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| Supporting hardware for EMC test setup |
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| dkonigs:
So I'm currently working on a product that will obviously have to go through EMC testing at some point. This product can be powered and/or controlled over a USB cable, and basically has two modes of operation: * As a standalone device powered via an off-the-shelf USB power adapter * As a peripheral device plugged into a USB host (e.g. computer), for both power and communications The test lab I've been talking to wants to do the testing on the complete system, rather than just the device that I've built. I obviously want to make sure I don't fail testing due to equipment that's not part of my device. As such, I'm going to need to select: * A USB cable for connecting the device to the power/data source * The USB power adapter for running the device in configuration 1 * A laptop computer (/w at least two other peripherals, like headphones, a hub, or a thumb drive) to run the device in configuration 2 Any recommendations for choosing these items? While I could easily just scrounge up any of these things, I really don't want to fail testing because one of these "external" devices is misbehaving in the lab. So I want whatever power adapter and laptop I can be certain won't have unexpected emissions, and ideally has emissions low enough that any testing issues are solely the fault of the hardware I'm actually intending to test. P.S. I don't plan to actually ship any of these items, except maybe the cable, with the device itself. |
| Tomorokoshi:
1. You may want to decide early about whether you ship with a cable or not. If you decide on one, you would want to test with it and stay with that. Changing it may require some basic engineering evaluation. If you don't ship, you save the cost and can test with whatever is around, with the potential that a customer may be more likely to encounter a problem. 2. Power supplies are tricky. I've evaluated products with a number of industrial 24V DIN Rail supplies. The testing results they publish are not ever in the same conditions as the actual product, so results with the complete system in the lab can be all over. For instance, it passed with the $100 supply but not the $30 supply. 3. USB supplies are... suspect. Test a few from reputable manufacturers. Ideally something with datasheets that list standards it was tested to. If the USB power supply is not ever shipped, consider rigging up a battery pack to run it directly. Perhaps 4 AA cells in a holder with at most a linear regulator. 4. For radiated emissions, the host computer can be set somewhat to the side. It may be possible to use a longer version of the USB cable to get it more out of view of the antenna. If failures are noted, you may need to test with either the device or the computer off to isolate if peaks are coming from the computer. For backup, bring a computer of a very different model. |
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