EMC pre compliance test equipment recommendations - Page 1
Forum section: electronics / testgear

author: TwinScroll
author_rank: Contributor
timestamp: May 05, 2021, 10:10:54 pm
content: Just curious on people’s thoughts / suggestions or advice on EMC pre compliance test equipment.The company I work for has given approval to spend up to around £8K GBP.We have a large test area (that is a long distance from other working areas) and we can improve on the shielding of the room / area if found needed, the cost for that would be separate.We already have a Tektronix MDO3000 scope with a 3Ghz spectrum Analyser option, but if a separate analyser will be easier to use and possible within budget that is an option.We mainly do DC powered equipment 12v / 24v typically less than 10Amps (sometimes marginally higher but that is rare).We want to concentrate on emissions over susceptibility to start with.Any suggestions on must haves, caution on items we are hardly ever likely to use etc would be great. I am thinking we need ::-Near field probe set-RF current monitor-DC LISN (ideally ability to measure Differential and Common Mode)-Spectrum Analyser (Big Ticket)-Far field Emissions Antenna or Antennas-Various high quality interconnection cablesBest RegardsTwinScroll

author: nctnico
author_rank: Super Contributor
timestamp: May 05, 2021, 11:21:58 pm
content: I'd forget about trying to measure far-field. You need to go to a lab for those measurements. Shielding a room isn't enough; the walls need to be non-reflective to avoid standing waves.Near field probes, LISN and some cables are good investments. Don't overdo the cables. RG319 cables are cheap and OK up to 1GHz. You don't have to break the bank for a spectrum analyser either. The 3GHz one from Siglent will do just fine.Also think about getting an ESD gun. ESD can be nasty to pass as well c.q. it is good to test how your devices responds to ESD discharges. Again this will require some room to setup because you don't want to damage other equipment.IMHO the biggest mistake is to think you can make accurate measurements with an error less than 3dB. Many tests require very specific test setups which take a lot of space. The best way is to do a pre-compliance run at an accredited lab and then use near field probes to see if you can lower emissions at the offending frequencies by modifying the circuit with a healthy margin.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 05, 2021, 11:30:03 pm
content: Thats a pretty tight budget, depending on what you want to achieve.For that money I doubt you'll get good data relative to the EMC limits (that takes calibration and $$$), but at least you'll see the obvious issues and will be able to evaluate mitigations.The NF probes and the LISN should get you most of the way there, at least as far as finding potential issues goes.You might consider an absorption clamp instead of far field antennas - takes less space, will get you to 1GHz, without needing an anechoic chamberShielding a room without adding absorbers might make things worse rather than better ( EMI gets bounced around inside the shield), unless you have a powerful source of interference you know you need to block.If the devices you are testing are small enough, another potential route is the GTEM cell. They can be used for both emissions and susceptibility.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2021, 11:52:49 pm
content: Conducted is easy enough, given that you aren't too picky about the precision of results, especially at high frequencies.Traditionally, it ends at 30MHz on the dot. There's no reason you can't look further -- just the sanity of making that measurement at all, versus who knows what's evaporating off the cables or enclosure...So, any time you can make a port-like measurement, it helps. For example, instead of measuring conducted emissions at a distance (after standard e.g. power cords and such), measure it at the enclosure -- assuming the enclosure is metallic so a good ground reference can be made there, and every connection exiting through that reference can be considered an RF port. (And if not grounded, then the nearest thing that can -- perhaps just floating the board over another ground plane and measuring all wires coming off the board.)An open air test, boards laid out over a ground plane, is still susceptible to ambient fields, which you'll have to subtract from the measurement somehow -- hopefully they're below threshold so your measurement is still meaningful, and if not, good luck with the shielding budget -- but given that hurdle is passed, it's a good way to get some idea of the wideband emissions from individual boards, or equipment.An adequate LISN can even be hand made (we have some excellent threads on that here), or they are easy to find for sale. Use the kind appropriate for your work of course; if your 12/24V DC equipment is like, automotive, look up the whatever standard is typically used for that; if it's more like uh, I suppose industrial kit would have to pass some relative of FCC Part 18, or the IEC/BS equivalent? Then, give that a look. (Although that might not be all that helpful as I think Part 18 is mostly OAT anyway, who needs LISNs?)Also add CDNs for stuff like telecom pairs, etc. YMMV, may not be the easiest thing for like CAN bus, since it's DC coupled -- Ethernet and some RS-485 can go through transformer coupled CDNs which is nice, when it can't you have to use an attenuating (resistor coupled) CDN so keep that in mind.I don't know what the MDO3000 spec option is like; if it's basically like any other spec, useful dynamic range, all the RBW settings and stuff, that's fine. If it has quasi-peak (QP) detection that's even better, but you can do precomp just fine with peak, too. I'd just be weary of anything that's just a regular scope with FT, those tend to have poor dynamic range, no spectrum averaging, variously no frequency offset or detector or RBW options, etc...Yeah, current probes aren't a bad idea, but be mindful of where those currents are going -- or not. Some stuff laid out over ground plane, will just have whatever resonances between the stuff, and not much resonance towards the LISN(s) since those are resistive terminated. Resonances on cables and equipment are pretty easy to spot: keep an eye out for peaks/valleys, and what physical lengths those frequencies correspond to.A couple 10-20dB wideband preamps, good idea. Attenuators too. Sometimes you want to use both simultaneously, just to have the safety padding, or freedom from reflections, and then claw back whatever SNR you have left since the spec probably doesn't have the greatest SNR (or rather, noise factor).Near field probes, seconded. Not really meaningful in terms of relation to radiated emissions -- they're more for tracking down culprits, and then you can decide what to do with it (improved routing, bypassing, ferrite beads, shielding, etc.).Yeah, ESD is a good tool, both for causing the upsets it's famous for, as well as a source of wideband RF. The low duty cycle makes it not a great substitute for the modulated CW used in immunity testing, but if you can deal with that (perhaps with an impulse or error detector on suspect circuits?) you can get some idea of general susceptibility too.Tim

