EMC/ EMI Testing- the BASICS

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 compliance 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
• EMC 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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