Admission Requirements Find out as much as possible about the course and talk to past students to learn about their experiences. Undertaking postgraduate coursework while working full-time can be challenging so it is worthwhile investing in ways to make your learning experience more effective to maintain a balance in your life. Ally Ribalko, Master of Engineering Science Postgraduate study in Electrical Engineering allows students to consolidate a specialisation from an undergraduate degree, change direction to a new area within the field, or lay the foundation for a career in research and development.
Depending on the application, fixed resistors are manufactured as precision resistors, semiprecision resistors, standard general-purpose resistors, or power resistors. Precision resistors have low voltage and power coefficients, excellent temperature and time stabilities, low noise, and very low reactance.
These resistors are available in metal-film or wire constructions and are typically designed for circuits having very close resistance tolerances on values. Semiprecision resistors are smaller than precision resistors and are primarily used for current-limiting or voltage-dropping functions in circuit applications.
Semiprecision resistors have long-term temperature stability. General-purpose resistors are used in circuits that do not require tight resistance tolerances or long-term stability. Typically, general-purpose resistors have a high coefficient of resistance and high noise levels.
Power resistors are available in wire-wound and film constructions. Film-type power resistors have the advantage of stability at high frequencies and have higher resistance values than wire-wound resistors for a given size.
The potentiometer is a special form of variable resistor with three terminals. Two terminals are connected to the opposite sides of the resistive element, and the third connects Electrical engineering handbook a sliding contact that can be adjusted as a voltage divider.
Potentiometers are usually circular in form with the movable contact attached to a shaft that rotates. Potentiometers are manufactured as carbon composition, metallic film, and wire-wound resistors available in single-turn or multiturn units.
The movable contact does not go all the way toward the end of the resistive element, and a small resistance called the hop-off resistance is present to prevent accidental burning of the resistive element.
The rheostat is a current-setting device in which one terminal is connected to the resistive element and the second terminal is connected to a movable contact to place a selected section of the resistive element into the circuit.
Typically, rheostats are wire-wound resistors used as speed controls for motors, ovens, and heater controls and in applications where adjustments on the voltage and current levels are required, such as voltage dividers and bleeder circuits.
Integrated circuit resistors are classified into two general categories: Semiconductor resistors use the bulk resistivity of doped semiconductor regions to obtain the desired resistance value. Deposited film resistors are formed by depositing resistance films on an insulating substrate which are etched and patterned to form the desired resistive network.
Depending on the thickness and dimensions of the deposited films, the resistors are classified into thick-film and thin-film resistors. Semiconductor resistors can be divided into four types: Diffused semiconductor resistors use resistivity of the diffused region in the semiconductor substrate to introduce a resistance in the circuit.
Both n-type and p-type diffusions are used to form the diffused resistor. A bulk resistor uses the bulk resistivity of the semiconductor to introduce a resistance into the circuit. Pinched resistors are formed by reducing the effective cross-sectional area of diffused resistors.
The reduced cross section of the diffused length results in extremely high sheet resistivities from ordinary diffused resistors. The implanted ions lie in a very shallow layer along the surface 0.
For similar thicknesses ion-implanted resistors yield sheet resistivities 20 times greater than diffused resistors. Varistors are voltage-dependent resistors that show a high degree of nonlinearity between their resistance value and applied voltage.
They are composed of a nonhomogeneous material that provides a rectifying action. Varistors are used for protection of electronic circuits, semiconductor components, collectors of motors, and relay contacts against overvoltage.
The electrical characteristics of a varistor are specified by its b and k values. The resultant k value of n varistors connected in series is nk. This can be derived by considering n varistors connected in series and a voltage nV applied across the ends.
The current through each varistor remains the same as for V volts over one varistor. The equivalent k value for a parallel combination of varistors can be obtained by connecting n varistors in parallel and applying a voltage V across the terminals.
The current through the varistors will still be n times the current through a single varistor with a voltage V across it. Thermistors are resistors that change their resistance exponentially with changes in temperature.
If the resistance decreases with increase in temperature, the resistor is called a negative temperature coefficient NTC resistor. If the resistance increases with temperature, the resistor is called a positive temperature coefficient PTC resistor. NTC thermistors are ceramic semiconductors made by sintering mixtures of heavy metal oxides such as manganese, nickel, cobalt, copper, and iron.The School of Electrical Engineering & Telecommunications offers a wide range of undergraduate and postgraduate study in all areas of the professions of Electrical Engineering and Telecommunications.
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