World of Electronics Engineering

Classification Of Solid And Energy Band.

2008-12-12T11:07:00.003+05:30

This post is further extension of previous posts,"Understand The Atomic Structure Through Bhor's Atomic Model."and "Different Types of Energy Band In An Atom Of Solid. ".

This post along with previous two posts will complete the information of "Atomic Structure."

We know that some solids are good conductors of electricity while others are insulators.There is also an intermediate class of semiconductors.The difference in the behaviour as regards their electric conductivity can be explained in terms of energy bands.The electrons in the lower energy band are lightly bound to the nucleus and play no part in conduction process.However,the valence and conduction bands are particularly important in ascertaining the electrical behaviour of various solids.

Solids are classified as below,

01)Insulators:-
Insulators are those substances which do not allow the passage of electric current through them.For example,wood,rubber,glass etc.In this,valence band is full but conduction band is empty.The energy gap between valence and conduction band is very large.that is why,a very high electric field is required to push the valence electrons to the conduction band.For this reason,the electric conductivity of such materials is nil under ordinary conditions.

At room temperature,the valence electrons of the insulators do not have enough energy to cross over to conduction band.Some of the valence electrons may acquired enough energy to cross over to the conduction band,if the temperature is raised sufficiently.Hence,the resistance of an insulator is decrease with increase in temperature.

02)Conductors:-
Conductors are those substances which easily allow the passage of electric current through them.For example,copper,aluminium.There are large number of free electrons are available in a conductor.In conductors,the valence and conduction band,overlap each other.Due to this overlapping,a slight potential difference across a conductor causes the free electrons to constitute electric current.

03)Semiconductors:-
Semiconductors are those substances whose electric conductivity lies between conductors and insulators.In this,the valence band is almost filled and conduction band is empty.The energy gap between valence and conduction band is very small.Therefore,comparatively smaller electric field is required to push the electrons from valence band to conduction band.

At low temperature,the valence band is completely full and conduction band is completely empty.Because of this,semiconductors behaves as an insulator at low temperature.As the temperature increases,more valence electrons cross over to the conduction band and the conductivity increases.It means,semiconductors has negative temperature co-efficient of resistance.

Refer all three posts for complete information on atomic structure.

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Understand The Atomic Structure Through Bhor's Atomic Model.
Different Types of Energy Band In An Atom Of Solid.
What are the different types of materials used for Semiconductors.

Different Types of Energy Band In An Atom Of Solid.

2008-12-10T13:29:00.002+05:30

This post is further extension of previous post"Understand The Atomic Structure Through Bhor's Atomic Model. ".Here you will find the information about energy band of an atom.

In case of single isolated atom,the electrons any orbit posses definite energy.However,an atom in a solid is greatly influenced by the closely-packed neighbouring atoms,that's why the electron in any orbit of such an atom can have arrange of energies rather than the single energy.So,the range of energies is known as "Energy Band".In other word we may say that,"The range of energies possessed by an electron in a solid is known as energy band".

When the atom in a solid,the electron in any orbit can have a range of energies.For instance,electron in the first orbit have slightly different energies because no two electrons in this orbit see exactly the same charge environment.Since,there are millions of first orbit electrons,the slightly different energy level forms a band,called first energy band.Similarly,second orbit electrons form second energy band and so on.Below are the important energy bands in solid.

01)Valence Band:-
The range of energies (Band) possessed by the valence electrons is known as valence band.The electron in the out most orbit of an atom are known as valence electrons.In a normal atom,valence band has the electrons of highest energy.This band may be completely or partially filled.For example,in case of inert gases,the valence band is full where as for other materials,it is only partially filled and accommodate more electrons.

02)Conduction Band:-
In certain materials,the valence electrons are loosely attached to the nucleus.Even at room temperature,some of the valence electrons may be detached to become free electrons and which are responsible for conduction of current in a conductor.Because of this,these free electrons are called as conduction electrons.The range of energies (Band) possessed by conduction band electrons is known as conduction band.All electrons in conduction band are free electrons.If a substance has empty conduction band,it means current conduction is not possible in that substance.For example,Insulators.

03)Forbidden Energy Gap:-
The separation between conduction band and valence band on energy level diagram is known as forbidden energy gap as there is no allowed energy state in this region.The greater the energy gap,more tightly the valence electrons are bound to the nucleus.We can push an electron from valence band to conduction band by supplying the extra energy equal to the forbidden energy gap.

I hope,this information will help you in electronics field.Classification of solid and energy band will be cover in next post.

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Understand The Atomic Structure Through Bhor's Atomic Model.
What are the different types of materials used for Semiconductors.

Understand The Atomic Structure Through Bhor's Atomic Model.

2008-11-20T06:14:00.003+05:30

In the field of Electronics Engineering,the study of atomic structure is most important in view to understand the conductivity material etc...If you know the atomic structure of any metal then you better know the electrical conductivity of that metal.That will help you to choose as conductors,semi conductors or insulators.

As you know,the size of an Atom is so small that it is most impossible to see it even with the most powerful microscope.Therefore,we have to employ indirect method for the study of its structure.Different scientists have given different theories regarding the structure of Atom.Out of that theories Bhor's Atomic Model is most adequate for understanding electronics subject.Although various refinements have since been made on Bhor's Atomic Model,we still believe in the law the Bhor applied to the atomic world.You can better understand the problems facing to electronics world by this model.

What is Bhor's Atomic Model?

