construction of 0-3000 watts digital wattmeter

ABSTRACTAs technology advances and mid-high tech devices become more readily available to engineering and technology students as well as hobbyists there is an increasing need for reliable, cost effective test equipment. Digital AC wattmeters are one of these increasingly useful pieces of equipment. There are currently many models of Digital AC Wattmeters available that have an impressive amount of capability and functionality. These models are expensive, and often have unnecessary capabilities considering the typical applications of undergraduate students and hobbyists. This project arose from the need for an inexpensive, functionally appropriate alternative to currently available Digital AC Wattmeters. It presents a detailed construction steps followed to achieve this feat.TABLE OF CONTENTS

Title Page

i

Certification

ii

Dedication

iii

Acknowledgement

iv

Abstract

v

Table of Content

vi

CHAPTER ONE

1.0Introduction

11.1Background of Study

11.2Problem Statement

11.3Objectives of Research

21.4Justification of Study

21.5Scope of Work

3CHAPTER TWO2.0Literature Review

42.1Wattmeter

42.2Types of Wattmeters

42.2.1Professional Wattmeters

42.2.2Digital Wattmeters

5CHAPTER THREE 3.0Research Methodology

73.1 Gathering of the Needed Information

73.2 Designing the Circuit

83.2.1 The Block Diagram of the System

83.2.2 Flow Chart and Schematic Circuit Diagram

93.2.3 Description of the Flow Chart

113.3 Description of the System Components

153.4 Current and Voltage Transformers

173.5 Power Supply Unit

173.6 Programming

183.6.1 Source Code

20CHAPTER FOUR4.0Test Results and Discussion

264.1Problems Solving

274.2Analysis of the Problems

274.3Remedies

28CHAPTER FIVE5.0Conclusion

305.1Recommendation

30REFERENCES

31CHAPTER ONE

1.0INTRODUCTION

1.1BACKGROUND OF STUDY

A wattmeter is a device which measures electrical power, a newer technologies have provided the ability to produce digital; wattmeters, these meters usually have a digital display and are portable, resulting in a more versatile and easy to use product. Because these devices are digital, the analog approach is replaced with digital circuits to read in and compute measurements. Digital devices offer the ability to read measurement of any frequency, and also compute many different quantities. Digital wattmeters provide versatile capabilities and accurate readings in a very short period of time. As stated previously, digital wattmeters can be found commercially; however, the groups device will function on a smaller scale not accurately available and include additional functionality. The available wattmeters on the market do not provide the ability to measure and display power factor within the same design.1.2PROBLEM STATEMENT Most electrical/electronic department in some tertiary institutions in the country still use aged analog wattmeter to satisfy laboratory needs for its circuit labs. This device takes a considerable amount of time to set up and use to obtain the desired measurements. In order to heighten the load/stress on the students, there is need for a digital wattmeter which will allow measurement to be taken faster, easier and more accurately than they can with the current equipment in use during their power factor experiment, as part of the electronic circuits course. 1.3OBJECTIVES OF RESEARCH

The objective of this project is to design a small, cheap and easily to produce 0-3000watt Digital Wattmeter. This Wattmeter will replace the analog labs today. The device will have input and output terminals for connecting the device to the system under analysis, as well as a digital display to more accurately convey the measurements. The user will be able to incomputerate this device within a circuit between the paper source and the load, and the device will in turn digitally display the voltage absorbed and power factor of the load. The meter will also display voltage and current.1.4JUSTIFICATION OF STUDY

Digital Wattmeter is an instrument which is used to measure the power consumption of an electric circuit or an appliance which is connected to the supply in terms of watts.Digital Wattmeter provides versatile capabilities and accurate reading in a very short period of time.1.5SCOPE OF WORK The scope of this work will be concerned only on digital Wattmeter ranging for 0-300 watt, how it works the functions of digital Wattmeter, why is digital Wattmeter important in electrical labs, the components use in building it and how they function.

