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Do I need to EMC test a pre-approved power supply? – EMC Explained

One of the most common questions we get asked when we send an EMC Test Plan / quotation to our customers is along the lines of:

 

“Our equipment is powered from a pre-approved CE marked power supply so we don’t need to do any AC mains EMC testing… right?”

 

If a power supply has already been EMC tested (if it has a CE or UKCA mark you would hope that this was the case) then it is a fair question – why should we retest it?

Adding AC mains specific tests into the EMC Test Plan adds time and therefore cost, something that some of our customers would like to avoid. For smaller businesses, the cost of assessment for EMC might be one of the largest external costs incurred on a project.

The main assumption driving this question is that EMC emissions – the noise that is coming out of the power supply and either back onto the AC mains or radiated from the power supply – is the only EMC problem we have to worry about. It’s the main one, but not the only one.

The pre-approved power supply will have been tested for immunity, but only the immunity performance of the power supply itself, not the equipment that it is powering.

Some noise will get through the power supply and into the equipment being powered. How does your product respond to this noise?

Also, how low are the AC mains conducted emissions from the power supply? Have you seen a test report? How reputable is the vendor?

Testing is the most reliable way to find out.

 

Our Recommendations

We generally recommend to our customers that they perform all of the applicable tests to the product.

(What, a test lab recommending testing? I’m shocked!).

Firstly, the tests are called up in the EMC standards, and for CE/UKCA marking, testing to a Harmonised Standard gets you a “Presumption of Conformity” to the requirements of the Directives – a pass without any further Risk Assessment or justification on your part.

Deciding not to perform the testing puts the responsibility on you to assess the remaining EMC risks. If you needed us to do this assessment for you or advise on it, the cost of a few hours of consultancy time would be equivalent to just doing the tests in the first place.

Secondly, EMC performance is often dictated by parasitic capacitances and inductances, component values that are not on the datasheet or intentionally designed into the product. Even knowing their magnitude does not give a good understanding of how they will interact. Testing allows us to measure their interaction under standardized conditions.

 

 

Risk Assessment Factors

As discussed above, our recommendation is always to perform testing on applicable ports, the AC mains port included.

If you are worried about costs or time taken for testing, then you might decide to omit some of the specific tests. The below table outlines some of the factors you may wish to consider when making this decision.

The more items that apply from the Risk Increasing Factors column, the less strong your argument becomes for not carrying out testing.

 

Risk Reducing Factors Risk Increasing Factors
Class II power supply (un-earthed)

 

Class I power supply (earthed)

Especially if the DC negative of the power supply output is connected to Protective Earth in the system.

Power supply comes from reputable vendor (e.g. Meanwell, XP Power, Recom, Traco, TDK Lambda, Puls, etc) Power supply comes from cheap or from far east supplier
Power supply external to product Power supply internal to product
No analogue or sensitive circuitry Analogue circuitry e.g. audio, 0-10V I/O, 4-20mA I/O

Sensitive, low level signals e.g. thermocouple, RTD

No other long (>3m) cables connected to equipment One or more long (>3m) cables connected to equipment
Main use in Basic (residential, commercial) EM environment Flexible use, could be used in Light Industrial or Industrial EM environments

 

If you are at all unsure then you should test the AC mains port with your intended production power supply.

For the ultimate in performance, or if the equipment is for flexible use (could be powered from an AC/DC supply or from a distributed DC power supply) then we would recommend treating the DC power input to your product as a signal port with a length greater than 3m.

This would then call up Conducted RF Immunity (EN 61000-4-6) and Electrical Fast Transient (EFT, EN 61000-4-4) testing to the power port at the appropriate levels for the end EM environment (e.g. Basic or Industrial)

One step further would be to apply line-to-line and line-to-earth surges to the DC input, assuming that the design already contains a transient surge voltage suppressing element like a TVS diode or an MOV.

Let’s take a look at some of the technical justification behind the selection of these items.

 

AC Mains Port vs DC Power Port

If you typically derive your equipment power from an AC mains power supply, then it is unlikely that you will fall under the DC Power Port classification.

The term DC Power Port in EMC terms means a very specific classification of port. We discuss this in some length in this article.

 

Power supplies do not always meet the regulations

A scenario that we have experienced on several occasions: the power supplies that end up with our customers or in our test lab are not the same as the ones in the manufacturer supplied EMC test report.

 

Another customer had similar problems on  power supply that they had received samples of in that the EMC performance varied wildly. In this case the clue was that the weight of the two samples was significantly different.

 

 

These power supplies were almost identical on the outside but significantly different on the inside. Same manufacturer and model number, different components. Imagine the conversation:

“I’d like to order some HM-A132 power supplies please”

“Certainly sir, which ones?”

“Erm…”

 

This is mostly related to cheaper power supplies sourced from China. We often see significantly different results to those shown in the manufacturer test report.

