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One Ferrite Is Not Enough

This would be a great Bond film title…

“So Blofeld, do you expect me to talk?”

“No Mr. Bond, I expect you to solve this radiated emissions problem!”

* laser noises intensify *

 

I was doing some radiated emissions problem solving on a smart LCD module and found an issue that is not new but I haven’t encountered for a while.

In this case, the solution required two ferrites. One on the I/O cable to the module and one on the flexible cable between controller and LCD screen.

Adding only a single ferrite in some cases INCREASED the emissions rather than reducing them, presumably an effect where the addition of the ferrite changes the resonant frequency of either one leg or the entire antenna to the troublesome frequency at 192MHz.

This reinforces the approach of:

  1. Always add new fixes to existing fixes already implemented. Whilst it might be the fifth change that worked, it might not have worked without the previous four.
  2. Once the last fix is in place and validated as working only then can you try and figure out what combination is actually required to solve the problem

The last step can get very busy, particularly if there are a large number of modifications applied. It might only be worthwhile if some are particularly expensive or difficult for the customer to implement in production. Different fixes for different budgets!

 

Graphical Guide to EMC: Near Field Probing (free eBook)

 

Download “The Graphical Guide to EMC: Near Field Probing” eBook here (40MB)

 

I have a love / hate relationship with textbooks.

They are thick, have lots of words, make me feel clever, and stop my bookshelf from floating away. They often have the one thing that you are looking for.

On the other hand, they have far too many (big!) words, too many equations with no context or explanation. I find it very difficult to sit, read and quickly gain an intuitive understanding.

 

I prefer to communicate with pictures. This is why my presentations are image heavy and text light. I’ve sat through far too many “PowerPoint Karaoke” sessions where the presenter reads the words on the slide.

Also I love the format of cartoons and graphic novels but you rarely see them outside of the fiction sphere. I’ve recently been thinking about what a combination of a graphic novel and a text book would look like.

 

With the recent acquisition of an e-ink tablet with drawing stylus to replace my 74 different notebooks and notepads I started sketching out some ideas for a guide to using near field probes. A subject that I’m often asked about and is complementary to our free Pocket Probe Set that we give away at shows and to customers.

One thing turned into another and once I started drawing I couldn’t stop. You can download the full eBook from the link at the top of this page or by clicking here.

 

 

I’ve released this under the Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license. This means you can share or adapt this work but you must provide a credit / link back to the original source (here). Any adapted work must be shared with the same licence terms.

 

I’d be interested to hear your feedback on the format and content of this mini eBook – please get in touch and let me know. If there is a positive response then more content may follow.

Thanks and all the best

James

 

 

self interference demo USB3 and 2.4GHz

2.4GHz Intra-System (or Self/Platform) Interference Demonstration

In this blog we are going to take a short look at noise and interference in the 2.4GHz band. Our example victim is a Zigbee controller and the sources are nearby USB3.0 devices and Wi-Fi sources.

 

Background

One of our customers makes these rather useful USB Zigbee Coordinator sticks, frequently used for controlling smart home or IoT devices like light bulbs.

These devices operate at 2.4GHz, a very crowded frequency band with Wi-Fi, Bluetooth and Zigbee all fighting for a narrow, congested slice of spectrum.

One of the common issues faced by users of this band is that of intra-system interference, sometimes referred to as “self” or “platform” interference. This is where components in the same system interfere with each other, primarily due to their proximity.

[Note: The counterpart to intra-system (within the system) in this context would be inter-system interference (between separate systems), which is what the conventional EMC test regime of radiated and conducted emissions and immunity seek to characterise.]

This common problem is something that our customer knows all too well from helping their clients integrate these Zigbee products into the end application.

So, during a recent visit to our lab for some testing on a related product, we spent some time investigating this noise on a typical setup.

 

Demonstration Setup

The setup in the below image is common to many users with a Raspberry Pi Model B and lots of stuff plugged in to the USB ports. In this case, a Zigbee adaptor (black case) and an USB3.0 SSD in close proximity.

These parts, including the spectrum analyser, is part of the customers in-house electronics development laboratory.

 

self interference demo USB3 and 2.4GHz

 

The effects of USB3.0 on the 2.4GHz spectrum are well known. A good example is this 2012 paper from Intel which

For this demo, we used a near field capacitive probe and a 2.4GHz antenna to measure noise in the 2.4GHz to 2.5GHz band local to the Raspberry Pi.

