Re: Rf flammable atmosphere ignition and Halfwave Dipoles
Dave Palmer wrote: Assuming that what I am actually taking about is dipole gain (I am a bit of an ignoramus I'm afraid) Can anyone give me a basic approximate formula for the variation of gain with frequency for frequencies that are up to a factor of (say) 10 away (above and below) from the resonant frequency of a half wave dipole. Is the maximum gain cyclic (e.g is there a resonance at, say, a dipole length of 1.5, 2.5 etc wavelengths or does the gain just disappear when the frequency moves away from a half wave dipole condition?). If the gain is cyclic what would be an approximate formula for the gain at, and around, these cyclic frequencies?(Note that I am not interested in polar diagram directions, merely gain) Dave, Resonance in a wire in space does indeed occur at particular and cyclic lengths; 0.5, 1, 1.5, 2 and so on wavelengths. For a wire connected at one end to ground, it occurs at multiples of a quarter wavelength. A non-resonant, _short_ dipole with 50 percent efficiency has directive gain of 1.64 dB (1.76 dB for perfect efficiency) above an isotropic antenna. In the classic _Antennas_, Kraus has its maximum effective aperture as about 0.12 square wavelengths. A half-wave dipole has 2.15 dB directive gain over isotropic and Kraus has its maximum effective aperture as 0.13 square wavelengths. This is the area from which power in the incident wave is delivered to the antenna. (You also need to account for inefficiency in the antenna when calculating the current that flows in it.) Page 13-2 of the ARRL Antenna handbook has a graph showing gain over a dipole of a wire antenna as a function of wire length (and the angle with respect to the wire at which this gain is realized). It is about 2 dB at 2.75 wavelength long, almost exactly 4 dB at 5 wavelengths long and then almost a straight lineup to about 6.5 wavelengths (about 5.2 dB). From this point to 10 wavelengths (about 7.4 dB) another line segment can be drawn that is not far from the actual plot. Johnson and Jasik have a formula (page 11-5, Antenna Engineering Handbook, Second Edition). I can try to enter it understandably from my ASCII account. E field in volts per meter = the product of: 1. The magnitude of field strength at a distance due to antinode current. (60 * current in amps at maxima)/distance from the antenna) 2. The envelope of the pattern lobes (inverse of the sine of the angle from the wire axis) (This is actually the maximum value of any lobe in the radiation pattern) and 3. Information about the angles of zeros of the pattern (this is either +1 or -1) (sin OR cos of the angle *(pi * length of the wire / wavelength) * cos of the angle) NOTE: cosine or sine depending on whether length is an odd or even number of half wavelengths, respectively. You can rearrange this to calculate the maximum current in a wire at any frequency at which it is resonant. (Kraus shows how the formula is gotten, taking the fields of all the infinitesimal dipoles comprising a dipole antenna of any length.) For a physical antenna, gain over an isotropic source is four times pi times the actual effective aperture, divided by the square of the wavelength. The maximum voltage on an antenna is determined by efficiency and radiation resistance (the antenna always re-radiates). If you can calculate the current flowing as a function of the incident field, you can calculate the voltage along the antenna. Kraus points out that because antennas are not infinitely thin, the current at minima does not actually go to zero. Therefore the impedance and voltage at those points does not go to infinity. However, for a thin wire the impedance at current minima such as the ends can be in the thousands of ohms. The radiation resistance of a dipole in free space is 72 ohms. If antenna current due to the incident field is 1 amp, this gives a power in the antenna of 72 watts. At a point on the antenna where impedance is 1000 ohms, this will give about 270 volts. I believe this is the significance of a dipole in an explosive atmosphere, as you have to protect from creating ignition sources. And at sufficiently high impedance, or high power, given small diameter or pointed structures, corona will develop even when another conducting object is not near enough to flash over. The ARRL Antenna book points out that a long-wire antenna's radiation resistance at current maxima is higher than 72 ohms. Also, you need to consider that the radiation resistance is a function not only of the resonant wire, but also of its exposure to reflected fields from ground and nearby objects. The graph on page 3-11 shows that a dipole's radiation resistance varies from zero when on a perfectly conducting ground, to almost 100 ohms at about 0.4 wavelengths above ground, down to about 58 ohms at 0.6 wavelengths above ground and oscillates around the 72 ohms value as height above ground is increase (though the excursions from 72 ohms become less and less). This has
