Absolute measurements of magnetic surface induction

Two methods have been used for, obtaining an absolute measurement of normal surface induction of a medium wavelength signal recorded on magnetic tape. One employs a nonmagnetic loop and an electrical procedure for determining its active rectangular cross-sectional dimensions. The normal surface induction is computed from these dimensions and the output voltage induced in the loop as the tape is transported at a prescribed speed across the active portion of the loop. The other is based on recording a dc signal of current level equal to the rms value of the ac recording current which produces the equivalent recorded signal as that for which the measurement is desired. A calibrated search coil is then used to measure the total remanent flux in a bundle of many layers of the dc recorded tape. The surface induction is then calculated for medium wavelength signals using existing formulas Measurements of surface induction obtained using the two methods provide equivalent results. The surface induction could be measured for a wide range of wavelengths using the nonmagnetic loop.