Film-Tech Forum ARCHIVE: Burning aperture plate

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Posted by Rob van Ede (Member # 1457) on 07-11-2003, 10:18 AM:

Hi,

about a week ago, one of our projectors started getting real hot around the gate. First, the aperture plate was blackened a bit, but it's getting worse: now the plates are getting so hot that pieces come off and the little window on the side got so hot that it cracked. The first plate is almost "burned up", so to say.
The strange thing here is that there was nothing changed on this projector, light output on the screen is good and the light falling on the shutter seems to have no hot spots either.

I realize that this is quite a problem and hope that the tech will come very soon as i don't know how to solve this and of course this is happening on our largest screen.

What could be the cause for a problem like this that starts so suddenly?

Projector: Ernemann 15
Lamphouse: Xenosol 2000
Lamp: Osram 2K

Thanks,
Rob

Posted by Ken Layton (Member # 133) on 07-11-2003, 10:29 AM:

Is there a heat filter on your lamphouse?

Posted by John Spooner (Member # 1565) on 07-11-2003, 11:18 AM:

Dear Rob and Ken.
I also would tend to suspect the heat filter as these types of lamps use a glass mirror and a dichroic heat filter of Jena glass mounted at an angle just before the dowser.
If the glass filter has broken or is missing, then the aperture will receive too much heat as you are experiencing.
At the very least, reduce your lamp current to as low as practically possible until your tech arrives.
John Spooner. South Australia.

Posted by Aaron Sisemore (Member # 145) on 07-11-2003, 11:59 AM:

Not being familiar with the Ernemann 15, I cannot know for sure... Is the gate liquid cooled? If so, has your cooling circulator failed or coolant level become low?

You may also want to check the exhaust fan as well- you would be suprised how much heat they actually take away from the lamp and projector gate.

-Aaron

Posted by Rob van Ede (Member # 1457) on 07-11-2003, 12:48 PM:

The projector used to have a heat filter in front of the douser. Last year it fell off and our tech assured the manager that this was no problem, so the machine now runs for about a year without heat filter. There have been no problems until last week, when this heat issue started. I must add that about a month ago, a new bulb was fitted (not by me). For tree weeks after that, there were no problems.
This afternoon, i talked to the tech (who is on holiday at the moment [Mad]

), and now he wants me to put the heat filter back in. Never done such a thing but i have to try, there's no backup so i'm pretty much on my own.
Yesterday i already lowered the current by about 5 A an it didn't really help. The problem is that crappy, uncalibrated current meter on the lamphouse: it tells nothing, so i don't know what i'm doing and i hate that. I now have a current measuring device to put over a cable (don't know the English word) but i have no idea on what cable i should measure. It should carry a one-way current according to the manual. Any suggestions?

The gate is not water cooled, and air intake is working (new air filter last week, so that shouldn't be a problem).

Thanks,
Rob

Posted by John Hawkinson (Member # 1135) on 07-11-2003, 01:39 PM:

Rob, the current going in to the lamp should be the same as the current going out, so it shouldn't matter which cable you measure. Just make sure you have a clamp ammeter that can measure DC current, not just AC.

--jhawk

Posted by Rob van Ede (Member # 1457) on 07-11-2003, 06:34 PM:

update:

i've managed to stop the burning by placing a blower very close to the gate, generating a lot of airflow. This way, there are no longer (strong) signs of burning on the aperture plate after a show. Will be able to keep the machine running till our tech is back in a few days.
I'm still wondering what might have caused this sudden temperature increase...

Rob

Posted by Bill Carter (Member # 156) on 07-11-2003, 09:04 PM:

My first guess would still be that something has changed in your exhaust system.

Posted by Gordon McLeod (Member # 33) on 07-11-2003, 09:10 PM:

On the back of many 15's is a pancake mufin fan check to see it is working it cools the shutter box

Posted by John Pytlak (Member # 331) on 07-11-2003, 10:10 PM:

If you are burning the aperture plate, it's very likely you also have so much heat that you are damaging your prints:

http://www.kodak.com/US/en/motion/newsletters/pytlak/fall97.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/winter97.shtml

A dichroic heat filter (or "cold" mirror) is usually required for power levels above 2000 watts.

Since this just started happening and the heat filter has been gone for quite a while, I suspect the lamp alignment/focus has changed, or you are overpowering the lamp.

Posted by Jason Burroughs (Member # 68) on 07-12-2003, 01:00 AM:

I too think it could be a malfunction of the exhaust system. Lack of proper exhaust will not only shorten bulb life, but result in a very hot projector, as well as a hot booth.

Posted by Rob van Ede (Member # 1457) on 07-12-2003, 04:13 AM:

The day after the small green glass broke, i ran a loop of 5 m trough the projector for 20 minutes and the image looked the same all the time. Upon inspection of the film afterwards, there was a very light "deformation" visible in every frame, no signs of color change though. I guess that with the extra fan and the lowered lamp current, i'm at the safe side (well, i hope).

Gordon, where exactly should i look for that pancake mufin fan? I know of two fans: one intake on the back of the lamphouse and one on top of the lamphouse for exhaust.

