Every where you look, you see a definition for Signal which more or less describes the same thing. So here I came up with my own definition of signal:
“Signal in general is: any entity which its properties reflect information about its source.”
According to this definition, a signal is a time variant entity that carries information of some kind. Like when you wave your hand, you send the information to someone. You want to say you have acknowledge them and want to initiate a communication with them. When you hear a horn you understand a car is approaching. When you see a light you know there is a source of energy there, and possibly someone close by. When you feel the cold you know there is a ghost close by! All the above are different forms of signal.
Electrical signals convey information such as references, data or etc. Any kind of signals such as light, sound and temperature can be transformed into electrical signals such as voltage or current. Therefore an electrical signal can be interpreted as any form of information depending on the circuit.
Signals can have any shape and form. They are usually measured relative to another changing entity. Time is one of the best references any signal can be measured upon, and that's why it's used very often. AC and DC signals are examples of signal forms, explained in Electrical Current section.
Whenever a signal is plotted on X-Y axes versus a reference signal or time, a waveform of the signal is achieved. Basically it is the form of a signal wave versus another entity. There are some famous waveforms generally used to describe most signals. Trying to model any waveform with these basic waveforms makes it much easier to do the calculations. Below is some of the common signal names, graphs and their formulas in time.
Note: Formula below shows the mathematical relation between the step, ramp and spike signals:
When a specific waveform in a specific time is continuously repeated in time, the waveform is called a periodic waveform. Waveforms below are examples of periodical waveforms. The shortest time in which there is a specific waveform representing the unit that makes the entire waveform when put back to back is called a Period and is mostly shown with T. In every T time the waveform repeats itself and can't be divided into smaller equal units, because as mentioned T must be the shortest time. The rate of repetition in time is called Frequency shown with f. Frequency is equal to the reverse of the period, as also shown in the formula of the sinusoidal waveform. The unit of frequency is Hertz.
Sinusoidal Wave Signal
In the sinusoidal formula above you see another parameter called Angular Speed, shown with Omega symbol, w. Assume you have a wheel that turns with some speed. You can pick a spot on the perimeter of the wheel as a reference. You can define the speed of this spot by amount of degrees it turns in a second. This speed is it's angular speed, which is mostly shown as radians per second (every radian is (2p)/360 of a degree as the perimeter of a circle is 360 degrees or 2p radians). If you only observe the movement of the spot in direction of the Y axis and plot it versus time, you get a sinusoidal waveform.
Square Wave Signal
On more important parameter used is Duty Cycle. In square waves, which the waveform in a period consists of two parts that can have different time lengths, duty cycle is used to show the ratio of these time divisions. The duty cycle is equal to the time when the signal is high to the time when the signal is low times 100, and is shown as a percentage. Using this parameter one can know what percentage of the period the signal is high.
Triangular Wave Signal
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