According to Bhor,
01)An atom consists of a positively charged nucleus around which negatively charged electrons revolve in different circular orbits.
02)The electrons can revolve round the nucleus only in certain permitted orbits.
03)The electrons in each permitted orbit have a certain fixed amount of energy of electrons.
04)If an electron is given additional energy,it is lifted to higher orbit.The atom is said to be in a state of excitation.This state does not last long,because the electron soon falls back to the original lower orbit.As it falls,it gives back the acquired energy in the form of heat,light or other radiations.

To better explain you Bhor's Atomic Model,I choose Silicon Atom as an example.It has 14 electrons.2 electrons revolve in the first orbit, 8 electrons in the second orbit and 4 in the third orbit.These electrons can revolve only in permitted orbits and not in any arbitrary orbit.Each orbit has fixed amount of energy associated with it.We can lift an electron from first orbit to second orbit by applying the energy (so that its total energy is equal to that of second orbit).When this lifted electron jumps from the second orbit to first.It will give back the acquired energy in the form of electromagnetic radiations.

So,from above description,you understand that each orbit has fixed amount of energy associated with it.Every orbit posses some energy level.The larger the orbit,the greater is its energy.It means,outer orbit electrons posses more energy than the inner orbit electrons.You may refer energy level diagram to better understand about energy level.There are different energy levels for different material atom structure other than silicon atom.You may find it by searching on net through search engine.

The remaining part of this atomic model will be covered in next posts.

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What Is Vacuum Tube Rectifiers And Its Application In Electronic Devices?

2008-07-30T19:42:00.004+05:30

For many applications,we required d.c. supply.Due to an economical proposition,the Electric Power is almost exclusively generated,transmitted and distributed in the form of Alternating Current.

For the successful operation of all Electron Tubes and Semiconductor Devices d.c. supply is required.Batteries can not be used for the purpose as they are costly and required frequently replacements.

Considering all these problems,it is necessary and also economical to convert available a.c. power supply into d.c. power supply.
Conversion of a.c. into d.c. can be achieved by Mechanical Devices also,yet Rectifiers are mostly used for the conversion purpose due to its simplicity,cheapness,efficiency,longer life and noiseless operation.

From above description we can define a Rectifier as "An Electronic Device that converts Alternating Current into Direct Current."

A Rectifier,changes a.c. supply into d.c. supply by eliminating the negative half-cycle of the Alternating Voltage.It may be thought of as a Switch that closes a load Circuit during the positive half-cycle of a.c. supply and opens the Circuit during the negative half-cycle.

Therefore,A Rectifier provides one-way path for Electric Current,means conduction takes place in one direction only.It is in this way that a Rectifier converts an Alternating Current into Undirectional Current.

Rectification Efficiency:-

The ratio of d.c. Power Output to the a.c. Power Input in a Rectifier is known as Rectification Efficiency.

Single Phase Vacuum Tube Rectifiers may be classified in two categories,that are as below.

01)Half-Wave Rectifier:-

It conducts only on the positive half-cycle of input a.c. voltage.

02)Full-Wave Rectifier:-

It conducts on both half-cycles (means positive and negative) of a.c. input voltage.A Full-Wave Rectifier Circuit can supply more d.c. output power than the equivalent Half-Wave Rectifier.

In this post I will cover this much information only,for the detail study,you can wait for another posts or find it out from searching elsewhere.

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What Are The Limitations In Operating Conditions Of Vacuum Tubes?

2008-07-29T14:22:00.006+05:30

The Vacuum Tubes will always give satisfactory performance in a Circuit if they are operated under proper condition.Actually this is the basic requirement of any Electronics Devices or Circuit.We have to take due care about the requirement of such Devices.Any deviation may result in the damage of the Vacuum Tube.The Vacuum Tube Manufacturers publish manuals indicating the limitations in the Operating Conditions.

There are many Limitations in Operating Conditions of Vacuum Tube,but following three are important from subject point of view.

01)Peak Inverse Voltage:-

The Maximum Reverse Voltage that can be applied across the Tube without Conduction in the reverse direction is known as Peak Inverse Voltage.

In the normal situation,the Plate of Tube is positive with respect to Cathode and Current flows from Cathode to Plate.However,if the Vacuum Tube is supplied with small reverse potential,normally no Current will flow.

If the reverse potential is increased,at one stage,the Electric Field becomes strong enough to tear Electrons out of the cold plate.As a result,Current starts flowing from Plate to Cathode (means in Reverse Direction).

This is undesirable and may damage the Vacuum Tube or other Electronic Circuit Elements.

02)Maximum Plate Current:-

It is the highest instantaneous Plate Current that a Tube can safely carry without damage to the Cathode and without undue Voltage drop in the Vacuum Tube.

03)Maximum Plate Dissipation:-

It is the maximum Power that a Vacuum Tube can handle without Overheating.During the Tube Operation,Electrons from Cathode bombard the Plate.

The Kinetic Energy of these Electrons is converted into Heat,due to which the Temperature of Plate Structure raises.If the Heat is produced faster than the Plate can dissipate it,the Temperature will rise to such a point as to either melt the Plate or cause Electron Emission from the Plate.

Therefore,Heat produced must be dissipated in order to keep the Plate Temperature within safe limit.

I have tried to give as much as knowledge,I have.You can search more details from other places.

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Different types of Vacuum Tubes and its uses.

Different types of Vacuum Tubes and its uses.

2008-07-19T07:44:00.005+05:30

An Electronic Device,in which the flow of Electrons is through a Vacuum is known as Vacuum Tube.

