| EMI EMC compliance test and testing services |
EMI EMC compliance test and testing services
- a summary, guide or tutorial about the basics of EMI EMC testing, EMC
compliance testing, and the EMC test equipment needed as well as EMC testing
services and EMC test labs or EMC test houses.
With the need for EMC compliance testing established as
an accepted standard, any new products that are designed and manufactured
today need to undergo testing to ensure that they meet the required
standards. Years ago before the standards for EMC tests were established and
the performance of electronic equipment did not meet the same standards,
different pieces of equipment would interfere with one another. Their
Electro-Magnetic Interference or EMI performance was poor. With the amount
of electronic equipment in the home, office and business increasing, the
need to improve the EMI performance of equipment and to establish standards
for EMC was seen. Along with the standards arose the need to demonstrate the
conformance of equipment, by establishing EMC compliance testing
specifications and ensuring that all equipment had a satisfactory EMI
performance.
Design for EMC compliance test
The first stage in any design process is to design the
product to meet the EMC compliance test requirements and any EMC testing
that is undertaken. To improve the EMI performance, it is necessary to
ensure that adequate filtering is in place to both prevent unwanted
radiation taking place, or to allow in unwanted signals. Much of this can be
undertaken by placing adequate filtering in any lines or cables entering the
unit. It is also necessary to ensure that the unit is adequately screened.
Within the unit, any sources of signals, or areas that are susceptible to
radiation should be isolated from any cables entering the unit, and the unit
should be well grounded.
If these and other precautions are observed during the
design, then the unit or equipment will have a much greater chance of
meeting and passing any EMC / EMI compliance test that may be undertaken.
EMI EMC test stages
In order that a product may pass its EMC compliance, the
EMC testing should be undertaken at various stages of the life of the
product. The exact nature of the tests, and if they need to be carried out
will depend upon the circumstances, the needs of the product, and the nature
of the introduction of the product. For example, if a product is being
bought in then there would be no need to undertake testing during
development for example.
Broadly there may be considered to be four stages
involved in EMC test:
- Development test
- Pre-compliance test
- Compliance test
- Production test
It is useful to be able to categorise the different
stages of EMC test as the requirements for each are slightly different and
different approaches may be taken.
Development EMC test
During the development phase of a project it is much
easier to make changes to an electronic circuit design. In this way tests
can be undertaken to ensure that the best possible EMC / EMI performance is
obtained. EMC filters, circuit layout, screening and other aspects of the
design can all be changed more easily at this stage.
EMC tests at this stage can be quite informal, and
although testing for EMI are undertaken, the same level of test equipment
and testing is not required as for the later formal testing stages.
Pre-compliance EMC test
The pre-compliance EMC testing is undertaken once a
representative working model of the final equipment is available. The
testing is normally performed at the development laboratory as part of their
product testing programme. Its main purpose is to check the performance of
the complete product and ensure that it has a good chance of passing the
formal EMI test that needs to be performed later.
EMC compliance test
Once the development of the product is complete, it is
necessary to undertake a full and formal run of the EMI EMC compliance
testing. This will ensure that the product meets all of its requirements
with respect to the standards it needs to meet. The tests that need to be
undertaken and their nature will depend upon the product, but need to be
sufficient to ensure that the product can conform to its EMI EMC standards.
Often it will be possible to undertake many of the tests
in-house, but there may also be a necessity for specialised tests to use one
of the many external EMC test houses. The decision about the location of the
tests will depend upon many factors including budget, the availability of
the required resources, and the standards that need to be met for the
particular product.
Production test
Although the main EMC / EMI test enables the product to
be sold, there is an obligation on the manufacturer to ensure that the
product continues to meet its stated performance. It is found that in any
production process there will be small changes as the supplied components
change. This can have an effect on the EMC test / EMI test performance, and
therefore there is an obligation on the manufacturer to perform some tests.
Typically these tests will be considerably less comprehensive and are only
required, possibly on a batch basis to ensure that there are no major
changes in the performance.
EMC test types
The testing that is required for EMI EMC compliance falls
into a number of categories. Some elements of EMC testing are essential
whereas others may be advisable to perform at the various stages during the
development cycle of the product.
- Conducted emissions
- Radiated emissions
- Conducted immunity
- Radiated immunity
- ESD immunity
- Transient immunity
- Surge immunity
The different types of EMC test require different test
technologies. However they all test essential electromagnetic compatibility,
EMC related elements for any piece of electronic equipment. The conducted
and radiated emissions and immunity are associated with the ability of the
equipment not to emit or be susceptible to radio frequency energy whether it
is carried and a radiated signal, or conducted over the leads entering the
equipment. Additionally the ESD performance is another essential parameter.
With static a part of everyday life, it is necessary to ensure that it is
not prone to damage by static discharges. Additionally the equipment must be
resilient to any transients or surges presented on any lines entering the
equipment. For example mains power is often subject to both surges and
transient pulses, and the equipment must be able to withstand these if it is
able to provide reliable operation.
EMC test equipment
There is a variety of EMC test equipment that is
required. The testing is normally carried out within a screened room, but
the EMC test equipment itself is also required. Typically much of the EMC
test equipment consists of either sensitive measurement receivers or
spectrum analysers. In addition to this the other EMC test equipment that is
needed includes the generators for any susceptibility tests.
In view of the cost and the use that would be made of the
EMC test equipment, many people opt to use an EMC test lab. However for many
organisations, it is cost effective to buy the EMC test equipment if only to
use when developing the main product, and undertaking initial tests, before
sending the product to a test lab for fully qualified tests.
Use of EMC test houses
While it is often convenient to undertake much of the EMC
testing in-house, there are many times when using external EMC test labs or
EMC test houses to undertake the testing. The use of these EMC test houses
have many advantages. While there are additional costs to using EMC test
houses, they have in-house knowledge and specialise in EMC testing. This
enables them to undertake the testing more quickly, and in addition to this
they may also be better placed to assist in providing solutions when
problems occur.
Another advantage in using EMC test houses occurs as a
result of the cost of the EMC test equipment. This is often very specialised,
and if little EMC testing is undertaken then it can remain idle for long
periods of time. While the EMC test equipment can be hired, it may be more
beneficial to use one of the many EMC test houses.
There are some points to note about using EMC test
houses. Apart from the additional cost, it is often necessary to schedule in
the testing into their forward load. This can sometimes require some skill
as programmes tend to move. However by liaising with the EMC test house, it
is normally possible to manage these schedule changes without too much
difficulty.
Summary
EMI EMC test and EMC compliance testing is now an
integral part of electronic product development. Although there are
differences in the regulations around the world, it is required for most
countries today. In any case, the fact that a product performs to its EMI
and EMC regulations means that it will operate satisfactorily in the
presence of virtually all other electronic equipment and also not cause
problems to them.
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