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Intercomparison of Electric Field Strength Measurements completed in the frame of the German Calibration Service (DKD)

27.11.2015

An intercomparison of Electric Field Strength Measurements was completed. The intercomparison was organized in the frame of the German Calibration Service (DKD) and the results and conclusions have been submitted to the Kleinheubacher Tagung 2015 of the Union Radio Scientifique Internationale (U.R.S.I.).

 

Field probes are widely used to determine the electric field strength, e.g. for proving personal safety in electromagnetic fields or for setting the test levels during electromagnetic compatibility interference testing. Both fields of application require accurate knowledge of the calibration factor of the field probe to be able to measure field strengths traceable to the SI units with known measurement uncertainty. In Germany, three laboratories are accredited for electric field strength measurements by the German Accreditation Service (Deutsche Akkreditierungsstelle – DAkkS). To assess the technical competence of the accredited laboratories an intercomparison was organised by the Physikalisch-Technische Bundesanstalt (PTB), the German National Metrology Institute, within the framework of the German Calibration Service (Deutscher Kalibrierdienst – DKD), which is the association of the accredited laboratories in Germany.

In addition to PTB, three accredited and one non-accredited laboratories took part in the intercomparison. As measurement artefacts both a small transfer sensor developed by PTB (Figure 1) and a commercially available field probe were used. The field strength values to generate a reading of 20 V/m were compared. The transfer sensor oriented parallel to the magnetic field (PH orientation) was used for a comparison between 300 MHz and 1000 MHz in 100 MHz steps and for 1000 MHz to 6 GHz in 500 MHz steps. The commercial field probe was oriented both parallel to the magnetic field (PH orientation) and parallel to the power flux density vector (PS orientation). It was used for a comparison between 100 MHz and 1000 MHz in 100 MHz steps and for 1000 MHz to 18 GHz in 500 MHz steps. The intercomparison shows that all laboratories are able to generate electromagnetic fields with the specified measurement uncertainty but that calibrations in PS orientation can be problematic. The outcome of this comparison was one of the triggers for re-establishing the standardization working group DKE GAK 767.4.3 “Feldsondenkalibrierung” which works on a first draft of a new standard IEC 61000-4-26 “Field Probe Calibration”.

 

  Fig. 1: Transfersensor developed by PTB for the accurate measurement of the electric field strength.