ferrite core material with improved magnetic permeability, allowing accurate measurement of ac signals in a extended frequency range that includes 50/60Hz. Absolute accuracy better than 1% at the nominal current and even better for lower primary currents. Two ranges of primary current measurement are available: 50A and 100A. The dimensions of the TT 50-SD are only 36.5 x 43 x 31.5 mm with an 8 mm diameter sensing aperture for non-contact measurement. The TT 100-SD measures 44.5 x 51 x 36.5 mm with a 16 mm diameter sensing aperture.