementing a subsystem that fed the voltage and current information into a computer for calculation would work well. The largest drawback to this system could be cost of quality voltage and current transformers.

It has been decided to implement the total consumption meter using two older analog wattmeters that can be obtained cheaply. This approach will simplify the design by allowing the wattmeters to do the calculations with current, voltage, and phase angle accurately. The output will be the terminals of the d’Arsonval movement as can be seen in Figure 7.1.1.

Since a home has two 120V lines and a neutral entering the breaker box the total consumption meter will have to have two separate wattmeters and their outputs will be added to give the total power. The connections of these two wattmeters can be seen in the schematic below, Figure 7.1.2.


Figure 7.1.2: Schematic of the wattmeters breaker panel connections in the home.

A standard home has a 200A service this means each hot leg (A and B in Figure 7.1.2) has the possibility of carrying 100A, if the electrician balanced the load legs reasonably as was assumed. Each individual wattmeter needs to be able to cope with 100A. The wattmeters being used can only accept 7.5A maximum. This means a 100A to 5A or 20:1 current transformer should be used to measure the current in each leg going into the breaker box. The computer that records the data will make up for this change by scaling its input data back up using a transfer function for the total consumption meter. This transfer function is described in the testing description below.

7.1.3 Testing Description

The following tests will be ran specifically on the total consumption wattmeter subsystem. The form that these tests will be recorded on is in Appendix A.

A-1)Test each wattmeter individually to make sure they function properly.

Acceptance criteria: Wattmeter reads the correct value.

A-2)Test the current transformers over as much of their operating band as possible to generate a plot of actual current vs. current out which can be used later to make a scaling factor or function that the computer will use to determine what the true power reading is.

Acceptance criteria: Data points are found to generate a plot that will cover the probable operating area, which is defined as 100A.

A-3)Test the output voltage at the coils of the d’Arsonval movement in the wattmeter over the whole operating range to see what kind of inputs can be expected at the A/D.

Acceptance criteria: if the d’Arsonval movement is linearly dependent on the voltage in the coils at the base of the needle over its whole operating range.

A-4)Implement the entire subsystem and generate a transfer function between the known power consumption as measured by the utility company’s watt-hour meter and the subsystems output to the A/D. This information will be used to fine-tune the A/D, and the scaling function the computer uses to generate the final data.

Acceptance criteria: if enough data points are found to generate a plot that will cover the probable operating area, which is defined as 100A.

7.2 Approach and Design of Roaming Meter

7.2.1 Technical Approach

Two approaches are being considered for the design of the roaming power monitor. The more difficult, but less costly, approach is to implement current and voltage transformers to scale down measurements before being input into the wattmeter from the household appliance being monitored. The use of (step-down) transformers allows a smaller low-rated analog wattmeter to be used as the base measurement tool. It is then expected that an electrical signal can be extracted from the wattmeter’s needle deflections that is proportional to the measurement itself. An A/D would make this signal usable by the central computer.