Dear experts, I've been looking at the differences between EN 55020:2007 and EN 61000-4-6:2009 with respect to conducted RF immunity and I was hoping I could get your professional opinion as I'm a bit confused. Apologies in advance for the long winded email.
1) EN 61000-4-6 works on the principle of having one injection point (e.g. CDN, EM clamp) and one termination point for the common mode currents. As I understand it, every port that has a cable and AE connected must be decoupled either by a CDN or a separate decoupling device (like an EM clamp?) to provide a high impedance path to the common mode current. EN 55020 clause 5.7 "Measurement of immunity to induced voltages" doesn't specify this "single current loop and everything else decoupled" approach in it's testing because injection onto the audio lines is differential mode onto the signal conductor itself and not common mode onto the ground. My first problem comes when considering injection of the unwanted signal onto the mains using the Mains Stop Filter (MSF). In this case the signal is injected common mode but the return path common mode impedance from the EUT to the generator is not defined (unlike the 150-ohms via a CDN in 61000-4-6). Our TVs used for monitoring often have a grounded mains connection and our antenna input from our streams network has the outside of the co-axial cable grounded. By having these connections to grounded inputs / monitoring equipment, the CM impedance to common mode signals on the mains earth is very low. In my opinion, these lines either need to pass through a CDN or other decoupling network of some kind with the same impedance requirements as set down in EN55020 Annex C.1 b) (RF chokes shall provide a sufficiently high RF impedance with respect to 150-ohms) over the whole frequency range) or even better in EN61000-4-6 clause 6.2.4 In our case most of our products are Class II (no mains earth terminal) so the impedance via the antenna input / monitoring equipment does not directly affect the mains earth. But the chassis still remains connected to earth as mentioned above which could affect the results. Should the antenna and the feed to the monitoring equipment be decoupled from CM currents? EN 55020 does not seem to have much detail regarding this - what are your thoughts on the matter? 2) The same question regarding the antenna feed for EN55020 testing also applies to EN 61000-4-6 testing in that since it has a grounded coax outer it should have it's own CDN or decoupling network. Note: monitoring equipment in this case has it's own CDN so isn't a worry. Would you agree? 3) The coupling unit type MC (mains leads) (EN 55020 figure C.2) is subject to the note in Annex C.1 which states that the impedance of the CM choke in the coupling unit does not effectivley meet the exact requirements of the standard in the range 0.15MHz to 1.5MHz. I don't believe that the MSF in EN55020 Figure D.3 does either. I think a coupling unit that meets the specification of EN 61000-4-6 Figure D.2 (and by extension EN61000-4-6 clause 6.2.4) should be adeqaute to use in place of the MSF / coupling unit type MC in EN55020 testing for injecting onto and decoupling the mains input. Would you agree? Thanks in advance James James Pawson Leading Hardware Engineer EchoStar Europe - 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]>
