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This topic comprises 2 pages: 1 2
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Author
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Topic: AP-3 Phase Control
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Steve Guttag
We forgot the crackers Gromit!!!
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Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 02-17-2007 09:37 PM
Think of the phase control thing as something else in the system that ages, almost instantly. And just like the @%@%#$ red LED readers, some seem to stay stable for a long time while others seem like they have one anode in the grave the moment they are put into operation.
Since the microswitch method is strictly an on/off thing...other than the switch itself becoming unreliable, the payout system does not age.
The motors do and can to the point that retiming is required. On a non-SCDC system, the take up circuit puts a resistor in series with the motor. The payout circuit does not receive this resistor so the payout is give an advantage in addition to the fact that the film that has left the payout platter that has not arrived at the take up platter gives the payout a speed advantage since its ID will be larger than the take up's OD.
AW-3s have the same issue with LEDs and sensors not being stable with some being rock solid for some time and others not so good. However, with the AW3, all three decks are completely independent (aside from the power transformer) so the drift in LED is not as pronounced in its effect until it is substantially out.
The SCDC can indeed work well though the best I've seen by far is Kinoton's E series. It is the best of all worlds. There is no calibration since it is a matter of "faster" or "slower" like a microswitch but without any of the moving parts to wear out. Also the film never deflects more than a couple of degrees before the speed is immediately corrected. Payout and takeup are independent. While some may not like it, the fact it is tied to the motor start of the projector means it does not have to deal with reacting to the film starting either.
Anyway...as to the "payout as a function of the take up speed" platters go...SPECO definately has the best design with the LP270. Their payout has three speeds. Coast, Take-Up speed, Full speed. This also ensure that no motor timing is ever necessary. They use a magnet and a pair of reed switches to switch modes. Generally, the full-speed is only used for thread up and when the show first starts. The platter decks are so heavy they naturally prevent jerky operation much the same as a flywheel would. On the negative side, since the decks are so heavy, they are slow to start and many give them a "push start" though if they are set up properly, that isn't necessary. They have extended their take up path to further make this unnecessary.
I don't know if I explained this better than Mark but I definately used more words!
Steve
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