Rough testing for emissions CE, FCC, etc.. - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: January 16, 2015, 08:46:56 pm
content: We are about 6 months from releasing a new product. It has high current switching and multiple DC/DC converters. This product will likely need to have emissions testing done for the various authorities. This is required by those who distribute the devices.This is all new to me. I have no understanding of what the guidelines are or where to even find the guidelines. I have spoken to other engineers that tell me horror stories of getting the emissions to a passable level, requiring a lot of very expensive lab time and re-work. What I am hoping to do, is try to setup a modest test system that will help me get into the ballpark at least before we show up at the testing lab.Does anyone with experience in this area know if this is possible to do for a few $k or is this a bigger setup? Keep in mind, I am only hoping and expecting to build something to get me close so that I can minimize obvious issues ahead of time. Considering that each pass through a lab and the subsequent re-work will cost thousands of dollars - I am willing to put some effort into this.The learning curve of understanding the measurements is also a concern. Not sure how difficult this idea is even if I have all the right equipment.

author: Mr Simpleton
author_rank: Unknown
timestamp: January 16, 2015, 09:12:05 pm
content: I guess what you can do is to have a spectrum analyzer and a proper wide band antenna, looking at signals coming from your unit.This will allow you to see if there is some substancial signals coming and allow for design modification.Once you have done what you think is enough, record the spectrum, and send the unit off for a complicane testing.Hopefully it will pass, and you do get a graph that you can compare with your own measurements... good to see how they match in the future. It it failsYou still can see with your set up what to do and reduce the emission by the requested amount.

author: jadew
author_rank: Frequent Contributor
timestamp: January 16, 2015, 09:29:26 pm
content: http://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry-Ott/dp/0470189304This might give you a bit of an insight into the issue. It has a chapter at the beginning quickly going over the FCC regulations and the testing procedures (maybe you manage to browse the first pages online).I think you will at least need a SA that can go up to 40 GHz, so that's a few kilo dollars from the start

author: Skimask
author_rank: Super Contributor
timestamp: January 16, 2015, 09:32:54 pm
content: Does anybody use the SEARCH function any more???

author: rx8pilot
author_rank: Super Contributor
timestamp: January 16, 2015, 09:50:29 pm
content: That video is helpful and relevant, but it does not cover radiated emissions. Radiated seems much more mysterious and challenging to detect.Will continue to search, search, search. "pre-compliance" seems to be a good keyword......

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 16, 2015, 09:55:39 pm
content: Quote from: rx8pilot on January 16, 2015, 09:50:29 pmTrue, you cannot do more at a normal EE lab. Also search for "Golden standard".

author: Howardlong
author_rank: Super Contributor
timestamp: January 16, 2015, 10:00:42 pm
content: Set aside a week just for the form filling and document preparation.

author: KJDS
author_rank: Super Contributor
timestamp: January 16, 2015, 10:23:09 pm
content: Set aside a day to make a list of everything, and I mean everything that you need to take with you. If you have spares of things that can possibly go wrong, take those as well.There's no need for a 40GHz analyzer, anything that covers up to 3GHz will do and they are readily available second hand. Make up a little loop of two turns of thick wire with about half an inch turn diameter and connect that to the end of a coax. Wave it round the equipment and see what leaks out.If equipment hasn't been designed to perform well with EMC then it's usually a lot of effort to make it good, possibly worthwhile hiring a contractor if there's one locally to help out. He may cost a few thousand, but if it saves weeks of struggling it's money well spent.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 16, 2015, 10:38:15 pm
content: Quote from: KJDS on January 16, 2015, 10:23:09 pmThat can be of help sometimes. A product needs anyway EMC compliance, radiated, conducted and immunity. It must be designed for that from the start of the design cycle. If that is not the case and after testing it appears that the product/prototype by it self is hopeless, a contractor can only advise you to start over doing it the right way.

author: jadew
author_rank: Frequent Contributor
timestamp: January 16, 2015, 10:49:43 pm
content: https://books.google.com/books?id=2-4WJKxzzigC&lpg=PP27&ots=ZSszRCzXFh&pg=PP26&redir_esc=y#v=onepage&q&f=false@KJDS, why will 3 GHz be enough? I'm asking because that book states that the FCC regulates the radiated emission in the 30 MHz to 40 GHz range. Is it because you don't expect content in that frequency range from DC/DC converters or is there some other reason?