This demonstrated the degradation of the noise floor with various levels of system activity including

  • Measurement of system noise floor
  • Presence of a USB3.0 SSD running a large file transfer using the dd Linux command
  • Activation of the Raspberry Pi internal Wi-Fi

The below image shows three traces under these different conditions.

 

spectrum of 2.4GHz band showing ambient noise, SSD noise and Wi-Fi emission

 

Experiment Conclusions

The conclusions we can draw about the in-band noise are:

  • Noise from the SSD raises the noise floor by approximately 10-20dB (a factor of x10 to x100)
  • The Wi-Fi transmission from the Pi is 40dB above the local noise floor. This will mask any received Zigbee signals from a remote transmitter.

 

In-Band vs Out-of-Band Sensitivity

Well designed radio systems are generally very robust to out-of-band interference i.e. anything outside of the narrow radio band that it is tuned to. For instance, a Zigbee radio system set to channel 20 (2.450GHz) will reject anything below 2.445GHz and above 2.455GHz.

 

Intra System Interference Diagnosis

Advice on diagnosing these issues is mostly outside the scope of this short blog. Differences in systems, components and ambient noise levels makes it impractical to offer guidance for all situations. However, some generic problem solving pointers are presented below.

A systematic approach to isolating the problem is required.

One of the primary rules of problem solving is to change only one thing at once and observe the effects.

In EMC terms, it is possible to change several things at once without realising it. Cable position, the specific port that a device is plugged into, location of nearby equipment and cables, even how firmly a connector is tightened will all make small differences that stack up. (Don’t use anything other than a torque spanner on those SMA connectors though!)

Another key rule is if you think something has made a difference, reverse the change and see if the problem re-occurs. Unless you can achieve consistency then you might be changing something else unintentionally, or the problem is caused by something outside of what you are changing.

Correlating the problem against time can help. Does it happen when something else happens (other devices on, or off, or switching, certain configurations, times of day, etc.) This can give clues.

Lastly, we should be looking for a significant step change in improvement to identify the issue. Phrases like “I think it made a bit of a difference but I’m not sure” indicates that we are dancing around the issue and not getting to the heart of it.

Ultimately, for a detailed understanding, the spectrum analyser is a key tool in gaining a proper grasp of this issue.

 

Solutions

The solutions to the problem are simple yet sometimes difficult – a technical balance needs to be struck.

Use of Ethernet rather than Wi-Fi on the Raspberry Pi.

It is not practicable to synchronise transmission from the Raspberry Pi Wi-Fi with that of the Zigbee stick. The simplest way of ensuring the Wi-Fi does not interrupt the Zigbee transmissions is to disable the Wi-Fi and provide network connectivity via Ethernet instead.

Depending on the installation this might not always be practicable but it certainly is more reliable.

 

Separation of components

Moving the antenna away from the noise source is usually the best way to achieve increased performance.

In this instance, placing the module at the end of a USB cable and away from other electronic items is a good start.

Another option that is not as ideal: a good quality SMA extension cable could be used to extend the antenna away from the problem area. This introduces loss into the RF channel, reducing signal quality.  Measurements made in our lab on a cheap extension cable from RS show a power reduction of 6.5dB at 2.4GHz for a 5m cable. This equates to a ratio of around 0.25 meaning we are broadcasting and receiving a quarter of the power we were before.

Also, it is still possible for the noise to couple onto the nearby module even without the antenna attached meaning the problem does not get entirely resolved.

 

Better quality components

Sourcing a bunch of cheap-as-possible parts from Amazon or eBay is likely to bring problems.

Using devices from big name manufacturers and buying from reputable sources helps. But, even reputable components are designed to a price point and can still cause problems if the other points in this blog are not taken into account.

USB cables can be a big source of the problem. Unshielded back shells (the part between cable screen and connector body) compromise the shielding to the point where their performance at high frequencies is equivalent to an unshielded cable.

The only way to tell if a cable is good quality is to perform an autopsy on the ends and check on the cable shielding

Remember that Pawson’s Law of Cable Quality states that the EMC performance is inversely proportional to the physical appearance. Braided covers, shiny plating, metal connector bodies, transparent mouldings etc are all indications of money spent on the OUTSIDE of the cable. EMC quality comes from the INSIDE and is not visible.

shiny usb cable vs boring usb cable

 

 

Hope this was useful! See you soon.

