Signal (electrical engineering)

As a signal is defined as a " physical size, in which one or more parameters of information about one or more variable sizes bear " or a " physical phenomenon whose characteristic variables can be used to display information."

An electrical signal is an electrical quantity such as current, voltage or resistance, if it is variable in some way so that it can receive and carry information. Suitable parameters for example equal value, peak value, frequency, phase shift angle or duty are eligible.

Carrier of information

For simple applications, the parameters of the signal comes directly to use, for example, the height of a thermal voltage for a temperature difference.

Alternatively, the information is called a carrier signal is impressed by modulation. Here, a property of the carrier is modulated in a simple case exactly, is named after the A., the modulation type. The average (or not modulated ) amplitude, frequency and other characteristics of the carrier signal with respect to the transmitted message no significance; the carrier is only required to adapt to the physical properties of the transmission medium. The selection of the modulated carrier signal property is subject to aspects such as error-free, fast, targeted transferability.


The presentation can be carried out as an analog or digital signal. According to another classification, a distinction (eg sine wave, square wave), stochastic signal (eg audio signal as noise, speech and music ) and binary signal (eg power cycle ) between periodic signal. Content can be used (eg, in control engineering ) as a control signal or alarm signal, the signal, eg as a measurement signal, audio signal, clock signal, signal for transmission of text / images or.


For the transmission of an electrical signal electric conductors are used, what is the essential distinction to the radio signal (electromagnetic wave as a carrier for information ) or to the optical signal (on fiber optic). But also, for example, the field strength of an electric field may be referred to as an electric signal ( despite the lack of electric conductor ) - in this case the transition to the radio signal is blurred. When high-frequency signals in the conductor must also be taken into account the wave properties ( eg, in the trace layout on a circuit board ), that is, there are some properties of a radio signal to carry.

Areas of application


  • In a system consisting of several interrelated devices is referred to in the metrology of a measuring chain, in which the devices to pass electrical signals.
  • In the control technology is referred to in the interrelated elements influence a signal by another as a sequence of actions. For the symbolic representation of the action flow is an action plan, called in older literature signal flow diagram.
  • Also in communications technology are between recording device (eg microphone ), and stations as well as between the receiver and output device ( such as speakers ) electrical signals usual; only the transmission channel used other signals.