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IAEI Magazine | Author: Stephen J. Vidal
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Stephen J. Vidal

Stephen J. Vidal, P. E., is president of Joseph J. Vidal & Sons, Inc., in Throop, Pennsylvania. He has a BSEE with a minor in physics from Wilkes College in Wilkes Barre, Pennsylvania and a MBA from City University in Seattle, Washington. He is a registered professional engineer with the Commonwealth of Pennsylvania and holds a master contractor’s license in Wilkes Barre. He also is a general class amateur radio operator KA3KEM.


Speed Control of Motors — An Introduction to Variable-Frequency Drives

Speed, torque, and horsepower are three interrelated parameters in motor control. The speed of a motor measured in revolutions per minute (RPM) defines a motor’s ability to spin at a rate per unit time. The torque of a motor measured in foot-pounds (ft-lb) is a rotational characteristic of the motor that is the algebraic product of force multiplied by distance. Electrically, one horsepower (hp) is equal to 746 watts. What is interesting about these motor parameters is that if you change one of the three variables, the other two are affected. For example, if you increase horsepower while keeping speed constant, torque increases.

Introduction to PLCs

The programmable logic controller (PLC) is a microprocessor-based system that accepts input data from switches and sensors, processes that data by making decisions in accordance with a stored program, and then generates output signals to devices that perform a particular function based on the application.

Magnetic Motor Starters as Controllers — A comparison of NEMA- and IEC-type devices

NEC Article 100 defines a controller as "a device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected.” Section 430.2 gives a more motor-specific definition: "For the purpose of this article [Article 430], a controller is any switch or device that is normally used to start and stop a motor by making and breaking the motor circuit current.”

Standard Motor Control Circuits

Single-phase and three-phase AC squirrel cage induction motors need some type of circuit to initiate a start or stop function. Usually single-phase motors and smaller horsepower three-phase motors can be started with full voltage across the line. However, larger horsepower three-phase motors require reduced voltage starting techniques.

What is Ladder Logic? Why is it important for troubleshooting motor operations?

Electric machines are very useful and efficient devices which operate through a variety of control circuits. These control circuits are made up ofinputdevices that sense a condition or situation andoutputdevices that make adjustments to change the situation. The symbolic language for this process is calledladder logic. Many of the diagrams used resemble the steps of a ladder; hence, the addition of the word "ladder” into the title.

How Do DC and AC Motors Differ?

Magnetism and its effects are keys to understanding the operation of a motor. Lodestone, a natural mineral, exhibits the characteristics of a bar magnet that has a north pole and a south pole — always. I say always because if you were to cut a bar magnet in half, the magnetic domains of the two new pieces would re-orient themselves to corresponding north and south poles.

Introduction to Electronics

We learned about fundamental atomic theory in the January issue. Protons and neutrons reside in the nucleus. Electrons revolve in orbits or more appropriately "shells” with different levels of energy around the nucleus. These electrons in the outermost valence shell are what we are interested in for our study of electronics.

Basic Test Instruments

Voltage, current, resistance, and power are fundamental electrical terms. We have taken a look at the definition of each, and have discussed calculation methods useful in solving for each. In the real world, how do we go about measuring these units? Test instruments or meters are the most common pieces of electrical equipment that measure these values.

Introduction to Transformers

A transformer is an electromagnetic device without any moving parts that allows for changes in voltage, current, and impedance. The goal of an ac power network is to generate a voltage on the generation side, step up the voltage for long distance transmission on the transmission side, and then step down the voltage for distribution to the load on the distribution side. Let’s look at an example.

Basic Electrical Calculations

Electrical calculations generally fall within two categories: dc circuit analysis and ac circuit analysis. In a typical engineering curriculum dc circuit analysis is introduced first with resistive networks. Once all the network theorems are discussed and evaluated, ac circuit analysis is introduced. AC circuit analysis is more complex and requires the use of calculus if the circuits are evaluated in the time domain. Usually the concepts of inductive reactance, capacitive reactance, and impedance simplify the circuit analysis in the frequency domain.

Electrical Fundamentals — Basic Electric Circuit Theory

A little bit of history is in order before we get into AC and DC circuit theory. In the latter part of the 19thcentury there were three principal players in the electrical generation and transmission industry. Thomas Edison, known as the "Wizard of Menlo Park” and most famous for his invention of the electric light bulb, was the main proponent of direct current (DC) transmission. George Westinghouse and Nikola Tesla were the main proponents of alternating current (AC) transmission. History documents this formative period in the development of electrical generation and transmission as the "War of Currents.”

An Introduction to Electrical Fundamentals

By strict definition a material can be classified as either a conductor, an insulator, or a semiconductor based on its electrical properties. Before getting into the definition of each of these, a brief introduction to atomic theory is in order.