James

 

 

 

conductive contamination underneath surface mount isolated power supply causing line to earth surge failure(marked up photo)

Surge Test Failure Due to PCB Manufacturing Process

We recently had a piece of customer equipment fail the IEC 61000-4-5 surge test at 2kV line-to-earth. There was a loud crack of an electrical arc forming, the unit stopped responding to communications and was making a hissing/squealing noise.

To give it the appropriate technical term, this was “A Bad Thing”.

Using the thermal camera we quickly found several hot components all on the 3V3 supply line that we supposed had been damaged by the surge. The hissing noise was the DC/DC converter in a cycle of burst mode trying to supply too much current before shutting down.

However these were all secondary side components on the isolated part of the system. How did the surge get across the safety barrier? The designer was using correctly rated parts and the PCB creepage distances were dimensioned correctly.

As part of the fault diagnosis process, we used our hot air solder rework tools to remove one of the isolated power supplies providing a low voltage supply to the AC mains monitoring circuitry. Underneath we found this:

 

conductive contamination underneath surface mount isolated power supply causing line to earth surge failure(marked up photo)

 

The samples had been hand soldered by the customer, unfortunately leaving a large amount of solder paste underneath the power supply.

Whilst this was not a short circuit across the safety barrier it did reduce the creepage distance significantly. When a 2kV surge (1.2/50us, 12 ohms) was applied from AC mains to earthed secondary this pollution was enough to cause an arc to form and into the 3V3 supply pin (centre right).

This voltage was enough to fry several components on the 3V3 line, rendering the board inoperative.

 

Lessons Learned

  • Hand soldering prototypes is OK provided you take great care in the process and cleaning the board afterwards
  • Professionally manufactured boards will generally avoid this issue
  • Apply a line-to-earth safety test on your AC mains powered products to check your samples
  • We are going to start a policy of performing a line-to-earth safety test on all AC mains powered products coming into the lab for testing from now on to try and catch problems like this.

 

 

test report extract showing all tests passed

Thoughts: First Time Pass Rate

This question popped up on one of the email lists that I’m a member of.

“Calling all labs – In your experience how many products pass the Unintentional Emissions test first time?”

I thought I’d share my response:

 

Speaking from my own experience. Over the last four years of running a consultancy, pre-compliance and low cost test EMC laboratory I would (very roughly) estimate that around:

  • 50% of products pass their desired radiated emissions limits without any modification
  • 33% or less pass all of the applicable tests first time without modification

 

The major caveats and notes here are that

  • These figures are for customers products where the EMC performance is not known before testing. We do a lot of work helping people solve existing EMC problems but we are not counting this in these figures.

 

  • Most of my customers are smaller businesses that can’t afford to employ an engineer to just look after compliance. That job role is either split amongst several people or the engineer in question has to look after quality, manufacturing, sustaining, thermal, system, and everything else. Speaking as someone who has designed many products and systems in the past, trying to design for functionality whilst simultaneously considering best EMC performance is HARD.

 

  • The products that pass first time generally fall into one of three categories
    • Products that we have design reviewed before the design was finalised
    • Retests of products that have already been through our lab once
    • Products that are very simple in nature

 

  • Our hit-rate at being able to solve our customers problems is around 90-95%

 

  • The “ones that got away” where we were unable to help deliver a compliant include
    • No action taken: Products where it was deemed by the manufacturer not economically feasible to modify the product (e.g. product going end of life)
    • No further communications from the manufacturer so we don’t get to find out what happened next (no news is good news, right?)

 

I would echo the sentiments of others on this thread regarding the need to design in compliance from the start.

One of the problems with the field of compliance is that it is too often “learned through experience in industry” and not explicitly taught. When it is taught at academic level it is often a surface treatment with a theoretical look at shielding or maybe crosstalk with no other practical context or background.

 

The split between industry and academia is one of the possible causes. Yes, there are exceptions to this but they primarily remain exceptions. I had discussions with a local university about some guest lectures on compliance and the theme of the response was “it doesn’t really fit into any of our modules” and “we can’t have it as an optional lecture as none of the students will attend”.