This work is limited to the component and accessories as obtained from the current diagram CHAPTER TWO

2.0LITERATURE REVIEW

2.1WATTMETERThe wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit. Watt is a derived unit of power in the International System of Units (SI), named after the Scottish engineer James Watt (17361819). The unit defined as one joule per second, measures the rate of energy conversion. Electric power is the rate at which electrical energy is transferred by an electric circuit.2.2TYPES OF WATTMETERSA wattmeter is used to measure the voltage in an electronic circuit. Originally only a tool of professionals there are now many different types of the device available that are both cheap and easy to use and available for home use. A wattmeter is generally used for checking on the power supply of a given power-outlet in a house and for estimating the electricity costs of different appliances. Like many technologies the device has gone digital.2.2.1PROFESSIONAL WATTMETERS The power company still uses a basic wattmeter to measure the amount of power that your house or apartment is consuming from the general power supply. The wattmeter measures both the amount of energy consumed and records the time when it was consumed. Generally these electric meters will be located somewhere outside a building so that a representative of the power company can come by in person to see the readings of the device.

2.2.2DIGITAL WATTMETERS According to Pearson Education Limited 2004, Wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy in watts of any given circuit.Digital Wattmeters have become available for home use and are capable of providing users with information that is far superior to that which was provided by the Wattmeters of professionals only twenty years ago. Instead of a very imprecise needle display, a digital Wattmeter measures the current which is passing through its cables at a thousand times a second, measuring every small change, and providing an average which is the true power supply.According to Aaron Fogle and Pat Rice in Ohio Northern University 2012, a Wattmeter is a device which measures electrical power, the meter can be analog or digital.The Wattmeter is an instrument for measuring the electrical power (or the supply rate of electrical energy); by Dr Sam Clay Ohio Northern University 2009.

CHAPTER THREE 3.0RESEARCH METHODOLOGY

Below is the flow diagram that illustrates the step-by-step processes that is been embarked on to accomplish this project work. The flow diagram of the project includes; Articles and researches related to the project study, block and schematic diagram of the project, flow chart and source code and programmable prototype and functional prototype .The expected outputs of each activity are also provided on the diagram as seen below.

Figure 3.1: Flow chart diagram of the step-by-step process of the project work

3.1 GATHERING OF THE NEEDED INFORMATION

The research work commenced by first gathering the needed information, which was useful in understanding more about the project study. Looking for articles in the internet about the microcontrollers and the ADC to be used in the project was a great help. Basic understanding on how to use the ADC was also an important thing to be considered. Aside from getting information from the internet, the research work also involved reading other resources such as reading related researches and publications. The research work also involved consulting some experts in the field in order to get more information on the project work.

3.2 DESIGNING THE CIRCUIT

Based on the acquired information, we were able to design the circuit. Firstly, we constructed the block and schematic diagrams of the entire system. Proteus simulator design suit is the software used in the schematic circuit design since it provides a means of running the software in the simulator before the real life circuit construction.

3.2.1 THE BLOCK DIAGRAM OF THE SYSTEM

The block diagram of this project construction comprises of the all the necessary components that makes up the entire digital wattmeter. The block diagram comprises of the Atmel AT89C52 8-bit microcontroller unit which is the brain base of the system, the 0804 ADC is used to convert the AC voltage and current source to digital wave forms, the 16x2 LCD screen module which is used as a form of visual display unit used in the project to display load power rating in watts, the auto reset unit resets the microcontroller after every micro-seconds execution of task, the crystal oscillator unit which plays a major role in clocking function of the microcontroller unit, the pull-up resistor is used to provide +ve 5volt power supply to PORT 0 of the microcontroller where the LCD display screen is interfaced, two transformers which are responsible for voltage and current waves sampling, 741 Op-Amp IC used as comparator to compare the magnitude of the AC voltage and current signals. Below is the block diagram of the digital wattmeter.

Figure 3.2: Block Diagram of the Digital Wattmeter

3.2.2 FLOW CHART AND SCHEMATIC CIRCUIT DIAGRAM

As shown in the above block diagram, the Digital AC Watt Meter consists of three main sections; analog signal conditioning section made up of the 741 Op-Amp chip, embedded signal processing section made up of the 0804 ADC chip and the 89C52 microcontroller chip and visual display section which is the 16x2 LCD screen used to display power output in watts. Figure 3.1 visually details the operation of the Digital AC Watt Meter Voltage and current representative wave forms are induced from the AC circuit then conditioned and digitally read by the 89C52 microcontroller. The 89C52 microcontroller is programmed to interpret the digital wave forms then calculate and output power of the input load in Watts on the 16x2 LCD screen. The visual output module for the wattmeter is a 5 volt 16x2 LCD, based on the HD44780 series. Below is the flow chart diagram of the digital wattmeter.

