On Saturday, July 31, 2010 11:58:01 am Don Stanley did opine: > Jon, Gene and Steve: > Thanks guys, I am glad I ask the question. > Most of my 3 phase work has been DC power supplies. > I had forgotten (or never realized) the sum of the 3 currents is zero. > Or is supposed to be. Sometimes the synthesis can leave something to be desired. In fact because of the lags that a fixed time delay to generate the 3 phases would have caused, in the now nearly 40 year old quadruplex 2" wide tape broadcast video tape recorders, that 3 phase 440 hz drive to the headwheel motors was actually 3 separate oscillators whose feedback to maintain the phase angles between them was mixed with the detected time base errors in order to speed up the feedback loop and make it stable, each oscillator then seeing the applied error in real time. They could literally adjust the speed of the motor so fast that the time base errors could be held to around 2 microseconds within 2 or 3 seconds of a dead wheel startup, with the target speed being 14,400 rpms, actually less by a 59.44/60 ratio when synced to an NTSC house src. In maintaining those machines 25 years ago, I found that the voltages from each phase amplifier often would be 20 volts out of balance without being an alarm able condition, so the 3 phases did not truly cancel. No output filtering was used as the 440hz sine wave wasn't too badly distorted unless the amplifier was in need of service.
One machine, late in the life cycle of the 2" format, the Ampex AVR series, had some very powerful servo amps, and could make a locked picture from a dead wheel in 400 milliseconds, or 40 milliseconds from a spinning standby mode. But, in operation that was expensive, as it drew 25 kw and needed that much cooling too. The sudden motion of the tape, going from 0 to 15 ips with 14" reels that weighed many pounds was handled by sucking the tape into a vacuum cleaner motor powered square tube about 4 feet long, lined with photocells that controlled the reel motors power, and they were very big DC powered motors. > Sincere Thanks > Don > > PS. Now I am going to get a shop radio so I don't forget this. Chuckle. Some background noise seems to quiet the savage beast, not to mention it might save some parts and broken bits by warning of impending weather that could effect ones power supply. Here in Weston, WV, we have one of those ma & pa ancient mary (AM) radio stations that does an excellent job of keeping us up to date on such goings on. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) You two ought to be more careful--your love could drag on for years and years. ------------------------------------------------------------------------------ The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
