Film-Tech Forum ARCHIVE: ORCON Ammeter question

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Posted by Frank Angel (Member # 248) on 08-26-2003, 08:52 AM:

We are using older ORCON lamphouses, model XH4500 (or something close to that) with 4500w bulbs. They are powered by the old transformer rectifiers (non-switching type) with the big wheel on top to adjust the amperage (see pictures of it in the Movies in the Park in the Pictures section of the FTForum). When I set it up a few years ago, I set the voltage to the OSRAM spec sheet for the bulb (possibly 45-50v, not sure, but it was to what the manufacture spec-ed). Then I set "The Wheel" to bring the amperage up to spec also. Problem is, the ammeter on the ORCON only goes up to 120a, whereas the bulb required something like 140 or 150 amps. I tried reading the amperage using one of those clamp meters but couldn't get a good reading so what I did was, I calculated how many turns the adjustment wheel took to make an increase of 5 amps and then just kept turning the extra turns to bring it up past 120 to where my calculations would make it reach the amperage that the bulb required. This brought the meter up to the area above 120 and before it "pinned" against the edge of the meter.

Thing is, this has begun to irk me to no end because I know this is not an accurate way to set this thing, although the bulbs seem to be doing just fine....very steady burns, no wandering arc or flicker, no darkening and no bubbles. Why would the meters be calibrated to only read 120 amps when the lamphouse is designed for 4500w bulbs? Or have the bulbs specs changed radically since the lamphouse was designed? And please excuse my vague-ary about the numbers.

And while I'm asking about the Orcon, does anyone know how to set the hours meter back to zero on these things?

We just added an additional exhaust fan on the stack that we got from Granger as the ambient temp in the non-air conditioned, out-in-the-sun-all-day booth can easily reach 90 degrees.

Frank

PS -- The ORCON -- it's a light sieve -- it leaks light from every joint. By the time I am done wrapping all the cracks with aluminum foil, the think looks like a huge Thanksgiving turkey ready for the oven.

Posted by Ken Layton (Member # 133) on 08-26-2003, 09:01 AM:

I believe that is actually only a 4,000 watt lamphouse. ORC lamphouses were rated lower than the model number. Example: the old M-1000 lamphouses is really a 700 watt unit.

Posted by Tim Reed (Member # 137) on 08-26-2003, 11:51 AM:

quote:
And while I'm asking about the Orcon, does anyone know how to set the hours meter back to zero on these things?

Install a new hourmeter. Resettable lamphouse hour meters are a recent thing. It's not really a good idea, because by zeroing it out, you lose your lamphouse history.

I've always thought there should be two hourmeters: one for the lamphouse, and a resettable one for the bulb hours.

Posted by Rick Long Jr (Member # 541) on 08-26-2003, 09:04 PM:

Chances are you're going to be close with the current, but I would want to verify it. Make sure the clamp meter you're using is able to read DC amps. Some lamps had adjustable shunts for the ammeter, though I don't recall seeing them in ORC lamps. Kneisley maybe?
BTW, Xebex lamps used to have both a resettable and a life hour meter.

Posted by Gordon McLeod (Member # 33) on 08-26-2003, 09:14 PM:

Most ORC's had a calibratable shunt

Posted by Paul G. Thompson (Member # 655) on 08-26-2003, 09:45 PM:

I simply dismantled the meters to "zero" them. It is a big pain in the rear, but it can be done.

Ken is correct about the ORC bulbs.

Gordon is also correcrt about the meter shunts. However, do not attempt to calibrate them unless you have something that will measure the current correctly. I have seen some of those damned things as much as 15 amps out of calibration.

[ 08-26-2003, 11:38 PM: Message edited by: Paul G. Thompson ]

Posted by Frank Angel (Member # 248) on 08-27-2003, 02:50 AM:

Thanks guys. I am going to get a good working DC ammeter and see where I am. Even if the lamphouse is rated for 4000W, there doesn't see to be any dire consequences so far. In fact it seems to be humming along just fine. I will check to see if anything looks amiss inside. But so far, so good....unless of course I find that everything is slowly charring away into brittle lumps of carbon inside.

Hell with taking the hour meter apart -- it's much easier just keeping a good record in the cardholder on the back of the unit.

Frank

Posted by Paul G. Thompson (Member # 655) on 08-27-2003, 04:27 PM:

Frank, just an ammeter might not do the job. Be sure to get the shunt with it. You might be better off with the meter you have. Use a ammeter clamp or something that is accurate so you can adjust the shunt properly.

Posted by John Walsh (Member # 168) on 08-27-2003, 06:15 PM:

You might consider hooking up and looking at it with an ocilliscope. Even though the installed shunt might be off, excessive ripple will tell you something's wrong.

