A signal is a "physical quantity in which one or more parameters carry information about one or more variable quantities", or a "physical phenomenon whose characteristic quantities can be used to represent 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 transport information. Suitable parameters are, for example, equivalence , peak value , frequency , phase shift angle or duty cycle .
Carrier of information
In simple applications, the parameter of the signal is used directly, for example the level of a thermal voltage for a temperature difference.
Alternatively, the information is impressed on a so-called carrier signal by means of modulation . In the simple case, exactly one property of the carrier is modulated according to which i. A. the type of modulation is named. The mean (or not yet modulated) amplitude, frequency and other properties of the carrier signal are irrelevant to the transmitted message; the carrier is only necessary to adapt to the physical properties of the propagation medium . The selection of the modulated carrier signal property is subject to aspects such as low-error, fast, targeted transferability.
The display can be made as an analog or digital signal . According to another classification, a distinction is made between periodic signals (e.g. sinusoidal signal, square wave signal ), stochastic signal (e.g. audio signal such as noise, speech and music) and binary signal (e.g. switching on / off). In terms of content, the signal can e.g. B. serve as a measurement signal , audio signal , clock signal , signal for the transmission of text / images or (z. B. in control technology ) as a control signal or message signal.
For transmitting an electric signal are electric conductors used, the essential distinction to the radio signal (electromagnetic wave as a carrier for information) or to the optical signal (at optical fiber group). But also z. B. the field strength of an electric field can (despite the missing electrical conductor) be referred to as an electrical signal - here the transition to the radio signal is fluid. When high-frequency signals must also be in the conductor whose wave-character are taken into account (for. Example, in the trace routing on a printed circuit board ), d. In other words, the properties of a radio signal come into play in some cases.
- In measurement technology, a system of several interrelated devices is referred to as a measuring chain in which the devices transmit electrical signals.
- In control technology , the influencing of one signal by another is referred to as an action sequence for related elements. An action plan, called a signal flow plan in older literature, serves to symbolically represent the processes of action .
- In communications engineering , too, electrical signals are common between the recording device (e.g. microphone ) and transmitter and between receiver and output device (e.g. loudspeaker ); only the transmission channel also uses other signals.
- IEC 60050, see DKE German Commission for Electrical, Electronic and Information Technologies in DIN and VDE: International Electrotechnical Dictionary Entry 351-41-17
- DIN 40146 communications engineering - basic terms , e.g. Z. Draft from July 2007
- Horst Germer, Norbert Wefers: Messelektronik , Volume 1. Hüthig, 1985, p. 13 ff
- DIN 1319-1: 1995: Fundamentals of measurement technology - Part 1: Basic terms
- Klaus Fieger: Control Engineering, Fundamentals and Devices , 1973, p. 9
- Rainer Ose: Electrical engineering for engineers - Volume 2: Applications , Fachbuchverlag Leipzig, 1999, p. 337