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Monday, 10 December 2012

Photosensitive optic fiber and bend-insensitive optic fiber

Optic fiber is widely used in communication. It consists of a core and cladding. Core refractive index is always greater than cladding refractive index. Some of the main types of optic fibers are Erbium doped fiber, termination fiber, photonic crystal fiber, photosensitive fiber, bend-insensitive fiber, high-index fiber and polarization-preserving fiber. In photosensitive fibers, refractive index is subjected to a change on an exposure to ultraviolet light. By doping proper amount of germanium and boron ions, sensitivity can be increased which finds immediate application in Bragg grating. Bragg grating is a periodic variation of the refractive index along the fiber axis.  This is used in pump lasers, optical filters etc. Bend-insensitive fibers are fabricated by increasing the numerical aperture. This reduces bending loss.

Tuesday, 20 November 2012

Centrifugal pump

Centrifugal pump is used to raise water from a low level to a high level. In these pumps, external driver is an electrical motor which drives the shaft resulting in rotation and fluid flow in directions opposite to those of a turbine. The main components of a centrifugal pump are a disc with vanes and the impeller revolving in a casing. The material used for the construction of impeller is bronze, aluminium bronze and stainless steel. The dynamic pressure caused by the rotation of the blades lifts the water from a low level to a high level. If diffusers are provided in pumps, they are known as diffusion pumps. In diffusion pumps, some fixed guide blades act as diffuser. Centrifugal pumps which are provided with volute chambers are known as volute pumps. Volute chambers are straight tapered ducts wrapped around the impeller. This helps to reduce the exit velocity. Commonly used types of impellers are closed type, semi-closed type and open type. Closed and semi-closed types offer superlative performance and efficiency but are expensive. Open type are less expensive and maintenance free but its efficiency is very poor.

Dual beam oscilloscopes and dual trace oscilloscopes

An oscilloscope is an instrument used for the measurement, analysis and display operations. Cathode ray oscilloscope makes use of cathode ray tube, a vacuum tube device. A cathode ray tube consists of an electron gun, two pairs of deflection plates, and a phosphor screen. The components of electron gun are heater, oxide coated cathode, anodes and a control grid. Heater heats up cathode and cathode emit electrons. Anode serves the purpose of fine focusing and acceleration of electrons towards screen. A dual beam oscilloscope has two different electron guns producing two separate beams. It also consists of two separate vertical channels and one horizontal time-base unit. Study of two separate waveforms simultaneously is the main purpose of dual beam oscilloscopes. But they are expensive. In dual-trace oscilloscopes, only one electron gun and one set of vertical and horizontal deflection plates exist. But dual trace oscilloscopes are capable of performing all the operations performed by a dual beam oscilloscope. An appropriate switching operation is helping to achieve this multifunction.

Monday, 5 November 2012

Microwave remote sensing

Remote sensing is the branch of science where information about an object is obtained by proper analysis of data acquired by a device which is not in contact with the object. Microwave band is a region of the electromagnetic spectrum with wavelength range mm-m. This band can be effectively used for remote sensing. There are two categories in microwave remote sensing. They are active microwave remote sensing and passive microwave remote sensing. Active microwave systems provide a self illumination model. Passive microwave systems record the energy of thermal origin emitted from materials. Imaging sensors and non-imaging sensors are used in microwave remote sensing. Most widely used imaging radar is Side Looking Airborne Radar, SLAR. Radars can be comprised of either real aperture or synthetic aperture. In the real aperture system, beam width and antenna size determines the resolution of the system. Synthetic aperture system yields better resolution due to the superlative signal processing techniques. Some factors which affects the microwave measurements are surface roughness, radar backscattering coefficient and radar wavebands.

Tuesday, 30 October 2012


The network layer of the internet is called internet protocol (IP). Internet protocol version 4 (IPv4) was implemented in the year 1984. The three important aspects of internet protocol are addressing, fragmentation, reassembly and routing. The four important addresses are hardware addresses (layer 2 MAC), network addresses (layer 3 IP), domain based addresses (email) and universal reference locator (URL). 48-bit addresses are used in ethernet and token ring. A 12-bit DLCI connection identifier is employed in frame relay. Telephone numbers are used in SMDS. CIDR is classless interdomain routing where address space is used efficiently by reserving the number of addresses needed for a subnet. DHCP is dynamic host configuration protocol and is used where only a few of the subscribers are logging in at a time. Domain Name System (DNS) is a distributed directory service which is used for the translation between IP addresses and names. DNS is also used for the control of internet e-mail delivery.

