Author: John Mulindi
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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…
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Basic Features of Autotransformer Starter
A 3-phase autotransformer is typically employed where star or delta starting provides insufficient starting torque. Each phase of an autotransformer consists of a single winding on a laminated core. This incoming supply is connected across the ends of the coils, and one or more tapping points (or a sliding contact) provide a reduced voltage output…
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Manipulating Devices & Actuators in Process Instrumentation
The function of the manipulating device is to influence the process variable. Its main purpose is to regulate a mass or energy flow. Mass flows can be either in gaseous or liquid state e.g. steam, natural gas, fuel oil, etc. The energy flows typically take the form of electrical energy. The energy supply can be…
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The Diac Features & Applications
Features of a Diac The diac is a two-terminal, semiconductor, bi-directional switching device. It can conduct in both directions. The diac closely resembles a PNP transistor without an external base terminal. Operation of a Diac The diac does not conduct except for a small leakage current) until the breakover voltage VS is reached, typically 20…
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ZigBee Wireless Protocol for Industrial Communication
ZigBee is an open wireless standard for low-rate networks. It is an IEEE standard 802.15.4 protocol. The physical layer radio operates at 2.4 GHz band carrier frequencies with direct sequence spread spectrum (DSSS). It supports a range of up to 70 m. Data transfer rate supported is 250 kbps. It supports sixteen channels. A ZigBee…
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Unijunction Transistor Features and Operation
The unijunction transistor (UJT) is a three terminal, single-junction device which exhibits negative resistance and switching characteristics totally unlike those of conventional bipolar transistors. The UJT consists of a bar of n-type having ohmic contacts designated Base 1 (B1) and Base 2 (B2) on either side of a single PN junction designated the emitter. An…