Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany
Tests of electromagnetic susceptibility (EMS) are part of the type of approval procedure for sound level meters in the field of legal metrology. Starting in January 1996 every electronic device on the European market has to have a label that indicates a certification of the device, which also includes requirements on electromagnetic susceptibility. The EMS test of sound level meters at the Physikalisch-Technische Bundesanstalt (PTB) are performed in a radio frequency anechoic chamber. The electric field strength is 6 V/m, the frequency range is 26--1000 MHz. The frequency is varied in steps of 4% and the signal is modulated with 1000 Hz (m=80%). An acoustical signal is applied to the sound level meter and the difference of the displayed levels with and without the electromagnetic field has to be within specified tolerances (0.5 to 2 dB). At the moment not all types of sound level meters comply with these tolerances; with instruments under test deviations up to 18 dB had been observed. The present test procedure will be improved for future regulations and standards (higher strength of field, wider frequency range, influence of accessories). Methods and results will be reported.