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Applied Industrial Technology

 Electrical Technology

It might be a good idea to refresh a few basic concepts about magnetism and electricity. 


     The standard amount of electrical charge is called the coulomb. The coulomb is a measure of how much electricity flows in any part of a circuit in one second.  This is called electric Current. One ampere is equal to one coulomb per second. When one coulomb flows in one second, the current flowing is one amp.

    We need a source of energy to pump the electricity around a circuit. This is usually provided by power supplies or a battery.  The power source provides the electrical pressure (Voltage) required to make an electric current flow. The standard amount of electrical pressure is called the Volt.

    A long thin wire works in the same way as a long narrow pipe.  A long thin cooper wire provides friction, which resists the current flow. This friction is called Resistance, and the standard measurement of resistance is called an ohm.

Series Circuit
    A series circuit is one with all the loads in a row, like links in a chain. There is only one path for the electricity to flow. If this circuit was a string of light bulbs, and one blew out, the remaining bulbs would turn off. The squiggly lines in the diagram are the symbol for Resistors. The parallel lines is the symbol for a Battery.
Click Here To See Other Electrical Symbols


Parallel Circuit    
    A parallel circuit is one that has two or more paths for the electricity to flow. In other words, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out there is still current flowing to the others as they are still in a direct path from the negative to positive terminals of the battery

Combination Circuit
    A combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a synthesis of the two. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.


 The Difference Between AC and DC

    In 1887 direct current (DC) was king. At that time there were 121 Edison power stations scattered across the United States delivering DC electricity to its customers. But DC had a great limitation, namely, that power plants could only send DC electricity about a mile before the electricity began to lose power. So when George Westinghouse introduced his system based on high-voltage alternating current (AC), which could carry electricity hundreds of miles with little loss of power, people naturally took notice. A "battle of the currents" ensued, but in the end, Westinghouse's AC prevailed.

    This is a simple explanation that shows the difference between AC and DC. A generator consists of some magnets and a wire that is wrapped to form several coils, known as an armature. A hydro turbo engine or some other outside source of motion moves the armature through the magnetic field created by the magnets.  In the example a loop of wire is spinning within a magnetic field. Because it is always moving through the field, a current is sustained, but because the loop is spinning, it's moving across the field first in one direction and then in the other, which means that the flow of electrons keeps changing.

    The electrons flow first in one direction and then in the other,  this is called alternating current


Alternating CurrentDirect Current




    One advantage that AC has over DC is that it can easily be "stepped up" or "stepped down" with a transformer. In other words, a transformer can take a low-voltage current and make it a high-voltage current, and vice versa.

    This comes in handy in transmitting electricity over long distances. Since AC travels more efficiently at high voltages, transformers are used to step up the voltage before the electricity is sent out, and then other transformers are used to step down the voltage for use in homes and businesses.

A transformer has two windings; the primary and the secondary. The primary is the coil which receives the energy (Ep voltage). The secondary is the coil which discharges the energy (Es voltage) at the transformer or the changed voltage. If the secondary voltage is lower, it is called a step down transformer. If the secondary voltage is higher, it is called a step up transformer.

   The secondary voltage is dependent upon the voltage of the primary , the number of turns of the primary windings, and the number of turns of the secondary windings.

    If the primary windings of a transformer have 100 turns of wire at 110 volts, and the secondary windings have 400 turns of wire, What is the secondary output voltage?

Ep / Es = Tp /Ts          110 / Es = 100 / 400          100 Es = 44,000          Es = 440 volts

    This would be a step up transformer from 110 volts to 440 volts.


Electrical Motors

    Determining the Type of Electrical Motor requires understanding of the many different motor applications.  What is the motor used for?..... Do you need to reverse the motor?......Does the motor require a large amount of power?..... Does the motor need to rapidly respond to changes in speed and position, or require high acceleration and deceleration?... Click on the the words type of electrical motor above to review four different motor types.

Controlling the Direction of a Motor

   A double-pole, double-throw changeover switch can be used to control the direction of rotation of a DC motor. These switches can be a slide, rocker, or toggle type switch.

    Look carefully at the current arrows. you should be able to see how the direction of the current flows through the motor and then changes the direction of rotation of the motor.

    Switches like this are used to rewind cassettes in cassette tape players, but industrial motors require more complex switching and  motor starting contactors because of the higher voltage and current requirements. Three phase power is required for most industrial uses.

Contacts, Relays, & Solenoids


    Contacts are referred to as normally open or normally closed. When a coil of a relay is energized, the plunger moves through the coil, closing the normally open contacts and opening the normally closed contacts.  When the contact is initially closed, there is a inrush of current which is about six to eight times the sealed current. As the plunger moves into the coil, closing the gap, the current levels drop to a low level. The contacts tend to get burned after thousands of repeated uses.


    Relays enable one electrical circuit to switch a second electrical circuit without an electrical connection between the two. Relays are used to interface low voltage circuits with large motors, bulbs etc.

Things to watch out for...


The resistance of the operating coil.


The number of poles and throws


Because they are mechanical devices, they will wear out in time.


Relays come in many shapes and sizes, choose the smallest relay which will operate 
effectively in your circuit.


As with all output devices, the first consideration is to make sure the working voltage and maximum safe current are compatible with the rest of the system.

A solenoid consists of a coil of wire around a ferrous core. When a current flows through the coil, it becomes a magnet, causing the iron core to move. It converts the electrical signal into linear kinetic energy. They are often used in pneumatic circuits when a valve has to be operated electronically to open and close the jaws of a simple robot arm.


Mechanical Switches

    Mechanical switches are hand operated, linear motion, or rotary motion components that control current flow in a circuit. They are often used as signal devises, to switch circuits on or off, or even to control the direction of motors by reversing the current flow. In machine control these switches are used to supply the plc with information relative to the position of a machine part like cylinder extend or retract.

Proximity Switches

    Proximity switches consist of a sensor used to detect the presence of an object without physical contact such as by magnetic fields, radio frequency, capacitive fields, and light rays. There are many more types of electrical switches, but these are the two most used in machine control.


    This is the basis of "how" Electricity works in modern manufacturing processes.