Examples of EMI Issues in real Products - Page 1
Forum section: electronics / beginners

author: aksg81
author_rank: Newbie
timestamp: February 06, 2017, 03:59:25 pm
content: Hello all!Longtime follower of the EEVBlog videos and Podcast, but new to this forum.Quick intro: Just completed my PhD in Power Electronics, hoping to make it in academia.I'm going to be talking about EMI and EMC issues to grad students in a lecture, and I am looking for real products that suffer from EMI issues.Of course the most common example is 2G cell phones causing noise in speakers and audio equipment, but Dave's video of EMI affecting the 1272 Multimeter is a little more... dramatic perhaps, as is the case of the GSM phone bricking the Fluke 87V.Are there any other examples I share with the students?

author: Benta
author_rank: Super Contributor
timestamp: February 06, 2017, 04:24:37 pm
content: You'll need to split your subject in two parts:Radiation.That mobile phone or other transmitters emit RF signals are part of their function and happens in controlled frequency bands. Uncontrolled radiation is the real problem, eg, from low-quality Chines switched power supplies. The EU is getting really tough on this with the EMC directive and associated CE marking, the US I don't know.Immunity to radiation.Your example of a 2G phone taking a Fluke 87 out of commission is bad design on the Fluke side. The phone is doing what it should do, but the meter is not hardened/shielded well enough.

author: aksg81
author_rank: Newbie
timestamp: February 06, 2017, 04:29:52 pm
content: Thanks Benta, but I'm mostly interested in examples of the second type.

author: tszaboo
author_rank: Super Contributor
timestamp: February 06, 2017, 04:59:45 pm
content: I had a product, where USB got dropped every now and then, until I put some common mode filtering on the data lines. It had 15m of cabling connected to it in industrial environment (motors and such).Another one, you could reset the device if you touched a certain connector (TVS diode solved that one).Another one, the 50 Hz went through the isolated power supply, appeared on the power line as common mode voltage, and manifested as noise on the measurement circuits. It was making some few microvolts of noise, but it is visible, if you measure with that accuracy.And my favorite was the HopeRF 433 Mhz data module. My boss couldn't start his car (due to the immobilizer) when it was transmitting.

author: janekm
author_rank: Unknown
timestamp: February 06, 2017, 05:06:38 pm
content: I'll just drop this here:http://www.compliance-club.com/archive/old_archive/Bananaskins.htm

author: coppice
author_rank: Super Contributor
timestamp: February 06, 2017, 05:07:27 pm
content: Its not hard to find products which misbehave when radio transmitters are around. There is plenty of test equipment that goes out of spec when a cell phone rings. There are still many products which simply lock up when a cell phone rings. Most products are still not tested with very high RF attack levels. People making products that must stay in spec tend to be testing at 30V/m or more these days. Other go for the minimum they can get away with, or don't bother testing at all.

author: dmills
author_rank: Super Contributor
timestamp: February 06, 2017, 05:13:49 pm
content: Back in my uni days I built a 20M band ham transmitter, and tested it with a dipole strung up across the engineering lab.Turns out the computer science folks minicomputer was one floor down, and possibly not as screened as it should have been... My hammering the brass was playing hell with their compute runs.There was a case over here a few years back of a a guy busted by the police for interfering with the aircraft emergency comms frequency on 121.5MHz, turned out to be a faulty plasma telly in his house.Then there are those recent reports of a 5K monitor that will not work if a wifi router is within a few meters, **embarrassing immunity fail**https://9to5mac.com/2017/01/30/lg-ultrafine-5k-display-router-disconnecting/.A handheld 70cms rig in a bag at a tweaky hifi show is also good for a giggle, BTW.73 Dan.

author: janekm
author_rank: Unknown
timestamp: February 06, 2017, 05:15:32 pm
content: Or if those are not enough examples, here's 855 of them:http://www.compliance-club.com/pdf/banana%20skins.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 06, 2017, 05:17:26 pm
content: Phone charge power adapter. The cheap ones (and, often, the manufacturer's branded products, too) interfere with the operation of capacitive touch displays.Not exactly an EMI/RFI problem, because capacitive touch is terribly sensitive to begin with (and therefore is easily knocked out, at induced fields much lower than recommended), but it's definitely the effect at work.Tim

author: PChi
author_rank: Frequent Contributor
timestamp: February 06, 2017, 05:46:00 pm
content: Another product suffering problems allegedlyhttp://www.bbc.co.uk/news/technology-38853962Waving transmitting 2 way radios around electronics is interesting.