A Vacuum Tube usually contains a Cathode which is called as Electron Emitter,an Anode which is called as plate (which is electron Collector) and one or more Electrodes called as Grids,for controlling the flow of Electrons between the Cathode and Anode.

These Electrodes are housed in highly evacuated glass envelope.The Anode is held at Positive Potential with respect to Cathode,so that Emitted Electrons are attracted to Anode to provide Current in Vacuum Tube.

The application of Vacuum Tubes are so varied that this has won a place in the Industrial and Commercial fields.These Tubes have been found wide applications in Radio,Long Distance Telephones,Sound Motion Pictures,Televisions,Radar and Industrial Automation.

Though Vacuum Tubes have been replaced by Semi-Conductor Devices these days,they are still used at many places in Electronic Circuits.

According to the number of Electrodes,Vacuum Tubes are classified as below.

01)Vacuum Diode:-

An English Physicist,Sir J.A.Fleming has first invented Vacuum Diode in 1904.This Diode is known as Fleming's Valve.This Valve was so insensitive that it found little immediate applications.Many improvements have been made later.

02)Vacuum Triode:-

An American Scientist Dr.Lee De Forest,has placed a Third Electrode in the form of Wire Mesh,between the Cathode and Anode of Vacuum Diode.The resulting Device was called Triode.It ushered in the Electronics Industry as we know it today.

03)Vacuum Tetrode:-

Although Triode can make Amplification,it presents the major limitations that Plate-to-Grid Capacitance causes feed back particularly at higher Frequencies.

The Plate-to-Grid Capacitance of a Triode can be reduced by inserting an additional Grid,called the Screen Grid,between the Control Grid and Plate.Such a Four Electrode Valve is known as Tetrode.

04)Vacuum Pentode:-

A Suppressor Grid,is inserted in between the Plate and Screen Grid of Tetrode to eliminate the undesirable effects of Secondary Emission.This gives Five-Electrode Valve and known as Pentode.

A Pentode,contains a Cathode,a Anode and Three Grids.The Grid closest to the Cathode is Control Grid,next is Screen Grid and the third is Suppressor Grid.

The Suppressor Grid is connected to the Cathode and serves to Suppress the effects of Secondary Emission.

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The Important Thermionic Emitters and its Properties.

2008-07-18T08:30:00.003+05:30

The substance used for Electron Emission is known as an Emitter.An Emitter should have the following Properties.

01)High Melting Point:-

As Electron Emission takes place at very High Temperatures,therefore,the substance used as Emitter should have High Melting Point.

02)Low Work Function:-

The substance selected as an Emitter should have Low Work Function so that Electron Emission takes place by applying small amount of Heat Energy.

03)High Mechanical Strength:-

The Emitter should have High Mechanical Strength to withstand the Bombardment of Positive Ions.

Important Thermionic Emitters:-

The High Temperatures needed for satisfactory Thermionic Emission in Vacuum Tubes limit the number of suitable Emitters to such substances as follows.

01)Tungsten:-

It was the earliest material used as a Cathode and has a slightly Higher Work Function.Below are the Important Factors in its Favour.
A)High Melting Point.
B)Greater Mechanical Strength.
C)Longer Life.

Besides this,Tungsten has following Disadvantages:-
A)High Operating Temperature.
B)High Work Function.
C)Low Emission Efficiency.

Tungsten can be used in application involving Voltage exceeding 5kV.

02)Thoriated Tungsten:-

A mixture of two metals may have a Lower Work Function than either of the pure metal alone.Thus,a Tungsten Emitter with a small quantity of Thorium has a Work Function of 2.63 eV,compared with 3.4 eV for Thorium and 4.52 eV for Tungsten.

At the same time,Thoriated Tungsten provides Thermionic Emission at Lower Temperature with consequent reduction in the heating power required.Thoriated Tungsten Emitters are used for Intermediate Power Tubes at Voltage between 500 to 5000 Volts.

03)Oxide-Coated Cathode:-

This type of Cathode consist of a Nickel ribbon coated with Barium and Strontium Oxides.The Oxide-Coated Cathode has Low Work function,operates at comparatively Low Temperature and has Higher Emission Efficiency.

However,the principle limitation of Oxide-Coated Cathode is that it can not withstand High Voltages.Therefore,it is mostly used in Receiving Tubes or where Voltage involved do not exceed 1000 Volts.

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How you can construct Cathode?

2008-07-17T11:00:00.002+05:30

The substance used for Electron Emission is known as Emitter or Cathode.

The Cathode is heated in an evacuated space to emit Electrons.
As Cathode is sealed in Vacuum,therefore,the most convenient way to heat it is Electrically.

The heating processes may be done by two methods.The Thermionic Cathode are divided into two types,

01)Directly Heated Cathode
02)Indirectly Heated Cathode

01)Directly Heated Cathode:-

In this type,the Cathode consists of Oxide-Coated Nickel ribbon,which is known as "Filament".The heating Current is Directly passed through this Nickel ribbon which Emits the Electrons.

The Directly Heated Cathode is more efficient in converting heating power into Thermionic Emission.Therefore,it is generally used in Power Tubes that needs large amount of Emission and in small tubes operated from Batteries,where efficiency and quick heating are important.

The principal limitation of this type of Cathode is that any variation in heater Voltage affects the Electron Emission and this produce "Hum" in the Circuit.

02)Indirectly Heated Cathode:-

In this type,the Cathode consists of a thin metal sleeve coated with Barium and Strontium Oxides.A Filament or heater is enclosed within the sleeve and insulated from it.There is no Electric Connection between the heater and the Cathode.

