An Integrating Type of Electronic Hysteresigraph

Abstract

An electronic hysteresigraph, which integrates without recourse to electromechanical means and is free of drift, has been developed. In operation, a search coil surrounds the magnetic specimen to be tested, and the specimen is then subjected to a change in externally applied magnetic field strength. The time integral of the potential induced in the search coil is a measure of the magnetic flux change in the specimen. The induced potential is applied to a solid‐state voltage‐to‐frequency converter which produces a series of output pulses, the number of which is proportional to ∫edt. These pulses are summed on a digital counter to give a measure of the flux change. A digital‐to‐analog converter then provides a dc output which drives the Y axis of an X‐Y recorder. A signal proportional to the applied magnetic field strength is simultaneously fed to the X axis of the recorder and a continuous B vs H plot is obtained. This is a real‐time mode as the response of the various measuring elements is practically instantaneous. In considering the integrator, it is interesting to note that absolute accuracy traceability in calibrating the voltage‐to‐freqency converter is referred directly to the volt, as represented by the standard cell, and to the second, as represented by a crystal‐controlled time base. This is in contrast to the generally used secondary standards of mutual inductance and current shunt millivolt drop.