What is a Hermetic Seal?

What is a Hermetic Seal

A hermetic seal is a seal, which is practically airtight. Such seals are secure against water vapor and other foreign bodies and thus ensures proper working of its contents.

Hermetic seals are vastly found in semiconductor electronics and optical devices.

What is Transformer Oil?

Transformer Oil

Transformer oil, or insulating oil, is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage switches and circuit breakers. Its functions are to insulate, suppress corona and arcing, and to serve as a coolant.

What is a Magnetometer?

What is a Magnetometer

A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument.

Applications

Magnetometers are used in ground-based electromagnetic geophysical surveys (such as magnetotellurics) to assist with detecting mineralization and corresponding geological structures. Airborne geophysical surveys use magnetometers that can detect magnetic field variations caused by mineralization. Magnetometers are also used to detect archaeological sites, shipwrecks and other buried or submerged objects, and in metal detectors to detect metal objects, such as guns in security screening. Magnetic anomaly detectors detect submarines for military purposes.

They are used in directional drilling for oil or gas to detect the azimuth of the drilling tools near the drill bit. Magnetometers are most often paired up with accelerometers in drilling tools so that both the inclination and azimuth of the drill bit can be found.

Magnetometers are very sensitive, and can give an indication of possible auroral activity before one can see the light from the aurora. A grid of magnetometers around the world constantly measures the effect of the solar wind on the Earth's magnetic field.

Different Types of Magnetometer

Rotating Coil Magnetometer

Hall Effect Magnetometer

Proton Precession Magnetometer

Gradiometer

Fluxgate Magnetometer

Caesium Vapor Magnetometer

Spin-exchange relaxation-free (SERF) atomic Magnetometers

SQUID (Superconducting Quantum Interface Device) Magnetometer

What is a Drive or Motor Controller?

What is a Drive or Motor Controller


A motor controller or drive is a device that serves to govern in some predetermined manner, the performance of an electric motor. A motor controller or drive might include a automatic or manual means for starting and stopping the motor, selecting forward or reverse direction of rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.

A motor controller or drive may vary in complexity. The simplest motor controller is a switch in case of small motors. The switch can be manually operated or can be automated using relays or contractors.

Complex motor controllers can be used to accurately control the speed and torque of the motor at desired levels.

Classification of Motor Controllers or Drives

On the basis of method of control

• Manually controlled
• Automatically controlled
• Remotely controlled

On the basis of the type of motor

• Permanent Magnet
• Servo
• Series Excited
• Separately Excited
• Alternating Current

What is a Drum Motor?

What is a Drum Motor

A Drum Motor, also called a motorized pulley, is a highly efficient geared motor drive enclosed within a steel shell providing a single component driving pulley for conveyor belts and the like.

The Drum Motor consists of a synchronous or asynchronous electric motor fixed to a stationary shaft at one end of the drum and directly coupled through the motor’s rotor pinion to a gearbox which is fixed to the other stationary shaft.

The main parts or a drum motor are the electric motor, the drum shell and the drum shaft.

What are Rotary Electrical Connectors? Advantages of Rotary Electrical Connectors

Advantages of Rotary Electrical Connectors over Slip Ring and Brushes

The conventional brush slip ring mechanism to convert a mechanically rotating electrical system to a static one, as in the case of generators, comes across various disadvantages like wear and tear, larger size, noise, etc.

Rotary Electrical Connectors make use of ball bearings and hence rotary electrical connectors have certain advantages over conventional brush slip ring mechanism :

1. Low wear and tear, and hence longer life
2. Extremely low noise of operation
3. Sealed Construction
4. Extremely low resistance, less than a fraction of a milliohm
5. Low Cost
6. Overall, very high reliability

What is a Norator?

A norator is a theoretical linear, time invariant, one port network which arbitrary current and voltage across its terminals. It represents a controlled voltage or current source with infinite gain. When inserted in the schematics of a circuit, a norator provides whatever current and voltage the outside circuit demands.

What is a Nullator?

A nullator is a theoretical linear, time invariant, one port network which has zero current and voltage across its terminals. A nullator has the properties of both a short circuit and an open circuit simultaneously. They are neither current or voltage sources, yet both at the same time.

What is a Nullor?

