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The top EMC Failures and Tips from 5 EMC Consultants

Andy Eadie Uncategorized 13 Comments

Do you ever wonder what the most common EMC failures are so that you can (hopefully) avoid them? Well I do, so I brought together 5 EMC consultants who work hands on with EMC troubleshooting to see what their experiences have been. I asked them to outline what the one or two most common EMC failures are that they’re called in to help out with, and also to give us some tips for ways to avoid them.

Here’s the great advice that they had to give….

Stu Benner

Owner EMConsulting, E3/EMC Design Engineer, iNARTE Certified EMC Engineer

stu_benner_emcI’m a consultant and most of my work is in the military/aerospace segment. By far the most the most common EMC problem I see is radiated emissions (RE) outages followed closely by conducted emissions (CE) outages.

RE problems are most often caused by poor shield termination techniques or poor printed wiring board (PWB) routing. The root cause of these is often poor design strategy or, should I say, lack of a design strategy. For example, if your strategy is to minimize shielding in your interconnect cabling, you must focus strongly on PWB design to control RE. Alternatively, you can implement an excellent cable shielding design and get away with a little less attention to PWB design. Typically I find there is no strategy other than “just do a little of this or a little of that and we’ll hopefully pass the test.” For designs that must meet strict requirements like the Army Ground requirements of MIL STD 461, good shielding and good PWB design are essential.

A particular RE problem I often see is disregard of lines/signals that carry steady-state or infrequently changing signal such as those that indicate on/off, pass/fail, transmit/receive, or a slow/non-changing analog voltage (called ‘discrete’ inputs/outputs in the mil/aero vernacular), as well as passive interfaces like thermistors. The associated circuits may not generate energy that would cause an RE failure, but that does not mean they are not an EMC problem waiting to happen. You must ensure that such circuits are routed away from noisy signals that could couple energy onto the lines and cause RE problems. These circuits are usually easy to filter heavily with a few simple parts. Remember that in the low state, these signals may effectively couple the circuit signal return (‘ground’) out of the unit. This is likely the lowest impedance common mode noise source in the unit. A similar situation exists when the signals are in the high state and are effectively connected to a voltage supply rail.

The frequent causes of CE problems are poor control of return current paths (particularly common mode current) or poor filter high frequency response due to parasitics. Most power supply designers do a good job of controlling differential mode current and designing filters. Unfortunately, it is often assumed that a low-pass filter’s nearly ideal low and mid frequency response continues upward in frequency. Due primarily to parasitic capacitance, filter attenuation can drop off significantly at higher harmonics of switching frequencies (on the order of several megahertz). Common mode return currents are a bit more insidious. The designer must ensure that there is a low impedance return path for CM current that stays local to the switching element. This requires careful attention to where the currents are generated and where they will flow, remembering that current will always favor the path of lowest impedance. CE problems likely occur if that low impedance path is outside of the unit.

Kenneth Wyatt

Electromagnetic Compatibility (EMC) Consultant and Trainer

kenneth_wyatt_emcAs a consultant, primarily working in the industrial, scientific and medical realm, I see radiated emissions as the number one issue. This is followed closely by ESD and radiated susceptibility. The issues causing radiated emissions are just as described by my colleagues above, however, I would add specifically that high speed digital signals crossing gaps in return planes are what keeps the bills paid here.

As for the immunity issues of ESD and radiated susceptibility, I believe these are cropping up more and more largely due to the fact that supply voltages to ICs have been decreasing from 5V to 3.3V to 1.8V to 1.2V, and even lower. Thus, the noise margins are substantially lower than in the past. Couple this with smaller die sizes and the proliferation of wireless, mobile phones, and other high-power communications systems and we’ve greatly increased the risk of interference and circuit disruption from nearby RF fields. The solutions are as described above.

Francesc Daura Luna

Director de CEMDAL (Consultoría de CEM) / Representante de “ams AG” y de “CFC Electronic” en España y Portugal

francesc_dauraThe 3 main issues that I encounter are:

#1 Radiated emissions. The solutions that I find usually involve good PCB design and good shielding at box and cable level.

#2 ESD problems. The main solutions for this involve good PCB design, good shielding at box level and using the correct immunity protection components.

#3 Conducted emissions. Main solutions: good PCB and switching power supply design. Correct filtering.

Patrick Andre

President, Principal Consultant at Andre Consulting, Inc.

patrick_andreI would say in general it is Radiated Emissions. However, I do have clients who struggle with other issues more than RE problems. For example, those who make switching power supplies have conducted emissions issues. A few of my aerospace clients have concerns about lightning. Interestingly, even the clients who have radiated susceptibility tests in the thousands of V/m don’t seem to worry about radiated susceptibility testing. The people who have that issue are groups like medical companies, where they have to measure extremely small voltages (biological levels) and they get subjected to radiated levels 10 orders of magnitude greater than what they are trying to measure. Fortunately, the frequencies are different enough to allow some good filtering to occur.

Most of my clients (about 80%) are aerospace manufacturers. So that might account for my answers.

Benny Lovan

Systems Integration/EMC Engineer Sr. at Lockheed Martin

benny_lovanI am an EMC Engineer that has worked in a test environment for 9 years. All the information from the previous contributors are great but you could also look at EMI problems and solutions from a test stand point. A good percentage of problems in RE (radiated emissions), as everyone has pointed out, are issues related to test setup. These issues include but are not limited to, shields of cables being less than adequate (due to customers not providing actual cables because of size limitations etc.), bonding of connectors to chassis being well into the 100’s of milliohms if not higher due to rubber (non-EMI) gasketing for moisture purposes or non torqued connections, passing cables through waveguide tubes instead of creating patch panels with bulkhead connectors (support equipment noise couples in really easily with large setups, when using things like signal generators or amplifiers, make sure to take this into account. On the flip side a patch panel will also help when using sensitive measurement devices for data collection during radiated immunity. A scope or analyzer is going to do its job well and show you the transmit signal, so if you’re monitoring your device in the transmit frequency band be sure steps are taken to assure your test setup isn’t causing you to think your device is failing.) and standards knowledge (often times test setups require kluged cables or connectors in order to meet a test setup which may cause unwanted EMI).

