Hello All. For those of you who have been following this thread, let me fill you in on what we learned. Our most recent problem was caused by a single bulb, second nearest our antenna. So we changed out all our bulbs with GE MVR400/U bulbs and we are back in business. Thanks to Mr. Woodgate, two bright individuals from GE Lighting contacted me and schooled me on metal halide lights.
As you may know, we were fighting intermittent noise from our metal halide lights in our 10 meter chamber. We troubleshot the problem to a single GE/Tungsram MH400/U/TU bulb. We speculated the problem was caused by a failure in the bimetal switch and starter within the bulb. I have been told by GE this is incorrect. Metal Halide lights function by generating a controlled continuous arc within the arc tube between two electrodes. This arcing makes noise. Period! Once the bulbs warm up the arc stabilizes and it generates less RF noise. But for reasons beyond anyone's control, the arc can intermittently go unstable for a few seconds causing increased noise (ever see the lights change color). This problem can vary from bulb to bulb and change during the bulbs life. Changing out the bulbs may help for awhile but we have to consider this the nature of this lighting technology. The chamber manufacturers mount these lights above the chamber in a box (high-hat) lined with ferrite tile to minimize the RF noise from the lights. Though this is a good approach and works well most of the time, when the bulb arc goes unstable it can still interfer with your testing. So, what do we do about it? 1. It helps to properly "burn in" new bulbs. Turn them on and let them burn in for 100 hours, turning them off for only 1 hour per day. This helps the arc to stabilize. 2. If you see noise from the lights during EMC testing, you will have to test with the lights off. 3. If you can't handle the darkness, then you need to have a secondary light source (stumble light) that will generate enough light to get you by, such as incandescent or halogen. Keep in mind that both these light technologies require more frequent bulb changes which can be a pain. Option 1: If you can't wait for standard Metal halide lights to recycle back on, you may consider changing, at least a couple fixtures to Pulse Start or Instant On lights which come back on a lot faster, even when hot. These lights may introduce new noise problems but if you have already decided to turn them off during testing then what does it matter. Option 2: We found that the lights nearest the antenna are most likely to cause noise that we can see while testing. So we are going to re-wire our lights so we can turn off all but the two farthest from the antenna (over our turntable). That way when we test we can turn off 6 of 8. If we have trouble with these two, then we only have two lights to troubleshoot instead of 8. I have a meeting with ETS-Lindgren in a couple weeks and the lighting issue is on our agenda. If anything new comes from it I will pass it on. Good luck, The Other Brian From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Monday, September 10, 2007 8:32 AM To: [email protected] Subject: RE: Trouble with Chamber Lights Does anyone have experience with "Pulse Start" Metal Halide lights? It appears as if they took the unreliable starter electrode, bi-metal switch and resistor out of the bulb and somehow use a high voltage pulse >from the ballast to start the bulb. One major advantage is the bulbs hot re-start much faster (don't have to wait for the bulb to cool off before the light will re-start). Anyway, we are speculating the problem with EMI noise from standard metal halide lights are in the bulbs and more specifically, in the unreliable bi-metal switch which falsely fires the starter electrode causing EMI noise. Pulse Start bulbs seem to not have those parts so maybe they are better. Or maybe they have there own problems. Any information would be appreciated. The Other Brian. From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Friday, September 07, 2007 9:40 AM To: Ray, Darryl P; [email protected] Subject: RE: Trouble with Chamber Lights Here is an update on our progress. We are six days into our investigation and it appears the problem is with the bulbs themselves. We thought we were using the GE MVR400 as many has recommended (read below) but still having trouble with them. The bulbs have a bi-metal switch inside which shorts out the sparker (starter) once the bulb gets hot. We are speculating that this switch is intermittent and will sometimes start up the sparker after the bulb has heated up and this is the source of the emissions. Because this problem is so