Design for EMC

The most difficult tests to pass in many ways

Design For EMC is a subject that can put fear into the heart of the most seasoned engineer, and be ignored by many in management. The problem is, if you cannot pass EMC testing, you will be severely limited as to where you can sell your products.

The difficulty with EMC is that the levels of emission and susceptibility for a given product are almost impossible to quantify closer than within about 10% of reality at the design phase.


The EMC plan needs to be defined very early in the product design cycle as it can impact the choice of components, housing materials and internal circuitry to name but a few issues. 

There are usually many ways to meet a specification for circuit and system operation, but choosing one that will not give the correct EMC performance in a particular situation can be very expensive indeed.

Key items are:

An earthing and bonding plan

Defining what standards must be met

Setting an EMC budget - this has nothing to do with money (directly), but more about how much emissions are acceptable at different points within the unit.

There is a lot more, of course, but this is a good starting point.


A note on EMC considerations

Perhaps what is most important is that EMC must be considered at every part of the design; every PCB, every module, every piece of wire, every connector. All of these will have a material impact on EMC performance.


But it's just a piece of paper in the end, isn't it? 

I have actually heard this from an engineering project manager who was concerned that product development costs were seen as too high; those are nothing compared to remediation costs if the tests fail (and with this attitude, they probably will).


The costs are quite high for testing. A typical EMC house in the UK charges about £1,000 per day (as of early 2018) for standard tests such as EN55023 and IEC 61000. If you need more stringent testing (such as MIL-STD-461 or DEF STAN 59-411 it may cost significantly more). Most of the tests take many days to complete and there is always a charge for the report. Doing the testing only once if possible makes economic sense.

There are no guarantees that you will pass first time, but an experienced EMC designer can certainly help to reduce the risk.


If you have failures, there is not only the cost of finding the issue, but also the cost of re-testing (and given that many EMC test houses are usually booked months ahead, there is a time to market penalty involved as 

well).


There is no 'one size fits all' in EMC (as is true in design generally), but if taken into consideration at the initial phase of design can save you a great deal of money in the longer term.


We are experts in design for EMC; if you have a new product (or a non-conforming one) that would benefit from our expertise, then why not contact us.