Posted by Richard Fowler (Member # 893) on 08-27-2003, 08:57 PM:

I sold the same lamphouse set to Gusman Theater, the site of the Miami Film Festival almost 20 years ago. This unit is basically set up for 4 kw operation. You could have a tech swap out the meter / shunt to one that goes to 200 ampere. The Orcon shunt has an adjustment slot to calibrate the meter to spec but a change out to higher amperage would make life more simple....but think of the "job security" while you twist the knob on the rectifiers [Wink]

Posted by Phil Hill (Member # 371) on 08-27-2003, 09:13 PM:

Frank, make sure the "clamp-on" meter is for DC too. Most are only for AC.

>>> Phil

Posted by Sam Hunter (Member # 1119) on 08-28-2003, 09:32 PM:

Speaking of CLAMP ON AMP METERS just how does that thing work?

Posted by Paul G. Thompson (Member # 655) on 08-28-2003, 11:45 PM:

Electro-magnetic fields. Just clomp it around the cable and it will read the current. They are quite accurate. Naturally, the higher the cost of the unit, the more accurate of a reading you would expect.

Posted by Sam Hunter (Member # 1119) on 08-29-2003, 12:47 PM:

I understand how ac clamp on amp meters work and know they rely on the changing magnetic field to induce voltage in the clamp loop like a transformer but dc does not change so there is only one magnetic field and it does not reverse polarity.
So my question is again, exactly what method do DC CLAMP ON AMP METERS use?

Posted by Tim Reed (Member # 137) on 08-29-2003, 12:53 PM:

There's still a magnetic field that surrounds each conductor and is proportionate to the amount of current flowing through it, it's just not changing direction.

Posted by Sam Hunter (Member # 1119) on 08-29-2003, 12:57 PM:

If you run dc through a transformer you get nothing on the other side.

The dc amp meter has to work on a different principal than an ac meter.

Maybe I am wrong about AC meters but I dont think so.

I left the above to reflect a change in knowledge [Big Grin]

I found this info on the net and now I understand:

"The actual movement mechanism of a clamp-on ammeter is much the same as for an iron-vane instrument, except that there is no internal wire coil to generate the magnetic field. More modern designs of clamp-on ammeters utilize a small magnetic field detector device called a Hall-effect sensor to accurately determine field strength. Some clamp-on meters contain electronic amplifier circuitry to generate a small voltage proportional to the current in the wire between the jaws, that small voltage connected to a voltmeter for convenient readout by a technician. Thus, a clamp-on unit can be an accessory device to a voltmeter, for current measurement. "

Enquiring mind(s) wanted to know.

Posted by Paul G. Thompson (Member # 655) on 08-29-2003, 01:43 PM:

Tim, is there a chance the DC clamp measures the electro-static field? If you stuff a magnet in it, it won't see it. I don't know... [Confused]

I remember an old DC line clamp that had to be calibrated everytime it was used. Calibration was done by holding the clamp next to the wire, and then the meter was adjusted for zero. Then the clamp was placed around the wire to obtain a reading. It was an old unit going back to the 1970's and it's acccuracy was not that great as compared to middle-of-the-road DC line clamps.

I have one that will do AC and DC with a digital read-out. I think it costed about 200 bucks, but it is accurate.

Posted by Sam Hunter (Member # 1119) on 08-29-2003, 01:48 PM:

Makes you say hmmmmmm doesn't it?
I emailed a meter manufacturer about it and am awaiting his reply.

Posted by Gordon McLeod (Member # 33) on 08-29-2003, 02:39 PM:

DC and AC clamps use a Hall effect transitor that measures the magnetic field around the cable Some in the DC mode measure the disturbance in a field of the clamp

Posted by Sam Hunter (Member # 1119) on 08-29-2003, 02:44 PM:

Yep, thats what I found out. (see above)

I got an answer from the manufacturer.

quote:
Greetings,

Thank you for your e-mail of 29 August 03.

The smaller ones generally use a Hall effect sensor in a gap in the core. This senses the magnetic field set up by the current in the aperture of the core.

Ours are different. Like US Patent 3768011, we build a core with winding resembling a current transformer. This is connected across a special peak current limited inverter. When direct current flowing through the aperture of the core upsets the magnetic state of the core, the inverter changes duty factor so as to send an average (DC) current back to the winding to nearly restore the balance of the core. We measure this restorative current and use it to provide an output and drive a meter.

Ours is a distributed sensor, also suited for building larger clamps.

I hope this helps.

[ 08-29-2003, 03:45 PM: Message edited by: Sam Hunter ]

Posted by Tim Reed (Member # 137) on 08-29-2003, 03:46 PM:

Sam, you answered your own question! [Smile]

quote:
Tim, is there a chance the DC clamp measures the electro-static field?

I'm not sure on the internal specifics of the meter (other than what Sam uncovered), but it's obviously using the field around the conductor in some manner.