A 0.1–500 Hz analog thin film BH hysteresis loop tracer with automatic Y-axis drift correction

An analog magnetic hysteresis loop tracer is described that simply and effectively corrects for the Y-axis integrator offset drift inherent in hysteresis loop tracers. In order to keep a small input offset of about 30 μV from being integrated over time into an output offset of volts, the integrator is reset once every cycle: A comparator is used to trigger a one-shot that engages a relay that discharges the integrator capacitor. The circuit was built with standard available and inexpensive parts, and allows stable BH hysteresis loop measurements to be made without Y-axis drift or distortion over a frequency range of 0.1–500 Hz.