VARISTORS
The name varistor came from variable resistor. Varistor is a pure electronic component used to protect circuits from transient over voltages making the circuit triggered. The function of a varistor is to provide increased current when voltage becomes excessively high. Varistor is also known as Voltage Dependent Resistor (VDR) since it depends on voltage.
The most common type we are dealing with now days is Metal Oxide Varistor (MOV). It is just like a Unijunction Transistor, since it allows current flow only in one direction. It contains mass of ceramic grains enclosed between two metal plates. The boundary between and its neighbour forms a diode junction. So when a small voltage is applied across the electrodes, only a small current passes due to the reverse break down at the junctions. Similarly when a large voltage is applied, due to thermionic emission large current passes through the junction. This behavior results in nonlinear current voltage characteristic.
Varistor can absorb surge in some ways but to some to extent. A typical surge protector power strip can be made using MOV’s. A varistor provides no equipment protection from inrush surge current. A varistor doesn’t control such events. Varistors have many applications on different electronic circuits. It can replace ordinary resistor in almost all functions, basically it can vary its resistance. So using varistors we can control voltage and current to the circuit. Thus we can protect the circuit from internal damage and severe short circuits.
What is a neural network?
The term neural network refers to be a club of biological neurons. But now this term is referred as artificial neural network which is composed of artificial neurons. So first of a comparison is needed between both the terms.
Biological neural network (BNN) is composed of natural and is connected in central nervous system or peripheral nervous system. They are destined to perform specific functions as ordained. Artificial neural network are fabricated with a group of artificial neurons. The name is so given because we know a neuron is the basic functional unit of our body which is capable of doing specific functions. These artificial ones are used to solve artificial intelligence problems. The artificial neural network (ANN) focuses on the detailed coverage of two types.
In BNN a single neuron is connected to other neurons and finally forms an extensive connection. These connections are called synapses and are connected with axons to dendrites. As such neural networks are extremely complex. Scientists need to melt the properties of BNN artificially in different areas. They ended up in the formation of ANN. The ANN concentrated in the solving of particular assigned tasks. It is successfully applied to speech recognition, face recognition, image analysis, adaptive control, to construct robots etc. Mostly now they are employed in the fields of statistical estimation, optimization and control theory. All neural networks take numeric input and numeric output.
The concept of neural networks emerged in the late 18th century. In the early 1950’s Friedrich Hayek was the one to posit this idea to the world.
The utility of ANN lies in the fact that it can be used to observe variety of functions. It can be used to determine the significance of seating arrangement in a class room. In real life it deals with function approximation, time prediction, blind signal production, data processing etc. Neural network software is used to research, stimulate, develop and apply ANN and BNN. Neural networks, with their remarkable ability to derive meaning from complicated or imprecise data, can be used to extract patterns and detect trends that are too complex to be noticed by either humans or other computer techniques. A neural network is not something that can be categorized in a single feature. It’s a day by growing branch of science. In all the ways above said neural network is a typical notable area that can produce drastic changes in technologies.
ELECTRO DYNAMIC TETHER
Tether means rope or chain used to fasten animals. In the case of space this tether finds application for connecting two space crafts. So tether is a term which needs key relevance that finds application even in space field. Physically a tether is a long flexible cable that connects two masses. When the cable is electrically conductive it is called as electro dynamic tether.
In the early 20th century Giuseppe Colombo came up with an idea of connecting two space crafts by means of some flexible cables. It also needed to be electrically conductive. So as a step forward to this idea NASA launched a shuttle to deploy a satellite on a tether to study the electromagnetic effects of a conducting tether as it passes through Earth’s magnetic fields ad a current was produced in the tether as it passes earth’s magnetic field, acting as an electric generator. This was the actual origin of electro dynamic tether.
There are mainly three types of electro dynamic tether employed systems available depending on the advantages.
1. Electro dynamic tether systems- In this type two heavy masses are separated by means a long flexible extensive electrically conductive cable. This can perform various functions in space craft.
2. In low earth orbit tether can provide electrical power and positioning capability for satellites and space crafts.
3. In the case of long term mission tethers could drastically reduce the amount of fuel needed.
Now tethers are made of electrically conducting materials like aluminium or copper. This provides additional advantages to the tethers. An electro dynamic tether is a device use to convert orbital energy to electrical energy and it works on the principle of electro magnetic induction. This can be used for power generation. Tethers found applications in orbit raising, lowering and debris removal. Another application of tether is artificial gravity inside space crafts.
ELECTRICAL POWERLINE NETWORKING
It is the method normally called home networking through which we are capable of interconnecting computers. This networking uses excited AC wire and power outlets to transmit the desired data to homes and different offices. Powerline networking allows sharing web access, printers, PC drives with all the existing wires, that means no new wires are needed to interconnect. Power line is one of the efficient methods for interconnecting computers. It uses electrical wiring in our house to create a network.
The main and key advantage of powerline networking is the PCs need not be put near the phone outlets instead the devices are connected through electrical output. We can’t start networking just by plugging in. Power line networking is based on Alliance home plug 1.o standard. With this type of networking we can interlink all the devices in our home without interrupting the working of each device.
As said earlier no extra wire is need for this networking. It uses standard plug or outlet to interlink and hence it is possible to access any where at home. It is easy to connect with Ethernet. Ethernet is a standard protocol for transferring data to and fro. Another notable feature is this type of networking provides maximum bandwidth and variable frequency band. This is the cheapest method for connecting different devices locating in various rooms.
IN this type of networking electrical power is transmitted over high voltage lines and distributed in low voltage lines. Proprietary specifications for power line home networking have been developed by a number of different companies within the framework. Power line communication modems are available for the data transfer. So lets conclude power line networking as one of the efficient and fabulous methods to interconnect computers.
What are Electrical Generators?
It is a device that converts mechanical energy into electrical energy. The source of mechanical energy may be a reciprocating pump or turbine. Essentially an electrical generator consists of two parts-magnetic field and conductors.
The energy conversion is based on the principle of production of dynamically induced e.m.f. This dynamically induced e.m.f is produced under Faraday’s laws of Electromagnetic Induction. The e.m.f causes current flow if the circuit is closed. A generator forces electric charge to move to an external circuit, but it doesn’t produce any charge. The charge is present in the windings of wire.
Dynamo was the first electrical generator capable of supplying power to the industry. It uses electromagnetic principles for the conversion of mechanical power in electric current
As described in electrical terms and mechanical terms generator consists of two parts
1) Mechanical-Rotor and Stator
Rotor is the rotating part of motor, dynamo, alternator and generator and a Stator is the stationary part of motor, dynamo, alternator and generator.
2) Electrical-Armature and Field
Armature is the power producing component of motor, dynamo, alternator and generator and Field is the magnetic field component of motor, dynamo, alternator and generator.
Generator uses field coils that require a current flow to be present in the field coils. (Equivalent circuit). Different types of generators now in use are vehicle mount, engine generators, human powered electrical generators etc.
As described above an electrical generator converts mechanical energy into electrical energy. It is a most common which we use frequently. This plays such a major role in electricity production.