intermittent, it makes it very hard to troubleshoot. After the lights warm up it may take hours to see if the problem is still there or not. We did the process of elimination method but we think we may have more than one bulb causing the problem. So as we are changing out the bulbs and plugging the lights back in, one at a time, we have to wait several hours or more to see if we can continue to the next light. It is strange that after 11 years with no problems we all of a sudden have nothing but trouble with these lights. We noticed the bulbs we installed six months ago, though they came in a box that said "GE", the bulbs say "TUNGSRAM" on the side. We found that Tungsram is a Hungarian company that GE bought. I wonder if Tungsram is making these bulbs now for GE and there is serious quality issues that is causing our problem. The new bulbs we are installing do say "GE" on them but they look identical to the Tungsram bulbs. Does anyone have good experience with other brands of metal halide bulbs like Sylvania? I can't believe a stupid light bulb has my chamber shut down for 6 days. Thanks to everyone for your replies. They have been most helpful. I keep posting on this topic so hopefully the information will be helpful to others someday. The Other Brian. From: Ray, Darryl P [mailto:[email protected]] Sent: Wednesday, September 05, 2007 7:24 PM To: Powell, Doug; Kunde, Brian; Stone, Richard; [email protected] Subject: RE: Trouble with Chamber Lights Brian, I have been involved with many EMC labs in particular the design and construction of semi anechoic chambers. This is trickily problem as these lights are intended for warehouses not RF chambers. Metal Halide lights are very efficient but can be noisy. I have had lots of trouble with intermittent noise spikes from the Metal Halide lights. Based on what I have learned, the noise is probably coming from the lamp itself and not the ballast. I have had had pretty good luck with the GE MVR400 series (400 watt) of lamps. Make sure you match the ANSI rating of the lamp to that of the ballast. This is critical. The bulbs do lose their lighting output rather quickly, and should be replaced about every 6 to 12 months. The lighting degradation is gradual and may not be noticed if your using the chamber frequently. I have made measurements over time on a given changer and the reduction is indeed measurable. There always a chance of getting a noisy lamp so have extras on hand. Also the lights need to be on for at least 10 minutes otherwise they will be spikee. Hope this helps. Darryl Ray Darryl P. Ray Principal EMC Engineer Covidien - Respiratory Division 5823 Newton Drive Suite 110 Carlsbad, CA 92008 Voice: 760-603-5882 Fax: 760-603-5369 email: [email protected] Please note new company name (formerly Tyco Healthcare) address, phone number and email address From: [email protected] [mailto:[email protected]] On Behalf Of Powell, Doug Sent: Friday, August 31, 2007 2:54 PM To: Kunde, Brian; Stone, Richard; [email protected] Subject: RE: Trouble with Chamber Lights Brian, We have been using tungsten for several years without noise problems. However, the life of the bulbs is very short (2-3 months). To combat this we purchase traffic signal bulbs. There are several features in these bulbs for temperature extremes, rough handling, etc. From my experience with these I think they will last about 2 years. The problem is that I cannot locate a flood light version of a traffic signal bulb, so this only works for general lighting. Thanks, -doug Douglas E. Powell Senior Compliance Engineer Corporate Product Compliance Advanced Energy Industries, Inc. Fort Collins, Colorado USA 80525 From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Friday, August 31, 2007 9:17 AM To: Stone, Richard; [email protected] Subject: RE: Trouble with Chamber Lights I forgot to add that we are seeing these spikes with nothing in the chamber (No EUT being tested) We have all other power going into the chamber disconnected, so the mast, turntable, applicance, camera and test power is all disconnected. We have evern disconnected all wiring going in and out of the chamber except for the Coax that goes to the receiver. The Other Brian From: Stone, Richard [mailto:[email protected]] Sent: Friday, August 31, 2007 11:11 AM To: Kunde, Brian Subject: RE: Trouble with Chamber Lights hi Brian, i find it hard to believe its the buld itself, the fixture and/or its wiring could be recieving transient or radiated emi within the ground plane from other equipment running locally. I dont recall the freq spikes that were showing up. I use standard 100wt flood lights in my chamber, the electrical to them