The worrying thing is if changes like this are being made on the basis of EMC, what changes are being made that affect Electrical Safety that are going unchecked? We can check that for you as well.

 

Cable Routing

If your power supply is integrated into your equipment then there is the possibility of noise on the AC mains cable coupling onto other nearby cables.

It is also possible for noise to couple (both to and from) components connected to the AC mains and internal system components. This could be an emissions (noise getting out) or an immunity (noise getting in) risk.

 

This is particularly likely if you are using slotted trunking and mixing AC mains cabling in with other cables.

 

 

 

This is less important for an external power supply like a laptop type charger or a plug top power supply as the AC mains cable remains outside of the equipment enclosure.

 

 

Power Supply Common Mode Impedance

Electrical noise inevitably gets coupled onto the AC mains bus. Normally this noise is coupled onto the AC mains Common Mode. This means all the lines together in relation to a high frequency “ground” reference plane.

The noise current through the power supply and equipment will flow something like this:

The noise reaching the equipment will have been attenuated by the Common Mode impedance of the power supply and the currents diverted through the parasitic capacitance of the power supply relative to the HF ground reference plane used in the tests.

Crucially, some noise still gets through to the power supply and will flow through the product. The magnitude of this current can be estimated or measured but relies on electrical parameters that are not on the power supply datasheet.

It is this noise current that we are interested in. How does it affect your product? The only way to find out is to perform testing.

 

Class I vs Class II Power Supply CM Impedance

The construction of a typical switch mode AC/DC power supply is broadly similar across a wide range of topologies. One of the main EMC variations results from if the power supply is Class I (earthed) or Class II (unearthed).

 

Class II

A Class II power supply relies on Double or Reinforced insulation between Live parts and user accessible secondary low voltage parts for Electrical Safety. There is no connection to Protective Earth. This kind of power supply is usually identifiable by:

  • the square-in-a-square double insulation symbol (IEC 60417 symbol # 5172)
  • a plastic earth pin on a UK mains plug (technical name is an ISOD or Insulated Shutter Opening Device)
  • An IEC C8 “figure-8” AC mains inlet socket with just two pins

 

Looking at the typical internal structure of a Class II AC/DC SMPS we can see that the components providing Common Mode noise attenuation are

  • the inductive common mode filter (Lcm)
  • the components across the safety isolation barrier, transformer Tx and class Y capacitor Cy

The value of parasitic parallel capacitance of the choke or transformer (or wanted series capacitance of Cy) will reduce the impedance ( Xc = 1 / [ 2 * pi * f * C ] ) and allow more noise current to flow at higher frequencies.

This capacitance is usually a low value to prevent too high a touch / leakage current to flow which would compromise Electrical Safety.

However, at EMC frequencies of MHz and higher this presents a much lower impedance allowing noise currents to flow through the cable.

 

block diagram of a class II power supply showing EMC immunity noise current through the power supply

 

Because current always flows in a loop, and because current always returns to the source, to close this common mode current loop we need to have return currents flowing. We usually think of these coupling capacitively onto a nearby metallic element like a nearby metal structure.

In the test lab we simulate this with a nearby metal plate but in real life this could take a number of forms (building steelwork, conductive cable trays, other wiring).

 

 

Class I (Or Class II with Functional Earth) Power Supplies

With a Class I power supply, the Protective Earth is connected to accessible metalwork for Electrical Safety reasons (prevention of electric shock). Basic insulation (or higher) is required between the live parts and user accessible secondary parts.

Possibly the protective Earth is also connected to DC negative somewhere in the system as well.

A Class II with Functional Earth power supply is similar from an EMC point of view but very different from an Electrical Safety point of view. In this case, the Earth is connected for functional reasons (reducing noise or EMC emissions) but the power supply still relies on Double or Reinforced insulation for safety.

This isn’t a very common power supply topology choice, so I was surprised to see it marked on my laptop charger power supply.

 

 

In both cases, when we apply common mode noise to the AC mains input (L+N+E) then the Protective Earth conductor allows the noise to bypass the common mode impedance of the power supply. It is for this reason that we view the use of a Class I earthed power supply as a higher EMC risk for immunity reasons.

 

block diagram of a class I power supply showing EMC immunity noise current through the power supply

 

 

How this noise couples into the rest of the equipment, its magnitude, and how it affects it depends massively on the construction of the equipment. Again, testing is the best way to determine this.

 

Conclusion

Power supplies and the equipment they power are not perfect and can have varying EMC performance depending on how you connect them and how the equipment is designed.

It isn’t always easy to estimate how likely EMC issues are, even for experienced engineers and problem like us at Unit 3 Compliance. It is for this reason that we would always recommend testing to characterize the unknown EMC performance.

If you do decide to omit some testing, then the Risk Reducing or Increasing Factors above should help with that decision.

Again, we hope that this guide was useful to you in some way. Get in touch with us if you have any thoughts, questions, observations, or (obviously) a need for EMC or Electrical Safety testing.

