Writing an EMC Test Plan

Why bother writing an EMC test plan?

You can think that it is not really necessary to write an EMC test plan because you will pay a lot of money to perform the EMC tests, so it should be included in the service. This is true, and some laboratories will include it in the service. However, there are some nuances that you will need to consider if you want a certification free of surprises.

EMC laboratories do not know your system

You might think that the system you are working in is user friendly and quite fast to install. I invite you to ask anybody unconnected to your system to start using it. You will find out that it was not as easy and as smooth as you thought.

Therefore, you will need to write a user manual. It has to be clear and to consider all the unexpected situations. When you are in an EMC laboratory, you do not want to waste the gold-priced time of tests trying to run your device.

You are the only responsible for the tests

Laboratories are able to perform tests, but they will do the tests you asked for. Even if there are other people who prepare the test plan, it will be your responsibility to check it and approve it before pulling the trigger of starting the test campaign.

Control and flexibility

When working in electronics development, it is normal to be asked for projects that are modifications of previous ones. If the market or clients require it, all products will need to be certified. This means that each product needs its own test plan. When you are in charge of writing the test plan, you are quite more reactive than if you depend on an external agent.

Expertise

During the process of an EMC certification, there are many things to learn: frequency measurements, tools, chambers, test environments…The learning curve is slightly steep but, once you have completed the first one, the rest will come much easier. Keep in mind that EMC certification is a compulsory step for all the companies developing new products, so at some point, they will need a person to do the tests. Getting knowledge can open some doors, do not miss the opportunity.

What information do I need?

Before starting to write a word in your EMC test plan, you will need to gather some information. 

Geography and market

First of all, verify in what countries would you like to sell your product. Different norms apply for the same product depending on the country. Even more, the market has a great impact on the difficulty of the tests. For example, industrial and home applications need similar tests but the levels for industrial systems are less restrictive.

Standards

Directly related to the previous point. Once you have defined the location and the market in which your product fits, you will need to base your test plan on the standards. There is a plethora of them, so select them properly. If you are not sure where to start, visit the Academy of EMC’s site.

Power, inputs, outputs

Depending on the power level and the power type (AC, DC), different tests will need to be performed. Also, power and signal wirings will be considered as different, so tests will not be the same. Prepare a clean document with all the connectors, their signals, type of signal, and their use in the final application. 

Final application

Whenever it is possible, the system to be certified has to be tested under real conditions. The problem is that it is not always possible because of many reasons: the real loads are not available, or they are too big. All the connectors used in the real application need to be connected during testing to loads similar to real ones. 

The most frequent situation is to have virtual loads connected to all connectors except, sometimes, a programming port, which is only used in maintenance or debugging. Virtual loads can be as simple as resistance when testing a power supply, or a microcontroller generating hall sensor signals to simulate a speed sensor within a motor controller.

Wirings

Wiring harnesses tend to be a point underestimated in cost and complexity. Building them takes time and needs specialized workers. The length of the wirings should be as closest as possible as the final application. In case you do not know it exactly, you will need to define whether they will be longer or shorter than a threshold. When cables are long, usually longer than 30 meters, additional tests have to be performed.

Conclusion

Writing an EMC test plan is a process that takes time, effort and knowledge. Each test plan is particular to each product, so they cannot be generalized. This article introduced the basic elements to write a test plan. Future articles will extend this topic and will give enlightful information to help you certificate your electronic products.