is not the same as the electrical wiring for the turntable motor... i would check that as well, you can filter that to. but it means taking off the heavy turntable and doign some maitnenance,but it did work for me a while back. good luck Richard, From: Kunde, Brian [mailto:[email protected]] Sent: Friday, August 31, 2007 11:00 AM To: Stone, Richard; [email protected] Subject: RE: Trouble with Chamber Lights We have confirmed that the problem goes away when the lights are off. For instance, last night we ran our receiver in Max Hold with the lights off and not a single spike (16 hours). There are two 100db line filters on the power to the lights mounded on the highhat bulkhead. In one experiment, we bypassed the line filter for two reasons; If something in the filter was causing the spikes, then the problem should have gone away. It didn't. Also, if the source of the spikes were outside the chamber or on the power line feeding the filter/lights, then the spikes should have increased in amplitude. They didn't. So we feel the problem is within the chamber, which narrows it down to the lights themselves or the wiring. Today we will continue to try and narrow the problem down to a single fixture, but as some have suggested, the problem maybe an inherent problem with the ballasts or the bulbs. So the problem may be with all the lights. Any additional information on known good ballast or bulbs would be helpful. Our electrician said that he installed GE bulbs, but could also get Phillips bulbs if we thought that would make a difference. If the problem continues to allude us, we could become desperate enough to replace all eight fixtures with new ones. Any recommendations on that front? Other than LED, is there a better choice than metal halide for chamber illumination? Thanks again for everyone's help. The other Brian (head still bleeding) From: Stone, Richard [mailto:[email protected]] Sent: Friday, August 31, 2007 9:40 AM To: Hall, Ken; Kunde, Brian Cc: Crumm, Al Subject: RE: Trouble with Chamber Lights Have you confirmed this with the power shut off to the bulbs? Perhaps its the circuit powering the bulbs instead. Also i have seen in my chamber sporadic emi spikes due to bouncing of all the unused shielded cables whos ends are sitting on the conductive turntable floor, and bouncing up and down, that was unique, but its gone once i insulated them from floor. Can anyone reccommend a feed thru filter where all the BNC, RJ45 connectors can be plugged in one side and then filtered out the other. This would be to stop ambients since the hole is 3 in diameter and 4 inches in lenght. i am gettign about 10 ambients, 6 radio, 1 aircraft and 2 local ambients. my eut and support cables only fill about 30% of the hole. thnaks richard, From: [email protected] [mailto:[email protected]] On Behalf Of Hall, Ken Sent: Friday, August 31, 2007 9:24 AM To: Kunde, Brian; EMC PSTC Cc: Crumm, Al Subject: RE: Trouble with Chamber Lights Hello, We had/have similar prolems and, I think, finally figured out it was the base to lamp connections arcing. Please le tme know it thishelps. Regards, Ken Hall From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Friday, August 31, 2007 6:06 AM To: EMC PSTC Subject: Trouble with Chamber Lights We have a Lindgren FACT10 (used to be called a FACT5) 10 meter semi-anechoic chamber built 11 years ago. Recently we have been seen sporadic spike emissions that interferes with our peak scans. We have narrowed the problem down to the chamber lights, which are 8 metal halide 400 watt lamps. We have replaced all the bulbs and the ballast but the problem is still there. We have replaced the line filters used on the light circuit; also no change. It is a real difficult problem to troubleshoot because the emissions are so sporadic. We started disconnecting the lights one by one. With fewer lights the problem seems to diminished, but it is like all the light generate this noise from time to time. Other than the startup noise from these metal halide lamps, I thought they are suppose to be very quite and not generate such EMI noise. I was hoping some of you chamber owners out there may have some insight into our problem. We are running out of ideas here. Could we have obtained bad or cheep bulbs? Is there a manufacturer of replacement bulbs that are better? Is there a newer light technology that is better than the 11 year old metal halide lamps? Any and all suggestions are welcome and appreciated. We are stratching our heads bloody trying to figure this out. Thank you all, The Other Brian LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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