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| EMC Pre-Compliance Visit: What to Expect and Bring? |
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| T3sl4co1l:
--- Quote from: techy101 on April 10, 2019, 03:52:28 pm ---The device delivers a constant current through a load and, for obvious reasons, we can't use a person in the chamber so we're using resistors as our loads. It monitors and displays the applied current via an ADC, but it seems to me this is not a reliable measurement method because it's dependent on the device operating properly in the first place. We currently use DMM's in line with the load resistor to verify the applied current, but I was cautioned that it's not the best idea to put a DMM in the chamber during immunity testing because we don't know how the test will affect the DMM itself. I'm at a bit of a loss then for how to verify proper device operation without the use of a DMM attached to the device. The cables used to connect to a patient are only six feet long so they won't reach out of the chamber. --- End quote --- Are your immunity results actually going to be representative? Without the ~100pF bag of mostly water at the end of those cables, you can't expect the same RF currents as in practice. Human analogs exist, which I imagine you could rent for a test; or if that's rather over-the-top, it might be okay to use a box of about the right size, with some resistors to it to model the ESR of a body. The DMM could even be shielded within, where it could be monitored with a camera if you like. :) Tim |
| joeqsmith:
--- Quote from: techy101 on April 10, 2019, 03:52:28 pm ---We currently use DMM's in line with the load resistor to verify the applied current, but I was cautioned that it's not the best idea to put a DMM in the chamber during immunity testing because we don't know how the test will affect the DMM itself. --- End quote --- Sounds like fun. They should document everything for you but it may not hurt to take a few pictures of the setup. You are right that meters can be a problem. Gossen was saying they test at 3V/m and call it an industrial. Here I am having some fun with a few of them. https://youtu.be/wYuzFtoHMqg?list=PLZSS2ajxhiQBTCU8Mq_i9jidT024A0dV6&t=829 Sometimes the equipment radiates and needs some help. Aluminum foil is my weapon of choice. Always good to carry a new roll.... :-DD Have fun. |
| coppercone2:
king james bible |
| pix3l:
--- Quote from: blueskull on April 10, 2019, 06:18:18 pm --- --- Quote from: pix3l on April 10, 2019, 02:59:53 pm ---If the device has external (USB) cables it's always useful to have some ferrite cable clamps on hand (EMC lab will likely also have some available but then you have to go with the ones they have there or retest once you've chosen a ferrite clamp). --- End quote --- As a side note for people buying gears: if it comes with a ferrite, it's not because it's awesome and the designer is being considerate. It's because they f*ed up the EMI. --- End quote --- True that :-X |
| Berni:
I can already tell you that the radiated emissions are going to be your new nightmare when i see it contains "four 5VDC->120VDC flyback converters" There are generally two things that cause a lot of radiated emissions, those are fast parallel data buses and switchmode power supplies. From the various switchmode typologies flyback tends to be particularly noisy and the high output voltage makes the already high inductor dv/dt even higher. The ESD test is mostly just a matter of putting protection diodes in the right places and the immunity test is mostly a matter of keeping your ports filtered and ground return paths near by. You can still do quite a bit of EMI precomplicance with a scope and FFT since most issues are visible under 100MHz |
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