Rob

Posted by John Walsh (Member # 168) on 07-12-2003, 09:45 AM:

This is the fan on the front:

This is the fan in the back:

Like several other things on an Ernamann 15, it looks like their engineers took all of 10 min. to design in the cooling system.

There is no water cooling option avaiable for this projector.

Posted by Rob van Ede (Member # 1457) on 07-12-2003, 10:08 AM:

John, thanks for the photos. We don't have the fan in front, just some passive cooling over there.
I've now run three shows with a large table fan next to the projector and without burning anything. I'll post what the cause for this al was when it's sorted out, i hope later this week.

Rob

Posted by Gordon McLeod (Member # 33) on 07-12-2003, 06:29 PM:

I have several 15's with both fans running on xetron consoles with 6k lamps and they stay nice and cool
Also the ernaman lamphouse has a cold light reflector (same as te kinoton) so the light shoul be fairly cold to start with

Posted by Rob van Ede (Member # 1457) on 07-22-2003, 10:31 AM:

The problem is solved now. It turned out to be caused by two tings, which are both very bad:
- two days before he left on vacation, the manager had decided to put the spare mirror in the lamphouse, because there was a slight unsharpness. He didn't document this and didn't know that that lamphouse used a cold-light mirror (all our other projectors have 1.6 kW bulbs and use the standard warm-light mirror). The spare mirror was a warm-light mirror.
- The bulb was run at about 90 A instead of 75, even after i turned it down about 5 A! The current meter on the lamphouse was not far off, like i was told by the one who trained me long ago. The rectifier was run over it's specs and miraculously survived, as did the bulb.

A day before the manager returned all the mess was repaired, and he was happy that it didn't get out of hand..... [Wink]

He was there when the place was built and didn't know what mirrors went in [thumbsup]

I'm very curious how this overloading of the bulb and the rectifier affects the life expectancy of those. The tech said it was a miracle that nothing broke and we should keep an eye on it.

Rob

Posted by Dave Macaulay (Member # 813) on 07-22-2003, 11:31 PM:

It sounds as if you've been running 2K bulbs at 90A for some time in this lamphouse. If you haven't had a problem during this time - while believing the amps reading was inaccurate - then don't get all paranoid now that you realize what's happening. If previous 2K lamps went full hours and the rectifier has worked reliably at 90-95A (about 2500W) then I think you should just set it at 75A and not worry.
Or use 90A and laugh at the suckers that pay extra for a 2500W lamp [Smile]

At Imax we used "special" 16500W lamps for some 3D systems, and the supplier's tech told me the only differences between the normal 15kW one and the "special" were 3 things - the price (more), the warranty hours (less) and the "16.5kW" stamped on the barrel.

Posted by John Pytlak (Member # 331) on 07-23-2003, 08:55 AM:

Rob:

Now that you know what happened, I would certainly run the lamp within the recommended current range, and NOT continue running the lamp at excessive current.

However, even with the higher current, the lamp survived so far. So I would suggest carefully examining the lamp to be sure there was no obvious permanent damage like crystallization of the quartz, bulging of the lamp envelope, or obvious damage to the seals. Use proper safety precautions (face shield, shrapnel protection, etc.) If the lamp appears normal, it's probably safe to continue using it, acknowledging increased risk of explosion.

Posted by Rob van Ede (Member # 1457) on 07-23-2003, 05:15 PM:

When all was repaired and the tech measured the current, he adjusted it to the rated current. Lamp seems fine, so it looks like we're safe.

Thanks again for all suggestions.

Rob

Posted by Ken McFall (Member # 845) on 07-23-2003, 05:29 PM:

I would have thought the manager would have been very aware of the need to make an entry in the diary.... it's plain and simply good practice to leave a note to say what's been done.

If nothing else you would have had it in the back of your mind as something that had changed when the problem started.

Good practice starts from the top.... You could so easily have damaged a print and lost revenue... would he have been so understanding if it had been your 'lapse' that had caused so much grief? I doubt it.

I have a real problem with 'everyone' and the cleaner being involved with running the projection room. Employ the right people for the job and let them get on with it.

That way they can expect professionalism. Controversial idea maybe [Big Grin]

Posted by Leo Enticknap (Member # 534) on 07-24-2003, 01:43 PM:

As Rob wrote, the manager just didn't know that there are different types of mirror, and probably didn't know that turning the current up had implications beyond making the light a bit brighter. He's got a dimmer switch on the halogen lights in his home, so what's the difference? [Roll Eyes]

I wouldn't go as far as Ken in suggesting that managers should never be involved in any way whatsoever with the projection operation, but I certainly would agree that they should receive - and be assessed on - proper training before they even think of faffing about with lamphouses.

Quite apart from anything else, as John points out, xenon lamps are a very serious health and safety issue. In fact they're possibly one of the most dangerous components of industrial machinery that anyone (outside the military) is likely to use. I've personally had two xenons blow up on me, and both were the result of being overrun (a lamphouse ammeter giving a false reading).

