I think this is a lot like the fable about belling the cat (where the mice decide it would be nice if the cat wore a bell, so it could not sneak up on them). All the mice agreed it was a great plan, until one old spoil-sport asked who was going to bell the cat. What I'm saying is that while this is a good idea in principal, the devil is in the details. Consider the easiest portion of the task, controlling cable radiation. This is easily done up to 1 GHz with a current probe. I believe there may be some current probe models now with ranges above 1 GHz. Regardless, at frequencies where the cable-under-test is electrically long, the current probe must be slid up and down the entire length of the cable to find a current maximum at each frequency. In order to have a meaningful limit, you would have to determine a reasonable worst case cable radiation efficiency as a function of frequency.
Emissions from enclosures follow the same physics but the application is much more difficult. Having measured and maximized surface currents, how do you then apply a reasonable worst case model to estimate the resultant electromagnetic field. This will strongly be a function of EUT enclosure geometry. Unlike cable lays, there is no simple model for how surface currents would launch an electromagnetic wave. I join contributor [email protected] in wishing you good luck! > -----Original Message----- > From: Lou Gnecco [SMTP:[email protected]] > Sent: Thursday, June 17, 1999 7:24 AM > To: [email protected] > Subject: Re: NEAR/ FAR FIELD CORRELATION ISSUES > > > Arun: > I heartily agree with everything you said. Well done! > > It will not be easy to sell this idea to the emc world. > When the standards are vague, acane and constantly-changing, and when > it is > unnecessarily expensive to set up and perform a test, this constitutes > what > is known in business as a "Barrier To Entry" that is, a way to > artificially > limit competition. Test laboratories (like us, for example) can charge > more > money when there are barriers to entry. > People who make special instruments and antennas for EMC > testing > (like us) would lose out if there were fewer barriers to entry. Also > people > who install & test shielded rooms, etc. There are substantial > entrenched > interests whose rice bowls would be threatened if emc became something > anyone could do. > > I personally believe that the process can and should be > simplified. > It would help the manufacturers, who are the ones that really drive > the > economy. > It would specially help small manufacturers. > > Like us. > > Lou > > > At 11:18 AM 6/17/99 +1000, you wrote: > > > > > >Greetings and Salutations! I was wondering if this could be mailed > out via > >the epc-pstc channels. > > > >I want to know if anyone is doing any work in "near/ far field > correlation > >to commercial EMC standard limits" area and possibly correspond with > them > >with a view to exchanging notes. > > > >Brief Follows: > > > >Brief: > > > >"Application of Near Field and possibly Surface probe techniques in > >Evaluating Emissions from source equipment and > correlating/quantifying this > >data to an OATS, LISN, Absorbing Clamp etc based measurement.." > > > >Details: > > > >We assume that the current EMC compliance regime around the world has > >quantified limits of compliance to which if every source equipment > adheres > >to, then it has a reasonable chance of performing as intended in a > real life > >situation, noting that the immunity threshold test levels are much > more > >stringent than EM emission limits. > > > >Current EMC measurements are very cumbersome, require large expense > in > >setting up and maintaining (calibrating) OATS, LISNS, Absorbing > Clamps, > >Ferrite tiled lined semi- anechoics etc. Despite this expense, the > >measurement uncertainities are still of the order of 6 to 10dB > (inherent). > > > >Every newly released EMC standard by IEC CISPR or CENELEC has > potentially > >new transducers and new headaches from point of view of sourcing and > >maintenance, calibration. EMC today is where Safety was 10 years > ago. I am > >of the opinion that EMC testing should be simplified and reasonably > >accessible to all end users. > > > >Continued progress and urban development has led to increasing levels > of > >broad and narrowband noise to the extent that ambient profiles > sometimes > >swamp out the limits; this has led to most test houses in the EU to > opt for > >GTEMS or semi-anechoics (referred to as "alternative all weather test > >sites") at considerable expense. > > > >Current techniques such as emission E Field prescanning in shielded > rooms > >prior to OATS based testing with biconilog antennae have the > drawbacks of > >"peaking" the emissions and reflections/standing waves. > > > >Hence: > > > >I propose to develop near or surface probe H (inverse of E) field > >techniques which actually senses the emission profiles and correlate > them to > >an Absorber clamp, or OATS or LISN (Common mode fix) or whatever. > Cables, > >panels, slots etc could be "sniffed" with a Loop and if it is > possible to > >correlate this near or induction field data to compliance limits then > it > >becomes very easy for individuals and organisations to do > precertification. > >Transducers could be simple and light weight, rugged, and physically > defined > >so that minimal calibration is required. EMI receivers will still > need > >calibration. > > > >With these techniques, you measure actually what comes off the source > and > >not the "peak" value of the bounced and direct rays within say the > Fresnel > >ellipse, or move the Absorbing clamp up and down the rail and peak > the > >field. > > > >Conducted emissions could be scanned by common mode techniques and > radiated > >emissions by surface or near scans. > > > >Currently, these techniques are used only qualitatively for > precompliance at > >board levels and more work needs to be done to bring them of age and > >reliability. (Am I right?) > > > >What I am proposing has a corollary with the bulk current or damped > sinusoid > >(NEMP- Nuclear EM Pulsing) or lightning injection techniques (CS 114, > 115 > >and 116 of 462D). With these methods, it was possible to achieve > identical > >or several orders of magnitudes higher levels of RF injection power > at a > >fraction of the cost of say an RS03 OR RS05(at least for the bulk > cable > >loom!). What resulted was a cheap, powerful and a more repeatable > test. > > > > > > > >Arun Kaore > >EMC Engineer > > > >ADI Limited > >Systems Group > >Test & Evaluation Centre > >Forrester Road, St Marys, NSW 2760 > >P O Box: 315, St Marys NSW 1790 > > > >Tel: 61 2 9673 8375 > >Fax: 61 2 9673 8321 > >Email: [email protected] > > > > > >--------- > >This message is coming from the emc-pstc discussion list. > >To cancel your subscription, send mail to [email protected] > >with the single line: "unsubscribe emc-pstc" (without the > >quotes). For help, send mail to [email protected], > >[email protected], [email protected], or > >[email protected] (the list administrators). > > > > > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