The heating Current is passed through the Heater and the Cathode is heated indirectly through heat transfer from the heater element.

Advantages of Indirectly Heated Cathode:-

01)As Cathode is completely separated from the heating circuit,therefore,it can be readily connected to any desired potential as needed,independent of the heater potential.

02)Because of relatively large mass of Cylindrical Cathode,it takes time to heat or cool and as such does not introduce "Hum" due to heater Voltage Fluctutions.

03)a.c. can be used in the heater Circuit to simplify the Power requirement.

What is mean by Filament.

It is the thin wire,denotes the element through which the Cathode heating Current flows.In case of Directly Heated type,Cathode is itself the Filament.Whereas,heater is the Filament in Indirectly Heated Type.

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Which are the Important Methods for obtaining Electron Emission?

2008-07-16T10:23:00.003+05:30

From my previous post,you come to know about "Emission of Electrons".This Electron Emission can be classified in four different types.

The details about that four types are as below.

The External Energy which is used for Emission of Electrons,may come from variety of sources such as Heat Energy,Energy stored in Electric Field,Light Energy or Kinetic Energy of the Electric Charges Bombarding the Metal Surface.

Accordingly,there are four principle methods of obtaining Electron Emission from the Surface of Metal.

01)Secondary Emission:-

When High-Speed Electrons suddenly strike a Metal Surface,they may give some or all of their Kinetic Energy to the Free Electrons in the Metal.
If the Energy of the striking Electrons is sufficient,it may cause Free Electrons to leave from the Metal Surface.This phenomenon is known as Secondary Emission.

The Electrons that strike the Metal are called Primary Electrons while the Emitted Electrons are known as Secondary Electrons.

02)Thermionic Emission:-

In this method,the Metal is Heated about 2500 Degree Centigrade to enable the Free Electrons to leave the Metal Surface.The number of Electrons emitted depends upon the Temperature.Greater the Emission of Electrons,with Higher the Temperature.This type of Emission is employed in Vacuum Tubes.

03)Field Emission:-

A strong Electric Field is applied at the Metal Surface which pulls the Free Electrons out of Metal because of the attraction of Positive Field.Very intense Electric Field is required to produce Field Emission.
Usually,a Voltage of the order of million volts per centimeter distance between the Emitting Surface and the Positive Conductor is necessary to cause Field Emission.

Field Emission can obtained at Room Temperature,that's why,some time it is called as Cold Cathode Emission or Auto Electronic Emission.

04)Photo-Electric Emission:-

In this method,the Energy of Light falling upon the Metal Surface is Transferred to the Free Electrons within the Metal to enable them to leave the Surface.

The greater the intensity of Light Beam falling on the Metal Surface, greater is the Photo-Electric Emission.Photo-Electric Emission is utilised in Photo Tubes which form the basic of Television and Sound Films.

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What is mean by Electron Emission?

2008-07-15T08:42:00.002+05:30

At Room Temperature,the Thermal Energy in the Conductor is adequate to break the bonds of the Valence Electrons and leave them unattached to any one Nucleus.These Unbound Electrons moves at random within the Conductor and are known as Free Electrons.

If an Electric Field is applied across the Conductor,these Free Electrons move through the Conductor in an orderly manner,thus constituting Electric Current.

Many Electronic Devices depend for their operation on the movement of Electrons in an evacuated space.For this purpose,the Free Electrons must be ejected from the surface of Metallic Conductor by supplying sufficient Energy from some external source.This known as Electron Emission.

Electron Emission:-

Metals are used for Electron Emission,as they have many Free Electrons.If a piece of Metal is investigated at Room Temperature,the random motion of Free Electrons is within surface of the metal.

These Electrons are free only to the extent that they may transfer from one Atom to another within the Metal Surface.But they could not leave the Metal Surface to provide Electron Emission.

This is due to the Metallic Surface offers a barrier to Free Electrons and is known as Surface Barrier.

If we increase the Kinetic Energy of Free Electrons,by giving sufficient external Energy,the Electron will cross over the surface barrier to leave the Metal.

The amount of additional Energy required to emit an Electron from a Metallic Surface is known as Work Function of the Metal.
The Work Function of pure metal varies roughly from 2 to 6 eV.

It depends upon the nature of the Metal,its purity and the conditions of its surface.It may be noted that it is desirable that the metal used for

Electron Emission should have Low Work Function,so that a small amount of Energy is required to cause Emission of Electrons.

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Some unbelievable uses of Electronics Engineering.
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Some unbelievable uses of Electronics Engineering.

2008-07-13T15:14:00.004+05:30

The Branch of Engineering which deals with Current Conduction through a Vacuum or Gas or Semiconductor is known as Electronics.

Electronics mainly deals with Electronics Devices and their utilization.Such Devices have valuable properties which enable them to function and behave as the friend of Human today.

Electronics has gained much importance due to its numerous application in Industry.

The Electronics Devices are capable of performing various functions.Out of that the main functions are as below.

01)Amplification:-

The process of raising the Strength of Weak Signals to Strong Signals is known as Amplification.An Amplifier,is used in Radio-Set where the Weak Signals are Amplified so that it can be heard loudly.

02)Rectification:-

The conversion of Alternative Current (a.c.) into Direct Current (d.c.) is called Rectification.Electronics Device can convert a.c.Power into d.c. Power with very high efficiency.This d.c. supply can be used for Charging Storage Batteries,Field Supply of D.C.Generators,Electroplating etc..

