Design And Construction Of A Digital Frequency Meter

Digital frequency meter measures power supply frequency in the range 48 – 52 Hz to an accuracy of three decimal places has been designed and constructed using an 8-bit micro-controller. In addition to determining the frequency and frequency deviation, it also maintains a system clock and a synchronous clock and finds the time difference between them as a measure of the time integral of frequency deviation over a given period.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• AIM OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• PURPOSE OF THE PROJECT
• PROBLEM OF THE PROJECT
• BENEFIT OF THE PROJECT
• LIMITATION OF THE PROJECT
• SCOPE OF THE PROJECT
• APPLICATION OF THE PROJECT

CHAPTER TWO

LITERATURE REVIEW

• BASICS OF DIGITAL FREQUENCY METETR
• DESCRIPTION OF HERTZ
• HISTORICAL BACKGROUND OF HERTZ

CHAPTER THREE

3.0     CONSTRUCTION METHODOLOGY

3.1      BASIC OF THE SYSTEM

3.2     BLOCK DIAGRAM OF THE SYSTEM

3.3      SYSTEM OPERATION

3.4      CIRCUIT DIAGRAM

3.5      CIRCUIT DESCRIPTION

3.6     DESCRIPTION OF COMPONENTS USED

3.7      POWER SUPPLY UNIT

CHAPTER FOUR

4.0      TESTING AND RESULTS

• CONSTRUCTION PROCEDURE AND TESTING
• INSTALLATION OF THE COMPLET DESIGN
• ASSEMBLING OF SECTIONS
• TESTING OF SYSTEM OPERATION
• CASING AND PACKAGING
• PRECAUTIONS WHEN USING A FREQUENCY METER
• BILL OF ENGINEERING MEASUREMENTS AND EVALUATION

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

• INTRODUCTION

Digital frequency meter is a general purpose instrument that displays the frequency of a periodic electrical signal to an accuracy of three decimal places. It counts the number events occurring within the oscillations during a given interval of time. As the preset period gets completed, the value in the counter display on the screen and the counter reset to zero. [1]Various types of instruments are available which operates at a fixed or variable frequency. But if any frequency meter operates at a different frequency than specified range, it could carry out abnormally. For measuring low frequencies, the deflection type meters are widely used. The deflection of the pointer on the scale shows the change in frequency. The deflection type instruments are of two types: one is electrically resonant circuits and other is ratio meter[2,3].

1.2                                             OBJECTIVE OF THE PROJECT

The objective of this work is to design an electronic instrument that does the function of measuring frequency. It usually measures the number of oscillations or pulses per second in a repetitive electronic signal.

1.3                                         SIGNIFICANCE OF THE PROJECT

A Digital Frequency Meter is a general-purpose, basic, digital counter for measuring, setting, and monitoring frequencies, for counting random events, and for industrial counting applications.

• Among its many frequency measurement applications are the test, adjustment , and calibration of oscillators, telemetering equipment, i-f amplifiers and filters.
• With appropriate transducers, it can be used to measure such physical quantities as pressure, temperature, strain, and weight.
• In conjunction with an optical or magnetic pickup, it will measure rotational speed also.

1.4                                                 SCOPE OF THE PROJECT

This device measures frequency. In scientific terms, frequency is the number of cycles per second in the signal. In terms of a layman, frequency of a signal denotes the rate of occurrence of the signal in certain time. Digital Frequency meter is basically simple counter systems with a limited time period for counting.

In this work, we design simple frequency counter system using timers and two meter. While one of the Timer IC is used to produce clock signals, the other is used to produce the time limited signal of one second [3].

1.5                                              PROBLEM OF THE PROJECT

The accuracy of a digital frequency meter is strongly dependent on the stability of its timebase. A timebase is very delicate like the hands of a watch, and can be changed by movement, interference, or even drift due to age, meaning it might not “tick” correctly. This can make a frequency reading, when referenced to the timebase, seem higher or lower than the actual value. Highly accurate circuits are used to generate timebases for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber, known as an oven controlled crystal oscillator or crystal oven[1].

For higher accuracy measurements, an external frequency reference tied to a very high stability oscillator such as a GPS disciplined rubidium oscillator may be used. Where the frequency does not need to be known to such a high degree of accuracy, simpler oscillators can be used. It is also possible to measure frequency using the same techniques in software in an embedded system [2,4]. A central processing unit (CPU) for example, can be arranged to measure its own frequency of operation provided it has some reference timebase to compare with.

Accuracy is often limited by the available resolution of the measurement. Resolution of a single count is generally proportional to the timebase oscillator frequency and the gate time. Improved resolution can be obtained by several techniques such as oversampling/averaging.

Additionally, accuracy can be significantly degraded by jitter on the signal being measured. It is possible to reduce this error by oversampling/averaging techniques.

1.6                                           LIMITATION OF THE PROJECT

• This circuit takes into account the signals with high duty cycle such that timing value of negative pulse is quite low compared to that of the positive pulse. This in turn can be erroneous.
• This circuit uses CMOS devices which are quite static and cannot be used with bare hands.
• This circuit is not accurate

1.7                                               BENEFIT OF THE PROJECT

Digital frequency meter can be used for:

• For testing radio equipment
• Measuring the temperature, pressure, and other physical values.
• Measuring vibration, strain
• Measuring transducers

1.8                                         APPLICATIONS OF THE PROJECT

• Frequency Counting
• Precise frequency measurements in radar based application.
• Pressure, temperature, strain, and weight measurements with proper transducer.
• Motor speed measurements are also possible with proper arrangement.

Microwave frequency measurements.