author: rx8pilot
author_rank: Super Contributor
timestamp: January 16, 2015, 11:04:12 pm
content: Our designs have had emissions in mind from the beginning as radiated, conducted, and immunity. The pit in my stomach is that my experience is limited so I am going off of book knowledge and observations of other devices. It could be anything from excellent to complete crap.I am hoping that 40Ghz is overkill. Just hoping that my device cannot possibly generate such frequencies. I have used lots of ferrites on power io. Hopefully solid enough ground planes on the PCB's. Lots of finger crossing in the end - expecting a steep learning curve.Quote from: KJDS on January 16, 2015, 10:23:09 pmThis sounds like an easy experiment to try. The challenge will be to have even a rough reference to get an idea of the upper limits.

author: KJDS
author_rank: Super Contributor
timestamp: January 16, 2015, 11:18:00 pm
content: Quote from: jadew on January 16, 2015, 10:49:43 pmIf a switcher is switching at a few hundred kHz, then I might possibly see the 1000th harmonic. The 10,000th harmonic, at around 3GHz for a 300kHz switcher is unlikely to have much energy. If it does, then the level of the 1000th harmonic will be very very high, making it obvious just on a 300MHz spec ana. I therefore conclude that unless you have a high frequency generator measuring above 3GHz is likely to be pointless.Processor and data clocks are another source of crap, especially if you have high speed data going from board to board. Even then, a 100MHz data stream will show up plenty of Harmonics below 3GHz to let you know a problem exists.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 16, 2015, 11:32:03 pm
content: For validating your product you will need anyway an accredited test house. The best way is to contact them and let them evaluate your product if it is near finished. Or if you are half way, to advise you how to progress. Test houses are also the best source for advice to find your way in the jungle of compliance testing. What books to read, what is needed and what is not and finally how to do it right. Use their expertise to learn, most are up to that too. It's not free and not cheap but worth every penny if it is a renowned test house. A good resource:http://www.compliance-club.com/and further the books of Keith Armstrong.

author: jadew
author_rank: Frequent Contributor
timestamp: January 16, 2015, 11:55:45 pm
content: @KJDSMakes sense, thanks

author: rx8pilot
author_rank: Super Contributor
timestamp: January 17, 2015, 12:13:27 am
content: My biggest fear is doing multiple passes through the tests which will be deadly. I still have some time and expecting at least one more spin on PCB's anyway. It is a good time to ID any glaring problems and fix them. Hopefully I could learn a few things about the process including how much time it may take for the various stages if I contact the lab early.The labs undoubtedly sees a huge range of scenarios and can probably help to avoid the most common mis-steps. Hopefully they do not laugh too much ;-)The paper work sounds very intimidating, but the bigger worry is identifying the most likely offenders and hush those areas as much as possible. Is it practical to do rough testing at the lab where they do a more general examination of a product that is still open to changes and expecting some issues. Essentially a truncated first pass at a lower cost and less paperwork for the purposes of guiding final design changes. It would be more $$ than buying gear and doing it in-house, but I would get better data and guidance for the money. The question is whether or not typical labs do that sort of pre-testing.Getting an SA and an antenna seems simple, but I would not know how to figure out the limits. I guess I could read some books and/or hire the lab. Hmmmm.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 17, 2015, 12:14:03 am
content: Quote from: jadew on January 16, 2015, 11:55:45 pm+1

author: rx8pilot
author_rank: Super Contributor
timestamp: January 17, 2015, 04:39:56 am
content: I am pretty sure that last post is equivalent to a parent stopping their child from pulling a boiling pot of water off the stove.Thank you for the wisdom.

author: nctnico
author_rank: Super Contributor
timestamp: January 17, 2015, 04:54:39 pm
content: Quote from: rx8pilot on January 16, 2015, 09:50:29 pmNot really. The biggest problem with radiated emissions is that making a circuit pass can require massive redesigns if the circuit has not been designed with passing a radiated emissions test in mind. The basic rule is to keep high current loops small, put series resistors in the gates of switching fets, use ferrite beads and common mode chokes on incoming and outgoing wires. If you have a 4 layer PCB the chance of the PCB causing too much radation is extremely small.The usual route is:- have a pre-scan performed to know at which frequencies the device is likely to fail- use a spectrum analyser and probe (easy to DIY) to find which component causes the radiation- modify the circuit- do the final testActually a compliance test consists of much more tests like susceptibility for surge, radiation and ESD.Regarding the test requirements it is best to consult with the test house doing the testing. They know which requirements apply to your product. There is no sense to try and figure that out by yourself. Sometimes the test engineers of the test house have different opinions on how to perform a certain test. The rules and regulations are very complicated. With compliance testing you have to remember that what counts is the end result: a piece of paper which says your product is compliant.