author: tautech
author_rank: Super Contributor
timestamp: May 06, 2021, 03:59:30 am
content: Quote from: nctnico on May 05, 2021, 11:21:58 pmYou can peel back more cost when the 1.5 GHz SSA3015X Plus can easily cover EMI precompliance needs however many select the 2.1 GHz model for the bit high BW and better TG spec it offers for GP SA work.All Siglent SSA and SVA models have an EMI promotion running where you get a set of characterised EMI probes and the EMI SW license for a much reduced cost when buying the 2 together.https://www.siglenteu.com/news-article/a-new-bundle-for-emi-pre-compliance-test/Such is the cost of EMI compliance testing just one fail will have funded one of these SA's and not needing to rework designs when you can do EMI tests as you go and have a product properly ready for testing by an EMI test house.

author: Berni
author_rank: Super Contributor
timestamp: May 06, 2021, 06:21:35 am
content: The most important item is to buy a RF shielding tent.These are simply boxes covered in a conductive RF blocking fabric. Typically they will include some sort of RF resilient door and a bulkhead panel on one side that includes passtrough RF connectors for your antennas and low pass filtered power passtrough to get DC power in, but not RF.Yes i know far field measurements are going to be garbage, you need a bigger room full of absorbers for that, but that will never fit into the OPs budget. But what this desktop sized RF tent gives you is excellent shielding from the environment. Unless you live in the Sahara desert or the rain forest. then there will be a LOT of RF junk in the air. This makes it difficult to tell apart your product from the other junk while also overloading high gain LNAs and spectrum analyzer inputs on high sensitivity settings. Doing the measurement in a shielded box keeps all of that out, so you know any signal you see is emitted from your DUT and not a giant multi kW transmitter on top of a near by hill.Don't try to RF proof an actual room because above a few MHz this becomes very difficult. To do it you need to cover the entire room in metal and join the metal pieces along all edges. Just a few centimeters of non joined edge forms a single turn inductor that picks up outside RF and re transmits it inside. This includes doors too that need RF shielding fingers all the way around. This is why its easier to simply buy a RF tent that is sown together to have no gaps in it.We have wide bandwidth LNAs fitted inside the RF tent to amplify the weakest of signals right after the antenna, producing a nice large signal out of the bulkhead N connector that goes to the spectrum analyzer. This makes the signal more resilient to picking up extra RF interference outside the chamber and helps reach the lowest possible noise floor on the spectrum analyzer. The gain of this amplifier is corrected by the spectrum analyzer by entering the LNAs characteristic curve.The setup is never meant to do precise calibrated measurements. Its main purpose is to detect and identify all the RF frequencies the DUT is emitting and reproducably measure there size. This way if you see any large peaks you know where the trouble is, track it down, and test modifications to try and reduce the peaks to a minimum. Then the real EMI test at the cert lab is just to verify you are under the levels. If you do fail EMI cert you will get a fail report that shows how many dB you are too high. So when you find a modification that reduces the EMI noise by that many dB you know you will pass the next time.