The number of times I hear “oh, thanks for that. No one has every explained it that clearly before” is worrying!

 

That’s my rant, hope it was useful

James

 

 

 

Thoughts on In House Pre-Compliance Test Equipment

From an email sent to a customer who asked for some feedback on their list of proposed EMC pre-compliance test equipment.

 

“On the subject of equipment, sounds like you’ve identified a nice little pre-compliance setup there! I agree that investing in equipment is a much better long term view than just hiring some in (for the common tests at least).

Com-Power stuff is very good, I use some of their kit myself. The TekBox stuff is very reasonably priced for pre-compliance and again, I use some of their equipment in my test setups. If you are making conducted emissions measurements with a LISN you’d be wise to put a limiter in series with your spectrum analyser input to prevent costly damage. Armoured cable isn’t strictly necessary as it can be difficult to handle, just regular good quality coax is fine.

As a substitute for radiated measurements you can use a current probe around cables as these tend to be excellent emitters of radiated noise. It helps if you already know what the problematic frequencies are. Again, Tekbox make some very reasonably priced probes.

I would also consider the Signal Hound SA44B or BB60C (I have one and I really like it) spectrum analysers as an alternative to the Tektronix one. There’s quite an in depth review of the BB60C here. Their software is easy to use and crucially is free with an EMC pre-compliance option.

If you need test equipment support, I usually talk to Joy Torres at Instruments 4 Engineers in Stockport. She is very helpful and can often get you access to good prices. joyt@instruments4engineers.com. I know she represents Tek, Com-Power and Signal Hound.

The main downsides of making your own emissions measurements is the amount of ambient noise from other electronics, radio sources, reflections off nearby surfaces, etc. It is good for “is A better than B” testing, but it doesn’t really get you to a “but does it pass?” kind of answer. This takes some practice to get right and to get to know your equipment.

The question you could ask yourself is “do I have both the capital and the time to invest in this solution?”. I’ve talked to other companies about their setting up of pre-compliance facilities in house and their struggles tend to be:

  • Engineers lack time to work on the EMC project aspects as well as their regular project work
  • A lot of up front time required to learn the variables of the test setups and standards
  • How to make useful measurements and interpret the results
  • How to match the results from this testing to predicted test lab pass/fail results (spoiler: it is very tricky)
  • EMC knowledge is not well shared amongst employees or the engineer who has the knowledge is on holiday / off sick / unavailable / working on something else

None of these obstacles are insurmountable with good planning and management  🙂  but it is worth going in with eyes open.

In my experience, the best weapon in the EMC armoury is not a spectrum analyser, nor an antenna, not even a full test lab. It is a design review. When we design something we define its EMC characteristics. Getting this up-front bit right is the key to shorter design cycles, fewer prototype runs, reduced time to market and much less stress. Working together to catch the problems before they become problems gives experience in how to design for EMC and the lessons learned can be carried forward from project to project. We’ve helped many customers this way and we’d be happy to help out on your future product ideas.

Similarly, if you want to run quick checks on equipment that needs equipment that you don’t have then we are happy for you to send us the kit via courier and to run the tests on your behalf. I appreciate that our office isn’t exactly nextdoor so anything we can do to help minimise disruption to you and your team would be our pleasure.”

 

Hope some of this is useful

All the best

James

 

Low Frequency, Common Mode, Conducted Emissions

Here is an interesting problem I had working on piece of industrial equipment. The customer had some conducted emissions failures at another EMC lab and needed some help resolving them.

The lessons from fixing this problem was that the first thought is not always the correct one, and that sometimes, all you need is a bit of green-and-yellow earth wire!

 

Outline

A block diagram of the system is shown below with the major components shaded.

An industrial power supply feeds power to the controller (a custom PCB connected to a Raspberry Pi) and to the power measurement board (measures the power consumed by the load).

 

 

Conducted emissions on both the Ethernet port and the AC mains port on the power measurement board were both dominated by a low frequency hump around 700kHz.

 

AC Mains

Ethernet

Notice how the shape or profile of the emissions is almost identical. To my mind, this points towards a single component in the system causing the same noise to be seen everywhere.

 

Simplify First

The first thing I wanted to do was to simplify the test setup as much as possible. I replaced the industrial power supply (often designed for Class A emissions performance) with my trusty Thandar TS3022S adjustable linear bench supply.