A nullor is a theoretical two port network composed of a nullator at its input and a norator at its output. Nullors represent an ideal amplifier with infinte current, voltage, transconductance and transimpedence gain. All the four transmission parameters of this two port network is zero.

Properties of an Ideal Operational Amplifier(Op Amp)

Properties of an Ideal Op Amp (Operational Amplifier)

1. Infinite Open Loop Gain
2. Infinite Bandwidth - the opamp can respond to all frequencies
3. Infinite Input Impedance
4. Zero Input Current - no current drawn by input terminals as input impedence is infinite
5. Zero Output Impedance
6. Infinite Slew Rate - change from one output state to another takes zero time
7. Infinte Common Mode Rejection Ratio (CMRR)

An ideal op amp can be modeled as a nullor.

What is Surface Tensiometer?

A surface tensiometer is a device designed to measure the surface tension of liquids.

A goniometer is used to measure the surface tension and interfacial tension of a liquid using the pendant or sessile drop methods. A drop is produced and the profile is then captured using a goniometer/tensiometer. The software then analyses the profile of the drop and makes a series of critical measurements. The surface tension is then calculated from these measurements.

What is a Goniometer? Define Goniometer

A goniometer is an instrument that either measures angle or allows an object to be rotated to a precise angular position.

Goniometers are classified on the basis of their filed of application,

In the field of Surface Science, a Contact Angle Goniometer is used to measure the static contact angle, advancing and receding contact angles, and surface tension. A gonioreflectionometer is used to measure the reflectivity of a surface at a variety of angles.

In the field of Crystallography, goniometers are used for measuring angles between crystal faces and to rotate samples in X-ray diffraction.

In the field of Physical Therapy, goniometers are used to measure an axis and range of motion in a joint.

In the fielf of Communication, goniometers are used for direction finding in signal intelligence applications for military and civil purposes like interception of satellite and naval communication.

What is Divergence Theorem?

Divergence Theorem

Divergence Theorem states that the volume integral of the Divergence of a vector field A, is equal to the total outward flux of the vector through the closed surface bounding the volume.

What is Divergence? Define Divergence

What is divergence? Define divergence.

Divergenceof a vector field A at a point, is defined as the net outward flux of A per unit volume as volume tends to zero.

Divergence operator takes Vector as input and gives Scalar as output

What are flux lines?

Graphical representation of field variations

Field variations can be represented graphically by using directed field lines, called flux lines or stream lines. These flux lines indicate at each point the direction and magnitude of the vector filed. Direction is indicated by the arrowhead, and the magnitude is indicated by the concentration of flux lines at a point or the length of the lines.

What is Gradient? Define Gradient

What is Gradient? Define Gradient.

Gradient of a scalar is defined as the vector which represents both in magnitude and direction, the maximum space rate of change of the scalar.

Consider a scalar A. Consider two constant A surfaces (surfaces throughout which A is constant) S1 and S2. Let A be A1 in on S1 and A1 + dA on S2.

Consider a point P1 on S. Consider point P2 on S2 such that P1P2 is perpendicular to both the surfaces. Consider point P3 near P2 so that P1P3 not perpendicular to the surfaces.

Change in A from P1 to P2 is same as change in A from P1 to P3, which is dA. But P1P2 being perpendicular is the shortest distance between the two surfaces. Hence, dA/dP1P2 > dA/dP1P3

Thus the rate of change of A is dependent on direction and hence can only be represented by a vector, which is the gradient of that scalar.


Gradient operator takes Scalar as input and gives Vector as output.

Phase Velocity and Group Velocity

Group Velocity

Group Velocity of the a wave is the velocity with which the changes in amplitude of the wave propagates. It is given by

Vg =dw/dk

where w = angular frequency
k = wave number

Phase Velocity and Group Velocity

Phase Velocity


Phase velocity of a wave is the velocity with which a particular phase of the wave (say, the crest) propagates. It is given by

Vp = lambda/T

Vp = w/k

where lambda = wavelength
                   T= time period of the wave
                  w = angular frequency
                    k= wave number

What is Crawling

Crawling

Sometimes, a 3 phase induction motor shows a tendency to run at a stable speed, which is much lower than the synchronous speed, 1/7th of Ns and is unable to pick up to its normal speed. This phenomenon is known as crawling.

