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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.