author: justanothername
author_rank: Regular Contributor
timestamp: May 06, 2021, 09:38:25 am
content: LISN + EMI receiver and Surge/Burst tester for the 24V supply inputs are units with you can easily make tests with, no need for an anechoic chamber or shielding.Good investment, we fail at these tests every time the first try. You can save half of the laboratory costs if you do them in-house at first.

author: KevinA
author_rank: Regular Contributor
timestamp: May 06, 2021, 06:24:39 pm
content: You can have all of my companies equipment free. You will need to do a lot of digging though.2012 the "new management" decided that an expensive technician was not needed, so I was replaced by two chassis swappers. Since no one knew what any of my equipment or spare parts were for, all of it went to the local tip. In there, you will find a full conductive emissions, radiated emissions test suite, spectrum analyser, software, TEM cell and all of the various coils for PAVI measurements.

author: Feynman
author_rank: Regular Contributor
timestamp: May 06, 2021, 06:33:23 pm
content: Quote from: TwinScroll on May 05, 2021, 10:10:54 pmThat's decent setup, I guess. As others mentioned, I'd forget about far field stuff with that budget. Instead of the far field antennas you could go for a TEM (open) or GTEM (closed) cell.If you want to do immunity tests, you probably want a RF generator that can do the very common 80% AM 1 kHz modulation and has enough output power (20+ dBm).

author: artag
author_rank: Super Contributor
timestamp: May 07, 2021, 10:55:37 am
content: Quote from: KevinA on May 06, 2021, 06:24:39 pmThat sucks.I hope you found a job somewhere more appreciative.Which tip ?

author: basilic
author_rank: Newbie
timestamp: February 17, 2024, 04:10:17 pm
content: Hey, I'm replying to your message because I'm currently at the next stage.Three years ago, I explained to our managers that we can't claim something is good without any measurement, and we failed our emission tests (conducted but with additional precautions, and then radiated).We were authorized to spend a little to purchase a spectrum analyzer (R&S FPC1000 3GHz, not enough budget for an FPC1500 or higher), a small biconical antenna (due to limited storage space), and a second-hand 50µH LISN. With this equipment, we successfully patched the design (both hardware and software patches).Last month, we failed the conducted immunity tests (for industrial level).After extensive discussions about the impossibility of reproducing the phenomena and solving it without many tests in the lab, we are planning to purchase more equipment for immunity testing: amplifiers, a TEM CELL, attenuators, and a generator.Regarding the generator, I'm seeking advice on the best choice, whether to invest in a new spectrum analyzer with a tracking generator (SSA3075X) or just a generator (SSA5060X).We need to test immunity up to 6GHz (previously limited to 2.7GHz) as per the standard.In either case (generator or spectrum analyzer), we will need amplifiers for conducted immunity (level 3 requires at least 40dBm with a CDN).If anyone has an opinion, I would appreciate hearing it before investing a significant amount of money without a clear direction.

author: nctnico
author_rank: Super Contributor
timestamp: February 17, 2024, 04:16:05 pm
content: I'd invest in a general purpose RF generator. For radiated immunity you'll also want modulation (at least AM). Another item you'll need is a power meter so you can measure the output of the amplifier versus frequency and create a correction table. With some simple Python scripting + pyvisa it is pretty simple to create an automated setup that sweeps through the frequencies.

