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| EMC conducted emissions pre-compliance testing with home-made LISN |
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| rx8pilot:
I need to buy a spectrum analyzer now..... Not only do I want to do pre-compliance conducted emissions tests, I want to learn more about the process of the testing. My products need to pass for certification, but they also have to work in electronically delicate environments where conducted and radiated emissions will actually cause problems. I already had some real world problems with immunity where my circuit shut down when exposed to emissions from nearby walkie-talkies - <6 inches. Having a proper setup and some additional education will allow me to test my circuits and the various nearby systems that will interface with it to create an understanding of what is happening. I figured it out by experimentation, but I need to go full in to be successful. Super thankful for this thread to kick-start the effort. Thank you for the posts. |
| uski:
--- Quote from: rx8pilot on October 13, 2015, 06:08:34 pm ---I need to buy a spectrum analyzer now..... --- End quote --- A DSA815 may probably do the trick, at least for conducted emissions. For radiated, the tests I had to do (depends of your product and market) go up to 4GHz so a DSA815 is not enough. But I think it's best to move that to a separate thread and keep this thread for conducted emissions. From my understanding CISPR 25 (for automotive) actually allows a spectrum analyzer to do the conducted emissions measurements. The EMI option from Rigol is nice because it gives you the 9kHz and 120kHz EMI RBW, and an EMI filter, plus some extra features (including the PC software - but it's a bit buggy as I've described). The HMS-X from R&S might also be an option. Their HMExplorer software is actually much better for EMI than the software from Rigol. You might want to get in touch with them and get a quotation, they may have some demo units for sale. --- Quote from: rx8pilot on October 13, 2015, 06:08:34 pm ---Not only do I want to do pre-compliance conducted emissions tests, I want to learn more about the process of the testing. My products need to pass for certification, but they also have to work in electronically delicate environments where conducted and radiated emissions will actually cause problems. I already had some real world problems with immunity where my circuit shut down when exposed to emissions from nearby walkie-talkies - <6 inches. Having a proper setup and some additional education will allow me to test my circuits and the various nearby systems that will interface with it to create an understanding of what is happening. --- End quote --- The way the tests are done are specified in the various standards. What you need first is to know which standards apply to your product. Then you can read these standards and figure out the setup. If you're serious I guess you should find a partner to help you (a company specialized in EMI testing and project management). I may have some to suggest if you want. For radiated immunity, you might look into a TEM cell. I heard mixed opinions about this technique, maybe someone with more experience can discuss it (again it might be best to start another thread). It can also be used for radiated emissions but I know you need a big one to get good and repeatable results. TekBox sells one but it's really, really small. Maybe you can find a bigger used one on eBay. My personal opinion (which can be challenged) is that for serious radiated emission testing, it's best to go into a chamber. For for conducted emissions it's easy enough to do it in house. EDIT (safety note): I would like to add that for mains-powered equipment, the LISNs used may be dangerous if used improperly due to the high leakeage current they generate. They must be grounded using two separate ground connections and must be checked before each use. So people can do it in house but the equipment can be dangerous when used by untrained people. Also of course the LISNs used in this thread are for DC powered low-voltage applications only. Near field probes can be used when trying to fix a radiated emission issue, once it's been identified in a chamber, and a TEM box might help (if you're very very careful when placing the product inside the TEM box) to do comparative measurements when attempting to fix the issue. --- Quote from: rx8pilot on October 13, 2015, 06:08:34 pm ---I figured it out by experimentation, but I need to go full in to be successful. Super thankful for this thread to kick-start the effort. Thank you for the posts. --- End quote --- Yes I really enjoy sharing with the community here :) we all learn from each other and it's awesome. uski |
| EMC:
Just a couple more thoughts on the Jay_Diddy_B LISN; particularly if a PCB revision is likely. 1) Add 1.6mm PCB edge mounted SMAs at each end for less error when VNA or SA + TG are attached. 2) Introduce two SPST switches. One to switch C4 & C5 out, for ISO 7637 configuration see attached (the caps would interfere with the transients, good app note from Teseq also freely available on the Internet on this). And, one to switch in a 50 ohm resistor to the BNC, just for convenience. Also, another thought to easily test the impact of high DC currents. It would take some testing to correlate; but, place a permanent magnet with a magnetic field proportional to the DC current of interest on each inductor. The core would saturate identically as if that DC current were flowing through the inductors. (Teseq app note http://www.tech-dream.com/Seminar/EMC_Test_Seminar%28Tim2%29.pdf) |
| Jay_Diddy_B:
--- Quote from: EMC on October 26, 2015, 02:05:07 am ---Just a couple more thoughts on the Jay_Diddy_B LISN; particularly if a PCB revision is likely. 1) Add 1.6mm PCB edge mounted SMAs at each end for less error when VNA or SA + TG are attached. 2) Introduce two SPST switches. One to switch C4 & C5 out, for ISO 7637 configuration see attached (the caps would interfere with the transients, good app note from Teseq also freely available on the Internet on this). And, one to switch in a 50 ohm resistor to the BNC, just for convenience. Also, another thought to easily test the impact of high DC currents. It would take some testing to correlate; but, place a permanent magnet with a magnetic field proportional to the DC current of interest on each inductor. The core would saturate identically as if that DC current were flowing through the inductors. (Teseq app note http://www.tech-dream.com/Seminar/EMC_Test_Seminar%28Tim2%29.pdf) --- End quote --- Why would you add the SMA connectors? I cannot find any commercially available LISN with RF connectors for power connections. Smaller LISNs use 4mm banana jacks, larger LISNs use screw terminals or Superior Electric connectors. I use a Pomona Adapter 1269: When the LISN is being used it is connected to the DUT with cables that are not controlled impedance. There is no real need to terminate the unused BNC connector in 50 Ohms. The 10 dB attenuator built into my LISN provides a maximum of 20 dB return-loss. Here is the simulation used to determine Z in: And the results show that if left unterminated the impedance is 60 Ohms: Since the LISN is being used for conducted emissions, not the full range of ISO7637 transients, the CISPR 25 configuration is fine, so there is no need to switch out the capacitor in parallel with the power supply input. If I was doing immunity testing to the transients, I would want to use a much better coupling capacitor, one with a Y safety rating. The inductor selection has been 'beaten to death'. Comparison between my LISN and commercially available LISNs, costing 10x to 50x more has shown that they work fine. Regards, Jay_Diddy_B |
| EMC:
The SMAs have much less error than BNCs. If I use SMAs I get impedance and phase for this LISN meeting CISPR 16; phase is a touch high at 150kHz. Variation over more samples will surely produce a phase fail at 150kHz. But, I have never seen a LISN so well behaved; it is good to 1GHz. i.e. can be used for conducted emissions to 1GHz to give a "pre-compliance" indication of radiated performance. ... more LISNs to build more tests to do more results to produce. PS SMAs and switches don''t have to be populated by eveyrone, just a good PCB mod to do if another PCB cut was done. PPS Yes there are no RF connectors on any commercially available LISNs. And test houses hate that; they have to send them out or get special fixtures made. |
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