Figure 3.3: Flow chart diagram of the digital wattmeter

3.2.3 DESCRIPTION OF THE FLOW CHART

ANALOG SIGNAL CONDITIONINGThe front end of the Digital AC Wattmeter accomplishes two tasks; induce voltage and current representative wave forms from the AC circuit and condition those signals to an acceptable voltage level in order to be read by the ADC interfaced to the 89C52 microcontroller.

INDUCING SIGNAL WAVEFORMS Two iron core transformers were are used to induce the current and voltage waveforms. Both transformers primary windings are rated at 220V and secondary windings are 6V providing a step gain of approximately 37. The current waveform inducing transformer circuit is connected to the AC circuit via its secondary 6V coil across an inline 1/10 ohm power resistor (see figure 3.4). The power resistor

induces the current wave form (1mV = 10mAmp). The transformer then provides the current wave signal a gain of 37. The signal is then conditioned by a precision rectifying circuit in figure 3.4 below. The voltage waveform inducing transformer is connected with its primary coil across the source voltage creating a 37 to 1V scale wave form of the voltage signal as shown in figure 3 .4. The signal is then conditioned by a precision rectifying circuit. Below is the schematic circuit diagram of the digital watt meter.

Figure 3.4: Schematic circuit diagram of Digital wattmeter

SIGNAL PROCESSINGThe properly conditioned signals are read via the 0804 ADCs output interfaced to the 89C52 microcontroller chip and the digital wave forms are stored in the controllers memory. Once the voltage and current signals have been converted to digital waveforms, software determines magnitude and phase difference. Power is them calculated and displayed via the LCD display screen. Figure 3.6 shows the flow chart diagram of the Digital Watt Meter software. The 89C52 microcontroller is programmed to execute these tasks using assembly language.ANALOG TO DIGITAL CONVERTERS AND SIGNAL READING

The 0804 ADC have an input range of 0 5 Volts and 8 bits of resolution (4.88 milli Volts per step). Two 0804 ADCs are used to sample the waveforms. Every other sample is current/voltage.

The sample rate is approximately 240 microseconds per two samples (one voltage wave sample and one current wave sample). The time difference between consecutive samples is negligible.INTERPRETING DIGITAL WAVE FORMS

The digital wave forms are stored in two memories. These memories contain the ADC step values of the wave forms. The memories are indexed to find the ADC's peak steps value of voltage and current. These values are converted to their equivalent real current and real voltage value from the AC circuit. This is accomplished by multiplying the ADC step level by the equivalent AC current or voltage level (i.e. by 5 ) and one current ADC step = .0021Amps, one voltage ADC step = .1773 volts. By tracking the number of samples between AC voltage and current signals by the ADC, there are 73.34 samples taken per 60Hz cycle. To calculate for the input active power in watts, the following formula is used P = VI cos. Active power consist of active component which is in phase with the applied voltage V i.e. I cos. It is also known as wattful component.

Mathematically

P = VI cos,

where;

V = A.C Voltage

I = A.C current

Cos = cosine of the angle of lead or lag

Then active power of the input A.C source is given as;

VA = cos = W.

From the above mathematical expressions, to get the actual power of any applied load to the digital wattmeter, the microcontroller is programmed in such a way that current magnitude and voltage magnitude of the applied load are compared, and arithmetic operation is then carried out in memories A and B of the microcontroller by multiplying Voltage (V) and Current (I) magnitude and their product is then programmed to displayed as power in Watts on the LCD.

3.3 DESCRIPTION OF THE SYSTEM COMPONENTS

THE MICROCONTROLLER UNIT This unit is responsible for receiving and storing of the converted AC signal by the ADC chip. Themicrocontroller then carries out arithmetic and logical operations on this signal and determines the magnitude of the AC signals (i.e. the magnitude of the voltage signals and current signals), then the microcontroller sends the corresponding result to the LCD display screen in order for the inputed load power rating to be displayed on the LCD screen.

THE FREQUENCY OSCILLATOR UNIT The frequency oscillator circuit unit in the above block diagram is made up of a 12MHZ crystal oscillator and two 30pf ceramic capacitors each connected in parallel with one terminal of the crystal oscillator. It is responsible for proper frequency timing operation of the Atmel AT89C52 microcontroller unit.THE AUTOMATIC RESET CIRCUIT

The automatic reset circuit in the above block diagram is responsible for resetting the microcontroller unit automatically after every micro-second execution of task. This unit is made up of a 10uf electrolytic capacitor and a 10k resistor.