Re: Marking Languages for Canada
Clause 1.7.2 says safety related markings should be in a language acceptable in the destination country. Since the markings are in English only, the power supply may be installed in the English speaking provinces without any problem. The Province of Quebec has language laws and regulations. A field inspector (in Quebec) can stop the installation because the English markings are not acceptable there. There are acceptable symbols that convey the same warning message. These symbols can be found in IEC 60417-1. You may advise your power supply vendor to consider using symbols in the future. Then the vendor will not have to worry about country in which the power supply is used. This should take of any language problem, be it French, Chinese or Swahili. The vendor may have to resubmit the new label artwork to UL for approval. Regards, Allen douglas_beckw...@mitel.com wrote: The key word in 1.7.12 is 'country'. At the moment, Canada is one country, with two official languages, either of which is legally acceptable. I will say though, that regradless of the law, I believe we are morally obliged to make safety instuctions as clear and understandable as possible, as a misunderstanding of an instruction could potentially cause a hazard to someone. That means, we translate important instructions/labels into French and English for Canada. Regards Doug soundsu...@aol.com@majordomo.ieee.org on 08/02/2002 11:37:56 AM Please respond to soundsu...@aol.com Sent by: owner-emc-p...@majordomo.ieee.org To: emc-p...@majordomo.ieee.org cc: Subject: Re: Marking Languages for Canada Gary McInturff wrote: I believe UL does require it, but as Rich pointed out it isn't always followed up, and II think is somewhat vague about it, intentionally I imagine. To be very specific about it one would have to know what countries the equipment will be installed in? Often the manufacturer doesn't know, or if they do initially that is subject to change. If you can't control the export then do you require warnings in Malayalam (Southern India I believe), Arabic, Japanese, Chinese, (which dialect). ad nausium. How about those countries where UL 60950 has no real standing. I think EN60950 has the same clauses and they are no more illuminating. 1.7.12 Language Instructions and equipment marking related to safety shall be in a language which is acceptable in the country in which the equipment is to be installed. This is pretty much on the mark. I was a manager at UL when this issue was put forth to the chief engineer's office. It was recognized that the standard required warning markings to be placed on the product in the appropriate language for the intended market, and the follow-up service procedures specifically included that requirement. However, it was also understood that there is no way for any UL follow-up inspector to know where the product was intended to be shipped, nor is it possible for a FUS inspector to evaluate a warning marking in Swahili, for example and determine its compliance with the standard. Therefore, the decision was to have the inspectors verify the english wording of the warning marking and place the burden of compliance with local language (other than English) on the manufacturer. Greg Galluccio www.productapprovals.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list attachment: akemevor.vcf
Re: Rf flammable atmosphere ignition and Halfwave Dipoles