All the best!

 

 

 

sketch showing dc power distributed around a building on busbars to a vriety of loads, and with a battery bank. There is an AC/DC charger for the batteries.

What is a DC Power Port? – EMC Explained

Everyone knows what a DC power port is, right? It’s this…

sketch showing an ac/dc adaptor and a piece of equipment with a dc power input - this is classified as a signal port for emc purposes

It’s got DC power on it, and it is a port on the equipment. DC. Power. Port.

Not in the context of EMC I’m afraid. Despite the similar name, the EMC definition for a DC Power Port (from the IEC / EN standards) is very different.

The DC Power Port is unfortunately mis-named. A better term would be “DC Mains Port” to indicate how similar it is in construction and EMC requirements to its counterpart “AC Mains Port”.

In this guide we will refer to it in this guide as a DC power/mains port and look at:

  • The EMC definition of a “DC Power Port”
  • The EMC implications of classifying a port as a “DC Power Port”
  • Examples of a DC Power/Mains Port
  • Examples of NOT a DC Power/Mains Port

Any port that doesn’t meet ALL of the definitions of a DC Power Port is just classed as a Signal Port, albeit one that happens to carry DC power.

Those key parameters are:

Criteria Met?
Local supply in a site / building / infrastructure? ???
Flexible use by different types of equipment? ???
Supply independent from AC mains? ???

 

Definition

The definitions in the Generic EMC standards of EN 61000-6-1 (immunity) and EN 61000-6-3 (emissions) lays out what a DC Power/Mains Port is:

 

EN 61000-6-3:2007+A1:2011, Clause 3.8

“d.c. power network

local electricity supply network in the infrastructure of a certain site or building intended for flexible use by one or more different types of equipment and guaranteeing continuous power supply independently from the conditions of the public mains network

NOTE Connection to a remote local battery is not regarded as a DC power network, if such a link comprises only power supply for a single piece of equipment.”

 

Let’s break out the key terms to understand the definition:

 

“…local electricity supply network in the infrastructure of a certain site or building…”

 

This suggests something wiring that is built into or spreads around a large area. A good example is the way that AC mains wiring is distributed around a building. Imagine this carrying DC instead of AC.

Typical cable lengths are probably around 10m or longer. Longer cables means they can act as antennae for low frequencies (longer wavelength). So we need to be concerned with power supply noise from our equipment on these cables that could radiated from them.

Longer cables will also pick up lower frequency common mode disturbances (conducted RF and surge) and present a larger surface for capacitive coupling of fast transients (EFT).

 

“…for flexible use by one or more different types of equipment…”

 

Use of the word flexible implies ease of use and simple connection to this power distribution system. Perhaps a common power connector (similar in nature to an AC mains plug) is used, or an agreed connector standard.

A DC Power/Mains bus that requires tools and time to connect to (example a fire alarm wired with Mineral Insulated Copper Clad (MICC) or “pyro” cable) might not meet the definition of “flexible” in terms of “ease of connection”. Nevertheless it would be flexible in terms of connection of different types of equipment (sounders, detectors, etc.)

 

“…guaranteeing continuous power supply independently from the conditions of the public mains network…”

 

The likely scenarios here are:

  • A “DC UPS” system where a bank of batteries are kept topped up by an AC mains charger
  • A DC micro-grid system where power is generated from sources like solar power

 

Importantly

1) Any port that doesn’t meet ALL of these definitions is just classed as a Signal Port, albeit one that happens to carry DC power.

2) Any piece of equipment connecting to this DC power supply is classified as a “DC Power Port” regardless of whether it supplies or consumes the power

 

EMC Tests Required for a DC Mains/Power Port

The classification of a port as a DC Power/Mains Port invites extra EMC testing to be applied.

 

Port Length Conducted

Emissions

EN 61000-4-4

EFT

EN 61000-4-6

Conducted RF

EN 61000-4-5

Surge

DC mains/power Any YES YES YES YES
Signal (with DC) <3m NO NO NO NO
Signal (with DC) >3m and <30m NO YES YES NO
Signal (with DC) >30m NO YES YES YES

 

Almost inevitably, unless the equipment has been explicitly designed as a DC Mains/Power port, there will likely be EMC test failures.

Conducted emissions invariably fails the limits. Usually the first system component after the input power connector are a series of DC/DC buck converters to change the input voltage down to levels that are needed in the system.

Buck converters suffer from noisy input nodes because of the high dI/dt requirements of the switching transistors. This needs to be mitigated through good quality high frequency decoupling and can cause noise at 20MHz upwards. Common mode chokes in the DC input may be required to mitigate this noise.

At lower frequencies, there will be current draw from the supply at the switching frequency of the DC/DC and at it’s harmonics. Unless low impedance electrolytics and a differential mode filter (usually an inductor in the 2.2uH to 10uH range forming a pi-filter) are used, the emissions from the port will fail the average limits in the 150kHz to 1MHz range.