All in all, a sit down with your local lab to find out facility requirements and how to optimize your chances of passing or at least a few pre-scans would assist in passing your test during formal scans.

Related Post: Essential EMC Design Rules to Avoid the 7 Most Common EMC Failures

Related Post: How to Do an EMC Design Review

Round-Up

Thanks very much to the contributors of this valuable information. If you want to contribute to the conversation, I’d love it if you could leave a comment below, or if you want to contribute a case study (anonymously), then just tell me about it using this short form here. Everyone benefits from this information, so sharing your experience will help us all to improve our knowledge and skills. If I get more input from EMC consultants or engineers, I may come back and add it to this article, or publish more similar articles.

Andy Eadie

Andy Eadie

Andy Eadie is a former senior hardware design engineer and former EMC test lab owner. He's had a weird fascination with magnets since 4 years old and has been publishing articles, eBooks and online courses since he founded EMC FastPass in 2014.
Andy Eadie

Comments 13

  1. By far the biggest problem is cabling in RE. Two areas stand out: shield terminations and braid/foil shielding. Need to run shield terminations 360 degrees to a conductive backshell – the pigtail shield termination (and variations thereoff) does not work. Cable shields – either double shielding (braid/insulation/braid) or braid and foil. Ordinary braid – 20 dB SE – braid/braid – 40 dB SE – braid/foil 60 db SE.

  2. Pingback: Essential EMC Design Rules To Avoid The 7 Most Common EMC Failures - EMC FastPass

  3. Agreed with all of the above.
    As far as test-setups are concerned: You cannot test a chain with a string, You need a bigger chain: Military equipment cannot be tested by connecting to non-hardened commercial equipment. Properly isolate your verification equipment with fiber-optics/filters etc.
    Design:You do not mix colours and whites in washing. Do not mix power/discretes with HF digital or other sensitive sigs in one connector.
    Knitted condom: You get that warm feeling, but the long term effects….Always use representative harnesses. It is (not) fine to pass the test with shielded harnesses, even if the installation uses twin flex. The idea is not to pass the test. The idea is to have a system that conforms to the spec in the installation.

  4. Hello all,
    I am working on electronics development from last 3 years. I am following layout guidelines and grounding and shielding in my designs.i have gone through many materials. The problem I am facing is not able to understand physics of failures due to emi/emc.

    Failure of function due to the noise I understood but if i try it to ask other ways like. I get symptoms of failure. I know the cause that’s it’s a noise which is killing it. And we know solutions in layout or harness.but who is the actual victim I am not able to understand. What things in electronics sub assembly gets affected in what way/ manner to what extent that it fails.

    If anyone guide me to this will be very helpful.

    Thanks

    1. Post
      Author

      Hi Rick, visualization of sources and victims falls under understanding how EMC coupling mechanisms work. That is electric (capacitive), magnetic (inductive), conducted and radiated (far field) coupling mechanisms. If you can visualize how these couple to various parts of your circuit and how they induce voltages/currents in susceptible parts then you will be able to work out how your circuit is being negatively affected.

  5. Why is it difficult – if not impossible – to find any consultants who specialize in, or even mention, EMP? I have immediate need for such an expert.

    1. Post
      Author

      Probably because they’re more rare than an Englishman buying a round at a bar ;). If you want assistance, I offer a service to help find experts in EMC. See emcfastpass.com/jobs for more details.

  6. How are the “mandatory rules” to pass the RF immunity at 100 or 200v/m in anechoic chamber in the 80MHz to 1GHz?
    Thank you

  7. Hi all,

    We have the 875Mhz and 625Mhz at two point is Fail EN55032 emission standard.
    The product is router. It is happen on 1G Wan mode. The system is 25Mhz crystal and it will up to 125Mhz when 1G Wan mode.
    Can you help me??
    Thanks!!!

    BR
    Keung

    1. Post
      Author
  8. Hi All,

    I have worked with EMC, EMR, EMP, TEMPEST, electrical safety, machinery safety and Radcomms for 40 years. I found that standards are just guidelines and a much better approach is to consider essential protection requirements and to take an engineering approach to design and solving problems. For example I worked on many military projects with a mixture of EMC, EMR and safety standards from different counties. Firstly I wasted a lot of time comparing these standards with one another. Then I worked out that I needed to consider the total environment, mission statement and modes of operation. Once I started taking a view of things outside the requirements of the standards I could focus on the design changes that would be necessary and the modes of operation that would require procedures to prevent problems.

    I have worked on the design of ships, trains, factories, buildings and 100s of items of electronic, electrical equipment and 100s of machines. To the best of my knowledge none of these platforms or devices ever had EMC or safety issues. None of the machines went out of control or harmed anyone. None of the military platforms failed to perform their missions.

    It is the essential protection requirements that matter and standards just give a presumption of conformity. If I had designed and tested with a standard centric view I would still be redesigning and testing many of the systems to this day. The devices need to be inherently safe and electromagnetically compatible.

  9. Hello folks i am new for this field how can i develop my self in this field.

    cold you please any one guide me for my success and our machine not meet standard criteria in Radiated Immunity test now i want to solve the problem.how can i solve this problem.

    also other one machine failed in Radiated Emission test in small margin i need your help to solve this both issues.

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