03)Conversion of Light into Electricity:-

This Conversion of Light into Electricity is known as Photo-Electricity.Photo-Electric Devices are used in Sound Recording on Motion Pictures etc..

04)Generation:-

Electronics Devices can convert d.c. Power into a.c. Power of any Frequency.When performing this function,they are known as Oscillators.Electronics High Frequency Heating is used for Annealing and Hardening.

05)Control:-

Electronics Devices find wide applications in Automatic Control.For example,Speed of Motor,Voltage across Refrigerator etc.. can be Automatically Controlled with the help of Such Electronics Devices.

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What is Thermistors means?

2008-06-30T19:32:00.002+05:30

Thermistor is a means of a term "Thermal Resisters".Thermistors are generally made from Semi-Conductor Materials.Most Thermistors have Negative Coefficient of Temperature Resistance i.e.Their Resistance decrease with increase in Temperature.

The Negative Temperature Coefficient of Resistance can be large as several percent per Degree Celsius.This allows the Thermistor Circuits to detect very small changes in Temperature which could not be observed with a Thermocouple.

Thermistors are widely used in applications which involves Measurements in the range of minus 60 degree Centigrade to 15 degree Centigrade.The Resistance of Thermistors ranges from 0.5 ohms to 0.75 mega ohms.
Thermistor is highly sensitive device.the Thermistor exhibits a highly Non Linear characteristics of Resistance versus Temperature.

Construction of Thermistors:-

Thermistors are composed of sintered mixture of Metallic oxides such as Manganese,Nickel,Cobalt,Copper,Iron and Urenium.They are available in variety of sizes and shapes.The Thermistors may be in the form of beads,rods and discs.

A Thermistor in the form of beads is smallest in size and bead may have a Diameter of 0.015 mm to 1.25 mm.(Beads may be sealed in the tips of Solid Glass Rod to form Probes which may be easier to mount than the beads).

Glass Probe have a Diameter of about 2.5 mm and a length which varies from 6 mm to 50 mm.Discs are made by pressing material under high pressure into Cylindrical Flat Shape with Diameters ranging from 2.5 mm to 25 mm.

The three important characteristics of Thermistor make them extremely useful in Measurement and Control Applications,these are as follows.

01)The Resistance:-Temperature characteristics

02)The Voltage:-Current characteristics

03)The Current:-Time characteristics

Applications of Thermistors.

Major Applications of Thermistors are Measurement and Control of Temperature they may be used for number of other applications.

01)Measurement of Temperature.

02)Control of Temperature.

03)Temperature Compensation.

The other Applications of Thermistors includes,

01)Measurement of Power at High Frequencies.

02)Measurement of Thermal Conductivity.

03)Measurement of Level,Flow and Pressure of Liquids.

04)Measurement of Composition of Gases.

05)Vacuum Measurement.

06)Providing Time Delay.

What is mean by Hygrometer?

2008-06-21T21:18:00.001+05:30

A Hygrometer measures the Value of Humidity Directly.Generally,the output of Hygrometer is used to indicate Relative Humidity.

Several Material exhibit changes in Electric Properties that are caused by Humidity.These are frequently used in Transducers that are designed and Calibrated to read Relative Humidity Directly.

01)Resistive Hygrometer:-

Some Hygroscopic Salts exhibit a change in Resistivity with Humidity.The most common is Lithium Chloride.This,with a Binder may be coated on a wire or on Electrodes.

Resulting Resistance changes cover a wide range for example 10 raise to four to 10 raise to nine ohm,as the Humidity changes from 100 to 0 percent.

This makes it impractical to design a single element to operate from 1 to 100 percent Relative Humidity.Instead several elements are used,each in a narrow range,with provision for switching elements.

Resistance is measured either with a Wheatstone Bridge or by a combination of Current and Voltage Measurements.

Most of these must not be exposed to conditions of 100 percent Humidity as the Resulting Condensation may damage the Device.Either they must be operated in a constant Temperature Environment or Temperature corrections must be made.

These are Accurate to within plus or minus 2.5 percent or plus or minus 1.5 percent in some cases.Response times are typically of the order of a few seconds.These are currently the most common Electronics Hygrometers.

A typical Resistive Hygrometer having a mixture of Lithium Chloride and Carbon which acts as Conducting Film.This is put on an Insulating Substrate between Metal Electrodes.

The Resistance of the element changes when it is exposed to variations in Humidity.The higher the Relative Humidity the more Moisture the LithiumChloride will absorb,and the lower will be it's Resistance.

The Resistance of the Sensing unit is a Measure of the Relative Humidity.Resistance should be Measured by applying Alternative Current (A.C) to the Wheatstone Bridge.

D.C. Voltage is not applied because it tends to Breakdown the Lithium Chloride it it's lithium and Chlorine Atoms.The Current flow is a Measure of the Resistance and hence of the Relative Humidity.

There are different types of Hygrometer are as follows.

01)Resistive Hygrometer.

02)Capacitive Hygrometer.

03)Microwave Hygrometer.

04)Aluminium Oxide Hygrometer.

05)Crystal Hygrometer.

How to Measure the Liquid Level by Different Methods.

2008-06-19T18:26:00.002+05:30

The Liquid Levels can be measure by different methods but following two are more important from the subject point of view.

01)Electrical Methods:-

The Direct Conversion to Liquid Level position to Electrical Signal is used in many instances.The measurements is generally done by two conversions,so that the Liquid Level is determined indirectly.