DC Mains/Power also requires the addition of the surge test in both line-to-line (DC+ to DC-) and line-to-earth (DC+ and DC- together relative to Earth) coupling modes.

The line-to-line surge of 500V (commercial/light industrial EM environments) or 1kV (industrial EM environments) with a 2 ohm source impedance is capable of damaging the first switching transistor it comes across on the DC line unless a Transient Voltage Suppressor (TVS) is employed between DC+ and DC-.

The line-to-earth test with a series impedance of 42 ohms (not the 12 ohms as used for the AC mains port test) tests the insulation of any isolated power supply and depends heavily on how (or indeed if) a Protective Earth connection is made within the system.

 

Examples of A DC Power/Mains Port

The sketch below tries to capture a typical DC Mains/Power port application

sketch showing dc power distributed around a building on busbars to a vriety of loads, and with a battery bank. There is an AC/DC charger for the batteries.

 

Criteria Met?
Local supply in site / building / infrastructure? Yes
Flexible use by different types of equipment? Yes
Supply independent from AC mains Yes

 

Specific examples include:

 

Telecoms

48V distribution around telecoms switching / data centers to power the equipment and to provide low levels of power to handsets in a Plain Ordinary Telephone Service (POTS)

 

Computing Data Centres

Large data centre and cloud computing providers like Facebook, Microsoft, Google, and Amazon are moving away from traditional DC>AC UPS systems and towards DC power distribution (380V, 200V, 48V depending on standards) to servers and other electrical loads.

The efficiency savings from not having to convert from AC power to DC in every load, multiplied by the number of loads makes for significant energy efficiency savings and heat reduction – some of the biggest costs for such facilities.

In addition, the DC to AC conversion loss in the UPS from battery DC voltage to AC voltage is removed. Instead there are just the batteries connected to the DC power bus.

 

Electricity Substations

Battery Tripping Units (BTU) are used to power monitoring and control equipment in electricity substations. The LV AC mains supply to the substation equipment (derived from the HV or MV feed) is considered to be an “auxiliary” supply. Control of the equipment is a requirement even if this power is not present. Common DC voltages are 220V, 110V, 48V, 36V, 24V.

 

DC Micro-Grid

Local power generation from renewable sources like Solar PV might be distributed around a power generating plant or a local area.

 

Emergency Lighting Central Battery Units

There is a requirement in Building Regulations to have fire exit emergency lighting powered separately so that in the event of a power cut the building occupants can find their way out of the building safely.

In smaller buildings this is usually achieved using emergency lighting with independent battery backup. However in larger buildings, a Central Battery Unit is used to provide power (and often control / monitoring functionality) to emergency lights spread throughout the structure.

The combination of data and DC power blurs the lines between a DC mains/power port and a Wired Network port. Both call up conducted emissions tests and similar levels of immunity.

 

Fire Alarm System

DC power is passed to different critical components of the fire alarm system (e.g. smoke / fire detectors, displays, alarm sounders) in a loop system from a central control panel.

sketch showing the connection of fire alarm components to a central panel - emc dc power port example 2

Criteria Met?
Local supply in site / building / infrastructure? Yes
Flexible use by different types of equipment? Yes [1]
Supply independent from AC mains Yes

 

[1] May be difficult to connect to and reconfigure but certainly flexible in terms of variety of equipment that could be connected

Interestingly, the EMC product family standard that deals with fire, security, and social alarms (EN 50130-4) only focuses on emissions from the AC mains port with no mention of DC power outputs. Since other standards address EMC requirements for DC Power Ports, including the Generic EN 61000-6-x series mentioned above, we have a path to bring in these requirements to the EMC Test Plan as part of the EMC Risk Assessment.

If using MICC / pyro cable, whilst the joints are required to be fireproof, there is no requirement for quality of termination for EMC purposes. Reliance on the shielding formed by the outside of the cable is contingent on a low impedance electrical termination which is not necessarily guaranteed.

 

 

 

Examples of NOT DC Power/Mains Ports

AC/DC Power Adaptor

sketch showing an ac/dc adaptor and a piece of equipment with a dc power input - this is classified as a signal port for emc purposes

Criteria Met?
Local supply in site / building / infrastructure? No
Flexible use by different types of equipment? No
Supply independent from AC mains No

 

In this event, the power bus with long cables is the AC mains interface that our AC/DC power supply plugs into (for non-UK readers: that is a UK AC mains plug).

The AC mains has all the EMC characteristics discussed above: long cables that can radiate noise (emissions) or have noise coupled onto them.

One question we get a lot is along the lines of:

“My product is powered from a pre-approved / CE marked power supply, so we don’t need to do any EMC testing on it… right?”

We’ve written a separate article to cover this interesting question.

