The control of flux waveforms in iron testing by the application of feedback amplifier techniques

By the use of a feedback amplifier technique, the voltage appearing across a search coil wound on a ferromagnetic core can be made to follow any desired driving waveform, and the inherent harmonic distortion effects arising from non-linear B/H characteristics are reduced by an amount approximating to the loop gain. The technique is applied in iron-testing circuits and to a.c. bridges to obtain sinusoidal flux waveforms, thereby avoiding errors in loss measurement which would otherwise arise from distortion effects. Three amplifiers are employed in a single-strip tester to obtain uniform magnetization over the length of the strip.