Video on Basic Electrical Instruments_Working Principles (playlist)

Basic video on operation of some electrical machines and concepts

1. woodencasing
2. springcontrol
3. singlephasemotor
4. pvcwiring
5. inductionwattmeter
6. fluidfriction
7. dynamometer
8. dcmotor
9. cleatwiring
10. alternator
11. airfriction
12. 3phasemotor
13. emf

Self Inductance and Mutual Inductance

Some detail about self and mutual inductance. Click here to download the file.

Series and shunt type Ohmmeter

There are two types of ohmmeters depending on the way the unknown resistance is connected with the meter. They are series and parallel ohmmeter. To know more. Click This link.

Galvanometer as voltmeter and ammeter

An ammeter or voltmeter is nothing but a basic galvanometer graduated to read either voltage (by connecting a suitable resistance in series) or as ammeter (by connecting a suitable resistance in parallel). A low low range voltmeter can be used to read high voltages by connecting a resistance in series as required or as ammeter by connecting a resistance in parallel and so is the case in a low range ammeter. The below download clearly explains and gives formula for selecting the suitable series or parallel resistances.

The below download is a source from www.citycollegiate.com.

Click To download

Online Interactive Learning on Electric Circuit Theory (Link)

Lesson 1: Ohm's Law
Lesson 2: Power & Energy
Lesson 3: Kirchoff’s Laws
Lesson 4: Resistors in Series
Lesson 5: Resistors in Parallel
Lesson 6: Node Analysis
Lesson 7: Mesh Analysis
Lesson 8: Superposition
Lesson 9: Thevenin & Norton
Lesson 10: Diodes
Lesson 11: Transistors
Lesson 12: Capacitors
Lesson 13: Inductors

Visit here (External Link-University of Texas)

Transient Response of RL & RC Circuit

Study the transient response of a series RL and RC circuit and understand the time constant concept using pulse waveforms. This helps in understanding the working of inductor and capacitor so that you can apply this knowledge in building your own circuit.

The below is an external link. (Source: lamar.edu)

(RC)

(RL)

 For more please visit http://www.ee.lamar.edu/EELABS/ELEN2107/index.html

Electroplating Process

Basic Process of Electroplating

Electroplating is the deposition of a metal onto a metallic surface from a solution by Electrolyses process. It is used for purpose of decoration and protection of the metal. Metals commonly use to plate surface are silver, chromium, cadmium, zinc, gold and copper. In the case of copper platting for example electroplating takes place by means of the reaction of Cu++ + 2e <====> Cu. Cu++ in this equation represent an ion that is carried to the metal surface to be plated, known as the CATHODE, from the source of the metal being plated, known as ANODE. The ion forced to the cathode by an external source such as a battery. The electrolytic solution is a salt of the metal being plated; in the case of copper plating. It is copper sulfate, CuSO4.5 H2O.

The appearance, adhesion, porosity, and protection value of electroplated coatings depends on several things, including the type of base metal be plated, the preparation of the metal to be plating, and the electrodepositing process itself.

Base Metal
It is not possible to apply high quality coatings to metals of poor quality. The composition of the base metal is usually known and controlled. The condition of the surface, including the degree and nature of the polishing processes, may also have a direct bearing on the characteristic and porosity of the coating.

Preparation for Plating
It is necessary to have the base metal surface chemically clean in order to secure good adhesion of deposits. The preparation usually involve cleaning that is, removal of grease and foreign particles and picking in the case of steel, or remove oxides or other compounds, and is some instances, to etch the surface. Because of a thin, natural oxide film, aluminum alloys do not usually respond to the cleaning and surface preparation treatments employed for other metals; special techniques must be used for such alloys.

Electrodeposition
In the plating process many variables are involved that are subject to control. The composition and temperature of the electrolytic bath itself must be closely maintained. Agitation of the bath often permits an increase in current density. Filtration, either continuous of intermittent, is often used to keep the solution free of suspended matter. The average current density should be kept within desired limits for the sake of uniformity in thickness and quality of coating.