THE PULL-UP RESISTOR UNITThis unit is made up of 8 pieces of 10k resistors connected in parallel to each pin of port 0 of the microcontroller unit and also in parallel to each other to a +ve 5volts power supply. The pull up resistors in the above block diagram is used to supply a boost voltage of +5volts to the port 0 pins of the microcontroller because port 0 has high impedance.

LCD DISPLAY UNITThe LCD (i.e. Liquid Crystal Display) unit is the output module of the Digital Watt Meter. The LCD used for the construction of this Digital wattmeter is a 16x2 character display LCD module based on the Hitachi HD44780. Figure 3.6 below shows the LCD output module of the Digital wattmeter.

Figure 3.5: A typical picture of 16x2 LCD module

3.4 CURRENT AND VOLTAGE TRANSFORMERS Two iron core transformers were are used to induce the current and voltage waveforms to the system. Both transformers primary windings are rated at 220V and secondary windings are 6v which provides a step gain of approximately 37.

THE 741 OP-AMP CHIPSThe 741 Op-Amp Chips is responsible for getting analog signals induced by the current and voltage transformers. The 741 Op-Amp chips is used here as a comparator to compare the magnitude of the input AC signals and rectified it to an acceptable level for the ADC chips

ADC 0804 CHIPSThe ADC 0804 chips gets rectified analog signals (i.e. current and voltage signals) from 741 Op-Amp chips and converts these signals to digital waveforms which is required by the microcontroller unit.The ADC 0804 chips is an intermediate unit between the analog signal processing unit made up of the 741 Op-Amp chips and the digital signal manipulation unit made up of the microcontroller chip.3.5 POWER SUPPLY UNIT

The power supply unit that is used to provide a 5volts regulated DC source for the Digital wattmeter. This power supply unit is made up of some descrete electronics components and a 220V 6-0-6V step down centre tapped transformer. The descrete component used for the power unit includes IN4007 rectifier diodes arranged in a bridge form to convert the 6V AC output from the transformer's secondary to 6V DC, a 22F/6.3v electrolytic capacitor used to filter any AC ripple left behind, and a 7805 voltage regulator IC which is used to regulate the 6V DC to 5V DC which is required by the microcontroller unit for its proper operation. Figure 3.6 below shows the schematic circuit diagram of the power supply unit.

Figure 3.6: Basic block diagram of power supply

3.6 PROGRAMMING

Programming of the system follows an orderly and systematic steps in order to arrive at a successful program source code by first drafting out the program flow chart which shows each lines of code and their functions, how program commands code flows in the internal memory of the microcontroller unit. In actualizing the whole process, MIDE-51 development environment is used to type the program source code, and after the source code have been successfully typed, a folder is created and the typed assemble language source is then assembled inside the created folder. This is done in order to convert the typed assemble language code to hex file which is to be load to the microcontroller unit with the aid of a device called programmer kit.

Figure 3.7: Program flow chart of the digital watt meter

3.6.1 SOURCE CODE

The source code as explained above is typed and assembled in the MIDE-51 development environment which converts the assemble code to hex file which is needed by the microcontroller unit. See program source code below:

ORG 0000H ;Starting task from memory location 0000H in hex

MOV P1,#11111111B ;Configuring P1 as input port

;;;;LCD COMMAND SET UP;;;;

MOV R0,#38H ; Use two lines and 5X7 Matrix

ACALL COMND ; Call command routine

ACALL DELAY ; Call delay routine

MOV R0,#0CH ; Display ON Cursor OFF

ACALL COMND ; Call command routine

ACALL DELAY ; Call delay routine

START: ;Starting the main program subroutine

CLR P2.3 ;making CS (i.e. pin 1 of the ADC) low

CLR P2.5 ;Sending Low-to-High signal to RW of the ADC

SETB P2.5 ;Sending Low-to-High signal to RW i.e. pin 3 of the ADC

INTR: JB P2.7,INTR ;Checking if conversion is finished, if yes INTR pin=0 if not poll till 1CLR P2.3 ;making CS (i.e. pin 1 of the ADC) lowSETB P2.4 ;Sending High-to-Low signal to RD to read data from ADCLR P2.4 ;Sending High-to-Low signal to RD to read data from ADCMOV A,P1 ;Copying current output from current converting ADCMOV B,P3 ;Copying voltage output from voltage converting ADC at P3CPL A ;Complementing the ADC's LOW output to HIGH outputCPL B ;Complementing the ADC's LOW output to HIGH outputMUL AB ;Multiplying AC signal (i.e. Current and Voltage signals)MUL A,#05 ;Multiplying the product of AB by 5 to give wattage in power

