Mass (electronics)
When mass (engl. Ground , abbreviated GND ) refers to a conductive body, the normally the potential is assigned to zero, which is the reference potential represents for all signal and operating voltages.
In principle, any node in an electrical circuit can be ground and used as a reference potential for determining all voltages in this network. The ground can be potential-free , but depending on the requirements, it is galvanically (electrically direct) connected to the electrical potential of the conductive ground via a protective conductor , which is referred to as grounding .
Often the electrical negative pole (-) of the supply voltage is also ground. The positive pole of the supply voltage (+) as well as all other electrical voltages and electrical signals of an electrical circuit refer to the ground potential. Ground is the common connection for most components. The positive pole of the supply voltage can just as well function as ground potential, the supply voltage (counting towards ground) is then negative; Examples are given below. A ground potential or connection can also be defined for AC circuits , see neutral conductor .
In older publications, the ground is also referred to as signal earth .
Ground connection as a protective measure
Electrically conductive housing parts and accessible parts of electrical equipment with hazardous voltages are either protective conductors connected to each other and earth (the protective conductor network of the electrical installation or an earth electrode), or they are connected by a protective insulation galvanically isolated from the network (see FIG. Protection class , see also earthed).
Relevant metal parts are also included in the protective measures for lightning protection, i.e. H. connected and grounded.
This means that the signal ground of devices must either be connected to the protective conductor (e.g. computer ) or the devices have a power supply that safely and galvanically isolates them from the mains (e.g. audio amplifier ).
Often it is not practical, possible or allowed to connect ground potentials directly to earth several times. Otherwise, large equalizing or interference currents could flow. With multiple connections, earth loops arise . See also operational earthing .
Examples
In automobiles and also in motorcycles and bicycles, the ground potential is the body or the frame. As a conductive part that extends over the entire vehicle, it also serves as a return conductor for the on- board network - only one line needs to be laid to each consumer. In automobiles, the mass is referred to as “terminal 31” across all manufacturers (see terminal designation ) and is connected to the negative pole of the battery.
For historical reasons, telecommunications systems such as the telephone network often have the positive pole of their power supplies as reference potential, this pole is also grounded. The supply voltage of a telecommunications system is z. B. −48 V or −60 V, measured against earth.
Older electronic assemblies with germanium transistors also often had the positive pole of the supply voltage as ground. The reason was the primary use of PNP transistors , the emitter connection of which has the most positive potential. Today silicon transistors are used, which are easier to manufacture than NPN-type - so the negative pole became ground.
On circuit boards , the ground potential is the most extensive conductor run, as most of the components are connected to it. It is often spread out as a surface over the entire circuit board ( ground plane , ground plane ) in order to avoid potential differences and interference.
In audio and analog circuits, however, the ground points of the signal inputs / outputs are connected to each other in a star shape on only one node - only this point is the actual reference potential, all other points of the ground can be different due to voltage drops due to high currents along the conductor tracks Accept potentials, causing interference signals .
In the case of personal computers , the ground potential is the housing and ground potential at the same time.
In the case of high-frequency systems and assemblies, the ground potential is always connected to the housing. This is also helpful with audio amplifiers in order to avoid interference. In both cases problems can arise if this signal ground is connected to the ground potential at several points (see hum loop , also ground loop). Reasons for such connections are lightning protection as well as protective grounding .
Help is at hand in antenna systems Mantelstromfilter in audio systems and in the laboratory isolation transformers or isolating transformer or differential inputs , which make it possible to interrupt the signal ground connection between devices.
Symbols and representation
In the circuit technology ( circuit diagram ), for reasons of clarity, the points with ground potential are usually not drawn connected, but each provided with a ground symbol that later symbolizes a connection in the real assembly like a signal name.
Internationally, the design of the circuit symbols for ground is specified in an IEC standard, which is available in German translation as DIN EN 60617-2. For the sign after 02-15-04, the hatching may be omitted if there is no ambiguity. The line that represents the housing must then be displayed wider.
Screw terminals are often attached to the outside of devices for additional ground connections. These can be additional ground connections for safety reasons (protective conductor connection) or separate connections for the signal ground or the housing (functional grounding). Both differ in the symbols attached as well as in the conductor cross-sections and requirements.
Web links
Individual evidence
- ↑ Wolfgang Böge (Hrsg.), Wilfried Plaßmann (Hrsg.): Vieweg Handbook Electrical Engineering: Basics and Applications for Electrical Engineers. Vieweg, 3rd ed. 2004, p. 795
- ↑ State Environment Agency North Rhine-Westphalia: Explanation of terms. (last accessed on November 21, 2015) (PDF; 129 kB)
- ↑ DIN EN 60617-2: 1997 Graphic symbols for circuit diagrams - symbol elements, identifiers and other circuit symbols for general applications , main section 15: Earth and ground connections, equipotential bonding