my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » The ZIPPER what is it, Is it the dowser? (Page 2)

This topic comprises 2 pages: 1  2

Author Topic: The ZIPPER what is it, Is it the dowser? Michael Cunningham Expert Film Handler Posts: 186 From: Anchorage, AK Registered: Nov 1999 posted 09-06-2004 10:06 AM                     My understanding of the names of these items is as follows. HAND DOUSER : built into the very front of the lamphouse. Usually consists of a big plate of steel on a hinge with a big handle sticking out the side for the operator to rotate it into or out of the light path. CHANGE-OVER DOUSER : playing card sized chunk of metal mounted on a pivot between the shutter and aperture. Moved into and out of the light path by an electric solenoid mounted on top of the projector by means of a vertical metal rod. Usually activated by the automation or a control button. MOTORIZED, ELECTRIC or AUTO DOUSER : this usually refers to a motor having been mounted on the shaft of the above-mentioned hand douser. The motor is wired in such a way as to open the hand douser when the projector motor is running and close it when the projector motor stops. Mostly useful in theatres that leave their bulbs running all the time. - Mike  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 09-06-2004 10:22 AM                       Gordon is right about the Thide c/o's. Anyone ever see the ones called Senator? And, who can forget the good ol' crappy Weavers?  |  IP: Logged Per Hauberg Jedi Master Film Handler Posts: 883 From: Malling, Denmark Registered: Jul 2000 posted 09-06-2004 04:10 PM                        quote: Antonio Marcheselli I've heard that, I'm not sure. And when You once have heard a Cinemeccanica do a c/o, You'll be sure to recognize it, even from first raw of the auditorium  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 09-06-2004 04:47 PM                        Anyone know if they ever manufactured a change-over mechanism that uses 12VDC coils instead of 115VAC? I am told that to minimize any 60hz hum into the mag penthouse heads, for the time that the solenoid is engaged, albeit only a second or two, using DC coils instead of AC will help. But then, if such a 12VDC zipper model is not commercially available, couldn't a full-wave bridged rectifier wired to the AC coils accomplish the same thing while still using the same coils and without changing any of the hardware? Rectifying the 115VAC would supply the coils with DC, unfiltered, yes, but much less chance of inducing any significant 60Hz hum into the mag heads. The only other alternative I see (if DC versions were never manufactured) would be to find replacement coils that physically can replace the existing AC coils. I don't quite understand what is different in a coil that makes it work on AC or DC? Just the windings are different? It's not clear to if there is any reason why supplying 115VDC to the coil would make it not function properly, except that it might get hotter faster? But for such short bursts, that wouldn't matter, right?  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 09-06-2004 05:11 PM                        Without a current limiting load of some kind, such a coil would look like a dead short to DC. It would probably open any circuit protection before the plunger could move. With AC, the coil will at least have some inductive reactance to it, and therefore not be a dead short.  |  IP: Logged Joseph Pandolfi Expert Film Handler Posts: 213 From: Milford, CT. Registered: Nov 1999 posted 09-14-2004 09:25 PM                     We still use the top one in the picture in two of the four Century's here. The other two have Kelmar's  |  IP: Logged Josh Jones Redhat Posts: 1207 From: Plano, TX Registered: Apr 2000 posted 09-14-2004 10:23 PM                        *Fart*  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 09-14-2004 10:29 PM                     Bill: Michael C. seemed to answer your question perfectly. Just to clarify what a motorized dowswer is: essentially it is an automatic "hand" dowswer that closes when the projector is not running. Theaters designed by Act III, and perhaps others, used vertically mounted bulbs that are on all day. To keep the changeover from burning up, the hand dowser would have to be closed during intermission. That's why they are motorized. AFAIK, Zipper = changeover. I have used autodouser synonymously with changeover. Is that incorrect, or is it just another case of one person calls it this, another calls it that, but both are right? Interestingly, RGM automation labels the fuse for the changeover as SHUTTER. I never understood that. If you ask me, that is definitely WRONG. A shutter is a shutter. Period.  |  IP: Logged Dan Lyons Jedi Master Film Handler Posts: 698 From: Seal Beach, CA Registered: Sep 2002 posted 09-14-2004 10:43 PM                     quote: Tim Reed And, who can forget the good ol' crappy Weavers? Not me! I have them at my theatre, along with icky RCA 1040's which have been leaking since 1947! danny  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 09-14-2004 11:04 PM                     Correct me if I'm wrong but wouldn't putting a rectifier on an AC line still give you some amount of 60 cycle hum? If you used a 1/2 wave rectifier, you'd get pulsating DC which would make almost as much noise as AC would. The electromagnetic field around the wires would still be expanding and collapsing 60 times per second, thus producing the possibility of interference. If you used a full wave rectifier you would end up with rippling DC. No where near as much interference but, since there is an expanding and contracting electromagnetic field, there's still a possibility. Now, I suppose you could isolate the rectifier from the area of the sensitive components by putting the rectifier in a metal box, some distance from the "danger zone" then running the wires with EMT/armored cable and ensuring the outside is grounded. But, then, again, if you used EMT/armored cable, you probably wouldn't have quite so much interference from AC anyway... No?  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 09-15-2004 03:52 AM                        I think you're right about rectifying the AC, Randy; you would still have pulsing 60hz, but I am not sure if the intensity would much as full wave 115vac. But I think that it is not the AC lines running to the solenoid coils which induce the 60Hz into the mag heads but the energized coils themselves....little electromagnetic transmission stations they are. The change-over mechanisms sit right up there not more than 10 inches away from the mag heads. I would surmise that even if you had 24VDC coils and fully rectified DC, you would still get a big, noisy thud when the coil activated...I mean, that coil it's still a huge magnet that's just been energized and then collapses; that's got to be seen by any magnetic pickup, especially the four mag heads and the super high-gain amplification they need, as one massive thud. But maybe not a THUD coupled with an equally loud 60hz HUMMMMM for the duration you hold down the footswitch. Obviously they couldn't figure out a solution when Altec designed the preamp system that was original with our system because they way they dealt with it was simple, the sound change-over button was a DPDT pushbutton. It was designed in such a way that as you pushed the switch in, the first contact that was made wasn't the sound circuitry but an 8 pole relay that shorted all channels to ground. The second contact which engaged about an eight of an inch further on the button travel, threw the actual sound change-over. If you hit the footswitch (solenoid change-over) a fraction of a second AFTER you pushed the sound button and you held the sound button in until AFTER you released the footswitch, then you were engaging the solenoid coils while the entire system was muted. Of course this left you with a second or two of a muted soundtrack, not what I would call an elegant solution, but I guess it is much better than the alternative. You hardly notice the "dead air;" but you sure do notice the 85db THUUUUDHUMMMMTHUUUD. Only thing I think would really work....wrap the damn C/O unit in mumetal (made from cows' hooves).  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.