The first conversion usually is Liquid Level to a Displacement through a Float in a Liquid or a Spring Loaded Plate in contact with the surface in the case of Granular Solids.

This Displacement is then converted into an Electrical Signals by a Secondary Transducer connected to Float or Plate.These are however,in many applications where this is not possible and hence other methods like Optical or Acoustic means or Gamma rays are used.

The Electric Transducers used for Level Measurements are
01)Resistive
02)Inductive
03)Capacitive

Now we will see about Resistive Method first.

01)Resistive Method:-

This method uses Mercury as a Conductor.A number of Contact Rods are placed at various Liquid Levels.

As Head "h" increases, the rising Level of Mercury above the Datum,shorts successive Resistors "R" and increases the value of "h" directly.

Advantages of Resistive Method:-

01)The System uses Low Voltage to eliminate danger to the operators and to prevent Arcing at the contact points.

02)The Signal can be transmitted to any desired point.

03)The Transducers can be used in Pressured Containers without Packing Glands or Shafts.

04)The unit is simple to calibrate since the distance between the levels of Contact Rods can be accurately measured and the indicated value may be checked for each measured value.

Disadvantages of Resistive Method:-

01)Due to Arcing at the contact points,it is not safe to use this Transducer in Explosive Atmosphere.

02)In order to have a step less indication of the Liquid Level,an extremely large number of Contact Rods are needed.

03)The Contact Rods are corroded by Corrosive Liquids.In addition,the Electric Charges promote Corrosion.

04)These Systems also present difficulties when there is Saturated Vapour above the Liquid Phase.

05)Any changes in the Conductivity of the Liquid causes serious errors.

What are the limitations of A.C.Tachometer Generators?

2008-06-17T08:47:00.001+05:30

In order to overcome some of the diffculties,A.C.Tachometer Generators are used.The Tachometer has Rotating Magnet which may be either Permanent Magnet or an Electromagnet.

The Coil is wound on the Stator and therefore the problems associated with Commutator (as in D.C.Tachometer) are absent.

The rotation of the Magnet causes an E.M.F to be induced in the Stator Coil.The Amplitude and the Frequency of this E.M.F. are both proportional to the speed of Rotation.Thus either Amplitude or Frequency of induced voltage may be used as a measured of Rotational Speed.

The Output Voltage of A.C.Tachometer Generators is rectified and is measured with a Permanent Magnet Moving Coil Instrument.(PMMCI)

LIMITATIONS:-

01)The difficulty with this system is that at low speed the Frequency of output voltage is low and hence it is very difficult to smooth out the ripples in the output voltage wave-shape and hence A.C.Tachometer Generators are designed to have a large number of Poles,so that the Frequency of output voltage is high,even at low speed.

02)High Speed is also present a problem.At high speeds,the Frequency increases and therefore,the Impedance of the Coil of TachoGeneretors increases. If good linearity is to be maintained in the input Impedance of the display device must be considerably larger than the Impedance of the Coil.

Drag Cup Rotor A.C.Tachogenerators:-

The Tachogenerators consists of a Stator and a rotor.The Stator has two windings mounted at 90 degree to each other.The two Stator windings are,
01)Exitation Winding
02)Sensing Winding

Advantages of Drag Cup Rotor A.C.Tachogenerators:-

01)A Linear Relationship between the output voltage and speed is obtained if the carrier frequency is 5 to 10 times larger than the frequency of the speed signal.For this purpose of excitation winding is supplied with a frequency of 400 hertz.

02)The Drag Cup type tachogenerators are rugged and in-expensive.Also,they requires little maintenance.

03)In some situations these Tachogenerators are very useful since they give a ripple free output.

Disadvantages:-

01)These Tachogenerators are hard to calibrate.

02)The output voltage is proportional to the product of speed and input voltage.

What is Tachometer Generators?

2008-06-03T07:04:00.002+05:30

Before going to Tachometer Generators we will see about Angular Velocity in short.

In many cases the only way to measure Linear Velocity is to convert it into Angular Velocity.For example a Speedometer uses the wheels rotational speed as a measure of Linear road speed.

The measurement of Angular Speed may be made with Tachometers which may be either Mechanical or Electrical type.

Electrical Tachometers.

The Electrical Tachometers are professed over Mechanical Tachometers for all applications because these Tachometers offer all the advantages associated with Electrical Transducers.

Electromagnetic Tachometer Generators.

There are two types of Electromagnetic Tachometer Generators called Tachogenerators.

01)D.C.Tachometer Generators.

02)A.C.Tachometer Generators.

The details of D.C.Tachometer Generators is as below.

01)D.C.Tachometer Generators.

D.C.Tachometer Generators consists of a small Armature which is coupled to the Machine whose Speed is to be measured.This Armature revolves in the field of a Permanent magnet.The Electro Magnetic Force (EMF) generated is proportional to the product of Flux and Speed.Since the flux of the Permanent magnet is constant,the voltage generated is proportional to Speed.

The Polarity of Output Voltage indicates the Direction of Rotation.This Electro Magnetic Force is measured with the help of moving Coil Voltmeter having a uniform scale and calibrated directly in terms of Speed.

Advantages are,

01)The direction of rotation is directly indicated by the Polarity of Output Voltage

02)The Output Voltage is typically 10 mV/rpm and can be measured with conventional type D.C.Voltmeters.

Disadvantages are,

01)Brushes on small Tachometer Generators often produce Maintenance problems,as their contact resistance may vary and produce appreciable errors.This is commutator and the brushes requires periodic Maintenance.

