EMI: I'm in or out the directive? (edit: poor man's testing method) - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: June 25, 2014, 09:15:47 pm
content: I'm about to sell a project essentially based on atmega328 @16MHz, 74 logic, linear and switching regulators, keyboard, display, some relays and mosfets.Since I haven't much money to spend with proper EMI tests, I'm trying to understand how much radiated emissions my project generates, and basically, I need to know only if I'm into the EU directive, doing a sort of pre-compliance test.With a 15-2700MHz RF explorer, a 50MHz DSO and a couple of beehive magnetic and e-field probes (with no preamplifier in between), I've analyzed the emissions of my project.Only with the probes really, really close (near contact) to a specific zone of the MCU, I've seen a 31.071MHz, 59dBm main peak and some harmonics up to 150MHz (with lower energy) using the magnetic field probe, and a 150KHz electric field near in contact with the switching regulator using the e-field probe and DSO.All the rest of the PCB areas shows basically no considerable activity.The problem is: how can I say that I'm in the directive or not for radiated emissions? I've NOT a RF test chamber nor a proper antenna, neither the proper instruments.Well, I guess that I can compare my project's emission values with similar projects that has already been CE approved: Arduino UNO boards, LiPo chargers that uses atmega328 and so on...Doing this, I discovered that my project radiates less or the same emissions compared to that devices.I know that this is really a poor man's test, but I'm confident that this method has it's own logic and that it does have sense: if they are EMI ok with those values, me too.What do you think about this testing? Can I trust my pre-compliance method for radiated emissions?

author: qno
author_rank: Frequent Contributor
timestamp: June 25, 2014, 09:34:32 pm
content: It is hard to say if you do not have a reference.Check the levels of a CE compliant device.You also have to comply to suseptability for external fields and esd.

author: mcinque
author_rank: Unknown
timestamp: June 26, 2014, 11:07:23 am
content: Quote from: qno on June 25, 2014, 09:34:32 pmIt's exactly what I did, and on more than one device. I wonder if this raw method it's reliable. Of course I want only to see if I'm into the limits, not to measure exactly emissions values with uncalibrated and cheap hardwareQuote from: qno on June 25, 2014, 09:34:32 pmOh yes, this is relatively easily achievable with a proper shielding, guards and esd discharge paths.

author: Precipice
author_rank: Frequent Contributor
timestamp: June 26, 2014, 11:26:07 am
content: Quote from: mcinque on June 26, 2014, 11:07:23 amShort answer: no. Not to within, say, +-30dB, to pick a figure by (somewhat educated, experienced) guesswork. Even chasing a single frequency that failed in testing, so you can really concentrate on making things as repeatable as possible, knocking 10dB (say) off with a fix on the bench, and measuring it before and after, is almost entirely unrelated to what it'll measure back at the test site.a 60dB fix, though, is probably real!Nearfield measurements are also almost entirely decoupled from the other half of the game, which is 'what gets coupled onto the wires leaving my product'.Quote from: qno on June 25, 2014, 09:34:32 pmOh yes, this is relatively easily achievable with a proper shielding, guards and esd discharge paths.If it was easy, people wouldn't fail test. I'm bitter, having just come off an extremely difficult few months getting an automotive product approved, but even on simple products, I'm never as confident as you sound.Of course, it depends how much you care / how much you've got riding on it.

author: mcinque
author_rank: Unknown
timestamp: June 26, 2014, 11:53:37 am
content: Quote from: qno on June 25, 2014, 09:34:32 pmOh well, probably I'm too confident due to my inexperience...

author: Precipice
author_rank: Frequent Contributor
timestamp: June 26, 2014, 12:24:01 pm
content: Quote from: mcinque on June 26, 2014, 11:53:37 amYeah - a few rounds of EMC testing will beat that out of youHave you asked any local EMC houses what a precompliance run would cost? It might not be as bad as you think?(It's why I'm building an EMC chamber at the moment. 2500 more screws to go, and I'll see whether it's RF-tight. I hate screws - but not quite as much as I hate failing EMC!)

author: Neilm
author_rank: Super Contributor
timestamp: June 26, 2014, 06:37:05 pm
content: Quote from: mcinque on June 25, 2014, 09:15:47 pmYou are measuring near field noise - not far field noise. EMI is usually measured at 3m or 10m with the antenna in vertical and horizontal planes. The unit is then rotated until the worst combination is found. This is done in either an Open Air Test Site (OATS) or a properly set up EMC chamber, the results of which are then correlated to the OATS. When you go into a chamber you will see it covered in ferrite tiles which are there to remove reflections. Dave did a tour of one a few years ago - look up the video. [EDIT - found it - Episode 202]EMC compliance is not easy - there are things you can do to improve your chances of complying, but unless you put your unit in a well sealed metal box (ie with no openings) you are liable to have potential problems. The only thing I have every tested that passed first time was basically in a solid metal box with only a very small opening. At that we had issues making sure the paint was not put in critical areas causing fails.I would have thought an emissions test would take no more than a day on a unit as simple as you have described, probably less.Neil