author: JPortici
author_rank: Super Contributor
timestamp: February 06, 2017, 06:35:19 pm
content: We had a product to use in a car hood that used a ts522 opamp for signal filtering (pwm)Due to not enough filtering the product would inject noise when the user made/received a call, sometimes inducing a malfunction, MIL on, engine limit.

author: JPortici
author_rank: Super Contributor
timestamp: February 06, 2017, 06:39:00 pm
content: It was tested for minimum, after that we knew better

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2017, 06:45:05 pm
content: I have an older USB Bitscope DSO that is very prone to spikes and frequently locks up the USB bus (yes I know that's a bit like saying PIN number but whatever) requiring me to close the software, unplug the scope and plug it back in. It is useless on anything remotely noisy without using a USB isolator between it and the PC, especially with a laptop that is plugged into the AC adapter. Even the inductive kick from small relays in a circuit will cause it to lock up.

author: Neilm
author_rank: Super Contributor
timestamp: February 06, 2017, 06:55:37 pm
content: I was re-testing instruments to a new standard and found one that locked up as the radiated RF was applied. The only way of recovering was to remove the batteries and let the on / off latching circuit discharge. It was not a popular instrument so I believe it was discontinued.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 06, 2017, 07:12:12 pm
content: Quote from: james_s on February 06, 2017, 06:45:05 pmI bet you a donut that they implemented the USB shield ground in utterly the most wrong way possible.Tim

author: babysitter
author_rank: Frequent Contributor
timestamp: February 06, 2017, 07:19:42 pm
content: Tesla P85_ (exact type unknown)... aborts charging when its standing standing right under a dipole used with nearly 1kW at the 17m ham band.

author: mmagin
author_rank: Frequent Contributor
timestamp: February 06, 2017, 07:22:47 pm
content: Here's a fairly widespread problem:http://www.intel.com/content/www/us/en/io/universal-serial-bus/usb3-frequency-interference-paper.html

author: max_torque
author_rank: Super Contributor
timestamp: February 06, 2017, 08:05:58 pm
content: Pluging a USB3.0 device into my MS Surface Pro4 kills the WiFI..............

author: dmills
author_rank: Super Contributor
timestamp: February 06, 2017, 08:58:37 pm
content: Quote from: T3sl4co1l on February 06, 2017, 07:12:12 pmNo bet, that is just so stupidly common.Regards, Dan.

author: radiogeek381
author_rank: Regular Contributor
timestamp: February 07, 2017, 02:24:32 am
content: This might be a little too broad an interpretation, but both stories are about the M in EMIAbout 20 years ago, I was sitting in my cube (in a large chip design group at Digital Equipment Corp)when I saw a field service tech carrying a very large monitor (CRT) to a nearby cube.An hour or so later, the same tech passed by with yet another monitor.And then a third.Curious, I followed him to a colleague's cube where the young engineer said "The monitor goesnuts and all the colors get weird every once in a while.""Like when?" I said."It wasn't happening at all until a week ago. They bring new monitors, but nothing changes."We sat together in his office for a few minutes and nothing happened. So, I asked him tocall me next time "the monitor goes nuts."Half an hour later, I hear the call. I walk down to his office and felt a breeze on the back ofmy neck. Then heard a low rumbling sound. Finally the sound stopped and the screenreturned to normal.There was a bodaciously large blower motor in the ceiling above his desk. As it spun up,the magnetic field from the motor was more than enough to screw up the screen (we'd alreadyencountered problems with old-fashioned "ringers" in our desk phones.)When I explained the problem to me, he asked "what can we do to fix it?" I really didn't thinkputting a couple hundred pounds of mu metal over his desk was the right thing, so we movedhis monitors to a "safer" place.----------------Later we found, after moving to a new cube farm, several monitors just had really bad colorfidelity in small sections of the screen. The effect was static. I went to the local hardware storeand bought a magnetometer (aka compass) and wandered up and down the aisles. Sure enough,wherever there was a screwed up monitor, the compass would swing.The frames of the canvas cubicle walls each had a steel vertical strut welded between thetop of the wall's frame and the base. I don't know for certain how a few of them were magnetized,but suspect that a large current (perhaps between the welder electrodes) passed near or throughthem while they were hot.Again, the answer was to move the monitors.Eventually we replaced them all with LCDs, but most of this took place back when dinosaursroamed the earth, and we had to do most of our computations using rocks and sharp sticks.