02)The input resistance of Meter should be very high as compared with Output Resistance of Generators.This is required to limit the Armature Current to small value.If the Armature Current is large,the field of the Permanent Magnet is distorted giving rise to non-linearity.

Application And Advantages of Digital Systems.

2008-06-02T12:35:00.002+05:30

In last topic,we have discussed about Digital Instruments and Analog Instruments.In this post we will see about Digital Systems and Microprocessors used for measurement system and control.

The major reasons for Digital and Microprocessor are.

01)Stability and accuracy of control.

02)Flexibility.

03)Lower cost per function.

04)Greater reliability and equipment life.

05)Human factors favouring Digital Interface.

The most general and versatile circuit that can be placed on a single Chip is the Digital Microprocessor.the Microprocessor is versatile because it can be programmed to perform an almost unlimited computing tasks.

Application And Advantages of Digital Systems.

01)The device used in Digital Circuits generally operate in one of the two states,known as,ON & OFF resulting in a very simple operation.

02)There are only a few basic operations in Digital Circuit which are very easy to understand.

03)Digital Technique requires Boolean Algebra which is very simple and easily be learnt.

04)Digital Circuit requires basic concept of Electrical Network Analysis which is easily learnt.

05)A large number of Integrated Circuits ( IC )are available for performing various operations.These are highly reliable,accurate and the speed of operations is very high.

06)The effect of fluctuations in the characteristics of the components,ageing of components,temperature and noise etc. is very small in Digital Circuit.

07)Digital Circuit have capability of memory which makes these circuit highly suitable for Computers,Calculators,Electronic Watches etc.

08)It is very fascinating & challenging field of study because most of the latest Electronics systems are Digital in nature.

Important Information about Analog and Digital Instruments.

2008-05-27T14:19:00.001+05:30

Electronics Voltmeters,Ammeters and Ohmmeters are use Amplifiers,Rectifiers and other ancillary circuit to produce a current proportional to the quantity being measured.

This current is measured by PMMC (Permanent magnetic moving Coil) instrument.

This is Analog type instrument.Now an Electronic Instruments are use Digital read out systems and in that case they are called "Digital Electronic Instruments".Till then,the Analog type of instruments are in use because of the economic considerations.

Also Analog and Digital instruments must perform the same functions i.e. measurement of Voltage,Current,Power and Circuit Parameters.The principle operation is different in each case.

Advantages of Digital Instruments:-

01)The Digital Instruments indicate the reading directly in Decimal numbers and therefore errors on account of human factors like due to parallax and approximation are eliminated.

02)The reading may be carried to any number of significant figures by merely positioning the decimal point.

03)Since the output of Digital instruments are in Digital form,the output may be directly fed into memory devices like Tape Recorders,Printers and Digital computers etc. for storage and future computations.

04)The power requirement of Digital Instruments are considerably less.

What is the use of TRANSDUCER in Electronic circuits?

2008-05-23T11:22:00.002+05:30

An Electronic instrumentation system consists numbers of components to perform a measurement and record its result.Now a days a generalized measurement system consists of Three major components.
01) An input device
02) A signal conditioning or processing device
03) An output device

The input device receives the measure and/or the quantity under measurement and delivers a proportional or analogous electrical signal to the signal conditioning device.Here the signal is amplified,attenuated,filtered,modulated or otherwise modified in format acceptable to the output device.

The input quantity for most instrumentation systems is a "non-electrical quantity".In order to use electrical methods and techniques for measurement,manipulation or control,the non-electrical quantity is generally converted into an electrical form by a device called a "Tranducer"

We can define a Tranducer as a device which,when actuated transforms energy from one form to another.

The broad definition of a Transducer includes,for example device which convert Mechanical Force into an Electric Signal.These device form a very large and important group of Transducers commonly used in industrial instrumentation area.The Instrumentation Engineers and Technologist are therefore primarily concerned with this area of instrumentation.Many other physical parameters,such as heat,intensity of light,flow rate,liquid level,humidity and PH value may also be covered into electrical form by means of Transducers.These Transducers provide an output signal when stimulated by a Mechanical or non-mechanical input.A photoconductor converts a Thermocouple,converts heat energy into electrical voltage,a force produces a change of resistance in a strain gauge,an acceleration produces a voltage in a Piezo-electrical crystal and so on.In all cases,however,the electrical output is measured by standard methods,giving the magnitude of the input quantity in terms of a analogous output.

ELECTRIC TRANSDUCERS

The art of electrical measurements has been mainly used for measurement of electrical quantities but its value in making measurements of non-electrical quantities in this new era of Automation is rapidly growing.In order to measure non-electrical quantities a detector is used which usually converts the physical quantity into a displacement.

This displacement actuates an Electric Transducers,which acting as a secondary Transducer gives an output that is electrical in nature.The Electrical quantity so produce is measured by standard methods used for electrical measurements.The result (Electrical output) gives the magnitude of the physical quantity or condition being measured.

The electrical signal may be a current or a voltage or a frequency and production of these signals is based upon electrical effects which may be resistive,capacitive,inductive etc.. in nature.

The first stage of a system may be simply be called a Transducer stage instead of detector Transducer stage by redefining a Transducer.
A Transducer,in general form,may be defined as a device which converts energy from one form to another.However this definition has to be restricted many times especially in the field of electrical instrumentation.

Keeping this restriction in view,a Transducer may be defined as a device which convert a physical quantity or physical condition into an electrical signal.