 

DC power distribution around a typical DIN rail electrical cabinet

sketch showing typical dc power distribution around a DIN rail equipped electrical cabinet - again this would be classed as a signal port

Criteria Met?
Local supply in site / building / infrastructure? No
Flexible use by different types of equipment? Yes
Supply independent from AC mains No

 

In this example, the Load represents the equipment we are interested in. There is the probability of noise coupling onto the DC power cable from other equipment inside this cabinet. For example a large industrial machine would typically have contactors and large Variable Frequency Drives running close by.

If we think this could be the case then we would recommend testing Conducted RF immunity (61000-4-6) and EFT (61000-4-4) regardless of the anticipated maximum length of power supply cable.

This would form part of the EMC Risk Assessment for the equipment, an important part of the decision-making process for what EMC tests to apply. If you’ve not considered EMC Risk Assessments before then get in touch with us and we can help!

 

Power over Ethernet (PoE)

sketch showing an example power over ethernet distribution - these are classed as Wired Network Ports under EN 55032

 

Criteria Met?
Local supply in site / building / infrastructure? Yes
Flexible use by different types of equipment? Yes
Supply independent from AC mains No [1]

 

[1] Depends on the power source for the switch, it could come from a UPS for no-interruption requirements like security or network infrastructure.

Supplying DC power over an Ethernet cable is a thoroughly good idea. High speed data, enough power to run a simple device, all over cables approaching 100m in length? Sounds great!

Each port in a PoE switch will have power provided from a dedicated isolated power supply. This provides isolation (both in terms of EMC emissions and immunity) between different segments of the PoE network.

Despite the potentially long cables, it still doesn’t quite meet our criteria for a DC power port. However similar EMC requirements for a DC power port are called up by other standards:

  • EN 55032 (emissions of multimedia equipment) calls up a requirement for conducted emissions on wired network ports
  • IEEE 802.3 specifies a voltage isolation between Ethernet cabling and the circuit at each end of 1500Vac. This will often help (but not completely resolve) with the surge requirements
  • The surge test of EN 61000-4-5 is not applied line-to-line as the Ethernet lines are considered to be “symmetrical” in the language of this Basic standard. The tight coupling between the pairs in the cable and floating / isolated nature of the signaling means that coupling onto these cables generating line-to-line surges is considered unlikely. Only line-to-earth surges are applied.

 

Daisy chain of DC powered devices all running from the same bus

sketch showing a daisy chained series of DC powered loads - classified as a signal port

Criteria Met?
Local supply in site / building / infrastructure? No
Flexible use by different types of equipment? Yes
Supply independent from AC mains No

 

 

Conclusion

Hopefully this guide has cleared up some of the confusion about DC power ports in the context of EMC.

If you are unsure about whether your equipment falls into this classification then you can always contact us if you need help.

We generally advise that if you aren’t sure if your equipment could be used in this fashion then you should design and test your product as if they do apply. It is easier to “not-fit” or link out unwanted components than to try and add them in later.

 

RCWL-0516 - board image from github.com-jdesbonnet

Compliance Assessment of a RWCL-0516 Doppler Radar Motion Detector

I’ve been helping a customer out with some EMC pre-compliance testing of their new domestic product which included a range of 3rd party modules.

One of these modules was an “RCWL-0516” 3GHz radar for motion detection. These modules are widely available but technical information is mostly reverse engineered by enthusiasts and hobbyists. The best collection of information seems to exist on this GitHub page.

RCWL-0516 - board image from github.com-jdesbonnet

The customer was very keen to use these devices but making some measurements and looking into the regulatory side meant that it got a Big Fat No from me.

 

EMC Radiated Emissions

Radiated emissions in the 1-6GHz band were in excess of the Average limit line by over 17dB.

RCWL-0516 - radiated emissions Class B domestic

This is normally OK for a radio system, as exceeding these limits is often required to achieve the desired range and operation. However this only works if there is a counter-part radio standard to refer to…

 

Analysis of the Regulatory Status of this device

  • No CE / UKCA marking applied to these devices – should not be sold in the EU / UK
  • No CE / UKCA marking Declaration of Conformity supplied by manufacturer – should not be sold in the EU / UK
  • No reference to technical standards used to assess the device to the Radio Equipment Directive
  • At present there are no radio standards published by ETSI for the use of this 3.1GHz band for this kind of application in the EU or UK.
  • This document from CEPT on the use of Short Range Devices gives more details about what radio bands can be used
  • 3.1GHz is not a Harmonised Frequency band. Instead, it is licensed, and operation is only permitted in some countries. The key to the table is at the bottom.

RCWL-0516 - CEPT radio band table

  • Even when taking this table into account, this band is only for UWB Location Tracking Systems.

