Film-Tech Forum ARCHIVE: Arc wandering in xenon lamp

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Posted by William Phillips (Member # 1162) on 09-10-2002, 03:33 PM:

I have just had a look at the arc through the view window and got frightened.
The tail of the arc seems to be riding higher than normall on the anode. I have noticed this before on this lamp and was woundering if anyone else has seen this on their lamps.
The arc normally behaves very well. The lamp is 1 month old and has done 240hrs. Its an Osram XBO1600HSC in a Cinemeccanica CX21H lamphouse with good cooling and the rectifier is an IREM N3X75DN.
Picture still looks good though.

Posted by Paul G. Thompson (Member # 655) on 09-10-2002, 04:06 PM:

What is your operating current, and how good is your power supply? What does the anode and cathode actually look like? Does it require a stabilization magnet? Has someone use a refrigerator magnet to post papers and stuff to the side of the lamphouse?

External magnets placed in the right locations can drive your Xenon lamp NUTS! Seen it happen.......

Posted by Richard Fowler (Member # 893) on 09-10-2002, 05:28 PM:

HS series bulbs generally do not use magnetic stabilization. The Xenex Pup did use a pole magnet but the Cinemeccanica unit does not.
Richard Fowler
TVP-theatre & video Products Inc. www.tvpmiami.com

Posted by Gordon McLeod (Member # 33) on 09-10-2002, 08:03 PM:

Probably just the lamp since it wasn't a problem I infer from your post in the past
those lamphouses don't use a magnet
Is the angle very steep?

Posted by John Pytlak (Member # 331) on 09-10-2002, 09:20 PM:

Might be worth looking to see if there is already uneven wear or "mushrooming" of the lamp electrodes, which could indicate excessive current ripple from the IREM rectifier.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by William Phillips (Member # 1162) on 09-12-2002, 02:38 PM:

Cheers all.
There is no magnet on the lamphouse and none holding any papers to the side.
The anode and cathode look ok. The lamp can operate between 50amps and 75amps ( according to the card that came with the lamp ) Normal current is 65amps. The lamp is burning at 58ish amps ( the meter is allways steady). I normally turn the current up a bit over the life of the lamp until I get to 65.
The projector is racked 12degrees . I think the max for the 1.6kw HSC is 20

Posted by John Pytlak (Member # 331) on 09-12-2002, 03:07 PM:

You could try rotating the lamp 180 degrees, just in case the electrodes are slightly out of position. Do all lamps now have the wandering arc in this lamphouse, or just the one? Does this lamp have a wandering arc in another lamphouse?

Posted by Pete Naples (Member # 761) on 09-12-2002, 03:09 PM:

What's the rectifier? The 3 phase Strong is very prone to a ludicrously high OCV on our 415v supply, the knock on is a high inrush current. If it's one of ours on ORC or Strong single phase XPS type then leaky caps in the choke circuit can cause high inrush, which tends to severly pit the electrodes, causing the arc to wander around, and what looks like a flicker on the sheet. If the flame is stable, but not central then maybe the rake is too steep for that lamp without a magnet, come to think of it I can't think of a lamphouse I've ever seen here without a magnet!

Posted by John Pytlak (Member # 331) on 09-12-2002, 03:18 PM:

Does orientation of the lamphouse relative to the earth's magnetic field have any effect on arc stability? Could there be strong localized magnetic fields in that location?

Posted by Richard Fowler (Member # 893) on 09-12-2002, 08:14 PM:

Most of the Cinemeccanica product does not use a magnet since they specify HS bulbs in most of their product....we have had problems with customers prefering to use another bulb such as a W/H series and we have installed magnets and bulb supports based on field problems. I like the adjustable magnet set-ups such as found in Kneisley and Kinoton and other units to fine tune the arc.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com

Posted by Jason Black (Member # 684) on 09-12-2002, 11:39 PM:

At the risk of sincere stupidity, what is arc wander? I feel like I know, but I've never heard of the term arc wander before... I'm assuming it's when the arc actually wanders in movement across the anode/cathode... hence the name. Or is it when the actual initial strike arc pattern varies?

Posted by Paul G. Thompson (Member # 655) on 09-13-2002, 01:10 AM:

Jason, the arc looks like a candle in the wind.

This can happen under some of these circumstances:
1. The cathodes and anodes are badly eroded due to age or defect.
2. Deformed anodes and cathodes due to poor power supply filtering.
3. Deformed anodes and cathodes due to excessive in-rush current.
4. Deformed anodes and cathodes due to long igniter "lay-on's."
5. Weak or mis-adjusted magnets if the bulb requires the use of them.
6. Operating a bulb with magnets when it does not want them.
7. Stray magnetic fields getting too close to the bulb.
8. Bulb being operated outside the recommended electrical parameters.
9. Bulb being operated outside the recommended mechanical parameters.

Just mentioning a few that come to mind...but it sure seems strange that I am using the word "parameters" quite a bit in some of the threads lately..

Osram used to supply a data sheet with their bulbs which dictated the mechanical positions a certain bulb may be operated within. Whether they still do or not, I don't know. I don't use Osram bulbs anymore. The last one I used was about 8 years ago.

Posted by William Phillips (Member # 1162) on 09-13-2002, 03:06 AM:

John, all the other lamps that I have had , I havent noticed the arc wandering- if it was though I wasnt looking in at the time.
At the moment we only have the 1 screen but building work has just begun on the new cinema.
Pete the rectifier is an IREM N3X75DN 3 phase.

Posted by Jamie Sanson (Member # 1161) on 09-13-2002, 06:21 AM:

HI all.

quote:
Does orientation of the lamphouse relative to the earth's magnetic field have any effect on arc stability? Could there be strong localized magnetic fields in that location?

John the lamp orientation relative to the earth dose not effect the stabiliy of the arc,how ever the size of the magnetic field needed at the site of the arc is small and is only slightly greater than the magnetic field of the earth.

quote:
The tail of the arc seems to be riding higher than normall on the anode

This is normal because the arc is not completely stationary.The tail of the arc is subject to slight fluctuations casued for example by gas turbulence in the lamp.Emission conditions at the cathode tip can also change resulting in the root of the arc moving

quote:
You could try rotating the lamp 180 degrees, just in case the electrodes are slightly out of position.

It is recommended that horizontal lamps be rotated 180 degrees halfway through their life.which in this case should be at 1500 hours for average life of 3000 hours.

quote:
The lamp is burning at 58ish amps ( the meter is allways steady). I normally turn the current up a bit over the life of the lamp until I get to 65.
The projector is racked 12degrees

Ok the -12 degrees does not help.Tiliting the lamp with the anode at the bottom is the worts position,the covection forces act increasingly against the xenon gas jet ang the instabiliy of the arc worsens dramatically,than at 90 degrees.I would recommend to run the lamp at the rated current of 65 amps 23 dc volts.

Jaime Sanson
Screend & sound technology.

Posted by System Notices (Member # 2357) on 03-27-2005, 03:41 PM:

It has been 926 days since the last post.