author: daveshah
author_rank: Unknown
timestamp: February 07, 2017, 12:39:58 pm
content: Quote from: T3sl4co1l on February 06, 2017, 07:12:12 pmWould you mind elaborating what scheme you prefer? I've seen so many different options online and in app notes - solid connection; connection through ferrite; connection through resistors sometimes with a cap in parallel; not connected at all...

author: CJay
author_rank: Super Contributor
timestamp: February 07, 2017, 12:53:23 pm
content: Quote from: radiogeek381 on February 07, 2017, 02:24:32 amMicrowave oven with a 'proper' transformer did almost exactly the same at a dental lab I sold a PC system to. Whenever someone warmed up a snack, the secretary's monitor made pretty, psychadelic patterns. It was on the other side of a brick wall to the microwave.

author: tszaboo
author_rank: Super Contributor
timestamp: February 07, 2017, 01:44:29 pm
content: Quote from: daveshah on February 07, 2017, 12:39:58 pmAFAIK, it has to go to chassis GND directly, if chassis GND is missing, then it has to go GND directly.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2017, 08:23:09 pm
content: ^More than a few app notes have suggested putting a ferrite bead between circuit GND and shield, which is absolutely the worst possible place to put one -- it makes the emissions and immunity orders of magnitude worse!Appnotes are helpful as often as they are cautionary tales of "spot the idiot move"...Tim

author: daveshah
author_rank: Unknown
timestamp: February 07, 2017, 09:17:41 pm
content: Quote from: T3sl4co1l on February 07, 2017, 08:23:09 pmDodged a bullet there - thanks.

author: timb
author_rank: Super Contributor
timestamp: February 07, 2017, 09:47:51 pm
content: Quote from: NANDBlog on February 07, 2017, 01:44:29 pmI've always connected the USB shield to the board's ground through a 100k resistor and 100nF cap in parallel and never had an issue. I'm pretty sure I picked it up from several app notes many years ago.I assume the idea is to filter any noise out. Though I'm not sure how effective it really is...

author: tautech
author_rank: Super Contributor
timestamp: February 07, 2017, 09:56:51 pm
content: Joe mentions EMI problems with his LeCroy in this post and on other occasions in this thread:https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1128792/#msg1128792But he playing with some pretty nasty stuff.

author: coppice
author_rank: Super Contributor
timestamp: February 08, 2017, 04:05:19 am
content: A few years ago we were working to harden utility meters against attacks from noise generating devices, obtained from back street sources, which are designed to cause the processors in these meters to lock up, and not register consumption. Over time the noise generators escalated, and the hardness we achieved responded to this escalation. The difficult point came when the noise sources were crashing every Tek and Agilent instrument on the workbench. Its hard to continue development of your product when its the only thing you have which doesn't fall over.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: February 08, 2017, 04:26:46 am
content: Quote from: janekm on February 06, 2017, 05:06:38 pmThis is awesome! Lots of examples...I got into Amateur Radio starting last year, and this has really opened my eyes to RF interference both from other devices and to other devices. The ham bands are just a small sliver of the spectrum too. It is a very interesting topic.

author: mmagin
author_rank: Frequent Contributor
timestamp: February 08, 2017, 04:59:24 am
content: Quote from: FlyingHacker on February 08, 2017, 04:26:46 amSoon you'll hate just about every piece of consumer electronics beyond a wristwatch or an (incadescent) light bulb.

author: KE5FX
author_rank: Super Contributor
timestamp: February 08, 2017, 05:53:13 am
content: Quote from: timb on February 07, 2017, 09:47:51 pmThe idea behind the parallel-RC connection is to break low-frequency ground loops that might introduce AC line noise into sensitive equipment like audio gear, without sacrificing RF ground integrity. It's better than leaving the shield floating or putting a bead or inductor in series with it, but I personally prefer a solid ground bond at all points of entry. That means that whatever goes wrong is somebody else's fault.The USB signal itself is differential and doesn't really care about shielding one way or another, but there's one potential exception to that. The handshaking that takes place during enumeration, when the host first recognizes the presence of a device, is single-ended in nature. If there are common-mode signal integrity problems for whatever reason, this is when they'll typically show up. About the only SI problems I've ever seen with USB (2.0 HS) have been related to handshaking.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: February 08, 2017, 04:22:44 pm
content: Quote from: mmagin on February 08, 2017, 04:59:24 amNo doubt. It really makes me look for devices in (shielded) metal cases, as they have far fewer issues in either direction. There are so many devices with no RF shielding of any kind these days. I used to complain about all that metal shielding getting in the way when I took things apart. Now I find myself adding it to new products!And this is the easy stuff to block... higher frequencies must be a real nightmare.