The idea here was to eliminate the industrial power supply from my inquiries.

 

 

Wow, what a big difference!

 

So the conclusion here is that the industrial power supply DC output is very noisy, that this noise is propagating through the system, and manifesting as conducted emissions on the outputs via a variety of coupling paths.

 

Differential Mode Filtering

Because conducted emissions noise in this lower frequency range tends to be differential in nature (+ve relative to -ve), my first thought was to implement a differential mode filter on the output of the power supply.

 

 

I’ve got a little filter prototype board that I use in situations like this. This pi filter was made up from two Panasonic FC series 470uF, 25V on either side of a Wurth 33uH iron powder inductor.

 

 

Unfortunately it did nothing to the emissions!

 

Could it be Common Mode?

This sounds like a obvious question to ask in hindsight. Most EMC problems are common mode in nature, I’m just used to thinking about LF conducted emissions as a differential mode problem.

Let’s try a common mode mains filter on the output of the power supply to see if this is indeed the case.

 

 

That’s much better! It looks like the problem was common mode noise after all.

 

This Time It Was Actually A Good Idea…

Common mode noise in this instance is current on both the DC output lines together. But, as I point out in one of my talks, current flows in a loop and always returns to the source. So where is this common mode current returning to? What is it’s reference?

Our common mode emissions measurements are being made in relation to the metalwork of our screened room test setup which is connected to the AC mains Protective Earth (PE).

The AC mains line to each LISN contains a PE connection and, inside the LISN, this is connected directly to the floor of the chamber.

Logically then, connecting the DC negative to the PE on the power supply will provide a shorter path for this common mode noise from the power supply.

 

 

Will this have the desired effect on emissions?

Yes. Yes it does.

AC Mains

Ethernet

 

Conclusion

Ooooooh, bloomin’ common mode noise. Not just for the higher frequencies but lower ones too!

This was a fun half day project fixing this particular problem. Much nicer to be able to recommend a low cost cable assembly than £$€ 20 worth of filter block.

If you’ve got any EMC problems then give me a call, I’d be happy to help.

 

 

dc dc converter emissions before and after with notes on sources

Li-Ion Battery Charger DC/DC Converter – Radiated Emissions Problem Solving

I had a challenging EMC problem solving project in the lab this week.

A customer making a miniaturised 4 cm^3 buck-boost DC/DC converter for Li-Ion battery charging was having radiated emissions issues. The small size meant that adding common mode chokes to filter the input and output connections wasn’t practicable so a more in depth investigation was required.

 

How bad is it?

Here are the emissions for the EUT without any modifications. The green reference trace is the AC/DC mains power supply being used to power the EUT. It is failing the Class B limit (blue) by some margin.

unmodified dc dc converter radiated emissions

Initial Isolation and Investigation

To investigate the emission radiation source (not the cause yet), I placed large clip on ferrite cores around the DC input cable and the battery output cable to reduce emissions directly from the cables.

 

dc dc converter with ferrites on cables

This improves some of the frequencies but not all of them. If the radiation was entirely cable related then this would have dropped the emissions significantly. As it hasn’t, we can conclude that the majority of the emissions are coming from the PCB.

The three peaks we’ll focus on are 180MHz, 300MHz and 500MHz.

Next step is to turn on the spectrum analyser and break out the near field probes. I’ve got a selection of commercial and home made probes but the ones I keep coming back to are the give-away probe cards that I have on my exhibition stand at trade shows.

 

Switching Noise Investigation

The location of the emissions for the 180MHz and 300MHz emissions was initially puzzling. Mostly it was centred around the drain of Q1. If we consider the operation of the circuit, Q1 is turned on permanently in boost mode with Q3 acting as the normal switching element and Q4 acting as a synchronous rectifier. Where is this switching noise coming from?

 

buck boost in boost mode

 

Those of you familiar with synchronous switching converter operation will be shouting at the screen right now. Of course, the answer is bootstrapping.

The high side N channel MOSFETs Q1 and Q4 need a gate voltage higher than their source voltage + their threshold voltage to turn on. In this kind of circuit, this voltage is derived from the switching node via a bootstrap circuit.

This explanation on bootstrap circuit operation from Rohm saves me from re-inventing the wheel.

Even though Q1 is nominally on all the time it still needs to perform a switching operation with Q2 to charge up the bootstrap capacitor powering it’s gate driver circuit.