author: mcinque
author_rank: Unknown
timestamp: June 26, 2014, 07:20:38 pm
content: Quote from: Neilm on June 26, 2014, 06:37:05 pmTrue, depending on device class (A/B).But I probably miss something:say that I go on a basement (zero RF from outside) and I measure near field emissions (or even "far" using a DIY log periodic antenna) of a couple of devices similar to mine (almost same components, MCU, quartz etc) that I'm sure to be full EMC compliant (note the "devices similar to mine" and "almost same components": I'm not comparing the emissions of an VHF transmitter to an ArduinoUNO board; say that I've designed an alarm clock and I'm using others CE alarm clocks as reference).Using an uncalibrated spectrum analyzer, probes and antenna, I get some values about their radiated emissions. Say that I find the clock frequency and its harmonics together with some other filth. Say that I find thatall this valuesnever go over 70dB. I store this number and I use it as reference limit.Using precisely the same measurement setup in the same location, now I power up my device and measure its radiated emissions, moving and rotating it until I find the worst scenario. Also here I find the clock and its harmonics and all the measurements values reach at max 60dB.Why my device shouldn't be into the directive?

author: Neilm
author_rank: Super Contributor
timestamp: June 26, 2014, 08:54:03 pm
content: I will make no pretense at being an expert in this field but how do you know your basement has zero RF? Is there an electric light in there? I have seen mains cables re-radiate EM frequencies at significant levels. What is behind the walls?Second, how do you know what the emission spectra of your reference devices are? If you want a transfer standard, there are noise sources that transmit known levels of noise, but they are also expensive.Thirdly, I have seen a demonstration with 2 PCBs. They had exactly the same components in exactly the same circuit. The only difference was the layout of the PCBs. There was about 20dB between the emission spectra of the two.Fourth, I once spent 2 months trying to track down a signal with spectrum analyser and calibrated probe kit. I could see it but there were other frequencies that looked far worse. Putting the unit into the GTEM at our in house facility showed the issue very clearly.The tests you have done could satisfy you that you have a very good chance to pass, but the equipment you are using is not calibrated so creating a technical file for CE compliance from this data would be laughed out of court if you were prosecuted for selling non-compliant equipment (that is the extreme case - I have never heard of anything more than fines or forced rework for EMI related issues). Showing a result from a recognised test house would probably be accepted as your due diligence.As my experience has been challenged on previous threads when discussing EMI and safety - I have spent the last 10 years designing test equipment and part of my job was to do EM testing at our in house facility. When the EMI standard our instruments have to meet changed, I ended up reworking the instruments that failed.

author: mcinque
author_rank: Unknown
timestamp: June 26, 2014, 09:19:52 pm
content: Thank you Neilm to reply to my post.Quote from: Neilm on June 26, 2014, 08:54:03 pmYou're right, probably I should have say "lowest RF possible". Using the RF explorer in that ambient I can see only noise floor.Quote from: Neilm on June 26, 2014, 08:54:03 pmOnly a led flashlight.Quote from: Neilm on June 26, 2014, 08:54:03 pmIt's easy to believe that.Quote from: Neilm on June 26, 2014, 08:54:03 pmAbsolutely. Any change to the design affect the emissions. But the point is that you CAN effectively notice the difference in excess. That's my only goal.Quote from: Neilm on June 26, 2014, 08:54:03 pmOh, you can bet it! It is not my intention to produce any technical file or report. I've not the experience/competence for doing it and, like you say, nor the proper equipment. I'm looking only for something that could see me if I could pass or not.What about using a mini DIY RF test shielded chamber? A medium size metal box properly shielded with no holes (I mean waterproof welded except for the RF out) to use it as test box?

author: Precipice
author_rank: Frequent Contributor
timestamp: June 27, 2014, 05:40:53 am
content: Quote from: mcinque on June 26, 2014, 09:19:52 pmYou can't see FM radio (88-108MHz) or cellphones or UHF TV? Hmm. Does an FM radio or cellphone work in the basement?Those are generally around or well above the limit line, round here. You might be in the middle of nowhere, of course - but if they're not showing at all, I think that shows how unrelated your near-field study is to an actual EMC sweep...A sweep with a DIY Log periodic (and a preamp!) would be a lot more convincing (but be warned that Log Periodic antennas need calibration, or at least confirmation that they're working properly) -www.ets-lindgren.com/manuals/3147.pdfshows some curves for a (presumably) well made one.You're going down a well trodden path, by the way. Welcome to the happy world of EMC on the cheap!(I still think you should at least talk to a local test house. Round here, they're very helpful, and may be able to offer you advice or more practical help. They definitely understand the difficulties tiny manufacturers face - not least because they want you to become a bigger manufacturer and use their proper services)

author: Neilm
author_rank: Super Contributor
timestamp: June 27, 2014, 04:50:44 pm
content: Quote from: mcinque on June 26, 2014, 09:19:52 pmBefore placing any equipment on the market, you should have prepared a technical file containing the arguments why it passes the relevant EU legislation, both EMC and safety requirements. These are used as evidence for the signing the Deceleration of Conformity. This should list all the standards it meets. Theoretically, these could be asked for by anyone who wants to sell the equipment. Practically, they are not usually asked for.

