On Monday 25 January 2016 13:29:35 John Kasunich wrote: > On Mon, Jan 25, 2016, at 01:23 PM, Gene Heskett wrote: > > Now if Marius can clarify by asking the driver to go 5 rpm, and > > getting 5 rpm exactly. Or driving it temporarily with line frequency > > power while watching it under flourescent lighting. If the blur is > > stationary, it is a synchronouse motor. If not, the blur will be > > drift CCW at whatever the slip angle is. > > Hopefully the info is on the nameplate and no testing is required. > > The tests suggested are tricky unless there is a load on the shaft, > at zero load the induction motor will be going very close to sync > speed.
Even unloaded, the slippage is usually north of 20 rpm & quite visible. Unless some enterprising motor maker ground some flats on the armature, which would make it synchronous at light loads. I saw one like that once, in a VCR turning the drum, using a variable frequency single phase drive. Unfortunately the scheme went to hell when the drum surface had been polished enough that the lubricating air film failed. That usually happened while the drum still had usable head tip projection. And the warranty didn't cover it=upset customer who bought a different brand of machine to replace it. Magnetic tape is quite abrasive when the temps and ambient humidity are both above 50F & 50%. At 75 & 75, you can wear out a 1000 hour prorated head drum in 100 hours. Clean air, cold & dry, is a different story entirely. We had a cheap 250 hour rated headwheel on one of the NETV time zone delay sites 3 machines, fail a rotary transformer winding at 7300 spinning hours. Sent it back to the rebuilder who fixed the rotary transformer connection, looked at the head tips and pronounced them to be good and serviceable yet so returned it no charge, we put it back in service and it was finally finished at around 9700 hours. A new 14" roll of 2" wide tape went into that room and wasn't replaced until the tails had been trimmed clean so often it could not hold a 1 hour program. Room held at 50F, 30 to 35% RH, no food, smoke or drink allowed in that room. Paid large dividends in reduced maintenance on $100k+ Ampex VR-1200's broadcast VTR's. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