Checking the datasheet, this switching operation takes just 100ns. That’s very fast indeed and explains the source of our switching noise!

The same bootstrap operation is happening to provide the drive voltage for Q4 but because the boost node is continuously switching this voltage is being provided without such a short switching event.

Due to space constraints it wasn’t easy, but I managed to get the microscope out and modify the board to accept a small but high current ferrite bead in series with Q1 drain.

 

 

500MHz Emission

It didn’t take long to narrow down the 500MHz emissions to the boost output diode D1 with a large amount of ringing on the cathode.

The interesting thing about this diode is that it is only conducting for a very brief period in the dead-time between Q3 turning off and Q4 turning on. Dead time between these parts is set at 75ns, again a very short time period. Good for reducing switching losses, disadvantageous for EMC emission.

 

dead time turn on for the parallel boost diode

 

The part selected for this was a slightly electrically over-rated 40V 1A, SMB packaged part with a reasonable capacitance. Switching 1 amp of current through this part for only a brief period of time before shorting it out and discharging the diode capacitance was causing the ringing to occur.

A ferrite bead was added in series to damp this as the customer wasn’t too keen to head down the rabbit hole of investigating specifying a lower capacitance rated new diode or looking at whether the diode could have been removed altogether at the expense of slightly higher power dissipation in Q4.

Interestingly, this is what the emissions looked like with the diode removed but still with the lower frequency emissions present from the input transistor drain. Note the wideband reduction in emissions above 300MHz.

 

dc dc converter emissions plot with the parallel diode d1 removed from the circuit

Solution

With both of the ferrite beads in place the emissions profile of the EUT was reduced to meet the Class B limits. With more time the peak at 160MHz could be investigated and further reduced but project time pressures and the customer understandably wanting a “good enough” result meant we concluded this investigation here.

 

dc dc converter emissions before and after with notes on sources

The end.

DC/DC converters are often provide a challenging EMC opponent when it comes to radiated emissions. I was glad of the opportunity to work on this project and provide a successful result for the customer. This is the kind of work that I love.

The advantage of being an EMC-consultant-with-a-test-lab combined is that this kind of work can be compressed into hours of work rather than days/weeks oscillating between your lab and the test lab. Problems Fixed Fast!

I hope you found this piece useful, get in touch via the usual channels if you have any questions.

Cheers,

James

 

 

 

HDMI? More like HDM-WHY? Thoughts on Cable Shield Grounding

Ladies and gentlemen, I present this week’s episode of “Crimes Against Cables”

 

Example 1: “I had some leftover components to use”

I’ve seen plenty of interesting EMC “solutions” over the last several years to deal with radiation from cables.

A common one is to separate the shield ground from the signal ground with some combination of components (beads, capacitors, resistors). This approach appears to be particularly common on industrial touch screen display modules for some reason.

poor USB cable grounding suggestions

 

This is (in 99% of cases) a bad idea. I’m not sure what you are hoping to achieve by this and, probably, neither are you 😉

In fact I dedicated a small part of a recent talk to discussing grounds and grounding – you might want to check it out.

 

Example 2: How to Break a Shield

Another notable poor example was an otherwise well crafted piece of military equipment. Shielded connectors and cables all over, it looked like it would be survive some serious electromagnetic abuse (as anything being tested to MIL-STD-461 should).

However,

insulating plastic insert bad idea

insulating plastic insert cross section detail

 

This ends up being not only an emissions problem but an immunity one as well as the cables are just as capable of conducting noise into the shielded case.

This sort of thing can be solved with something like an EESeal type component or by a secondary external screen over the entire assembly.

 

Example 3: Plastic Fantastic

I’ve even seen ferrite cores that were just a moulded plastic lump to appear like cores. Maybe it was a “special” plastic? I never found out, it didn’t help the emissions either.

vga cable ferrite just plastic

But this next one was a first even for me.

 

Example 4 – The Strangest Decision Yet

I was performing a full set of EMC tests to EN 55032 and EN 55035 for a customer. The product had a HDMI interface so obviously there were radiated emissions problems.

The first step as a diagnostic was to use some copper tape to make a connection between the connector shell and the metal back plate – the anodised chassis and EMI gasket material provided was not making a good contact.

