Dave & John: Certainly I agree that all of a lab's LISNs should be on periodic calibration. Anything that's in you signal path, or that affects the signal being measured, should be controlled in the lab environment.
If there is a concern about how well the LISN creates the "artificial" impedance that it is supposed to present to the EUT, then there's three ways to verify that. First, you could specify the LISN be characterized with the facility powerline filter. In effect, this is a characterization of your whole facility. Not bad, but certainly cumbersome, especially for those labs that have to send everything to an outside metrology lab! Second, you could characterize the LISN using several extreme impedances placed on its input (short or open). This would satisfy me, but possibly someone might wonder if there might not be some strange interactions at intermediate impedances. So, to satisfy EVERYONE, you might be forced to use a large number of input impedances, or even asked to somehow present a swept impedance. That could be a long science project. Third, you could design an LISN such that the inherent circuit precludes any powerline impedance from affecting the EUT side impedance (to some tolerance). That way, all you would have to do is characterize the EUT side impedance once, and also verify that the circuit components are also unchanged from the original design. I guess I lean toward the third option, since it puts more of the burden on the LISN designer (who ought to be a super expert), and simplifies the workload on the test lab's staff. Ed Price [email protected] WB6WSN NARTE Certified EMC Engineer Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty > -----Original Message----- > From: Spencer, David H [mailto:[email protected]] > Sent: Tuesday, January 27, 2009 10:46 AM > To: Price, Edward; [email protected] > Subject: RE: Calibration Standards for LISN > > Ed, > > I've seen white board presentations at the IEEE Symposia, > that suggest that the AC mains impedance does impact the > final conducted emissions reading. A quick glance at Lab 34 > (or CISPR 16-4-2) show that in terms of uncertainty the LISN > impedance variations can account for as-much-as 3.6dB. > > All that being said, I didn't write the standard. I don't > see any variation in my facility when I connect or disconnect > the LISNs. > > BUT, as many lab are accredited these days and it is part of > a standard that many use, it's worth at least taking a look > at if for no other reason than quantifying the uncertainty > rather than using the generic figures (which I'm sure no one does). > > > Regards, > > Dave Spencer > EMC Engineer > Xerox Corp. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of Price, Edward > Sent: Tuesday, January 27, 2009 1:25 PM > To: [email protected] > Subject: RE: Calibration Standards for LISN > > So I would have to deduce then that ANSI C63.4 is > schizophrenic, in that it doesn't trust the specified LISNs > to work as they say they should. If the standard wants you to > measure the LISN plus your facility filter, then you are > characterizing your facility, not just the LISN. > > Logically, where does it end? Surely the impedance of the > local powerlines has a slight effect on the overall > impedance, and then what about the generators at the power > station? Of course, I'm being absurd here, but why can't they > just spec a LISN that provides sufficient isolation under all > conditions? > > > Ed Price > [email protected] WB6WSN > NARTE Certified EMC Engineer > Electromagnetic Compatibility Lab > Cubic Defense Applications > San Diego, CA USA > 858-505-2780 > Military & Avionics EMC Is Our Specialty - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
