Key Principles of Electrical and Electronic Systems

Most of the modern mechanical systems incorporate some electrical or electronic equipment. One only has to think of cars with onboard computers, high-speed electric trains, processing plants, printing presses and even the domestic multiprogramme washing machine. The list is endless. It is therefore essential for the mechanical engineer and mechanical engineering students to understand how electrical and electronic devices work.

Let us look at some the key principles of electrical and electronic systems that most of the mechanical engineers will encounter during their careers to solve practical examples.


Amplifiers are used to reproduce voltage signals several times larger than the original. Simple amplifiers may be constructed using discrete transistors, more advanced designs incorporate a form of integrated circuit called an operational amplifier. With a few components, it is possible to construct an amplifier that will add some independent signals or one that will integrate a signal, for example, to convert the output from an accelerometer to a velocity.


Capacitance examines how capacitors work and the effect of connecting capacitors in series and parallel and connecting a capacitor in series with a resistor.

Digital electronics

Digital electronics begins with an investigation of combinational logic and how logic gates may be used to construct control circuits. Sequential logic introduces the bistable, the simplest form of the memory cell and the basic component in any computer or microprocessor. Analogue-to-digital converters and digital-to-analogue converters transfer data between analog and digital systems and vice versa. They are essential for the control of complex machines.

Direct current circuits:

Direct current circuits study the relationship between voltage, current and resistance and examines ways to analyze simple circuits. We also look at how bridge circuits can be used to measure resistance and strain.

Electromagnetic systems;

Electromagnetic systems investigate the relationship between electric currents and magnetic fields. It also investigates how a varying current flowing through an inductor will induce an electromagnetic force in the inductor. It examines how force is exerted on a current-carrying conductor contained within a magnetic field, the principle behind the design of electric motors.

Alternating current circuits

Alternating current circuits are widespread. It demonstrates how we analyze circuits comprising any combination of resistors, inductors, and capacitors supplied by an alternating voltage. It investigates how the different components affect the current and power dissipation.

Semiconductor rectifiers

Semiconductor Rectifiers are used to convert alternating current to direct current. Electricity supplies are alternating, but most electronic devices require direct voltage supplies. Simple rectifiers produce a series of unidirectional current pulses. Where the magnitudes of the pulses are too large for an application, current smoothing or voltage stabilization is used.

Three-phase circuits

Three-phase circuits are used to supply electricity to industrial users.As most industrial machines are connected to such systems, it is in the interests of safety that mechanical engineers should understand how such systems work. This part examines the two most common forms of three-phase connection: star and delta.


Transformers are used to convert alternating voltage and current levels. They have no moving parts, consume little power and are used in a wide variety of applications from chargers and power supplies for small electronic equipment to the transmission and distribution of electrical power. They may also be used for electrical isolation where there is a risk of personal injury.

AC induction motors

AC induction motors provide the drive for many mechanical systems, such as industrial pumps, fans, compressors, and mills. This section explains how these motors work and discuss variations in the torque versus speed characteristics, to help users choose the most suitable motor for each application.

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