RCWL-0516 - CEPT radio band table part 2

  • Following the documents further down the chain, the ECC/REC/(11)09 mentioned above refers to two documents:
    • TR 102 495-5 for use of Ultra Wide Band for location tracking operating in 3.4 to 4.8GHz. This device is not UWB and not operating entirely in this band.
    • ECC REPORT 120 requirements for UWB Detect-and-Avoid for operation in this band. This device has not such capabilities.
  • The only way that this radar device can be considered legal to operate is if it meets the Class B (domestic) emissions limits in the 1-6GHz band.
  • Currently this is not the case. With this example product, emissions will need to be reduced by 17dB or more to comply.
  • The oscillator used relies on parasitic components between PCB elements. Tolerance of components, PCB manufacturing tolerance, values over temperature means that frequency stable operation is not practicable.
  • From a regulatory standpoint, these devices should not be touched with a barge pole
  • Other motion detector products exist – I’ve not linked to any as I don’t want to unfairly endorse anything I’ve not investigated further or tested myself.

 

Summary

Anyway, I hope this clears up some of the questions about this device.

I can’t recommend using these devices at all. If you are going to use one of these then keep an eye out for interference with other systems. Don’t even bother if you want to make something that you can sell at the end of the process.

Cheap 3rd party modules like this are usually cheap for a reason.

Thanks to Charlie Blackham for pointing me in the right direction with the radio standards.

 

 

 

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

 

 

 

Choosing EMC/Radio Standards for CE/UKCA – Generic vs Specific

A short post prompted by a (summarised) request from a customer:

 

We’d like to test to the following standards for our CE/UKCA marking

– EN 61326-1 (Class B emissions, Industrial immunity)
– EN 61000-6-2 (Industrial Level Immunity)
– EN 61000-6-3 (Class B Emissions)

 

This customer is very compliance conscious, as their products end up in all kinds of harsh and hazardous environments where they are protecting the health and safety (and lives in many cases) of their customers.

As such, it is understandable that they want to “throw the kitchen sink” at the EMC performance. Selecting Class B emissions and industrial immunity is a great way of demonstrating the robustness of your product in a wide range of electromagnetic environments.

So, why not quote all of the standards on the Declaration of Conformity (DoC)?

 

CE and UKCA

This article was originally written with CE in mind. It also applies to UKCA, just replace “Harmonised” with “Designated” as far as the standards go and you’ll be fine.

 

Guidance is Available

Thankfully the European Commission has published guidance on selecting Harmonised EMC and Radio standards for assessing the product to.

In each of these standards, a primacy or order of application, is given to the Harmonised Standards.

 

Guide for the EMCD (Directive 2014/30/EU)

4.3.2.2 Relevant harmonised standards

The selection of the relevant harmonised standards is the responsibility of the manufacturer.
When the manufacturer chooses to apply harmonised standards he shall select them in the following precedence order:

– Product-specific standards (if available)
– Product family standards (if available)
– Generic standards

Product-specific (family) standards are those written by ESO’s taking into account the environment, operating and loading conditions of the equipment and are considered the best to demonstrate to compliance to the Directive.

 

An example of a product specific standard would be EN 61326-2-6Electrical equipment for measurement, control and laboratory use – EMC requirements – Part 2-6: Particular requirements – In vitro diagnostic (IVD) medical equipment (IEC 61326-2-6:2012)”

These product specific standards often refer back to the root family standard, EN 61326-1 in this case.

Only if the manufacturer’s equipment does not fall into a product standard should the generic standards be applied.

 

Guide to the Radio Equipment Directive 2014/53/EU

5.2 Generic harmonised standards vs product specific harmonised standard

A manufacturer which has the intention to apply a harmonised standard for the conformity assessment of its products, has to apply in priority the product specific harmonised standard and only if this one is not available, the generic one, in order to benefit of presumption of conformity with the essential requirements of the RED.

 

Applying Multiple Standards

There are cases where applying several different Harmonised Standards could be the correct thing to do.

For example, if the equipment is a piece of measurement equipment that incorporates a lot of IT functionality (networking, data storage, PC control) then the manufacturer could decide to assess against EN 61326-1 for laboratory equipment and against EN 55032 for IT equipment. Both standards would appear in the test report and on the DoC.

 

Check Annex ZZ

One of the commonly overlooked Annexes (Annecies? Annecii?) is this one at the start of the standard. This details what Essential Requirements from the Directive are being covered by the standard.

Important: not all standards cover all Essential Requirements. You must check Annex ZZ carefully against them.

If you end up needing to apply more than one Harmonised Standard to a product to cover all of the Essential Requirements then you should state this on your Declaration of Conformity.

 

Presumption of Conformity

Remember that using Harmonised Standards (or Designated Standards for UKCA) gives you a “Presumption of Conformity” without further requirement to demonstrate compliance with the relevant directives/laws.

As this interesting piece on kan.de notes:

 

“Ultimately, the presumption of conformity is no more than a reversal of the burden of proof. This means that a product complying with the relevant [harmonised] standards may be challenged, for example by the market surveillance authority, only if actual evidence can be produced that the manufacturer has violated the requirements of the directives.”

