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Topic: Projector speed issues

Larry Shaw
Expert Film Handler

Posts: 238
From: Boston, MA, USA
Registered: Mar 2000

posted 02-10-2004 12:26 AM

All DP-70's and FP-16's/18's are sync motor equipped. Very few DP-75's or FP-20's are. Easy to tell if they are sync of course....they have a toothed belt.

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Jeff Joseph
Expert Film Handler

Posts: 131
From: Palmdale, CA, USA
Registered: Jun 2000

posted 02-10-2004 03:29 PM

So now I'm running both projectors at 24 fps... would anyone have known if it was 24.1? Yeah, me.

Jeff

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 02-10-2004 07:58 PM

John Hawkinson said:

quote:
frequency stability of the grid
However, it is not true that frequency change only happens in igloo/generator land. While power companies do strive to hit around 60.0 Hz (and probably no more significant figures), that is an average number over the course of a day. Within that time, frequency will drop during heavy load periods and will be artificially increased during low load periods to make up for it. I think you can expect to see variations of +- 0.1Hz within the course of a day in a major metropolitan area.

Mark Gulbrandsen said:

quote:
sync motors are only affected by frequency shifts, something that rarely happens today except up north of the border with the Hydro companies.

I said:

quote:
Say what? Surely you must be referring to the folks way up north, running their iglo off of a generator.

I said that since Mark implied that frequency shifts are worse north of the border than elsewhere in North America, when in reality any phase shifts are going to be very similar throughout each interconnect area (the Eastern Interconnect covering two thirds of Canada and the US, the Western Interconnect covering most of the rest of the two countries and the third interconnect covering most of the state of Texas (ERCOT)) since generation is synced by HVDC links, leaving phase shift to only be caused by distance and load.

Further, as load approaches maximum generation levels (as it is now), phase shift is less and less contained to a metropolitan area, only contained to the interconnect zone.

So yeah, the phase shift exists throughout the entire grid, although not quite as high as the 1% swing that John suggests. Under NERC's A1 and A2 control performance standsards frequency error (in Hz) upper & lower standard deviation was 0.002 and something like -0.001. Under NERC's present CPS1 & CPS2 standards it is about 0.004 and 0.001. Of course peaks are higher than standard deviations, but it is extremely rare for the deviation to be greater than +/- 0.5%.

Also, in case anybody cares, the system is usually monitored to 5 or 6 sig fig.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-10-2004 09:20 PM

Daryl,
Am Aware of alot of what you have said as I have studied how power companies have monitored and conrtoled frequency way back to the days of the Warren Type A clock. I had one of these clocks a number of years back and it was very interesting. Definately not accurate to 5 or 6 digits, but back in the early 1900's it set a new accuracy standard of about plus or minus 1 hz or better over a 24 hour period. That was pretty darn good for 1916 and this clock controled many a power plant till the early 50's! Actually I wouldn't be too surprised if there were a few of these clocks still being used in some remote parts of the world.
Warren Type A Link: http://www.my-time-machines.net/warren_master_clock.htm

As for long term drift today its so neglegable as to go undetected by modern electrical and electronic equipment. With sync motors any frequency deviation over the short term...seconds or less is what affects them most and might even be noticable in sound playback without adaquate film stabilization. If it was required in a special application, 3 phase externally driven motors can be made even more accurate over the short and long haul by refrence to a crystal standard or atomic clock, something that is quite easy to do with todays technology.

As for shifts North of the border.... thats what I am told by people I have met that live up there.

Mark @ CLACO

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 02-11-2004 12:48 AM

I might as well throw my two cents in the jukebox.

When films are run overseas, they at least used to, run them at 25 FPS and then apply pitch correction to prevent it from sounding 'screatchy'

JJ

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 02-11-2004 08:46 AM

pitch correction I doubt that as until the advnt of digital synthesis pitch change in reel time was very difficult to do ad maintain any semblence of sync

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Edward Jurich
Master Film Handler

Posts: 305
From: Las Vegas USA
Registered: Jul 2003

posted 02-11-2004 11:20 AM

A projector running 2-3% fast, probably a spin-off from the old top-40 radio days of playing 45's at 47RPM [Big Grin]

(hey Hooper, remember that?)

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William Hooper
Phenomenal Film Handler

Posts: 1879
From: Mobile, AL USA
Registered: Jun 99

posted 02-12-2004 12:58 AM

They need a plate reverb for dialog in the center channel. And the projectionists should do phone bits over the music in the closing credits.

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Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 02-12-2004 02:46 AM

Dick sed:

quote:
This of course won't work in Europe with our much maligned (by North Americans )50Hz system.

Dick:
Bars = 50(Hz) x 2 x 60/rpm
[Smile]

Frank sed:

quote:
It's easy to figure out the speed of your projector by timing a known length of film, but THEN what?

It's a sight easier using the disc, and more accurate.

Frank also sed:

quote:
why would I want to?

It's a troubleshooting tool.

John sed:

quote:
(Can we agree to reserve the term "strobe" for the actual use of a stroboscope and use some other term for the patterns?).

FWIW, the proper name is stroboscopic disc. They go back at least as far as disc recording, if not further.

quote:
If there's any interest, drop me an e-mail with your sprocket sizes, tooth-counts, and rpms, and I will summarize here and produce such a thing.

Hey, cool! I would volunteer to do this, but I'm making TRAILERS for the next couple of weeks -- drive-ins are getting ready to open in a few months. [Wink]

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 02-15-2004 04:41 AM

I guess it goes to show ya, dont believe everything you read [Smile]

Josh

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