Ed's answer is right on as usual. I would add a few particulars. The effective height of a tuned dipole driving a matched load is its physical length divided by pi. The source impedance of a tuned dipole is 72 Ohms. Those two facts will allow you to calculate the power available at the antenna terminals. I really don't think that for the purpose you cite that it is necessary to worry about out-of-band characteristics. It sounds as if what the spec is saying is that any fortuitous conductor can be assumed to have the power-gathering efficiency of a tuned dipole of the same length. Then if you had some maximum power level that was assumed safe in an explosive atmosphere, you could work backwards and determine the allowable field intensity, and hence the appropriate distance from an emitter of known characteristics. My interpretation of what you said may be way off, but if it is correct, I am interested because I see a problem. The problem is in how you determine the maximum allowable power allowed in the explosive atmosphere. If it is simply heating, that is relatively straightforward but I don't think it can be heating alone. I think the limiting factor will be if the field intensity were high enough to strike an arc, and the energy associated with that spark is to be compared to what will ignite the explosive atmosphere. But I don't know how you use a dipole to calculate the energy of a spark induced by an intense electric field induced between metallic objects in the field. I did this by accident (and my microwave oven was never the same afterwards). Many years ago I bought a jar of peanut butter which had a metallized freshness or security seal. I didn't realize it was metallized. I stored it in the fridge and one day popped it in the microwave for a few seconds to soften it. What I didn't realize is that when I had previously torn off the seal I hadn't gotten every bit of it and metal strips still were affixed to the rim of the jar. It was quite a show - arcing and sparking. The microwave radiation frequency is - despite what any number of participants in this forum believe - 2.45 GHz and that means a wavelength is about 12 cm or 5 inches. A quarter wavelength would then be 3 cm or 1.2. I think the arcs were drawn over shorter distances than one quarter wavelength. It was about a 1 kW microwave oven. I honestly don't know if that is power input, or magnetron output, and in any case I don't know what the effective field intensity in the oven cavity was. But I do know that is a lot less power than most radars put out. -- From: Price, Ed ed.pr...@cubic.com To: 'k3row' k3...@eurobell.co.uk, emc-p...@majordomo.ieee.org Subject: RE: Rf flammable atmosphere ignition and Halfwave Dipoles List-Post: emc-pstc@listserv.ieee.org Date: Fri, Aug 2, 2002, 6:11 PM -Original Message- From: k3row [mailto:k3...@eurobell.co.uk] Sent: Friday, August 02, 2002 2:03 PM To: emc-p...@majordomo.ieee.org Subject: Rf flammable atmosphere ignition and Halfwave Dipoles Can anyone help me? The overall context of this question is the extraction efficiency of a dipole representing a generic mechanical structure from the point of view of rf fields ( 30 MHz) and ignition of explosive and flammable atmospheres. A British standard I have been looking at assumes that the structure has the rf energy extraction efficiency of a half wave dipole (I am ignoring here the extra gain also assumed due to the potential for the structure to behave as an antenna with extra gain). The basic question is to do with the extraction efficiency of a dipole versus frequency, since, if the rf frequency is known and the structure is known then it need not be assumed that the structure will act as a half wave dipole (the frequency and structure dimensions may not be compatible) My specific questions are these: Assuming that what I am actually taking about is dipole gain (I am a bit of an ignoramus I'm afraid) Can anyone give me a basic approximate formula for the variation of gain with frequency for frequencies that are up to a factor of (say) 10 away (above and below) from the resonant frequency of a half wave dipole. Is the maximum gain cyclic (e.g is there a resonance at, say, a dipole length of 1.5, 2.5 etc wavelengths or does the gain just disappear when the frequency moves away from a half wave dipole condition?). If the gain is cyclic what would be an approximate formula for the gain at, and around, these cyclic frequencies?(Note that I am not interested in polar diagram directions, merely gain) I am not entirely sure that I have made these questions very clear - but I hope so. Has anyone got any formulae or does anyone know where I can get some? In hope Dave Palmer, UK Dave: A quick answer is that the efficiency of a dipole antenna is cyclic with frequency. Let's assume you have a center-fed dipole whose arms are each about 25 cm long. Connect a signal generator to a coax feeding the center of that
RE: Rf flammable atmosphere ignition and Halfwave Dipoles