 

Annex ZZ of a Harmonised Standard is your friend when it comes to understanding this link between the standards and the directives.

 

When the DoC Doesn’t Quite Cover It

This example of EN 61326-1 illustrates one of the problems of applying a Harmonised Standard that has multiple levels within it.

In this case, the EMC performance of equipment complying with EN 61326-1 could fall into one of six distinct categories.

Emissions

  • Class A (industrial)
  • Class B (domestic)

Immunity

  • Controlled (shielded and filtered environment)
  • Basic (domestic/commercial)
  • Industrial (heavy machinery)

On the face of it, a product tested to Class A / Controlled (poor EMC performance) can’t be distinguished from one that has passsed Class B/Industrial limits (excellent EMC performance).

What to do?

The way I suggest overcoming this and informing the end user a little more clearly about the performance of the product is to explicitly state in the DoC what levels the product was assessed against during any testing.

Example:

 

This equipment was assessed against the following Harmonised Standards:

 

– EN 61326-1:2013Electrical equipment for measurement, control and laboratory use – EMC requirements – Part 1: General requirements” (Class B emissions, Industrial Immunity)

 

I hope you enjoyed this short dive into standards land. It’s a nice place to visit but you wouldn’t want to live there!

Speak soon,

James

 

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

 

 

EMC Certification is not just a rubber stamp by the test lab!

“Do You Do Certification?”

“Do you do certification or just pre-testing?”
“Can you certify our products?”
“Can you do EMC testing even though you aren’t accredited?”

The concept of “certification” is an interesting and, judging by these real customer enquiries that we’ve received, a confusing aspect of EMC testing.

The short answer to the questions above is “no, you do, in a way, most of the time, for most things” but like most short answers it isn’t particularly helpful.

To help clear this up, lets have a quick look at declaration vs certification for EMC testing to CE marking (EMCD & RED), UKCA Marking, and “FCC” CFR 47 Part 15B, lab accreditation and the operating philosophy of Unit 3 Compliance.

In summary:

  1. Unit 3 Compliance test results are valid for a wide range of regulatory approvals, including CE marking, UKCA marking, and FCC
  2. In the context of the CE Mark, there is no such thing as a ‘CE certificate’ or a ‘CE certification’ process. Same applies for UKCA.
  3. You (the manufacturer) “self certifies”; or rather you legally Declare your product to be compliant with the EU Directives or UK SIs
  4. UKAS Accredited Laboratory testing is not mandatory for CE, UKCA and many FCC tests.
  5. For the USA (FCC) certification does exist but it depends on the product. Many products are exempt from certification.

 

Unit 3 Compliance Test Results Validity

Regulatory Regime

Product Type

Unit 3 Compliance can be used for testing?

CE Marking &
UKCA Marking

EMC or Radio Equipment Directive

Yes

FCC

Unintentional Radiators (Part 15B)

Yes

FCC Unintentional Radiators with FCC Approved Radio Module

Yes

FCC

Intentional Radiators (Part 15C) with a non-FCC approved radio

Pre-compliance only.

Accredited laboratory required for final test

 

 

CE Marking

When CE marking for selling products in the EU, most electronic products are going to be covered by either the EMC Directive (2014/30/EU) or the Radio Equipment Directive (2014/53/EU). The latter refers to the wording of the EMC Directive anyway.

In all cases, the manufacturer “self certifies” by assessing the product (usually to a Harmonised Standard) and then producing and signing a Declaration of Conformity (a legal document) to confirm that their product meets the Essential Requirements of the Directives in question.

Note that the directive requires the manufacturer to “assess” the product. It doesn’t specifically require testing of a product. However, by testing the product to Harmonised Standards, you gain a “Presumption of Conformity” to the requirements of the Directive.

However, testing is the best way to determine performance; EMC behaviour is largely dictated by parasitic components that are not generally present on the design documents.

It is then up to the manufacturer to ensure that all future products remain compliant through control of production.

Try searching either of these Directives for the following:

  • certificate
  • certification
  • accredited
  • accreditation

and you will find that these words are only used in relation to a Notified Body (NB) or an EU Type Examination Certificate provided by such a body. This approach is only mandatory for a narrow range of products or applications (e.g. where no Harmonised Standard exists for the Radio part of the equipment).

Similarly, there is no requirement to use an ISO 17025 accredited laboratory for any of the assessment activities. Accreditation is managed in the UK by UKAS and as such are sometimes referred to as “UKAS accredited laboratories”. This also includes testing submitted to a Notified Body to support an EU Type Examination Certificate process.

In summary:

  • There is no “certification” of products for CE marking
  • Using an accredited laboratory is not mandatory for CE marking
  • Whilst not strictly required, testing is definitely the best way to determine EMC performance

 

UKCA

EU laws have been transposed into UK laws so the same requirements for CE marking apply to UKCA.

