posted 02-07-2005 09:29 PM                    

It doesn't matter how well the projector, itself, is grounded. The charge on the film will be grounded-out as the film goes through the projector but, once it leaves the projector and goes back to the platter, it will start charging up again.

Now, you've got a giant insulated, rotating disk and a giant band of insulating material passing over insulated rollers all gathering up electrostatic charge as they go.

What you have here is a giant Wimshurst Machine! An early form of electrostatic generator!

Yes, a Speco platter is a giant electrostatic generator, IMHO!
Spin those platters fast enough and you could probably generate a spark that could kill a man!

(Well, in theory only, at least. )

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From Wikipedia, the free encyclopedia.

The Wimshurst machine is a form of electrical generator developed by British inventor, James Wimshurst, in 1832. It is a historical electrostatic machine for generating high voltages. It has a distinctive appearance, with two large contra-rotating discs mounted in a vertical plane, and a spark gap formed by two metal spheres.

The machine belongs to a class of generators called influence machines. This means that they separate electric charges by electrostatic induction, or influence. Earlier machines in this class were developed by Wilhelm Holtz (1865 and 1867), Toepler (1865), and Voss (1880). They were more efficient than the earlier machines that worked by friction.

The machine is self-starting, meaning that it requires no electrical power supply to create the initial charge. It does, however, require mechanical power to turn the discs. The output of the machine is a constant current. The spark energy can be increased by adding a Leyden jar, which is an early type of capacitor suitable for high voltages.

See also

* Electrical generator
* Static electricity
* Testatika

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posted 02-08-2005 10:59 PM                    

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Those made by speco are honestly not worth the money. They caused to many false shutdowns and in some cases had to be weighted or tied down to prevent the false shutdowns.

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OR... You could quit dickin' around and just do what I found the kids had done in one theater I got called to:



However, the best solution I have seen is to take a thin rubber band and tie them down. That way, you prevent accidental bumps and bobbles from tripping them but, if there is a real need, the rubber band will break.

posted 02-09-2005 02:09 AM                    

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Yes, a Speco platter is a giant electrostatic generator, IMHO!
Spin those platters fast enough and you could probably generate a spark that could kill a man!

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posted 02-09-2005 09:51 AM                       

quote: Ian Bailey

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Why do Specos have this static problem?Can it be reduced or eliminated?

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STATICIDE
TOPICAL ANTI-STATS

For more information on all our products and to order please contact us via email or phone us direct on (61) 02 9496 0500.

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posted 02-09-2005 10:42 AM                    

The Speco gains electrostatic charges by "influence". (AKA: Electrostatic Induction.)

Every time the film passes over (or near) a non-conductive surface a little bit more charge gets built up as the electrons get pushed around when they repel each other. Positive and negative charged areas develop on the film. Every time the film passes over a roller that charge gets multiplied. It probably pases over 8 or more rollers on its way back to the take up.

Then the film gets back to the take up where it winds itself into a big spiral... Basically forming a giant capacitor. Because the Speco platter is painted, there's no way for the charge to be "siphoned off" to ground. (Or someplace where it can be put to use.) It just sits there and builds and builds. A lot of it discharges into the air if the humidity is high enough. If you live in a dry climate or if it's winter time when indoor humidity gets low, there's not enough water in the air to bleed the charge off.

The electrostatic induction is different than the triboelectric effect. (AKA: Charging by friction.)
Just by putting your hand NEAR a moving/spinning reel of film it is possible to build up a charge powerful enough to cause a xenon lamp to light up momentarily. I did it once by accident, sitting at the rewind bench. Then I did it again to show everybody else. (The lamp was inside its clamshell.)

My first solution would be to strip the paint off the platter(s). But the problem with that is that they are made of regular steel. They would probably rust in a very short time. Making them out of heavy aluminum or stainless would probably be too expensive.

My second solution would be to make that last roller on the takeup out of metal or graphite which would conduct any charge that has built up on the film to ground.

Third, if you can find a piece of Christmas garland that has metallic fringes you can put it near the top of the takeup elevator and be sure it's conducting to ground. It doesn't have to touch the film, only pass very near. (Within a few milimeters.) It will allow some of the charge to bleed away before it gets would up into a giant capacitor.

I have tried it and it does work a little bit. I never had time to really research it, though. It was shortly after that when I decided to quit messing with it and I went out and got myself some FilmGuard.

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Electrostatic induction
From Wikipedia, the free encyclopedia.

Electrostatic induction is a method by which an electrically charged object can be used to create an electrical charge in a second object, without contact between the two objects.

The effect can be demonstrated using an electroscope, which is an instrument for detecting electric charge. The electroscope is first discharged, and a charged object is then brought close to the instrument's terminal. This causes a redistribution of the charges inside the electroscope, so that the electroscope's terminal gains a net charge of opposite polarity to that of the object. At this moment, the electroscope has not acquired a net charge: the charge within it has merely been moved around. An electrical contact is then briefly made, e.g. by using the experimenter's finger, between the electroscope terminal and earth. This causes charge to flow from earth to the terminal, attracted by the local surplus of charge at the terminal. The electroscope now contains a net charge opposite in polarity, and slightly weaker than, that of the charged object. When the electrical contact to earth is broken, e.g. by lifting the finger, the extra charge that has just flowed into the electroscope cannot escape, and the instrument retains a net charge.

Numerous electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, rely on this principle.

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Triboelectric effect
From Wikipedia, the free encyclopedia.

The triboelectric effect is an electrical phenomenon where certain materials become electrically charged after coming into contact with another, different, material. The polarity and strength of the charges produced differ according to material and surface smoothness. Amber, for example, can acquire an electric charge by friction. This property, first recorded by Thales of Miletus, suggested the word "electricity", from the Greek word for amber, elektron. Other examples of materials that can acquire a charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur.

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posted 02-09-2005 10:50 AM                       

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Anti-Static Brushes
Cinema Platter Systems
A Static and Dust Control Product
The Kinetronics StaticWisk© SWG-625 anti-static platter brush is used to stop ‘Brain Wrap’ on cinema platter systems. The soft conductive synthetic fibers plus the conductive nature of the construction result in effective static dissipation from polyester based film. A six-foot (2m), heavy-duty, coiled grounding cord effectively drains static electric charges off the film. The SWG-625 brush is mounted magnetically to the platter tower and can be adjusted with a double ball joint for easy alignment.

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