author: AndyC_772
author_rank: Super Contributor
timestamp: January 17, 2015, 05:46:58 pm
content: There's a lot of good advice here.I think you have two major problems, though:- your product has already been designed, but not by someone who has a good deal of first hand experience in designing products to pass radiated emissions testing, and- you don't have experience of the test process either.Both problems need addressing before you have a realistic chance of getting your product certified as compliant. Without some outside help, you're likely to spend a lot of time and effort discovering that you probably do have a radiated emissions problem, and then a lot more time and effort failing to fix it properly. It's not something you can usefully work on in an ordinary lab environment; even if you have access to a spectrum analyser, without a controlled environment in which to use it, you'll never know what to make of what it shows you.See if you can get a recommendation for a lab, and book them for a half day pre-compliance session. They'll test your product 'as-is', and give you a good idea of what needs fixing for production. This is the information which will guide everything else you do between today and the time of the final test.If you don't have an engineer on site who has first hand experience of designing for EMC, it may well be worthwhile hiring someone who does to look at your design. Radio emissions can be a bit like trying to fit a balloon into a small box with holes in it; every time you block up one hole, the balloon just sticks out of the other holes all the more. The only way to contain it fully is to block upallthe holes, or reduce the size of the balloon.What this means, is that you need to ensure that all the sources of noise within your product are adequately addressed, and that every possible route for noise to get out is filtered somehow. A session in the lab is a very good way to highlight which cable you forgot to filter, or which part of the circuit you didn't do such a great job of laying out.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 17, 2015, 06:17:19 pm
content: Quote from: rx8pilot on January 17, 2015, 12:13:27 amThey do not laugh, they are there to get you through the validating process and to get you on the right track too. You are switching high currents and have a lot of DC/DC converters you told. The PCB design alone for that is an art by itself to keep sources of radiation small.Test houses also can do a "Quick scan" (or pre scan). A quick scan is just a course examination to see how your product does concerning EMC. Takes usually half a day and will cost you around $500. That quick scan shows you how far you are off from the regulatory boundaries and where in the frequency domain. If it is just a 3 dB off, it is easily fixed usually, but if it is 12 dB or more above the limits, you will have a bigger problem. If you are lucky you are within regulatory boundaries but that is almost never the case with SMPS stuff in a first round up.I spoke earlier about a "Golden standard". The prototype tested in a quick scan becomes your "Golden standard". That one was examined in a calibrated environment and with calibrated test receivers, antennas and so on. Now you can use that golden standard as a reference for further engineering to solve EMC issues. At your own lab all things are different from the test house. So thanks to your golden standard, you now know the frequencies and how much you have to improve to comply with the regulations. The trick is to leave your golden standard untouched further on (and forever) and use that as a reference for comparison.Validating for compliance requires a calibrated test set up. This is huge expensive and involves a lot of specialized knowledge. Not many companies can afford that themselves. But thanks to your golden standard you don't need that yourself. A good SA up to 3 GHz, some low cost home brew E and H sniffers and a home brew LISN suffice to get the engineering done: Simply compare your progress to your golden standard in your own lab. Hameg has an affordable SA suite suitable for this, as well as affordable readymade E and H sniffers.http://www.hameg.com/611.0.html?&no_cache=1&L=osmlugndjcfI myself do use a 10 years old forerunner of this.If you are confident with the progress and think you tackled the frequencies that where off by comparison with your golden standard, it is time for a next quick scan at the test house to see if there are still some loose ends. If that is ok then you are up for a real extensive compliance test.