;;;;OUTPUTING ADC's RESULT;;;;

OUT1: CJNE A,#1,OUT2

ACALL 05WATTS ;Displaying load wattage on 16x2 LCD screen

















OUT10:CJNE A,#10,OUT11



















































ACALL 175WATTS ;Displaying load wattage on 16x2 LCD screenOUT36: JMP START

*************************

DELAY ROUTINE

***********************

DELAY: MOV R3,#05

DELYA: MOV R2,#03

DELYB: MOV R1,#02

DJNZ R1,DELYA

DJNZ R1,DELYB

RET

END ;Denotes the end of assembly language source code

CHAPTER FOUR

4.0TEST RESULTS AND DISCUSSION

After the constructed of the digital wattmeter we run a test with the meter (digital wattmeter) to check if it will give us an accurate result. Some load were plug in the meter and the following results were gotten.Load (Plug in)Result (Displayed in LCD)

60 watt bulb 55.5 watt

75 watt television set70 watt

80 watt refrigerator 75.5 watt

We did not get the exact voltage of the load due to some factors to be discussed.There was a power loss in the transformer inside the wattmeter due to heat and vibration in the transformer.Also the voltage generated by Enugu Electricity Distribution Company (EEDC) is not up to the amount they should generate and distribute, EEDC generate and distribute 150V 180V instead of 220V 240V, this also contributed to us not getting the exact load (watts) in our results.4.1PROBLEMS SOLVING

When constructing the projective discover or encounter some difficulties which draw us back when constructing our project, most of them were;

Power failure

Burning of components

Components failure

4.2ANALYSIS OF THE PROBLEMS POWER FAILURE: This was a huge setback for us during the construction of this project, we had serious project, and because of there were no power for us to do our job or the construction, it help in delaying us, and it was a setback on our own side. BURNING OF COMPONENT: While constructing our project we discovered that most of our components got burnt due to high voltage, components like the capacitors, etc and most of the components when they are not in good condition and we use them, it got burnt too when we use them.

COMPONENT FAILURE: Components failure is another problem we encountered during the construction of this project, most of the component we got after construction, we never discover that the components are not working again; most times the cause of this may be from the way we packed the components.

4.3REMEDIES

The remedies of the problems we encountered include; For power failure, what we did was to get generator, to produce our own power so that we can do and complete our project.

Burning of component; what we did was to find out why our components was burning and solved it, after which we replaced the component back and go on with our construction. Component failure; in order not to waste time when we had component was sample, we last changed all the component that burnt bad and continue with our work.CHAPTER FIVE5.0CONCLUSION In conclusion Digital Wattmeter is a device which measures electrical power, Digital Wattmeter provides versatile capabilities and accurate readings in a very short period of time.Digital Wattmeter is an instrument which is used to measure the power consumption of an electric circuit or an appliance which is connected to the supply in terms of watts. Digital devices offer the ability to record measurement at any frequency, and also compute many different quantities.

Digital Wattmeter have become available for home use and are capable of providing users with information that is far superior to that which was provided by the Wattmeters of professionals only twenty years ago.5.1RECOMMENDATION

We will recommend Digital Wattmeter in most electrical/electronics department in some tertiary institution in the country, to help them satisfy laboratory needs for its circuits labs because it provides versatile capabilities and accurate reading in a very short period of time.REFERENCESAaron Fogle and Pot Gilas, 2012, Ohio Northern University.Blackout of 2003: Description and Responses. Available on:http://www.persc.huise.eduhttp://www.persc.huise.edu/wattmeter

C.A Canizares, F.C., Acvarado, C.L Demarco, I. Dobson, and W/F Long, (May 14, 2005) Wattmeter Analysis. Version 1.3.4 Software and Document.Dr. Sam Clay, 2009, Ohio Northern University.

Pearson Education Limited, 2004 Wattmeter as an Instrument.

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construction of 0-3000 watts digital wattmeter

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available wattmeters

digital devices

digital display

digital circuits

professional wattmeters

types of wattmeters

chapter four4