author: sandy
author_rank: Contributor
timestamp: June 27, 2014, 05:28:12 pm
content: Hi, I dont want to demoralise you ,but sooner or later you will realise how much time you have wasted with these tools. You must at least try to buy a second hand spectrum analyzer and get it calibrated, this will help you rectify at least 50% of your problems. You simply cannot rely on DIY tools. If you want to rely than imagine your self batteling with the norms and guidelines of 'The International Electrotechnical Commission' with and arsenal of DIY and uncalibrated probes . Sorry but no hope here as they measure in nano watts with great accuracy to make a pass or a fail.

author: mcinque
author_rank: Unknown
timestamp: June 27, 2014, 06:58:55 pm
content: Wait wait... I never stated that I want toskipthe report. I want only to do some kind of a pre-compliance. This could save money when I'll send the device to the test site.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 27, 2014, 07:40:06 pm
content: Quote from: mcinque on June 25, 2014, 09:15:47 pmIsn't that like about 800 Watts?

author: AndyC_772
author_rank: Super Contributor
timestamp: June 27, 2014, 08:00:04 pm
content: Just to back up what others have said, the work you've done is all good and worthwhile if it convinces YOU that your product would pass radiated emissions if you were to submit it for testing.It will not, however, convince anyone else, because it's not complete, quantitative, or representative of the test setup that's mandated by the standards.If you're confident that it would pass testing first time, then now is the time to go ahead and send your kit to a lab for a formal test.As well as radiated emissions, you likely also need to test for ESD and both radiated and conducted immunity. If it plugs into other equipment, or the mains, then you may well need to do conducted emissions too.I know it's not what you want to hear, but besides the 'negligence + hope' approach, there's really no valid alternative to doing at least some testing at a calibrated test facility - sorry.

author: mcinque
author_rank: Unknown
timestamp: June 27, 2014, 09:23:20 pm
content: Quote from: PA0PBZ on June 27, 2014, 07:40:06 pmOops! minus-59dBm

author: mcinque
author_rank: Unknown
timestamp: June 27, 2014, 09:29:40 pm
content: Quote from: AndyC_772 on June 27, 2014, 08:00:04 pmQuote from: AndyC_772 on June 27, 2014, 08:00:04 pmexactly.Quote from: AndyC_772 on June 27, 2014, 08:00:04 pmAbsolutely agree.Quote from: AndyC_772 on June 27, 2014, 08:00:04 pmIt is floating since it runs only on battery and does not have any plugs or connections with other devices/equipment. I'm confident that I should not comply conducted immunity, only radiated. Am I wrong?

author: AndyC_772
author_rank: Super Contributor
timestamp: June 28, 2014, 06:51:37 am
content: If it doesn't plug into anything else, then that implies no cables (correct)?If so, then there's no conducted testing to do. It also dramatically improves your chances of getting through radiated emissions and immunity first time, because in my experience something like 80% of all noise problems are related to the cables. No cable == no efficient aerial.

author: qno
author_rank: Frequent Contributor
timestamp: June 28, 2014, 07:35:50 am
content: What is your battery voltage?In a distant past I worked for an EMC house and tested a baby phone that run on a 9V battery.The carrier was so weak that it did not extended above the limit at 3 meters.The harmonics where hardly visible.So if you are running on batteries and you did not build a specific transmitter with an big end stageyou do not have to worry.A shielded box is not necessary, look at your SPSU for your laptop. It is plastic.What you need to do is keep the current loops as small as possible.Easies way to do this is use a 4 layer PCB with one layer dedicated to ground.So every track runs over or under its return.This keeps the loops very small so your track will not radiate.It also makes it very difficult for tracks to pick-up unwanted signals.

author: Precipice
author_rank: Frequent Contributor
timestamp: June 28, 2014, 08:08:30 am
content: Quote from: AndyC_772 on June 28, 2014, 06:51:37 amNo charger either? If so, then yes, everything's a whole lot easier. I still think that nearfield sniffing is slightly too unrelated to 'real' radiated to count very much, but a 1m sniff with an amplified antenna in a quiet room might correlate reasonably well. Don't forget to rotate the product, and raise / lower the antenna.Quote from: AndyC_772 on June 28, 2014, 06:51:37 amYep. How come everything I ever make looks like an electric octopus? Cables everywhere...

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 08:25:52 am
content: Quote from: AndyC_772 on June 28, 2014, 06:51:37 amCorrect for the PCB. For the entire project there are a couple of cables that goes from the PCB to the front panel of the case, connected to 5V pushbuttons, reed switch and on/off switch. Should I use shielding? The return path should zero any currents.Quote from: qno on June 28, 2014, 07:35:50 am14.8V.Quote from: qno on June 28, 2014, 07:35:50 amNo specifics transmitters were built on the PCB. There is nothing that can radiate intentionally anything: every IC and the switching regulator are properly (at least I think!) decoupled/filtered, there aren't floating pins or traces... in some way I've tried to apply all the suggestions and rules I've read (but maybe I haven't read - or understand? - enough)Quote from: qno on June 28, 2014, 07:35:50 amThis is a good advice that I've followed. All the (small) currents should be zeroed by the near return path/cable GND.Quote from: qno on June 28, 2014, 07:35:50 ammmm... this would raise dramatically the costs of the pcb manufacturing.Quote from: Precipice on June 28, 2014, 08:08:30 amYes, no charger.Quote from: Precipice on June 28, 2014, 08:08:30 amI dont' have a proper amplifier (I should need something with a very wide band)... what do you suggest?