author: coppice
author_rank: Super Contributor
timestamp: January 17, 2015, 06:30:11 pm
content: Finding RF emission and susceptibility test labs is usually a pain. Even in cities with big electronics industries there are seldom many around. They are expensive to use, and its really expensive to equip a compliant one of your own. Preparing for ESD testing is much simpler. $20k will get you the kit you need. It doesn't require a huge amount of space, although health and safety will have you using it in a protected area, where only trained personnel can use it. A similar amount will get you the kit for surge testing and transient testing, and it can be used in the same area as the ESD test equipment.Doing rough RF emission testing, to pre-screen your design for serious flaws, is not too hard. A spectrum analyser and wideband antennae will get you started. The specs you need to pass are easy to obtain, although it can take some time to work through and understand them. The RF susceptibility tests are a bigger problem. You need a large screened anechoic room, which is very expensive. Screening alone isn't too costly, but without expensive anechoic treatment the reflections inside the room will make your tests meaningless. You need to blast a lot of RF energy at the device under test, swept across a wide frequency range. You can't just go blasting that out without screening, unless you are far from the madding crowd. It will disrupt people's legitimate comms activities.When using an external lab you need to make sure you learn from every test failure. One of the biggest problems is failing a test, and then just scratching your head because you have no ideawhythe test failed. You usually have to hand over your equipment to a test house for formal testing. Don't do this for any other tests. You need to work with the test house to pinpoint the cause of the failures which will probably occur on your first pass of testing.EMI/EMC and ESD (testing for both damage and operational stability) compliance causes some of the biggest headaches in product development today, but the number of engineers who are good at this kind of work is very limited. There are some excellent analysis tools you can feed your board level designs into, which will predict the results from the board itself to pretty good accuracy - provided you give the software sufficiently complete information about your design, and all the components in it. Its surprising how few people use these, although the price tag is clearly part of the reason.

author: nctnico
author_rank: Super Contributor
timestamp: January 17, 2015, 08:40:03 pm
content: Finding a good test house can be problematic. In my experience the best test houses are the ones which at least allow you to be there when the device is being tested. The test house I prefer to use actually demands an engineer who worked on the design to be present during the test to make fixes if necessary. They also have a large selection of components available to make last minute modifications. In their opinion they don't serve their customers well with just sending a device back together with a letter saying 'failed'.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 17, 2015, 08:55:43 pm
content: Quote from: nctnico on January 17, 2015, 08:40:03 pmIt's right test houses can differ in quality and approach, but never came to one with plain yes/no results. They all give you detailed measurement results.

author: nctnico
author_rank: Super Contributor
timestamp: January 17, 2015, 09:01:19 pm
content: Quote from: Pjotr on January 17, 2015, 08:55:43 pmYes and no. I have dealt with test houses which made it very hard to reach the test engineer who performed the test and get a meaningfull answer regarding what failed precisely and what to do about it.

author: georges80
author_rank: Frequent Contributor
timestamp: January 18, 2015, 12:45:04 am
content: The test house I used last year had you sit through the entire test with the test engineer. You got to help set up your equipment in the test room and got to see everything that went on (camera pointing into the room while the test is running). Took 5+ hours for the entire test cycle (EMI/EMC for FCC B).This was a digital board, ddr2/ddr3/flash/ethernet/usb/4 hdmi channels at full HD, SOC running at 1GHz as the CPU and 6 DC:DC switchers on the board. Fortunately I had access to an RF 'wizard' that provided many tricks of the trade for the PCB layout, including termination of high speed clock/data signals (and their via ground paths), via fencing on the outside of the PCB edge, connector stubs (various length traces versus equal lengths - within skew limits to ensure all the HDMI signal transitions were time spread versus all in sync) etc etc.I had access to my own SA and a LISN for ensuring our conducted EMC appeared 'clean' and also a scanning bed (emscan ->http://www.emscan.com/) to look for 'hotspot/radiators' on the PCB.Between the above we passed the FCC B tests without any reworks/redesign of the PCB. Our first attempt failed (very early into the test) when we found our (cheap) wallwart powersupply was an EMI horror. Went back with a better wallwart that I pre-tested with my LISN and we passed everything.So, make sure you have good quality cables for everything feeding into/out of your unit. Make sure all external devices (we had 4 LCD monitors, 4 keyboards, 4 mice, power input and ethernet all connected) and cables are 'good quality'. We had to put all the peripheral equipment in a shielded box that rotated with the test platform that had our unit to be certified on.During many of the emission tests, the platform rotates and the antennas that are 'scanning' go up/down and also rotate. Quite involved and all takes time and has you on the edge of the seat worrying.The test engineer (at a decent lab) will work with you to help resolve/identify issues. The lab we went to even had a large assortment of ferrites, copper tape and tools etc in case you need to 'tweak'. They also only hired EE's as test engineers so as to be able to provide assistance.I was pleased to see that the pre-testing I did showed many of the same EMI/EMC peaks and characteristics to the actual lab tests/results. That means my methodology and tools were indeed useful to minimise the risk of failure in the lab.Good luck with your projectcheers,george.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 21, 2015, 01:49:27 am
content: Quote from: AndyC_772 on January 17, 2015, 05:46:58 pmTrue. True. True.I have dealt with some of the usual suspects. Multi-turn ferrites on all I/O, slew rate control on all the routing FETs and SMPS. The SMPS designs have snubbers to minimize ringing, the PCB's are 4 layer with big unbroken GND planes, High current traces are big and very short, i2c bus is slew rate limited and only 100Khz. This is all in a machined metal case, but with openings for LED's, switches, connectors. So, I have at least put the basics in place, although it is still likely too elementary for a final test. Hoping that the initial efforts allow for tweaking as opposed to total do-over.Quote from: georges80 on January 18, 2015, 12:45:04 amThis is what I was hoping for. A hands-on and visible test. I am very curious how much I would need to bring to the test. This product is powered by any variety of power sources from batteries to horrible quality SMPS. It would be to my advantage to power from batteries, but do I need to provide a "worst case" supply? The outputs are the same, if I power a resistor bank it will be an easier test than having to power a dynamic load full of FPGA's.Rough in-house testing still seems like a reasonable path. Especially true since most of the gear needed is part of my purchasing plan anyway.Pre-Scan tests with the lab sound really great to generate the "Golden Reference" to compare with. The hard data and the conversations with the technicians and EE in the lab would easily cover that expense.Next up, start the lab search. I will have the next REV of the PCB's (7 of them for this project) in a few weeks. It would be fantastic to do a first pre-pass in a month.Also, looking for an experienced and qualified EE in this field to 'have a look'. This is not as easy as it sounds. I have known a lot of EE's some good and some terrible and some are amazing. They all SAY they are amazing though.

