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Electromagnetic Compatibility (EMC) of equipment

Electromagnetic Compatibility (EMC) of equipment

The electromagnetic compatibility of electronic apparatus and devices is their ability to function properly in the given electromagnetic environment without disturbing this environment too much by its own emissions.

If the requirements of the basic or product (family) specific European standards (EN) are met, one would presume, that the general aims of protection of the national German EMC act or the European EMC directive would be met.

Appropriate standardized EMC tests (immunity tests against conducted and radiated disturbance signals, electrostatic discharge, and emission measurements) are being offered as PTB's internal service for conformity assessments.

Fig.: EMC Chamber at PTB.

EMC tests of electronic equipment are carried out according to the EMC act (for affixing the CE mark) and/or special requirements and construction rules. For investigations on interference of complex installations, an on-site testing system is available for rental.

Fig.: Control room of the EMC chamber.

 

Procedures for evaluation of EMC test environments

The electromagnetic compatibility (EMC) of electrical and electronic devices is investigated in two parts. One is the susceptibility test to assess the tolerance of the devices to external electromagnetic influences caused by radiation or line-conducted disturbances, for their fault-free operation. In the second part the non-intentional electromagnetic emissions are measured, for both radiated fields and line-conducted disturbances.

 

For these measurements several test sites have been developed. Among these are various TEM wave guides, antennas in semi- of fully-anechoic chambers, reverberation chambers and many others. To cover the broad spectrum of test facilities with regard to their special features, separate standards have been developed in the past.

 

However, all of the different test sites are being used with the same intention, which is to show compliance of the devices under test (DUT) with the protection requirements within the given limits stipulated in the German Federal EMC act and related standards. From the point of view it is firstly irrelevant, in which test site the results have been obtained. Within the measurement uncertainty, the results must be comparable, but need not be correlated.

 

The data to be obtained in emission measurements are physical quantities, namely the electrical field strength or the interference voltage. For both an uncertainty budget can be established. For susceptibility tests an appropriate physical quantity needs to be established, for which the uncertainty budget can be calculated.

 

Free-space as reference

Under free-space conditions the maximum of the unintentional signal radiated by a non-trivial, stable emitter is numerically calculable. If such a device ca realized in practice numerical calculations and measurements in real environments can be compared. The deviation between both yields a limit for the uncertainty (Udo Kappel). Considering surface charges and currents on canonical test structures like spheres and rectangular boxes as a gage for comparability, the uncertainty budget can be calculated. The surface currents are not only a measure for the empty field strength, but for the interaction of the DUT and the field generator as well. Again, the deviations between theoretical values and measurement results allow for the estimation of the uncertainty (Thorsten Schrader).

Contact

Kai Baaske
Tel.: +49 531 592-2212
Fax: +49 531 592-2256
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