Electromagnetic compatibility
The electromagnetic compatibility ( EMC) refers to a usually desirable state that technical devices do not affect each other disruptive due to unwanted electrical or electromagnetic effects. It deals with technical and legal issues of unwanted mutual interference in electrical engineering.
Basics
The use of electric energy is always associated with the conversion of electromagnetic field energy into other forms of energy, such as heat ( light bulb ) or mechanical energy (motor). Heat energy can be released as electromagnetic heat radiation into the environment, for example. Furthermore, moving electric charges produce magnetic fields, which also affect their environment. The fields do not necessarily remain within the electrical equipment, but can also spread outside of the equipment. Fields that propagate freely, can penetrate electrical equipment and affect the function of the equipment. Resources that serve the radio communication, such as mobile phones or radio receivers, are characterized by intentional release (mobile phone) or infiltrating Wanted ( Radio Receivers, mobile phone) fields from.
The electromagnetic compatibility includes all unintentional or intentional malfunctioning electrical or electronic equipment, eg by electric, magnetic or electromagnetic fields and operations. This includes interference from currents or voltages are already included.
Essential to ensure the electromagnetically compatible function of electrical equipment whose proper construction and design. Detection and confirmation of interference and a sufficiently low interference are regulated by EMC directives and EMC standards.
The European EMC Directive defines electromagnetic compatibility as follows:
From this, the essential protection requirements are derived, which must any electrical equipment that is placed on the market comply. The protection requirements specify that on the one hand for emissions of the equipment must be so low that, for example, radio receivers or other equipment in the interference environment are not unduly influenced. This is a limitation of the sources of interference (so-called interference suppression). On the other hand, the expected to the resource acting disturbances ( fields, interference or interference ) whose function does not affect. Thus, the apparatus must be constructed sufficiently immune to interference.
For resources that comply with the relevant EMC standards, it may be assumed that the safety requirements are complied with. The VDE or the DKE is responsible in Germany for the creation and editing of the standards. Lately, the standards are increasingly aligned at the international level. Therefore, international for Germany standardization organizations such as IEC, CENELEC and CISPR play an increasingly important role.
Theory
The usual Störkopplungsmodell is based on the concepts of noise source, coupling path and sink. The interference generating equipment is referred to as the interference source (german source or culprit ), the affected equipment is as a noise receiver ( engl. victim or load). This may be caused by the source to an influence of the valley, the fault must go to the sink in order to work there as a disturbance variable. The path between source and sink is called coupling or coupling path. Criterion of the quality of a signal transmission in the EMC of the signal to noise ratio.
A distinction is made between natural and technical noise sources and noise. As an example of a natural source of interference is considered a flash, natural sinks can be living things. Typical technical sources of interference are frequency, typical technical noise receivers are, for example, radio receivers.
The influence of living organisms by electrical, magnetic or electromagnetic sizes we also speak of electromagnetic environmental or EMF. Protection against lightning is treated lightning protection under the term. Protection against electrostatic discharges is also often considered separately.
The following coupling mechanisms can be distinguished:
- The Galvanic coupling, technically accurate impedance coupling, arises at common impedances of Störstromkreises with the circuit of the sink. This may be common components or line sections of both circuits, eg flow over the transient currents that couple stresses across the impedance of the common line section. For PCBs, an impedance coupling occurs possibly also inadequately sized ground traces and decoupling capacitors. Note: At least at this point, the term impedance coupling is technically preferable to the usual concept of galvanic coupling, since a capacitor has no electrical connection.
- Capacitive coupling means the influence of an electric field, for example by coupling to run parallel conductors in a cable or cable duct or guided in parallel tracks on a printed circuit board. This effect can occur, for example between parallel lines guided with high impedance termination impedances.
- Inductive coupling refers to the influence of a noise receiver through a magnetic field. The Inductive coupling is caused by magnetic field coupling, usually in conductor loops, eg between parallel-guided conductive loops, each having low impedance termination impedances.
- From radiative coupling occurs when an electromagnetic field is applied to a sink. Electric conductors of a cable or circuit boards can act as an antenna and, for example, to receive radio or radio signals that occur on the conductor as interference.
Types of Disorders
- There are dynamic disturbances of current carrying conductors that change in time and static disorders (especially magnetic and capacitive interference ), which remain permanently unchanged.
In the EMC distinction between wired and field-related disorders.
- The conducted disturbances are transmitted from the noise source directly on the supply or signal lines to the sink.
- All capacitive and inductive influences of electric and magnetic fields are known as Field-related disorders or short interference.
Interference avoidance
To avoid malfunctions is EMC-compatible design of systems or devices. Among the known actions include shielding, filtering electrical circuits, the twisting, the use of symmetrical signals and some other measures. Often, interference by an appropriate Massegebung and avoiding extensive Störstromschleifen be avoided. Are effective, depending on the interference situation either interrupting or closing the combination electrical masses, for example to avoid the above-mentioned galvanic or impedance coupling. By selecting appropriate pulse frequencies interference to nearby radio receiver band-limited can be avoided.
Technical implications
The electromagnetic waves, for example, in circuits generate voltages or currents. This can result in the worst case failure of the electronics in the simplest case to a noise in the TV. The electromagnetic compatibility ensures that, for example, do not fail pacemaker or the electronic control system of motor vehicles and aircraft at least up to a specified disturbance. In aircraft, the use of mobile phones is possible, under certain conditions, but generally not permitted coverage (see LuftEBV ). Among the requirements in aviation include a proof of the electromagnetic compatibility of the aircraft with the mobile radio standard. Special attention claims the electromagnetic compatibility in industrial machinery and equipment. Here often powerful electromechanical actuators and sensitive sensors must work together smoothly in a confined space.
Effects on the environment
Electromagnetic waves also have an impact on people and the natural environment. The branch of environmental electromagnetic compatibility ( EMC-E ) deals with the impact on the environment and living organisms.
Regulatory
The lawmakers write to the EU before the Inverkehrbringern of electrical appliances to comply in Germany by the Act on the electromagnetic compatibility of equipment, the applicable safety requirements, which are set by limit values for immunity or for interference emission in relevant standards.
More on this topic can be found under the heading of CE marking information for the EMC Directive, which must often be used in conjunction with the Low Voltage Directive.
As a rule, compliance with the protection requirements shall be presumed if applicable to the device harmonized European standards are adhered to in order to ensure all our customers and citizens trouble-free operation of electrical equipment. This often means that the one who offers a device on the European market, EMC tests, or equivalent means of compliance applies to detect the EMC. As an equivalent detection methods are suitable, depending on the complexity of the device, even simple plausibility considerations. For example, a light bulb except the filament does not contain any electrical or electronic components, taken by itself during operation no limits for radio frequency emissions to exceed.
During the last years, the requirements were harmon Siert within Europe in many product areas, the limits and conditions of various countries are same, enshrined for example in the EMC Directive.
In Germany, the Federal Network Agency (formerly the Regulatory Authority for Telecommunications and Post), the Federal Office for Radiation Protection and the armed forces as part of the Regulation on the detection method for limiting electromagnetic fields, the competent authorities to monitor compliance of safety requirements or limits.