Transactions section: Preprint of corresponding pages from the current annual AIEE transactions volume: Dynamic measurements on electromagnetic devices

FOR the investigation of relays and similar electromagnetic apparatus, data giving the variation of current and flux as well as the motion of the armature during the operating cycle are of great value. The rapid-record oscillograph¹ has been used extensively for current measurements and, where a moderate accuracy is sufficient, is very satisfactory. Data on the flux also may be obtained by graphical integration of oscillographic data, but such a process is laborious and, unless great care is taken, is of doubtful accuracy. The development of a shadow-graph attachment² for the oscillograph provided a means of measuring armature motion at the same time and with the same order of accuracy as the current measurements.