Deatils about Cathode Ray Oscilloscope.(CRO)

2008-05-21T14:38:00.003+05:30

Generally many people known about Cathode Ray Oscilloscope (CRO).Because the CRO is a very useful and versatile laboratory instrument used for display,measurement and analysis of waveforms and other phenomena in electrical and electronics circuit.

No other instrument used in electronics industries is as versatile as the Cathode Ray Oscilloscope.It is widely used for trouble shooting of radio and television receivers as well as for laboratory work involving research and design.

With an Oscilloscope,the wave shape of a signal can be studied with respect to amplitude distirtion and deviation from the normal.Also we can measure voltage,frequency and phase shift by using an Oscilloscope.

The normal form of Cathode Ray Oscilloscope uses a horizontal input voltage which is an internally generated ramp voltage called "Time Base".This horizontal voltage moves the luminous spot periodically in a horizontal direction from left to right over the display area or screen.The vertical input to the CRO is the voltage under investigation.The vertical input voltage moves the luminous spot up and down in accordance with the instantaneous value of voltage.The luminous spot thus the traces the waveform of the input voltage with respect to time.When the input voltage repeats itself at a fast rate,the trace (Display) on the screen appears stationary on the screen.The Cathode Ray Oscilloscope thus provides a means of showing(Visualizing) time varying voltage.As such,the CRO has become a universal tool in all kinds of electric and electronics investigations.

Cathode Ray Oscilloscope operate on voltage.However,it is possible to convert current,strain,acceleration,pressure and other physical quantities into voltage with the help of transducers and thus to present visual representations of a wide variety of dynamic phenomena on CRO.
CRO are also used to investigate waveforms,transient phenomena,and other time varying quantities from a very low frequency range to the radio frequencies.

Oscilloscope have been evolved continuously,and they are now available which can measure frequencies upto 1 Giga hertz and observer events as small as 20 hertz. in duration.

Many additional features are available with some Oscilloscopes and these are includes built in Digital multimeters and Counters.

The Oscilloscopes are progressively getting smarter,and many are Microprocessor controlled.They have the ability to calculate several features such as rise time or pulse width of the measured waveform,and to display these values along with the display of the waveforms.They are easier to use and internal routines often act as a guide for the user,and display a warning if there is any error in setting.

Although,most Oscilloscope are monochromatics,colour Oscilloscope are finding increasing applications in computers and television.

The application of Oscilloscope have been enhanced on account of many recent developments.Most present days Oscilloscope are capable of accepting two or more inputs displaying them simultaneously.
This may be achieved through,using a split beam or by using a multiple beam tube.Sampling Oscilloscope are used for high speed applications.These Oscilloscope employ time sampling through and through their use it is possible to measure signals of about 20 Giga hertz.They can only detect a repetitive waveform and work on the principle of taking sample once every cycle,over several cycles,each sample point being shifted from the previous point.The complete picture of the waveform is stored and can displayed as a stationary signal.

What are the different types of materials used for Semiconductors.

2008-05-11T17:21:00.001+05:30

An electronics engineer comes in contact with a large variety material in the manufacturing of a apparatus,electronic machines & electronics devices,radio,TV,electronic gear,automatic & remote control equipment.In transmission line design,we must have knowledge material.In computer memory device too,

We must have an understanding of the construction of IC's & Semi Conducting materials.The materials used in various branches of electronics engineering they are divided into two large groups.
The first group comprises of construction materials which mainly go into the manufacture of bearing and auxiliary parts and components of electrical and radio devices,such as mounting frames,cases,dials,heat sinks,etc...
The second groups includes materials use for the fabrication Wires,Cabels,Wave guides,Antennas,Insulators,Capacitors,Resistors,Inductors,Transformers,Electric Motors & Generators,Magnets,Diodes & Transistor,FET& integrated Circuits (IC),Electromechanical Transducers,Lasers,Light Detectors,Computer memory devices & so on.

According to electrical properties,the materials can be classified into the following groups.
01)Conductor materials
02)Semiconductor materials
03)Super Conductor materials
04)Magnetic materials
05)Ferromagnetic materials
06)Insulating materials (Dielectrics)
07)Ferromagnetic materials
08)Ferroelectric materials
09)Gaseous Insulator
10)Gaseous Conductors

In this fast developing society,electronics is the most important branch of engineering.Electronics devices are being used in almost all the industries for the quality controls and automation.the branch of electronics which deals with current conduction through a vacuum or gas or semiconductor.

Now we will see about semiconductor.
Certain substances like Germanium,Silicon,Carbon etc.. are neither good conductor like copper nor insulators like glass,wool,rubber etc. that's why we can say,semiconductors are those substances whose electrical conductivity lies between conductors and insulators,for example Germanium,Silicon,selenium,carbon.The resistivity of semiconductor materials lies between 0.01 to 50 ohm centimeter at room temperature.The resistivity of semiconductor is not constant,but varies with many factors.The resistivity can be controlled by an electric field,voltage,temperature,illumination and impurity.Such resistivity controlled materials then works as transistors,varistors,photoelectrics and rectifiers.

Properties of Semiconductors.

01)The resistivity of semiconductor is less than an insulator but more than a conductor.

02)Semiconductors have negative temperatures coefficient of a resistance. i.e.The resistance of semiconductors decreases with the increasing temperatures and vice versa. for example Germanium actually an insulator at low temperature but it becomes a good conductor at high temperature.

03)When a suitable metallic impurity ( Arsenic,Gallium etc.) is added to a semiconductors,it's current conducting properties changes appreciably.This is the most important property.