This didn’t help so I buzzed the connection with the multimeter to make sure I had some continuity and… nothing.

No connection between the connector shell and PCB Ground.

OK, so there must be a capacitor in series with the shield connection. Fetch the capacitance meter and… 1.2pF.

The board designer had neglected to connect the shield of the HDMI to PCB Ground. It’s a new one for me!

The addition of copper foil to bridge the connector pins to nearby solved the emissions problem but left me wondering why someone thought that was a good idea.

 

I’m going to leave you with this closing thought:

I’ve yet to come across an EMC problem where floating or not connecting a shield ground has improved the situation.

 

 

 

ukca mark

Brexit & UKCA Mark Updates

Because of the United Kingdom leaving the EU, the CE Mark will no longer be recognised as demonstrating conformity with UK legislation.

Instead the CE Mark will be replaced by the UKCA mark (UK Conformity Assessed) which will be required to sell your products in the UK. This mark can coexist with the CE mark on the same label.

The transition period starts this coming January 2021 and UKCA marks become mandatory for the UK on 1 Jan 2022.

Whilst it sounds like a year in enough time to get everything in order think back to university and how much time you had to finish your dissertation – am I right? Start sooner rather than later, especially if you have multiple products.

unit 3 compliance ce mark to ukca mark transition

This applies to goods sold (“placed on the market” to use the correct term) in England, Scotland and Wales. Northern Ireland will still require CE marking due to the Irish border.

 

How can we help?

  • Preparation of UK Declaration of Conformity
  • Updating your Technical Documentation to meet the new requirements
  • EMC or safety testing to meet the technical standards required

 

Action Stations for UKCA

You will need to create a new “UK Declaration of Conformity” similar to the EU Declaration of Conformity (which you will still need for CE marking). Contact me if you need a template. If you’ve been a customer and we’ve performed CE marking testing for you then we’ll be sending out UK DoC templates for your products before the end of this year.

The EU Technical Documentation that I’m sure you keep up to date for all your products will need an additional section with references to the UK Statutory Instruments (equivalent to the Directives) and Designated Standards. Let me know if you need some help with this.

Add the UKCA mark to your product label. You can find image files on the gov.uk website. It must be at least 5mm high.

It can be applied as a temporary label until 1 January 2023 after which it must be “permanently attached” in the same fashion as you currently apply the CE mark.

The product, or documentation where this is not possible, must have the manufacturer’s name and UK address shown. If the manufacturer is outside the UK, this must be the importer’s address.

 

UK Manufacturers Selling to EU

You are now a “3rd country” and will need an EU Sales Office (assuming you don’t already have one) whose address and contact details will need to go on the EU Declaration of Conformity. Various companies offer an “EU Authorised Representative Service” which can be found with a little searching.

If you use a UK based Notified Body, they will probably have already been in touch to discuss what is happening with your compliance certification. If not, get in touch with them sharpish and ask about your compliance status.

 

Key Dates

1st January 2021

UKCA becomes valid and can be placed on electrical / electronic products to demonstrate conformity with UK legislation.

CE mark enters transition period but is still valid for 12 months.

This transition period applies if you currently self declare CE compliance using an EU Declaration of Conformity (the vast majority of products do this).

 

1st January 2022

CE mark ceases to be valid in the UK.

UKCA mark becomes mandatory.

 

Legal Eagles

The EU directives relating to CE marking are already UK law. SI 2019 No. 696 will modify the below SIs (and more) to add UKCA marking and change the terminology. All compliance documentation must refer to these Statutory Instruments instead of the EU Directives.

Notified Bodies become Approved Bodies.

Harmonised Standards become Designated Standards and use the BS prefix (e.g. BS EN, BS ETSI EN). No list of Designated Standards is available yet, this is likely going to be published around 1 Jan 2021 where the list gets transposed from existing standards.

Edit: List of Designated Standards is now available on the gov.uk website

Most standards change at a slow pace so we’ll have to wait and see how quickly changes to the IEC, CENELEC and ETSI standards filter through to the UK standards list. Certainly no massive changes in technical requirements will happen overnight.

 

References

Guidance: Placing manufactured goods on the market in Great Britain from 1 January 2021 (Gov.uk)

Guidance: Guidance Using the UKCA mark from 1 January 2021 (Gov.uk)

UKCA information from the clever chaps over at Conformance.co.uk