Author: John Mulindi
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Radio Frequency (RF) and Microwave – Multiple Choice Questions & Answers (MCQ3)
The Answers have been provided at the end of Questions. Q1. What is the approximate bandwidth of radio frequency (RF) electromagnetic waves? A. 300 Hz to 300 GHz B. 20 Hz to 20 kHz C. 300 Hz to 3000 GHz D. 300 MHz to 300 GHz Q2. In spectral analysis the following factors are considered…
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How Ground Fault Interrupter (GFI) is used as a Safety Device
The function of a ground fault interrupter (GFI) is to disconnect the power if a current leakage to ground is detected. GFI is also termed to as Ground fault circuit interrupter (GFCI). We have two types of ground fault interrupters: those designed for life protection and those designed for equipment protection. GFI used for life…
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Features of Stepper Motors & How they are applied in Industrial Control
A stepper motor is a permanent magnet or variable reluctance DC motor that has the following characteristics: It is able to rotate in both directions It can move in precise angular increments It can sustain holding torque at zero speed Can be controlled with digital circuits Stepper motor moves in accurate angular increments, known as…
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Single-phase and Three-phase Power Systems
Single-phase Power System To help us understand single-phase power system, consider the sine wave shown in figure 1(a) below of a 120 Vac single-phase power connected to a plug. We know very well that, voltage is the difference in potential between two points. Therefore the sine wave in figure 1(a) shows only the voltage difference…
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Types of Resistors
Resistors perform two basic functions in a circuit: they limit current flow and set voltage levels within a circuit. We have various kinds of resistors e.g. fixed resistors, variable resistors, digitally adjustable resistors, photoresistors, fusible resistors, etc. Generally, resistors can be broadly categorized as: Fixed Resistors Fixed resistors are those whose value cannot be changed…
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How Servo Motors are used in Process Control
Servo motors are continuous motion mechanisms that use feedback signals to provide position and velocity control in a closed loop system. Servo motors can rotate to a given position be stopped and reversed. The angular position and speed can be precisely controlled by a servo loop, which uses feedback from the output to the input. …
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How to Tune the PID Controller
Before we discuss how to tune the PID controller, let’s look at some basic facts about PID Controller. Basic Facts about PID Controller Many control systems use a combinational of three types of control i.e. Proportional + Integral + Derivative (PID) control. The foundation of the system is the Proportional Control, adding Integral Control provides…
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Methods of Protecting Instruments from Explosive Atmospheres
The protection method used in a specific hazardous location depends on the application, the technology available and the specific explosive atmosphere present. In this article, we discuss the following methods of protection: Table 1 provides the summary information for each protection method. The codes are used in the markings or labels for apparatus and enclosures.…
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Hazardous Locations Classifications
A hazardous location is defined as a location where fire or explosion hazards exist due to the presence of flammable gases, vapors, or liquids, combustible dusts or ignitable fibers. Fire explosions can occur in a wide range of industrial environments e.g. refineries, petrochemical plants, oil rigs, chemical processing facilities, grain silos, etc. Fire or explosions…
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Functional Safety in Instrumentation Systems (SIS, SIF & SIL)
Functional safety is the risk reduction provided by the functions implemented to ensure the safe operations of the process. The IEC 61508 standard covers functional safety of electrical/electronic/programmable electronic safety-related systems. The purpose of IEC 61508 is to use safety instrumented systems that reduce risk to a tolerable level by following the overall hardware and…