Rigol DSA815-TG EMC Pre-compliance questions  - Page 1
Forum section: electronics / testgear

author: myreki
author_rank: Newbie
timestamp: July 14, 2021, 01:36:16 pm
content: Hello,I have recently started to learn more about the world of EMC and trying to do some pre-compliance testing of a device I'm developing.The device consist of a housing, a small stepper motor and an oled display.We have a Rigol DSA815-TG unit at our company but unfortunately we dont have much training on how to use the unit so I'm turning to you guys for some helpThe product will be tested for emission according to standard EN 61000-6-3 which I understand follow the CISPR22.We have the S1210 EMI pre compliance software so I'm using this to control the DSA815.I have the S1210 software setup like this for emissions testing:So the limit line for Quasi-peak is loaded into the software fine and displayed on the graph.should the pre-scan be peak as i have it setup here? For the final scan, i guess i should use QP since this is what is indicated by the limit line?I'm using the Rigol near filed probe NFP-3-PI and have placed it so it is very near a small OLED display where i have seen problems.I then run the pre scan and get the following results:i can clearly see a lot of frequencies above the limit line, but the limit detector only select one frequency to be investigated further. Does this make sense?I was expecting all frequencies above the margin (white line). Is this what the margin is supposed to be used for? to give some room before passing the actual limit line?I have not made any settings to the instrument itself. efore running the test pressed the "preset" button.During test, the rigol displays Input attenuation 30 dB.btw, how close to the DUT should i hold the test probe? The Rigol test probe NFP-3-PI is supposed to be kept within 10cm of the test object. I have mine basically in contact with the PCB. just a small plastic housing in between. is this how it should be done? if i move it away a couple of cm, the noise is no longer detected.I guess its difficult to say how these results would translate into what is measured at the actual test lab at a distance of 10m?Thank you for reading this far! now lets get into conducted emissionMy product only has a input for 24VDC. The unit will be supplied together with a separate AC/DC power supply from CUI.I have a DC LISN from tekbox. Does it make any sense to connect it between the 24VDC output of the power supply and the input of the DUT or are the conducted mains measurements only relevant for the AC mains?I noticed that in the CISPR22 that the limits are:I tried doing a measurement on 24V DC but i got some alarming results....Below is an image of what was recorded during pre-scan:as you can see the emission levels are very high all the way up to about 4MHz. But I dont know if this measurement is at all relevant?For a final lab test, I guess i need to stay below both the average and QP levels?If i were to purchase a LISN for AC. would this be a good choice?https://emcsupplies.com/products/tekbox-50uh-line-impedance-stabilisation-network-lisn-cispr-16-tblc08Thank you for reading and i hope someone can give me some input!

author: Kean
author_rank: Unknown
timestamp: July 15, 2021, 12:27:58 pm
content: I don't really have the time or enough experience to answer all your questions, but happy to give a few pointers after having a bunch of designs go through compliance testing with most of them passing on the first time.- I have no experience with the S1210 software other than looking at the brochure. I use the Tekbox software to automate my tests. With that software doing a preset isn't required as it will configure the DSA for the selected test.- Running Quasi-Peak measurements is VERY SLOW, especially with a low cost SA. So you use the simpler peak detect to find frequencies of interest, and then only measure around those points with Q-Peak.- The Tekbox software has a setting for how many peaks to select for the Q-Peak scan, and you get a chance to adjust those before running that scan. If you have only one being selected by the S1210 software following the first scan then maybe there are some other settings described in the manual around that.- Measurements with a near field probe are not really something you can compare against the limit lines. The measurements are in no way calibrated. The near field probes are typically used for finding where on the PCB a problem emission is originating, and then doing comparison measurements before and after making various changes to get an idea of how much improvement you might get on a real test.- Typically you would run a pre-compliance scan of your design at a lab, then if needed use this gear to try correct any issues. This is especially helpful when less experienced. You could easily waste days of your time and not have any idea if what you are looking at is an actual issue.- Using some pre-compliance gear with "typical" calibration data like the Tekbox TBTC2 TEM cell or TBLC08 LISN will give more meaningful data to compare against limit lines, but having a scan from a lab to compare against is really helpful to see you have the gear and DUT set up properly. I own and use both of these devices, as well as the Tekbox DC LISN, and the only one I'm semi confident in is the TBLC08. Of course you need to correctly set up the tests, and even with the Tekbox software automating parts of the process there are a lot of mistakes that are easy to make.- The correct use of a DC LISN is a bit more complex than an AC LISN, so make sure you review the Tekbox app notes. They're also generally quite helpful if you have specific question about their gear or software. There are some good posts on this forum about using and building DC LISNs.- If you are supplying your final equipment with a CUI power supply, then I would recommend that you run tests with that on an AC LISN. That is what the compliance lab will very likely want to do, and how you should write your user manuals. Any customer who uses a different power source could see completely different emissions and the manual should probably warn about this. For reference one of my earlier products failed initial conducted emissions tests with a cheaper supply, but it passed as soon as we retested with a CUI PSU that I had originally recommended. Of course it then went on to fail radiated emissions, but only in one particular operating mode.- You want as much margin as possible below limit lines, I aim for greater than 6dB. But it is only indicative, and a lab scan using calibrated equipment and chamber may show completely different results to what you measured. It can depend on things like the DUT orientation, cable loops and routing, and other factors like ground planes placed correctly per the standards.- Take a look at the free blog posts and paid courses from places likehttps://emcfastpass.com/- Maybe you can attend a free EMC course from a local company like Wurth. I've attended a few, and they include some useful info along with the usual marketing. Also a good networking opportunity with local EEs.- Finally, keep in mind that emissions testing is just the start...HTHKean