A ferrometer for the determination of the a.c. magnetization curve and the iron losses of small ferromagnetic sheet samples

The paper describes the design and properties of a ferrometer for measuring small (about 30mm × 200mm) ferromagnetic sheet samples. The test specimen is magnetized by an open-ended coil fed with a sinusoidal voltage, and the variation of magnetic flux with time remains practically sinusoidal up to 1.4Wb/m2. Feedback amplifiers and rectifiers are employed to deal with the electromotive forces proportional to the time derivatives of the field strength and flux density in the test specimen, which are induced in the pick-up coils, in such a way that the peak values of field strength and flux density can be read directly from moving-coil milliammeters and the iron losses from a wattmeter. The measuring ranges of this instrument are: Frequency: 50¿250c/s. Field strength: 0.002¿500amp/cm when f = 50c/s. 0.0004¿100amp/cm when f = 250c/s. Magnetic flux density: 0.0004¿10Wb/m2 when f = 50c/s. 0.00008¿2Wb/m2 when f = 250c/s. Iron losses: 8×10¿8¿5×103 watts/kg when f = 50¿250c/s. Cross-section of specimen: 4¿40mm2. The measuring ranges of field strength and magnetic flux density are dependent on frequency, and owing to the design of the instrument, the measuring ranges of the different quantities are partly also mutually dependent. In consequence, part of the above-mentioned measuring ranges have no practical significance (e.g. 10 Wb/m2 when f = 50c/s and 5kW/kg).