author: AndyC_772
author_rank: Super Contributor
timestamp: June 28, 2014, 09:13:33 am
content: Ah... so, you have a 2 layer board and some internal cabling.Without a solid, unbroken ground plane, you're just asking for trouble.It's all about loop area, which governs how efficiently the board works as an antenna. If you have a track carrying a current on a layer immediately above an unbroken ground plane, then the return current can and will flow in the plane, and will approximately follow the route of the track above it. The loop area depends on the trace length and the layer-to-layer spacing in your PCB, which is usually small. This means the PCB is an inefficient antenna, which is exactly what you want.Without a ground plane, the loop area still depends on the trace length, but now also depends on the length of the (routed) ground and the spacing between each current-carrying trace and the corresponding ground trace. This area is typically *much* larger, so the PCB acts as a much more efficient antenna. A lot more energy is radiated or absorbed by your circuit.Also, without power and ground planes, you have very poor decoupling above 100 MHz or thereabouts, and any current spikes drawn by your circuit will cause corresponding high frequency voltage spikes due to the inductance of your power and ground traces. These can radiate.For all but the most completely trivial circuits, I don't use anything less than a 4 layer board. It's not worth it. Unless you're making thousands of units, the extra cost of a couple of PCB layers will be small compared to the time you spend testing and reworking the product when it has EMC or signal integrity problems.

author: Precipice
author_rank: Frequent Contributor
timestamp: June 28, 2014, 09:17:34 am
content: Quote from: mcinque on June 28, 2014, 08:25:52 amThere's a link in herehttp://www.edn.com/electronics-blogs/emc-emi-rfi-esd/4378157/An-EMC-Troubleshooting-Kit--Part-1b-Emissions-to "This $50 module covers 20 to 3000 MHz, has a gain of 18 to 23 dB, noise figure of 2.7 dB andcan handle up to +10 dBm power input. It runs off 12 V DC."Basically just a minicircuits ZX60-3018GS+ module on a bit of board with connectors and a battery.Curves are herewww.minicircuits.com/pdfs/ZX60-3018G+.pdf- it's not flat, but neither will your antenna be!You can get better noise performance elsewhere, but it's not _bad_.That entire EDN series is worth a read, if you hadn't found it before.

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 11:23:25 am
content: Quote from: Precipice on June 28, 2014, 09:17:34 amOrdered!

author: dannyf
author_rank: Super Contributor
timestamp: June 28, 2014, 11:27:31 am
content: Get an LED + loops of wires. Put the led + loop next to a few known compliant devices and your device and see how bright the LED is.Cell phone flashers will do the same.

author: Precipice
author_rank: Frequent Contributor
timestamp: June 28, 2014, 12:10:57 pm
content: Quote from: dannyf on June 28, 2014, 11:27:31 amI'm assuming you're kidding, yeah?By the time you're even remotely comparing your unintentional radiated power with a 0.5W (or more) intentional transmitter, you've got some pretty serious EMC issues!

author: Tabs
author_rank: Regular Contributor
timestamp: June 28, 2014, 03:40:37 pm
content: For what its worth:test houses charge around £1200+/-200 per day or £3-4k for a full suite of tests.It depends on what product family standard your product is covered by and what tests it tells you to do.seehttp://ec.europa.eu/enterprise/policies/european-standards/harmonised-standards/electromagnetic-compatibility/index_en.htmfor european EMC harmonised product family standards. If you dont think any apply then the generic residential,commercial and light industrial standards apply and you will have to decide which ones to apply.Being battery powered with only internal cables connecting to a front panel makes things a lot easier for you so I would expect the test house to charge much less (since there are no surge/bursts/EFTs and no conducted immunity or conducted emissions to worry about)The EU allows you to self declare but it would be in your interests to do this based on evidence.BTWEven when you do have evidence from a test house, you still only have the presumption of conformity and if your product still fails in real use then its your problem, but at least the courts will see that you did due diligence.That being said, it looks like you only need radiated emissions and radiated immunity.The test house will charge much more for radiated immunity because they need amps, couplers and power meters. The setup and run time is longer because you have dwell times at each frequency.The most important one for you in this case is radiated emissions because this has the potential to interfere with other people equipment.Problems with immunity will give you customer relation problems and will only cause legal issues if one of them takes it that far.It sounds like this is a 'hoby/enthusiast' product so the above may not happen. (If this is meant to be a proper consumer product then you need to test).If test houses still aren't cheap enough then hire a spectrum analyser and antenna. If your basement is quiet you should see the SA noise floor. If you do see something then make a note of its characteristics so you can distinguish it from spikes caused by your product. Don't take the difference between the two readings. If your basement is not quiet then go to the middle of nowhere (get a SA with a battery option) and use it as though it was an OATS.If still too expensive then then use the near field techniques just to see what frequencies are floating around your product.IMHO: your'e more likely to fail in sub 50MHz region. These will mostly be down to common mode imbalance in your cables.