If you feel comfortable examining the lamp in the way John describes, fine. If not, replace it now. As the manager made the mistake in deciding to overrun it without realising the implications, he should sign the purchase order for a replacement, no questions asked.

Posted by Michael Schaffer (Member # 1204) on 07-24-2003, 01:52 PM:

I had xenon lamps exploding in lamphouses, but I never had one explode on me so far (The Force is with me). So I am curious to know how drastic the explosion of a lamp in cold state actually is. I have heard very different dramatizations.

Posted by Leo Enticknap (Member # 534) on 07-24-2003, 02:34 PM:

Sorry, the definition of 'on me' is at issue. One of them really was, i.e. fragments of quartz hit the protective gear I was wearing. I was removing lamp after it had died during a show. After failure the lamp was left for three hours with the fan running (the remaining shows of that day were run with the other projector in that screen, which was equipped for both changeover and platter operation) before I touched it. The second lamp exploded in situ in its lamphouse a few seconds after being struck, so that doesn't really count as 'on me', granted.

The former explosion was of a cold lamp. The noise didn't sound very much - it was a dull 'thud', which was a bit deceptive. There was scarring around the plastic tube into which the lamp had been half inserted at the point of explosion, and I was finding bits of quartz all over the projection box for days afterwards. I wasn't actually in the room during the second explosion, which happened while the lamp was actually lit. But I'm told that it was an almighty bang.

Posted by Michael Schaffer (Member # 1204) on 07-24-2003, 05:13 PM:

I once had a lamp exploding in a projector a few meters away from me. It was only a 1,2K , but the crashing sound was indeed very loud. We opened the lamphouse and were greeted by chaos and destruction: the lamp had taken the reflector (Kinoton glass reflector) into the next world. Even the douser was warped.
On the other hand, your experience with a cold explosion confirms what I heard from other sources. Obviously the cold explosion isn't all that bad. Which doesn't mean we don't want to wear appropriate protection - those shards are still viciously dangerous. But some people tried to tell me that even a cold explosion was an enormous event which even the face mask doesn't protect you from... [Wink]

Posted by Leo Enticknap (Member # 534) on 07-25-2003, 06:02 AM:

It might have been many years ago. People I've met who worked with the very early generation of xenon lamps in the late '60s and early '70s tell me that they operated under a lot more pressure, were more volatile and more prone to spontaneous, unprovoked explosion than today's lamps. Basically xenon lamp technology has gradually got safer over the years, to the point that they will virtually never blow up unless they're abused in some way.

The (1.6k) lamp which I had explode inside a lamphouse didn't totally destroy the mirror as it was a metal-backed one, but it did cause quite a bit of grief.

Posted by Rob van Ede (Member # 1457) on 07-25-2003, 07:02 AM:

I have to add that our manager is also the head of projection and that he has 30 years of experience. He just doesn't have an idea of the dangers of these lamps or of any technical details (calls the entire sound rack an amplifier): he wears no protection at all when changing lamps. I once commented on that and he said this: " my eyes are protected by my glasses ". I only have three years of experience so i how could i know more than he? [Mad]

That's all the response i get. This way it's sometimes very difficult to discuss some technical issues like the current trough a lamp or bad EQ-ing. This is just the way it is and i'll have to live with it i guess.

Rob

Posted by John Pytlak (Member # 331) on 07-25-2003, 09:33 AM:

quote:
...he wears no protection at all when changing lamps. I once commented on that and he said this: " my eyes are protected by my glasses "

Without proper eye (and face) protection, the LAST thing he will ever see is that exploding xenon lamp!

Have your manager read this for information about the dangers of xenon lamps:

http://www.sylvania.com/business/photo/pdfs/ENGR_BLTN11.pdf

http://osat-ext.grc.nasa.gov/gso/manual/chapter_26.pdf

http://www.ltilamps.com/Media/hgxe_tech_article.pdf

http://www.navitar.com/download/xenon_man.pdf

And remind your manager that when the doctors are pulling shards of quartz shrapnel out of his body, they don't show up on x-rays. [evil]

Posted by Frank Angel (Member # 248) on 07-25-2003, 04:54 PM:

Anyone know of a good source for the complete protection package -- face, hands and body protection? Anyone sell them as a package? A few years back the bulb manufacturers would have that protection equipment; now you have to search for it piecemeal. Plus, I assumed the kit the manufacturer sold was tested for the necessary protection. I don't know what I am looking for in terms of the gloves or the protective jacket. Is the Tyvek jacket that I saw with one xenon installation kit enough to stop shards of quartz that are traveling at the speed of friggin light and the force of an M16 bullet? And what kind of gloves. STANDARDS damnit....gimme standards.

Frank

Posted by Jean-Michel Grin (Member # 1360) on 07-26-2003, 02:32 AM:

In one of our theater the aperture plate was verry hot too; finally we solve the problem with an align-o-tron and checking the working distance between the mirror and the aperture plate.
An accuratte setting of the mirror is verry usefull...

About the protection clothes an face mask for changing xenon bulbs: I know a projectionist who never protect his face, changing the bulb with bare hands, drinking a beer and smoking a cigarette while doing the job [Eek!]