-Original Message- From: k3row [mailto:k3...@eurobell.co.uk] Sent: Friday, August 02, 2002 2:03 PM To: emc-p...@majordomo.ieee.org Subject: Rf flammable atmosphere ignition and Halfwave Dipoles Can anyone help me? The overall context of this question is the extraction efficiency of a dipole representing a generic mechanical structure from the point of view of rf fields ( 30 MHz) and ignition of explosive and flammable atmospheres. A British standard I have been looking at assumes that the structure has the rf energy extraction efficiency of a half wave dipole (I am ignoring here the extra gain also assumed due to the potential for the structure to behave as an antenna with extra gain). The basic question is to do with the extraction efficiency of a dipole versus frequency, since, if the rf frequency is known and the structure is known then it need not be assumed that the structure will act as a half wave dipole (the frequency and structure dimensions may not be compatible) My specific questions are these: Assuming that what I am actually taking about is dipole gain (I am a bit of an ignoramus I'm afraid) Can anyone give me a basic approximate formula for the variation of gain with frequency for frequencies that are up to a factor of (say) 10 away (above and below) from the resonant frequency of a half wave dipole. Is the maximum gain cyclic (e.g is there a resonance at, say, a dipole length of 1.5, 2.5 etc wavelengths or does the gain just disappear when the frequency moves away from a half wave dipole condition?). If the gain is cyclic what would be an approximate formula for the gain at, and around, these cyclic frequencies?(Note that I am not interested in polar diagram directions, merely gain) I am not entirely sure that I have made these questions very clear - but I hope so. Has anyone got any formulae or does anyone know where I can get some? In hope Dave Palmer, UK Dave: A quick answer is that the efficiency of a dipole antenna is cyclic with frequency. Let's assume you have a center-fed dipole whose arms are each about 25 cm long. Connect a signal generator to a coax feeding the center of that dipole (let's not worry about impedance matching yet). You can now start a frequency sweep at 1 MHz, and continue through 1 GHz. If you had placed a dual directional coupler into the coax line, you would see periodic changes in the amount of RF power reflected from the antenna. Remember that reflected power is power not radiated, so reflected power is an indication of antenna efficiency (radiating ability). At certain frequencies, you would see a marked decrease in the reflected power. Minimum reflected power would be at about 300 MHz, but you would also have seen dips (indicative of resonances) at 150 MHz, 75 MHz, 37 MHz, etc. If you are concerned about extraction efficiency, you can remember that efficiency of an antenna is reciprocal. Once you get above the fundamental resonant frequency, you will also see the periodic resonances, at 2Fo, 3Fo, 4Fo, etc. For some good weekend reading, look at the ARRL Antennas Handbook, or the ARRL Radio Amateurs Handbook. The RSGB also has some fine (but slimmer) publications. Regards, Ed WB6WSN Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military Avionics EMC Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis
RE: Hazardous Area Designations/Certifications
The areas Zone 1 and 2 are defined by EN 60079-14 EEx d is type of protection flameproof, defined by EN 50014, and is suitable in Zone 1. EEx n includes type of protection nA, nC, and nR, defined by EN 50021 and are suitable for Zone 2. Take a look at http://www.fmglobal.com/research_standard_testing/product_certification/s296 .html for an explanatory poster comparing US, EN, and IEC standards in this area. Bill Lawrence Senior Engineering Specialist, Hazardous Locations FM Approvals, an FMGlobal Enterprise 1151 Bos-Prov Tpke Norwood, MA 02062 781-255-4822 william.lawre...@fmglobal.com -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Chris Maxwell Sent: Monday, July 29, 2002 10:52 AM To: EMC-PSTC Internet Forum Subject: Hazardous Area Designations/Certifications Hi all, I have been asked a question regarding the following: use in a Zone 1 and Zone 2 classified area. This equipment shall be certified EEX d and EEx n by a relevant authority (e.g. BASEEFA, CENELEC etc.) and shall be suitable for Gas Group IIB and Temperature Class T3. Can anyone elaborate on the above information? What standard defines Zone 1 or Zone 2? What standard defines EEX d and EEX n? What about Gas Group IIB and Temperature Class T3? Any clarification, elaboration, elucidation and/or explanation that the group members could provide would certainly be appreciated. Thanks, Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list attachment: winmail.dat