The main cause of crawling is the presence of harmonics in the flux set up by the stator windings. Due to the non linearity in the magnetization characteristics, the flux set up by the three phase stator winding, though carrying a sinusoidal magnetizing current, is of non sinusoidal shape.
We know that any non sinusoidal wave can be expressed as a combination of a number of sinusoids of fundamental and higher order harmonics.
Among the higher order fluxes, even harmonics can be ruled out due to the symmetry of rotating machines. So only the odd harmonics remain.

For third harmonics, the angle between the adjacent windings is 3*120 = 360 == 0. Hence it produces no effect. Similarly the 9th,15th etc. So only 1,5,7,11,13,17 etc will participate. In that Fundamental causes normal torque. 5th harmonics causes braking torque.

Frequency of seventh harmonic is 7 times supply frequency. Hence speed is 1/7th. Hence the motor finds a stable speed near 1/7th Ns and refuses to build up speed.

What is a Slip Ring Rotor

Points in Slip Ring Induction Rotor

• Rotor terminals are connected to slip rings at the end of the shaft
• Rotor Windings are wound for the same number of windings as the stator windings
• Rotor terminals are usually connected in star
• Working : A lever mechanis is used which has two positions, START and RUN. When in START position, the brushes are kept in contact with the slip rings ans resitances can be inserted into the circuit. After starting, the resistances are slowly reduced and finally, the lever is put in the RUN position where the brush-slip ring connection is opened and the slip rings are shorted.

What is a Squirrel Cage Rotor

Points on Squirrel Cage Rotor

• The rotor bar assembly is in the shape of a squirrel cage, hence the name
• 90% of all induction motors are squirrel cage, because i is extremely rugged
• Rotor core has rotor stampings punched into it
• Copper bars are driven through the slots and ends are welded to form end rings
• The rotor bars are slightly alligned to the shaft axis due to skew provided while stacking the rotor windings. This skew provides two advantages 
• Reduces themagnetic hum, hence motor runs quietly
• Reduces locking tendency of rotor.
• Rotor circuit is permanently closed. No resistance can be added to it

What are the Disadvantages of Three Phase Induction Motors

Disadvantages

1. Speed decreases as load increases, unlike Synchronous motors. The spped control auxiliarry can cost upto ten times the cost of the motor

2. Low starting torque, unlike Direct Current motors.

What are the Advantages of Three Phase Induction Motors

Advantages of Three Phase Induction Motors

1. Simple in construction : So large numbers can be constructed inexpensively

2. Extremely rugged construction 

3. Low cost : As construction is simple

4. Reliable : As it is extremely rugged

5. Low Maintenance : Only periodic dusting is required

6. Simple starting arrangement : Small motors can be started directly

7. High Efficiency : Full load efficiency is 85% to 94%

8. High Power Factor : Full Load power factor is 0.85 to 0.92

What is Electrical Resonance

Electrical resonance occurs in an electrical circuit when the impedance between the input and output is minimum.

Consider a circuit with a capacitor and inductance in series. When the capacitor is charged, it stores some energy in its electric field. When this charge gets discharged through the inductor, a current flows through, a varying current through the coil causes a build up of magnetic energy in the inductor. This magnetic energy causes an emf to be produced accross the inductor and supplies current to the capacitor, thus chargin it. This process is repeated continually. Due to some losses in the circuit (owing to non ideal characteristics of the capacitor and inductor), some energy is lost.

So energy gets transferred continuously from electric energy in the capacitor to the magnetic energy in the inductor.

What is Resonance

When a system is excited by energy, it tends to osccilate. The system oscillates at much higher amplitudes at certain frequencies than at other frequencies. This tendency of a system is called Resonance, and the frequencies corresponding to high amplitudes are called resonant frequencies.

Example. Acoustic resonance of musical instruments, resonance of electrical circuits, nuclear magnetic resonance

So a system can be made to oscillate by applying small excitation at resonant frequencies. So the system filters out all frequencies other than its resonant frequencies.

What is this blog about?

Daily Dose of Electrical and Electronics Engineering is a blog totally dedicated towards the academics of the academic degree of B.Tech in Electrical and Electronics Engineering. I will be posting certain portions of topics which have to be studied during the aforementioned course. I dont think anyone not related to B.Tech in EEE will have anything to do with this blog, but feel free to browse through the theories of Electrical Engineering and Electronics Engineering...