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 08:16:00 pm
content: Thank you tabs for you detailed post.However, since this will be an hobby/enthusiast product for a very small niche, I often ask myself if I really need to do all this. I'm putting a big effort in this and sometimes I think that I wasting my time (and money).I strongly believe that most niche-products like arduino relay or display shields, crap digital multimeters, rubbish power supplies modules, disgusting tx-rx modules, all sold by various European online shops have not even saw from a mile a piece of paper that talks about EMI and EMC. And no authority is preventing or acting against this products.Take for examplethis moduleproduced bythiscompany and by Sparkfun also in Europe.I've one of this crap modules and I've seen many differences comparing to a serious Aurel tx module likethis(I know it's not the same frequency but this is not the point: both frequencies are well regulated here.The sparkfun module does not have any declaration of conformity nor meets any EN requirement, it hasn't even the metal crystal oscillator case connected to ground... judging by its price you can easily imagine what kind of crap it radiates when turned on, or its frequency stability. The Aurel instead shows a crystal clear razor-centered main tone with basically nothing in the surroundings. As a serious tx module should do.We have a chinese crap toy tx module vs a serious EU-made tx module, fully certified and compliant.Even if the manufacturer of the crap module is in asia, the reseller is still responsible for putting on the market something that is not CE compliant.But if this was true, noone here would sell that garbage. Neverthless, almost every hobby/enthusiast electronics european online shop, sells that filth with no issues.This makes me think that if you're not in a big market, you can sell whatever you like: noone will catch you. But this is not fair.

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 08:25:37 pm
content: Quote from: AndyC_772 on June 28, 2014, 09:13:33 amI appreciate your thoughts, seriously.But I wonder how many simple commercial products (like alarm clocks for example, or cheap bench power supplies) can be EMC compliant using internal cabling and 1 or 2 layer PCB without any ground plane

author: AndyC_772
author_rank: Super Contributor
timestamp: June 28, 2014, 08:36:29 pm
content: They may well be compliant, but they'll have been tested to be sure. They may well not be rev 'A' PCBs either.Not having a ground plane doesn't mean your product won't be compliant, but it does mean there's a greatly increased risk that it won't be compliant on its first iteration compared to a board which does have a ground plane.2 or 3 PCB revisions to identify and fix EMC failure points is not at all unusual, especially if you're not experienced in EMC design to begin with.

author: qno
author_rank: Frequent Contributor
timestamp: June 28, 2014, 08:50:58 pm
content: A 4 layer board is hardly more expensive than a 2 layer board.Maybe 20 % when ordering 100 pc.

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 09:04:35 pm
content: Quote from: AndyC_772 on June 28, 2014, 08:36:29 pmImho, anything that is compliant shows with more or less pride a declaration or a certificate. Or at least, you can find it if you search. There is nothing to find about that products.Many power tx modules or cheap DMMs has not even a known manufacturer. They could not even sell them...Quote from: AndyC_772 on June 28, 2014, 08:36:29 pmThat's what I am!

author: Tabs
author_rank: Regular Contributor
timestamp: June 28, 2014, 09:56:05 pm
content: mcinque,I understand the point you were trying to make, its not fair to compete against cheap shit from asia sold through dummy retailers who dont care about CE or FCC etc.In your particular examples 433MHz tx modules operate in an unregulated ISM (Industrial, Scientific, Medical) band (70cm i think). This band is used by radio hams and RC plane hobyists and doent require a licence in the US [Can an american ham confirm please?). The start and stop bands are different in each country but I think 433 is safe. The module is also limited to +14dBm which I think is below the limit.They still have to comply with EMC in other bands.Check where you are, but I think these bands are internationally agreed and are part of an ITU-R regulation. Again check and confirm for yourself.Also, transmitters fall under the R&TTE directive which means they have to be licensed (if operating at a regulated frequency above the limit)Just doing a very quick google search showed:http://www.arrl.org/news/fcc-proposes-to-fine-texas-radio-amateur-7000-for-malicious-interferencehttp://www.ce-mark.com/euen.htmlhttp://www.compliance-club.com/archive/old_archive/980816.htmlhttp://www.southgatearc.org/news/may2010/ofcom_prosecutions.htmIt seems big corporations and the little guys are being prosecuted.Just a couple of months ago I was checking emissions problems with a new product. Spent ages thinking it was the PSU, I got to end of my tether and proved it wasn't the PSU. In the end I got desperate and removed the PSU board and powered the unit off Duracell batteries. The product stopped failing which kind of says it was the PSU. I put the PSU back in, cut the power tracks on the secondary rectifiers and powered from the battery. The unit failed. Turns out it was SPI on my shitty little microcontroller. The slew rate was high (this is where the emissions come from, not the slow datarate).If you've got anything that remotely looks like a square wave then I'd test. Especially if you have SPI talking to a display on the front panel over those cables. The frequencies may not be high enough for the cable to act as an antenna but it depends on slew rate. Thats the thing with EMC, you can plan for it, but ....

