John's concern (see attached email at the end) is on target, but there is a solution.
I have the isolation transformer wired so that line and neutral from the wall outlet connect to the primary side. The windings ratio then provides a step-up so that I get 230VAC across the secondary (this is so that I test with "European" voltage). Ground makes no connection on the primary side. On the secondary side, I tie ground to one side of the secondary winding. This terminal is then wired as "neutral" in the isolation transformer's output cord. Even though ground and neutral are tied together at the secondary, I use a three wire output cord for the secondary output. The output is wired as a "hot" (Brown), "Earth" (Green/Yel) and an "Earthy neutral" (Blue). I didn't invent this, I have seen it in some test setup literature and it is recommended in the Keytek CE Master manual. (The manual has a section on operating the unit behind an isolation transformer). It appears to work for LISNs as well. LISNs, by nature have a mains filter (reference CISPR 16 or EN 55016). In my case, the LISNs integral filter just wasn't enough. The copier in the other room was just too darn noisy. I couldn't get a clean measurement to save my life until we hooked up the isolation transformer. From John's email it appears that his solution was to use additional mains filtering (using components other than an isolation transformer) this sounds like another perfectly good solution. Measurements with our isolation transformer - LISN setup seem to be repeatable when compared to outside lab measurements. We just used this to troubleshoot and correct a failure measured at an outside lab (hi guys, you know who you are) within the past couple of weeks. This is only my experience, others may see a drawback to this method. As always, when you're messing with AC, be CAREFUL. 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 | > -----Original Message----- > From: John Woodgate [SMTP:j...@jmwa.demon.co.uk] > Sent: Thursday, November 29, 2001 12:44 PM > To: emc-p...@majordomo.ieee.org > Subject: Re: LISN Calibration > > > I read in !emc-pstc that Peters, Michael <mpet...@analogic.com> wrote > (in <61c1e83d9da9d311a871009027d617f001632...@peaexch1.analogic.com>) > about 'LISN Calibration', on Thu, 29 Nov 2001: > >If you have not already done so, I would recommend an isolation > transformer. > >Many factories and office buildings have a great deal of ambient > noise that > >will interfere with your measurements. > > That could be a bit problematic. The LISN was designed to work with > normal mains supplies, in which the neutral is earthed or earthy. You > may not get the same results with a floating supply. > > My LISN has a mains filter on the incoming supply. CISPR16-1 mentions > that this may be necessary and, by implication, allows it. > -- > Regards, John Woodgate, OOO - Own Opinions Only. > http://www.jmwa.demon.co.uk > After swimming across the Hellespont, I felt like a Hero. > ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