author: basilic
author_rank: Newbie
timestamp: February 17, 2024, 04:47:59 pm
content: If the budget were unlimited, I would prefer an A-brand. However, after many hours of consideration, I only have a budget of 12-14k€ to purchase a setup for conducted (10Vrms 150kHz - 80MHz AM 1kHz) and radiated immunity up to 6GHz (10V/m and 3V/m).With this budget, my preference is towards Tekbox amplifiers and brands like Siglent for the generator, supplemented by some near-field probes and a DIY CDN.In the 61000-4-6 standard, the level is set as continuous wave (CW) without modulation, and I can use our oscilloscope to perform this calibration.I can't quite grasp the distinction between an RF generator (aside from being more powerful but not sufficient in terms of output level, as far as I see it, primarily used to generate continuous wave frequencies) and a spectrum analyzer with a tracking generator. Admittedly, I've never used it.

author: nctnico
author_rank: Super Contributor
timestamp: February 17, 2024, 05:07:15 pm
content: Do you really need to go to 6GHz for radiated immunity? Recently I got a product tested and in the 1GHz to 6GHz band, only a few spot frequencies (the LTE bands) where tested at the EMC lab.Unless your product fails those tests, I'd concentrate on the 80MHz to 1GHz band because in that range your product is mostly likely to be affected. For the pre-testing I did, I used this (surplus) amplifier:https://nl.aliexpress.com/item/1005004001551855.htmlwhich works pretty well but I've used it up to 5W as I couldn't dissipate more (see below). I've also seen a 16W version. Be sure to mount it on a heatsink though.If you are going to use an open-sided TEM cell for radiated immunity testing, make sure to also get a shielding tent to contain the RF field. And you'll need a dummy load of some sort to terminate the TEM cell. I bought a Mini-circuits 5W, 20dB attenuator for this purpose (from Mouser as I wanted to get the real deal). The advantage of using an attenuator is that you can also use it to test the amplifier gain.Another neat test to do is see at which level a product fails when subjected to radiated fields. For practical purposes 10V/m is a bit low; it is possible your product ends up receiving much more due to faulty equipment which is still your problem because your product misbehaves. I'd make sure that it stays OK up to 30V/m.RF generator versus tracking generator: The generator typically gives a cleaner tone (less harmonics) and has a more precise output level. With a tracking generator you can typically choose a few levels and thats it. If you are going to drive an amplifier, you will want the ability to adjust the output level to follow the frequency characteristic of the amplifier while doing the stepped sweep.

author: basilic
author_rank: Newbie
timestamp: February 18, 2024, 08:20:58 am
content: For the level, we will conduct our tests at a higher level than required by the standard. The goal is to succeed in the certified lab and exclude uncertainty from our system. We will not declare conformity solely based on the limit line.We use the 61000-6-2 standard for industrial radiated immunity.In the 2006 version, the test levels for radiated immunity with 80% AM (1kHz) are as follows:80MHz to 1GHz: 10V/m1.4GHz to 2GHz: 3V/m2GHz to 2.7GHz: 1V/mThis standard changed in 2019 (we were not aware of this change), and now the levels are:80 to 1GHz: 10V/m1.4GHz to 6GHz: 3V/mwithout specifications... but in the 61000-4-3, we can only cover the phone and RF emitter.I know there isn't a problem with the TEM cell (up to 1GHz) or probe (up to 6GHz) to achieve this level with a small amplifier (0.1W or 0.5W), and it's not an investment for our company (can be placed in current expenses).I checked the output level resolution in the band 150kHz to 80MHz; we need 38.5dBm (7W) as the output for a 10Vrms test, according to the standard (61000-4-6) on a CDN.For the spectrum analyzer: SSA3075X-Plus is designed for -40 to 0 dBm by 1dB step (similar on other spectrum analyzers).For the generator: SSG5060X is designed for -110 to 15dBm by 0.01dB step.In any case, we need an "expensive" amplifier for the conducted immunity.To achieve this level, we would buy an amplifier TBMDA-CDN25 that provides up to 44dBm with a 0dBm input (3 dBm maximum input).If I understand correctly, with the spectrum analyzer and amplifier, we can conduct this test from a minimum level of 4dBm to 39dBm with a maximum of 34/35 steps and much finer steps, and start at a much lower level with the real generator, right?I don't know if the cleaner tone is an argument for an immunity test.I will make calculations to see the effect of a 1dBm change on the signal level (I will try to do this on Monday using LTspice to simulate steps of the spectrum analyzer).