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EMC Testing: Needed? What is it?

What’s the issue?

Harking back to pre-Brexit days (and now in the UK – nothing has essentially changed other than labelling), standards were introduced via the EU that mandated testing for electronics devices to ensure that products neither suffered because noisy electromagnetic conditions, nor that they caused such conditions in the first place. Some of us are old enough to remember when a motorbike could interference on a television: fortunately those days are long gone. 

Testing is usually done via Test Houses (costs about £1,000/day and will probably take the best part of a week) that have specialist equipment and appropriately qualified staff. The topic is highly technical, and Test Houses have been known to do little to help clients with this – smoke and mirrors. This article is designed to help companies decide what’s needed and then select appropriate Test Houses to do the testing – if it is necessary. 

What is EMC?

EMC stands for electromagnetic compatibility. As described above, it is a standard for how immune electronics are from electronic noise in the atmosphere, and whether they contribute unacceptably to such noise in the atmosphere. 

The degree to which the above is the case for a given set of electronics is determined by tests – complicated tests conducted in Faraday cages (rooms that screen out all noise). Organising and passing such tests can be problematic, but it shouldn’t be. Read on for a bit of help. 
How do I get EMC Testing done?

The following are the phases to consider:

  • Determine whether there is a need: It is possible that no testing is needed at all, or perhaps some intelligently conducted risk assessment can justify not conducting the tests. This phase is unfortunately not something that can be assessed without technical qualifications. It will take a combination of product knowledge and engineering. The Electronics Machine is always willing to give such guidance gratis. 
  • Find a test house: this really is a case of horses for courses. Some companies just need the box ticked, others really need to know that the device has outstanding EMC performance. There are test houes of each type. Googling will quickly find local suppliers, or feel free to contact the Electronics Machine for some recommendations.
  • Determine what national and international standards that must be met: there is a section below that gives guidance on this. Selecting the standards is a daunting process because of the multitude of them, but it isn’t as bad as it seems. The first thing to get on the radar is the absolute rule that the client chooses the standards. Some unscrupulous test houses may try to convince a client that a standard needs testing because it is revenue for them. The Directive is very clear that the client decides what does and doesn’t apply: not the test house. The section below gives guidance on this, but don’t hesitate to contact the Electronics Machine for some guidance.
  • Managed expectations: it is easy to become disillusioned because testing doesn’t always pan out as hoped. There are some good reasons for this and a philosophical demeanour can do a lot to ease things:
    • it is not uncommon for there to be test failures. More often than not these can be overcome without re-design, but be prepared for a worst case scenario of remedial design.
    • demand a proactive response and explanation for the test house. Schadenfreude testing is a mark of a lesser test house – all good ones will help.
    • regardless of success or failure, the test house must deliver a report and certificate if appropriate. Demand this.
  • Don’t re-test with every change: an ignorant and purist approach to testing would demand a re-test of EMC every time the design changes, even if just one resistor has changed. This is needless cost and delay. An existing and EMC approved design only needs risk assessment to determine if whatever changes are proposed are likely to affect EMC results – if not no further testing is needed. 

What Standards must I meet for EMC?

To be brutally frank, EMC standards are a bit messy because of conflicting influences. Some governing organisations (CENELEC particularly) have put emphasis on generic standards covering EMC testing, but these standards are being superseded by product specific standards. Product standards are likely to win the day, and therefore it is important that product specific standards that apply to a particular product are chosen. There are also market specific standards, e.g., automotive and military. It is best to decide what standards apply to a given product in conjunction with the test house, but it must be emphasized that the choice is with the client. For speedy and simple EMC testing, choose only standards that are absolutely necessary. Extra standards bring little or nothing in kudos and add considerably to development time and cost. If assistance is required in addition to that offered by the chosen test house, please don’t hesitate to contact the Electronics Machine.

How is EMC testing structured and policed? 

It is important not to misunderstand the conflicting forces and responsibilities that apply to EMC. It is certainly not a case of a test house pass absolves of responsibility entirely, although this is certainly the reason that many companies use for external testing. The following are rules that should be uppermost in a client’s head when going through the EMC testing process:

  • Responsibility for compliance always lies with the entity that places the product on the market. It isn’t possible to delegate this responsibility.
  • Theoretically, there is an infinite amount of testing and checking that can be done to confirm compatibility of a product with the market. It isn’t possible to do everything, so the dilemma becomes how much testing needs to be done to reduce the risk of market failure to acceptable levels. This extends beyond EMC to all testing. This is a judgement the client must make. A classic case of this is associated with the R 

How do I select an EMC Test House? Selection criteria/checklist?

One common myth is that EMC test houses are technocratic organisations that will impose test conditions on the client: not so. The standards explicitly state that it is the client that states what tests will be conducted, not the test house. This puts the client in control of the test plan, but it also burdens the client with the responsibility for ensuring compliance with the spirit of the law. It is a double edged sword. All in all it is better like this because it is in the commercial interest of test houses to over specify need. 

How do I plan EMC testing, and what contractual obligations can I put on the Test House?

One of the issues with the use of test houses is that there is a feeling of lost control. It can be quite debilitating and leave one like a rabbit in the headlights. This can be mitigated by creating a test plan. This will allow the important items to be identified, checked when done, and generally reduce the feeling that the test house holds all the cards. The key elements for the test plan are:

  • Description of the equipment under test (EUT).
  • The interaction the EUT has in a larger system, if such exists.
  • The configuration of the EUT as part of its system: there may be multiple ways in which the EUT could be used that must described.
  • A test matrix
  • Revision control
  • Statement of test objectives

It is more than likely the test house will need to assist in the compilation of this report. The Electronics Machine can also give guidance. Don’t hesitate to contact the Electronics Machine if assistance with test planning is required.

Where do I find my EMC Test House?

There are a plethora of test houses. Take pot luck and use what’s written above if you like or feel free to contact the Electronics Machine for guidance.

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