author: AndyC_772
author_rank: Super Contributor
timestamp: January 21, 2015, 07:45:19 am
content: Quote from: rx8pilot on January 21, 2015, 01:49:27 amSounds to me like you've done a pretty good job. You've certainly put a lot more thought into design for EMC than some boards I've been asked to fix.QuoteIf your power supply is sold on its own, then it's perfectly valid to test it using batteries and resistors. If it's sold with accessories - or if you recommend (but don't supply) some - then you should test with them.In approvals terms, you're responsible for noise generated by your own equipment, but not anyone else's. There's an important caveat to consider, though...I've bought many power supplies which claim compliance, and maybe they are on their own. However, when I come to test MY product, powered by a "compliant" power supply, I discover that the power supply is so noisy there's little or no margin left for my product. The combination of the two units together goes over the limit.At this point, I have a choice. Either redesign my own product, incorporating "heroic" filtering to ensure it emits virtually no noise at all, or buy someone else's power supply. Commercially, the latter option is almost always more attractive.It's a discussion I've had with many power supply manufacturers. There's a difference between a PSU being legally compliant, and being quiet enough to be commercially acceptable. If I am to buy it for resale with my product, a PSU alone needs to pass EMC *with margin*, under *all* load conditions, which of course is a more stringent requirement than it's required to meet in order to qualify for a CE mark.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 21, 2015, 12:41:48 pm
content: Regarding power supplies: You are responsible for the product as a whole, "As sold"ANDused as intended/advertised. In many cases a qualified of the shelf one is the most effective option. But even then, it needs still to be tested in combination with your product. It is in fact an integral part of product and you may not rely on the specifications of the manufacturer alone.A LISN can be build yourself at low cost, sure. Been there done that. I would not recommend it due to isolation issues and uncertainties it brings up, it needs to be calibrated anyway. A commercial one costs around 1K$ and is in most cases a lot more cost effective.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 21, 2015, 05:52:24 pm
content: Quote from: joeqsmith on January 21, 2015, 05:24:37 amAwesome! That is kinds of what I imagined when I started this thread on "Rough Testing". The idea being to ID the the most likely offenses before embarking on the long and expensive final testing. Combining this sort arrangement with a Pre-Test at an accredited lab could provide some actionable data and allow me to tweak the design on my own without multiple test passes. I understand that it does not guarantee a passing grade, but looks like it will offer a fighting chance.Thank you for the pics of this setup! My entire project will easily fit in a similar cookie can.Quote from: AndyC_772 on January 21, 2015, 07:45:19 amWell, there is some marketing benefit if I can successfully filter and condition a crap PSU to functioning well with sensitive loads on the other end. Being that this a field system generally operated by non-technical people - I can expect lots of bad things to happen. For example, it is not unlikely that someone will power this via a putt-putt gas powered generator with wildly variable frequency and noise going into a random marginal quality SMPS and then pass the joy on to us. If our design could deal with that mess, we would have a marketing advantage and possibly an easier time during certification. I am going to get a generator to characterize.....