 

FCC

When seeking to comply with the “FCC” requirements of CFR 47 Part 15 for sale of products into the USA, we need to consider the type of product we are making and fit it into one of these categories.

  • Unintentional Radiators are products that can generate RF energy but are not designed to radiate it. Essentially, a product that does not contain a radio (like Bluetooth or Wi-Fi). Examples would be a power supply, a desktop PC, etc. (defined in 15.13 (z))
  • Intentional Radiators (defined in 15.13 (o)) are products that intentionally emit RF (e.g. mobile phone, Wi-Fi router)

A complicating factor are Radio modules that have undergone a Modular Approval process (15.212). This is an easy way to add radio functionality to your product. These have already been reviewed by a Telecommunications Certification Body (TCB) and approved by the FCC.

Provided an approved module is installed into your equipment in line with the OEM instructions then your responsibilities as manufacturer are to verify that the combination of Unintentional Radiator and Radio Module do not infringe any radiated emissions limits.

15.101 shows the paths available (SDoC or Certification) for different types of Unintentional Radiator.

2.906 Self Declaration of Conformity can take place in any test laboratory whereas 2.907 Certification has to take place in an FCC registered laboratory (must me nationally accredited to ISO 17025). In all cases the provisions of 2.948 measurement facilities apply.

 

 

Accreditation

Accreditation of laboratories is a slightly different subject. Accreditation is a method by which the test procedures of a test laboratory are verified by an independent 3rd party (e.g. UKAS in the UK) to be compliant with ISO 17025.

Similar to ISO 9001, ISO 17025 is a quality management system that demonstrates a laboratory is operated to a certain standard. 17025 also extends this quality system to the tests being carried out where the individual test procedures and personnel are checked by an external assessor.

This is useful to demonstrate competence of the lab to their customers. It also demonstrates (but does not guarantee) the quality of test results have met a certain agreed basic standard. Some manufacturers choose to always use accredited laboratories for their testing for a variety of reasons e.g. their quality policy might dictate it.

 

At Unit 3 Compliance, we choose not to be an accredited laboratory.

Accreditation costs a lot of time and money in fees, inspections and internal paperwork. This cost ultimately gets passed on to the customer. By remaining un-accredited we can keep our fees around 33% less than an accredited laboratory.

Many accredited labs subscribe to a business model of employing multiple technicians to perform the day to day testing whilst retaining a couple of engineers for consultancy and compliance paperwork. The operation can end up as a bit of a sausage factory – seeking to have a full calendar of testing and turning the handle as quickly as possible.

The fallout from this is that test reports often take a a back seat and are delivered weeks after the testing has been completed and in the event of problems you might not have time in the relevant test area to perform diagnosis of the problem before you are hurried out for the next customers’ scheduled test to take place.

Most people at the test lab have been working in that environment for most of their working lives. This makes them very capable at performing the tests but their lack of experience with product design means the staff are frequently not as capable of knowing how to change the design to fix EMC problems.

You might get informal suggestions of “try and improve the shielding” or “you need a ferrite on that” but beyond that the likelihood of getting good quality problem solving advice is low.

I certainly don’t want to tar all accredited labs with the same brush. There are good labs and good engineers out there. However with some labs it can be pot luck whether you get Technician A (interested, helpful, keen, knowledgeable) or Technician B (uninterested, jobsworth, clock watching).

Whilst many accredited labs do have experienced personnel on site, getting access to them in a time or cost sensitive manner is often hard. Because of the requirements of accreditation and the need for impartiality, many labs run their consultancy services as a separate division within the company. Sometimes they aren’t even in the same building as the test lab! Inevitably these services have to be accessed outside of the test cycle leading to delays.

 

comparison of emc lab capabilities

 

How we operate

 

Unit 3 Compliance is not a sausage factory. Our motivation is doing interesting work and solving challenging problems for people who care about their products.

We are significantly cheaper than an accredited lab, putting EMC testing within the budget of startups and smaller businesses. It also makes it more economical for medium to larger companies to run ongoing quality control checks, product cost down exercises and experiments.

We have a strong product design background, particularly in design for EMC. We can suggest, trial and optimise EMC fixes during the test process rather than send you back to base to figure it out for yourself. These fixes take into account the nature, volume and cost of the product – there’s not one fix that is suitable for all applications.

First time EMC pass rates are generally low. Of all the products that I’ve tested, less than 20% have passed first time. Many of those passed because we reviewed their design first from an EMC perspective and made suggestions for improving the design.

Because we have a strong background in fixing EMC problems and not just testing, we can resolve your EMC problems faster than anyone else. This is not an idle boast but something we genuinely believe. Every problem we fix makes us faster and better next time and this compounding experience is available to you.

We turn every test session into a miniature EMC class, explaining the tests, why we perform things the way we do and how it sits into the larger framework of standards, directives and compliance. We work hard to acquire our experience and love to share it with our customers.

If you’d like to benefit from this then get in touch.

 

 

 

References