Sunday, 21 October 2012

Transmission line distortion and loading

The main two varieties of distortion in transmission line are frequency distortion and phase distortion ( or delay distortion). Both frequency distortion and phase distortion are not due to any non-linearity of the system and hence they are linear distortions. The correction for frequency distortion in a transmission line is possible by using a two-port network, called equalizer. This network is mounted at the receiving end which is designed to have transmission loss complementary to that of the particular transmission line used at least over the bandwidth of interest. Measurement of phase distortion is carried out in terms of delay distortion coefficient.  Delay distortion coefficient which is also known as differential delay is the difference between the maximum and minimum group delays for frequencies within a specified band. Four methods that can be adopted for a distortion less line are reducing R, increasing G, reducing C and increasing L. Increasing the inductance (L) of the line is called loading. There are two types of loading mechanisms- continuous loading and lumped loading. In continuous loading, inductance of the line is increased uniformly along the length of the line. In lumped loading, inductance coils are wound on torroidal magnetic dust cores which are connected periodically and in series with the transmission line.

Tuesday, 16 October 2012

Global hydrologic system

Hydrological cycle is a system which comprise of components like precipitation, infiltration, runoff and evaporation. A hydrological system can be defined as a structure in space, bounded by a defined boundary that accepts rain water and or other inputs, operates on them internally, and produces them as outputs. The global hydrological system consists of three parts. They are atmospheric water system, surface water system and sub-surface water system. Precipitation, interception, transpiration and evaporation take place in atmospheric water system. Overland flow, surface run-off, sub-surface outflow, groundwater outflow and runoff to the streams and the oceans Take place in the surface water system.  Infiltration, groundwater recharge, sub-surface flow and groundwater flow take place in sub-surface water system.

Saturday, 6 October 2012

Principles of energy conservation

Recycling of waste is an important component here. We can make use of this in paper industry and aluminium can manufacturing industry where used product has an intrinsic value. In Japan, more than half of its waste materials are recycled. Modernization of technology can also be used for energy conservation. Developed countries are using modern technologies and are able to reduce the energy consumption during production. Waste heat utilization is a significant way of energy conservation, especially in glass industry. Flue gases produced from the furnace of a glass industry can be used for the generation of electric power by proper mechanism. The exhaust from backpressure turbine during electric power generation can be used for crop drying and similar applications. If there is any condensed water vapors, we can use it for heating fish farm, poultry farm, pig farm etc. Optimum use of proper types of energy and fuel can save energy considerably. Cogeneration where electricity and heat are generated in a single installation is an excellent tool for energy conservation. Manpower skill is an important component in energy conservation. Proper training has to be given to improve their skill and attitude. Proper training helps them to carry out proper operation and maintenance.

Tuesday, 25 September 2012

Electronic fuel control system

Electronic fuel control system is employed in automobiles to determine accurately and precisely the mass air flow rate into the engine. Electronic fuel control system also performs the task of regulation of fuel delivery with optimum precision. The fuel delivery regulation is in such a way that the ratio of the mass of air to the mass of fuel in each cylinder is as close as possible to stoichiometry. The main components of a electronic fuel control system are throttle position sensor, mass air flow sensor, ignition systems, fuel injectors, engine coolant sensor, engine position sensor and exhaust gas oxygen sensor. Fuel injectors regulate fuel delivery and ignition systems sets optimum ignition timing. Crankshaft angular speed is measured by engine position sensor.  Output signal generated by exhaust gas oxygen sensor is dependent on the concentration of residual oxygen in the exhaust after combustion.

Monday, 13 August 2012

Losses in transmission lines

There exist three types of losses during power transmission through copper cables. They are copper losses, dielectric losses and radiation (induction) losses. Copper losses are due to the resistance of the conductors. Here energy is dissipated in the form of heat. Loss may also occur due to skin effect where expanding and collapsing electric fields about each electron encircle other electrons. As a result of skin effect, encircled electrons suffer retardation leading to power loss. If there is a dielectric material between the conductors, it will result in dielectric loss. Polyethylene dielectric material is preferred in conductors which causes feeble dielectric loss. Induction losses arise when the electromagnetic field about a conductor cuts through any nearby metallic object and a current is induced in that object. This is a power dissipation loss. When some magnetic lines of force about a conductor fails to return to the conductor during cycle alternation, causes radiation losses.