author: mcinque
author_rank: Unknown
timestamp: June 28, 2014, 11:19:00 pm
content: Quote from: Tabs on June 28, 2014, 09:56:05 pmExactly. And please mind that I know Italian retailers that aren't dummy, but well regulated ltd. companies, with their responsibility. The CE directive is well clear: the manufacturer and the retailer ARE responsible for what they put on the market. So I ask: if they sell crap things, shouldn't they be prosecuted by law? And since the answer is YES, why they continue to operate without any fine?Quote from: AndyC_772 on June 28, 2014, 09:13:33 amjust for test, I've tried to route the PCB with 4 layers, 2 inners with the signals and 2 outers grounded like the literature suggest to keep all the emissions inside.Forgetting that I should modify some trace witdh, the result is that I need another 2 layers since the pre-routing fails (many ratlines impossible to route). Apparently there are too much components and nets on the board for only 2 inner layers. So I should use 6 layers... Of course in this case I can't manage the costs, at least for a niche product like this.Back to the main thread, I quickly summarize my goal:pre-test my device for radiated EMIIf I was a firearm manufacturer, and had to deal with power limit of 2000J for my new handgun, I would obviously need instruments to measure wich energy my new product has.Without having a chronograph to measure the bullet speed and a scales to know its weight it would be hard to calculate its energyin numbers.But I need to know ONLY if I'm UNDER the 2000J limit, I don't need to know the value.I can measure the power of a "compliant" firearm and compare it with mine. I can shoot to layers of cardboard until I find how much layers stops the bullet of the "compliant gun". At that point, if my gun, using the same projectile, DOES NOT penetrate more than 3/4 of layers than the number the compliant gun does, it's mathematical to have a compliant gun.I cannot declare how much energy my gun has, but I can state safely that its under 2000J.Applying this logic in my case I've thought this method:1. use a cheap, uncalibrated spectrum analyzer (RF Explorer 27-2700MHz), near field probes and diy log periodic antenna (with preamp) in a "RF quiet" basement2. compensate the uncertain calibration of the instruments by collecting radiated emissionsfrom similar EMC-certified devices, settingthe lowest valueas emission limit3. use this values as a threshold for radiated emissions4. test my device with the setup and see if something goes over the threshold.So now I have:1. a testing setup2. a threshold value to be observed -I understand that I have NOT a calibrated hardware but his spectral response MUST have the same linearity with my product both with CE compliant product, so knowing the "limit value" to observe, it should be idiot-proof to know if you're exceedings the emissions.And at this point in my mind the REAL point is the following:if I find that my product emissions arewell below(I said WELL BELOW!) the threshold,even with an uncalibrated cheap setup like thisI cannot be wrong: the device is EMI compliant.At that point, how much sense does it have to pay € 900 for a certificate that states it's compliant when every product, by law, can benefit of the "presumption of conformity" (where the unconformitymust be proven by the authority)?!?! And even if the autority tests my device, how can they prove that is not EMI compliant when it's measured that it radiates less than CE approved products?I'm well documented in this and even a EMC center consultant that I've asked to told me that there is no law that prescribe mandatorily an EXTERNAL EMC test with a report. It's a choice every manufacturer does. You can do it internally and if you're sure, you can declare it as compliant (and take all the responsibilities, the same is if you pay for the EMC test, it's ALWAYS your responsibility). I know "nothing ventured, nothing gained".I know and I'm sure that is something that I'm missing, otherwise we wouldn't have so many EMC test centers and all manufacturers could save much money doing thinks like I saySo could someone please explainwheremy lack of knowledge makes me feel so safe?EDIT: with his great uCurrent sold all over the world (so even in EU) Dave has gone thru all this annoying EMC testing?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 29, 2014, 12:59:37 am
content: Quote from: mcinque on June 28, 2014, 11:19:00 pmThis is not a useful approach, as unlike the firearm example where you are measuring a single one-dimennsional value, each of the other devices will have their own spectrum of emissions, and at many frequencies, the level will be below the noise floor, so this will correspond to an unnecessary "strict" limit. You also don't know if they actually meet the standards any markings claim.Testing outside of a shielded anechoic chamber is pretty much impossible as there is so much (continuously changing) ambient signal.Your basement won't be much quieter unless it is very very deep.Even in a quiet environment, a non-anechoic area will have all sorts of reflections which means that very small changes in position of EUT and antenna can make huge differences in readings.

author: dannyf
author_rank: Super Contributor
timestamp: June 29, 2014, 01:04:16 am
content: A more quantitative approach is to use a RF probe - they are fairly simple to build.The LED approach I outlined earlier will work as well and is more visual.Since you don't know the absolute value, you will need to use a known compliant device or devices for "calibration".

