Classification of Electrical signals

There are so many types of electrical signals that classifying them by physical characteristics or other methods helps to organize the type of equipment needed, the necessary testing procedures and measuring equipment, and address any safety concerns or regulations.

Classification of signals assists in circuit analysis, processing and validation. Signals can be classified according to any of their physical properties, intended use, and visual and mathematical properties.

Types of Electrical signal

The way they classify signals may refer to individual signals or the entire system which handles that type of signal.

Electrical system (AC-DC system):

Two electrical systems are currently in use. Everyone is using alternating current (AC) and direct current (DC) and we need both.

A sinusoidal time-varying signal is an alternating current (AC) available from the familiar power receptacle. It’s generated by generators and available from power plants delivered as a three-phase sinusoidal signal to buildings and individual residences.

Direct current (DC) is available from standard voltage (1.5V DC, 9V DC) batteries, generators or power supplies designed to supply the specific voltage required for the circuit or appliance. (24V DC, 120V DC, 48V DC).


Frequency classification of signals identifies the methods of spectrum and propagation. Visual, audio, RF, microwave, air / vacuum / space wired, fiber optics. Frequency identification of AC signals.

Clock speed, processor machine instructions per second (MIPS) and pulses per second (PPS) may be used in DC systems with system clock driving circuitry.


Both power systems AC and DC are classified as either low or high voltage. The IEEE defines AC and DC standards with each dedicated papers, conferences, laboratories, and research. In general, the definitions are as follows:

  • Low voltage AC: 1000 V and below; DC: 3200 V and below
  • High Voltage: AC: above 1000 V
  • Ultra High Voltage: 1000kV or Greater AC Systems

Much lower signal levels are used in digital systems where logic families dictate voltage requirements. Transistor logic usually requires 5VDC, whereas higher and lower voltages can be used by CMOS and low power systems.


Signals in electrical circuits can be classified by the continuity of amplitude values — analog or digital. 

Analog AC signals such as the sine and cosine waveforms have constantly changing values ranging from the minimum to the maximum range of the signal

Digital signals contain specific amplitude values. Digital binary systems only have 2 values, typically between 0 and 5V DC


Time continuity can also classify the signals: a continuous signal has values for all time values without breaks or areas where the signal exists. Sine and cosine waveforms are continuous where there are discontinuities in the tangent waveform where there are values.

Discrete signals have values at only specific times. A sampling circuit yields signal values only for times the sampling takes place.

Deterministic and Random signal:

Deterministic signals can be predicted by past behavior and totally captured by mathematical equations. All possible results are known and risk factors do not exist. Deterministic signals are useful in communications where it is important for modulation techniques to know the exact values of a carrier signal.

Random signals are not predictable and represented by probabilistic functions, familiar from the theory of probability, such as the function of Poisson. Circuit noise is usually a random signal, and is a model.

Synchronous and Asynchronous:

Control signals may be classified as synchronous or asynchronous. The timing of logic and processing functions is driven by repeated periodic clock signals. When the logic levels all change state based on the timing of the clock, the signals are synchronous, synced to the clock. Logic levels at component inputs only come into effect when the clock signal is timed.

Asynchronous signals, regardless of the clock cycle, have output logic states that change at any time. Reset signals can be received at any time, causing output levels to reach predetermined states irrespective of the time of the clock.

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