Six reasons to conduct early EMC testing

24Jun

Typically conducted at a specialist lab at the end of the project, EMC testing can lead to frustration when the tests fail.

Unfortunately, many projects trip up at this last hurdle, with radiated emissions regularly cited as the top reason.

The cost of testing is already high, but re-testing often stretches the planned budget and slows down the entire project. Upon failure, engineers need to investigate the source of the problem, at a stage in the project when the integration of all the components can make this difficult.

Avoiding EMC failure often stems from building pre-compliance testing into a project from day one. In the software industry there is a move to introduce testing earlier in the product development cycle. Likewise, this thinking is now evident in the hardware industry; investigating emissions from a device during each major development stage is a sound approach.

There are a number of advantages of pre-compliance testing:

1) Detect errors early

The earlier product deficiencies are identified in the development process, the easier they are to fix. Pre-compliance testing can be used to focus on any areas identified as potential causes for concern and enables solutions to be found early.

The risk of a design failing is often relative to the time taken to start testing, so designers that leave testing to the project end are completely reliant on the design team’s skill and experience.

Early analysis can also drive system decisions. EMC also encompasses the system and mechanical changes that may be required. These may include adding EMI shields, coating boxes or adding EMC foam to fill any leaks/gaps in an enclosure.

2) Test to compliance standards

Using an anechoic testing chamber before formal testing can determine whether or not a design will meet relevant compliance standards. The ability to test to EN55022, EN61000 and EN61000-3-2, as well as MIL-STD-461, for emissions provides confidence in the design.

A spectrum analyser and near field probe can be very useful for finding the location of emitters, once they have been identified as presenting radiation above the required limit, but less useful before a calibrated scan at a required distance has been done. What may appear to be a problem at close range with a probe, can disappear in a chamber - and the reverse is also true. Testing to a known standard early on focuses attention on real problems.

3) Integrate testing into development

When testing is integrated into development, a testing chamber and expert advice is available during the entire project lifecycle. Design engineers that offer EMC pre-compliance testing as part of their services will be continuously on the lookout for areas of risk during product development.

4) De-risk your project

Early EMC testing can de-risk a project by determining many, if not all, non-compliance issues prior to submission for formal testing. This is one of the ways the time taken on pre-testing pays back over the course of the project. The end design is much less likely to fail, saving the resulting costs and delays associated with board re-spins and excess test house charges.

5) Eliminate over-design

Early EMC testing can reduce design costs by decreasing over-engineering. Before a product is tested it is not known where the problems might occur. This can lead to unnecessary counter-measures being added; countermeasures that will present for the lifetime of the product.

In addition to a BOM cost impact, there is also a bearing on the mechanical constraints. For a very tight design, it is crucial to optimise EMC filtering, which can be large, at an early stage, as adding filtering later on, once mechanical tooling is committed, may prove impossible. This is particularly the case with power line filtering using common mode chokes or Pi filters.

6) Other uses of pre-compliance equipment

As well as EMC testing a product when it is first produced, “look-sees” can be carried out as obsolete parts are replaced, or board layout changes. As CE marking is a self-certification process, this data can often be used to justify retention of the CE mark by reference to comparative measurements on the original unit. Clearly, this depends on the scope and type of the change.

Similarly, tests can be carried out on comparative signal strengths of antenna configurations.

Summary

ByteSnap Design has set up a testing chamber to support radiated emissions scans of customer’s products. This provides the ByteSnap team with additional ability to eliminate many of the problems prior to formal testing by extending our scope for agile design.