2005 Events:

January 27, 2005: "Sinewave Vs. Impulse Frequency Responses For a Sampled - Data Control System" by Hubert Hagadorn

Abstract: Impulse and sinewave frequency responses are determined for a basic sampled data control system. To this end the sinewave frequency response transfer function of a sampler is determined. This differs from a sampler's impulse transfer function, and corresponds more nearly to that obtained by a frequency response analyzer. The sampler's response is shown to exhibit anomalies at frequencies that are odd multiples of half the sampling frequency. Inter-relationships between the control loop impulse response and sinewave loop responses for open and closed loop conditions are shown. Unlike for linear systems, open loop sinewave responses can differ depending whether loop responses are taken with the loop physically open or closed. An example control system compensated for a deadbeat response is assumed. Step input time response plots are shown, and Nichols charts illustrate the different loop frequency responses.

bio: Hubert Hagadorn received a B.S. degree in Electrical Engineering from Lafayette College in 1959, and an M.S. degree in Electrical Engineering from Northeastern University in 1967, where he specialized in signal detection theory. Companies he has worked for include RCA, Daystrom, Honeywell, Mohawk Data, and Ampex. At Honeywell diverse projects included developing algorithms for character recognition, developing a ferrite-ceramic head technology, designing linear motors and also an emergency head retraction system for disc drives. At Ampex projects included the design of phase-locked capstan and scanner servos for helical and transverse scan tape drives. Other projects included the design of linear and switching power supplies located on and off-board the scanners. Additionally, studies were conducted on head selection, head motions and excursions and associated G-forces for automatic scan tracking servos, where multiple heads within a helical scanner are dynamically positioned so that recorded tape tracks are followed at various playback speeds. Hubert Hagadorn holds five patents relating to magnetic heads, oscillators, and timepieces. He is a member of Tau Beta Pi, Eta Kappa Nu, and the IEEE Control Systems Society.