author: AndyC_772
author_rank: Super Contributor
timestamp: June 29, 2014, 07:05:50 am
content: It's a common misconception that putting a noisy track on an internal layer, sandwiched between planes, is needed to suppress emissions from it. Putting it on an outer surface with a solid plane on the layer below is also effective, and although you'd need a physical prototype or 3D field solver software to actually prove it, there are several 'mental models' you can use to help understand why this might be the case.You have:- return current immediately underneath the noisy trace, therefore a very small loop area and, therefore, an inefficient radiating antenna- very high quality capacitance between the signal and ground, formed by the PCB itself, with minimal series inductance which leads to good high frequency (100+ MHz) performance- electric field lines terminating on the plane, rather than radiating off into space. Putting a solid lump of copper right next to the antenna is exactly what the data sheets for things like Bluetooth modules tell you NOT to do, for just this reason.Turning a 2 layer board into a 4 layer is, therefore, pretty trivial. Keep the top and bottom layers just as they are already, but put ground on layer 2 and power on layer 3.It sounds as though you might be using an auto-router, right? Don't.I understand your frustration when it comes to comparing your equipment against 'known compliant' samples, but a couple of reasons why it's a poor way to demonstrate compliance are:- the near field spectrum of a piece of equipment is not the same as the far field spectrum. The range of frequencies that are detectable will be the same, but the amplitudes vary dramatically.- just because a piece of kit is claimed to be compliant, doesn't mean it will be. The emissions spectrum from a product depends on its physical orientation, cables attached, reflections from its surroundings, and variation from sample to sample.Arguments based on total radiated energy don't stand up, because the test limit is a limit on emissions in any particular direction, not just an overall total. You can't assume that your product radiates equally in all directions, and if it radiates predominantly in one direction, it can still exceed the limit even if the total radiated power is low.It's entirely true that you don't have to have your product formally tested by law. It is, however, the case that the only way to actually be sure your product complies with the relevant standards is to do so.If the authorities test your product - which is, incidentally, quite unlikely - then they will do so according to the prescribed methods in the relevant standards. If your equipment passes, then that's fine, but unless you've carried out that same test yourself beforehand, you have no way to know that it will do so.

author: mcinque
author_rank: Unknown
timestamp: June 29, 2014, 08:25:42 am
content: Quote from: mikeselectricstuff on June 29, 2014, 12:59:37 amhmm... this is damn true. I didn't consider itQuote from: mikeselectricstuff on June 29, 2014, 12:59:37 amI've learned to not trust a compliance of a product only by looking at its markings. It's better to find its declaration of conformity to have a chance to know if it's compliant.Quote from: mikeselectricstuff on June 29, 2014, 12:59:37 ammmm.... understood. What about building a "mini" RF anechoic chamber with a shielded metal box and rf adsorber inside? It could be helpful or I haven't any chance?Quote from: mikeselectricstuff on June 29, 2014, 12:59:37 amDamn, reflections are really important and it's a behaviour that I've never take in consideration.Quote from: AndyC_772 on June 29, 2014, 07:05:50 amWell, I've just tried what I've found on literature; for sure the practice and experience are definitely better than theoryQuote from: AndyC_772 on June 29, 2014, 07:05:50 amThanks!Quote from: AndyC_772 on June 29, 2014, 07:05:50 amOh, often I use autorouting only to see if the all the nets are routable: if the software miss a couple of nets it's easy to understand that you can do better manually, but when he miss something like 15 nets I've learned that I can do very few things to complete the board.Quote from: AndyC_772 on June 29, 2014, 07:05:50 amA very good point to explain why my idea is not good.Quote from: dannyf on June 29, 2014, 01:04:16 amThat's exactly what it was on my mind.So, to end this thread, even with my cheap hardware and a DIY calibration based on compliant devices there is no doubt that I can't do to do a pre-compliance without an RF anechoic chamber.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 29, 2014, 09:21:24 am
content: Quote from: mcinque on June 29, 2014, 08:25:42 amCorrect, but what you can do is identify where any peaks are, and see what can be done to reduce them, you just can't get any absolute figures.

author: nctnico
author_rank: Super Contributor
timestamp: June 29, 2014, 10:24:20 am
content: Quote from: mcinque on June 28, 2014, 08:16:00 pmThey don't have to. Modules are parts and therefore not required to have a compliance certificate. Even modules with approval may fail to comply when built into a product.

author: nctnico
author_rank: Super Contributor
timestamp: June 29, 2014, 10:49:10 am
content: Quote from: AndyC_772 on June 29, 2014, 07:05:50 amI agree. A while ago one of my designs a 6 layer board with a 1GHz SoC and lots of switchers went through EMC testing. There was no difference between the readings with the board inside the metal casing or not. All the radiation came out through the wires.Also something interesting happened during the test: there was a 90MHz spike which caused some confusing since there is no clock on the board which could produce that. A quick look around revealed the lab technician forgot to put a filter clamp on the cable going into the EMC shielded room. The 90MHz was a radio station.

author: mcinque
author_rank: Unknown
timestamp: June 29, 2014, 12:50:42 pm
content: Quote from: nctnico on June 29, 2014, 10:24:20 amThe parts that don't need to be testedmust be sold only to tech personnel, not to hobbyst.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 29, 2014, 12:55:31 pm
content: Quote from: mcinque on June 29, 2014, 12:50:42 pmCitation?

author: Niklas
author_rank: Frequent Contributor
timestamp: June 29, 2014, 01:36:12 pm
content: Quote from: mcinque on June 28, 2014, 11:19:00 pmThe company that imports goods into the EU is the one that is responsible to make sure that the product complies with applicable standards. The main problem is that many trading companies are just only trading companies and therefor lacks the technical knowledge. To hire a consultant to do the verification cost money and may consume all the profit margin of the product. A Chinese manufacturer can put whatever marking(s) they like just to boost their sales. They don't have to face possible fines, recalls etc and got their money in the bank before the shipment has left the country.I have seen both electronics and water boiler for a steam sauna produced by an Italian company that was everything else than CE compliant. A customer wanted to integrate our control panel (the user interface) with parts from another producer (hidden for the user). During our review of the electronics we found several safety related issues, where a weak PE connection was the worst. Also the wires that went to the heating element were standard PVC insulated ones not rated for the high temperature. The result was that we adapted the SW in our power electronics box to suit the application and we also replaced the wire harness attached to the heating element.As long as the producer and/or importer can just slap a CE mark onto the product, without a significant risk of getting caught, the problems will continue. The local regulatory agency in Sweden only starts to look at a product after customers report to them. How many customers know about this agency and the possibility to file a report? Not so many I guess. The life cycle for many imported products is often very short and the regulatory agencies are usually quite slow.One more thing about Italian products even if it is a bit off topic. If I ever was in the situation to purchase trains, I would never even consider something that was designed or produced by Ansaldo Breda. Their sales team might be good, but their finance or engineering teams are quite disappointing...

