Author: John Mulindi
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Features of Optical Modulators in Telecommunication Systems
Light emitting PN junction devices such as LEDs and laser diodes are easily modulated by superimposing signals on to the injected current. This is direct modulation. Laser diodes in high-bit rate and long-span optical communication systems are often used under direct modulation. The downside of direct modulation is that, it results in chirping which limits…
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How to Perform a Brake Test on a DC Motor
Testing is usually performed on DC machines to establish efficiency and power losses. A brake test is a direct technique that involves applying a brake to a water-cooled pulley mounted on the motor shaft as demonstrated in Figure 1.0. This brake test method is typically used on small motors. The brake band is fixed with…
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Transformer Substations in an Electric Power Supply System
The greater part of the substations in the power systems are focused on changing of the voltage level of the electric supply. These are termed to as transformer substations since the transformer is the key component used to change the voltage level. Transformer substations may be classified further into the following substations depending on the…
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How the Photoelectric Effect Influences Semiconductors
A photoelectric effect is any effect in which light energy is converted to electricity. When light strikes certain light-sensitive materials, it may cause them to give electrons or change their ability to conduct electricity or may cause them to develop an electrical potential or voltage across two surfaces. When a surface is exposed to electromagnetic…
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Features and Classification of Substations
A substation can be defined as an assembly of apparatus used to change some characteristics like voltage, AC, DC, frequency, power factor, etc., of electric supply. Substations play a key role in power systems. The continuity of supply depends largely upon the successful operation of substations. Thus, it is imperative to exercise utmost care while…
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How to calculate the Power Factor Correction
Let us consider an inductive load taking a lagging current I at a power factor cosΦ1. For us to improve the power factor of such a circuit, the solution is to connect equipment in parallel with the load which takes a leading reactive component and partly cancels the lagging reactive component of the load. Figure…
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How solid-state soft starting of Induction motors is done
Solid-state soft starting is the most commonly used technique for starting induction motors. It provides a smooth build-up of current and torque; the maximum current and acceleration time are easily adjusted. The only problem with this technique over conventional starters is that the mains currents during run-up aren’t sinusoidal, which can lead to interference with…
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The Principle and Application of IMPATT Diode
The Impact Avalanche Transit Time (IMPATT) diode is a high power radio frequency (RF) generator that operates from 3 to 100 GHz. IMPATT diodes are manufactured from silicon, gallium arsenide or silicon carbide. An IMPATT diode is reverse biased above the breakdown voltage. The high doping levels produce a thin depletion region. The arising high…
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The General Principle of using a Servo Motor for Position Control
Servo motors are typically employed in closed-loop position control; for example let us consider the following application, where the angular position of the output shaft is intended to follow the reference voltage (ϴref). The potentiometer mounted on the output shaft provides a feedback voltage proportional to the actual position of the output shaft. The voltage…
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The Shockley Diode Features & Operation
The Shockey diode is a four layer sandwich of PNPN semiconductor material very similar to the SCR but without a gate as illustrated in the Figure 1.0 below: The Operation of Shockley Diode A Shockley diode can be turned ON by applying enough voltage between anode and cathode. This voltage will cause one of the…