Finally, the anodes should ordinarily be of such composition and structure as to maintain the metal concentration and the pH. Where insoluble anodes are used, the metal content is maintained by replenishment.
Most commercial plating with potentials of conducted with motor generator sets, usually with potentials of from 6 to 12 volts, and with current outputs, depending on the area of work to plated and the current density.

Single Phase Induction Type Energy Meter

Construction of Induction Type Energy Meters

There are four main parts of the operating mechanism

1.       Driving system

2.       Moving system

3.       Braking system 

4.       Registering system

Driving system

·      The driving system of the meter consists of two electro-magnets.

·      The core of these electromagnets is made up of silicon steel laminations.

·      The load current excites the coil of one of the electromagnets. This coil is called the current coil.

·      The coil of second electromagnet is connected across the supply and, therefore, carries a current proportional to the supply voltage. This coil is called the pressure coil.

·      Consequently the two electromagnets are known as series and shunt magnets respectively.

·      Copper shading bands are provided on the central limb.

·      The position of these bands is adjustable.

·      The function of these bands is to bring the flux produced by the shunt magnet exactly in quadrature with the applied voltage.

Moving System

·         This consists of an aluminum disc mounted on a light alloy shaft.

·         This disc is positioned in the air gap between series and shunt magnets.

·         The upper bearing of the rotor (moving system) is a steel pin located in a hole in the bearing cap fixed to the top of the shaft.

·         The rotor runs on a hardened steel pivot, screwed to the foot of the shaft.

·         A jewel bearing supports the pivot.

·         A pinion engages the shaft with the counting or registering mechanism.

 Fig. 1 Single-Phase Energy meter

Braking System

·         A permanent magnet positioned near the edge of the aluminium disc forms the braking system.

·         The aluminium disc moves in the field of this magnet and thus provides a braking torque.

·         The position of the permanent magnet is adjustable, and therefore braking torque can be adjusted by shifting the permanent magnet to different radial positions as explained earlier.

Fig. 2  Point Type

Fig. 3 Cyclo-meter Register

Registering (counting) Mechanism

·         The function of a registering or counting mechanism is to record continuously a number, which is proportional to the revolutions made by the moving system.

·         By a suitable system, a train of reduction gears the pinion on the rotor shaft drives a series of five or six pointers.

·         These rotate on round dials, which are marked with ten equal divisions.

·         The pointer type of register is shown in Fig. Cyclo-meter register as shown in Fig can also be used.

Errors in Single Phase Energy Meters

The errors caused by the driving system are

·         Incorrect magnitude of fluxes.

·         Incorrect phase angles.

·         Lack of Symmetry in magnetic circuit.

The errors caused by the braking system are

·         Changes in strength of brake magnet

·         Changes in disc resistance

·         Abnormal friction

·         Self braking effect

Faraday's Law of Electromagnetic Induction

Faraday's Law of electromagnetic induction is the basic principle behind the operation of Transformer, Induction motor, DC motor, DC generator and several other special machines.

It states that, the electromotive force (EMF) produced in a conductor is proportional to rate of change of magnetic flux linked with the conductor.

In other words,

For a transformer, Induction motor:
"Whenever a conductor is placed in a varying magnetic field, an emf is induced in the conductor."

i.e. in transformer and induction motor, varying magnetic flux is produced by exciting a coil with a time varying (AC) supply which links with the secondary (in transformer) or with the rotor conductors (in induction motor).

For a Generator:
"Whenever a conductor moves in a magnetic field such that it cuts the magnetic field, an emf is induced in the conductor."

Here in generator, flux linked with the conductors is varied by means of a mechanical force. i.e. the conductors are moved into and away from the magnetic field which means that when conductor moves towards a magnetic pole(field), flux linkage increases and when it moves away from a pole, flux linkage decreases thus a varying flux linkage is achieved mechanically.

For a motor (Converse):
"Whenever a current carrying conductor is placed in a magnetic field, it experiences a force."

Here, assume there is magnet (stator) and a current carrying conductor wound on a core(rotor). Current carrying conductor will behave as an electromagnet with it own poles. Now, the interaction of the stator and rotor poles produces a force (attractive or repulsive) which is directed in a rotational path to produce rotating motion of the motor.