author: sandy
author_rank: Contributor
timestamp: June 29, 2014, 01:53:59 pm
content: Quote from: mcinque on June 28, 2014, 11:19:00 pmBut who is comming forward to make a complaint against them and pursue a case, are you readymcinque? . I think the answer is No, because once you get a compliance certificate your anger will be over. So who will give a sacrifice and fight international cases and in return become bankrupt? . They will bribe authorities and start a fresh business? isnt it.

author: dannyf
author_rank: Super Contributor
timestamp: June 29, 2014, 01:56:42 pm
content: QuoteBecause we have competing priorities and limited resources to pursue them all.There are unlimited number of things that we should do but we don't do, because of that.

author: Precipice
author_rank: Frequent Contributor
timestamp: June 29, 2014, 02:45:25 pm
content: Quote from: mcinque on June 29, 2014, 08:25:42 amThis is harder than you might think, I'm afraid.The amount of absorbing material you need, and the distance between your unit and the antenna, plus some way to move the antenna (or unit), means that you end up with a big chamber that looks a lot like a real EMC chamber.You can investigate TEM cells, but they're more for susceptibility than emissions.(I've got a 1.2x2.4x2.4m shielded chamber that I use when I want to investigate stuff at home. (It's built out of sections of an ebay chamber - these things are often modular, so you can make them whatever size you like). It's big enough to get me, a test unit, an antenna and a spectrum analyser in, reasonably comfortably. It's nice because there's no external noise - but reflections mean that if anything moves, amplitudes change by tens of dB. It'll be interesting to see how much improvement packing all the spare space with absorbent cones will make - at the moment, it's more useful to contain emissions than it is as a precompliance chamber.)Also, while I feel your frustration - I think there's another level yet to come. It's when youjustfail compliance testing. One peak half a dB over, or a tiny disturbance during susceptibility, that you might not have noticed, but you did...I'm now building a much bigger proper anechoic chamber, so I can get some proper results. Again, second hand off ebay. Had to rent an industrial unit to build it in

author: mcinque
author_rank: Unknown
timestamp: June 29, 2014, 04:39:51 pm
content: Quote from: mikeselectricstuff on June 29, 2014, 12:55:31 pmGuide for the EMC Directive 2004/108/EC, see attachments.If a component/part is for the end user (like the hobbist for example), it must comply with the directive.The end user should not care about the emissions or any else concerning the emissions or any else related to the directive.If a component is sold to tech personnel that will certify the EMC of the final installationit can be excluded from the directive.It's who installs the hardware that must produce a certificate of conformity and compliance. The guide tells clearly that to be excluded the component/part must not be available to the end user.Take for example a PC video card. It's only a "module". It's a part that cannot absolve a specific function without be installed into a PC. But its available at the end user, and must comply the EMC directive.I'm confident that I cannot produce and sell to the end user a video card that once installed interferes with tvs, radios and mobile phones and then justify me saying "it's only a module, it's not my problem".

author: AndyC_772
author_rank: Super Contributor
timestamp: June 29, 2014, 06:32:07 pm
content: It's a whole new can of worms if you're selling something like a video card.Even the simplest card, with no active components at all, can pick up noise which exists inside the chassis of a compliant product and radiate it to the outside - thereby rendering the system non-compliant.Of course, your add-in card isn't allowed to make a compliant system non-compliant, but the difficulty is that neither item is necessarily in any way deficient. Unless your add-in card has superlative shielding, there's always a risk that someone will plug it into a particularly marginal (but compliant) host system - but you get the blame for making it non-compliant with your card.In this case, a good approach is to be able to present a formal test report for some other system, with your card installed in it, so you can demonstrate that your card isn't responsible for the noise.

author: mcinque
author_rank: Unknown
timestamp: June 29, 2014, 07:10:42 pm
content: Quote from: Niklas on June 29, 2014, 01:36:12 pmQuote from: dannyf on June 29, 2014, 01:56:42 pmQuote from: sandy on June 29, 2014, 01:56:42 pmHearing this comments strengthens my conviction that probably I'm wasting my time and all the EMC certification is a big trash of money and time for any product that isnotpopular like the iPhone or isn't in a big market with many competitors.Quote from: Niklas on June 29, 2014, 01:36:12 pmEven if many italians thinkonlyabout soccer 24h/day, even if ours politicians are the worst of the world and even if we don't have patriotism or any respect for our country, not all italian products are so bad. Breda is a company where politicians has put their hands. Many engineers probably were hired in that company because of politicians pressure, not for their competence.