The secret life of shielded boxes
This whole thing with EMC, CE marking, function, requirements and regulations – it can become costly rather quickly. Testing to get a CE marking are not know for being cheap; a convenient and accessible solution to potential issues are shielded boxes, but does that really solve the problem?
Jan Eriksson, Area Sales Manager at Detectus by Pendulum Instruments – a company that develops, manufactures and sells EMC test systems – has some information that indicates that the boxes are not always the salvation they are touted to be.
Today, you have the possibility to simulate emissions from a product. But that just exactly what it is, a simulation, not a reality. No matter how good, accurate and exact it may be, it is not an objective reality, which is also precisely what Jan thinks we should be more interested in.
As previously mentioned, a common solution to headaches caused by EMC is to put the “issue” in a shielded box and – “tada” it all works. But it’s really not that simple. Jan says that there are a set of questions that needs to be answered before we can “check the box” and call the problem solved.
Firstly, what's going on in the box? Sure, when we lift the lid everything looks good, but when everything is in there and running full speed, how does the system handle itself in the company of reflective walls?
The risk of the system interfering with itself is an existing one. It might not always be an issue, but its still a risk. As is the risk that the metal casing turns the box into and amplifier – which is also something that should be examined before anyone says "problem solved".
In practical terms, it is also difficult to avoid leakage from the shielded box. In order for it to be practically useful, leakage points will be created, from openings required for maneuvering, air intake, fans and contacts. Then, of course, weak points can occur when splicing the metal. It is through these openings from which we will see emission leakage and it also these which will ultimately determine how good the shielding will be.
This is where Jan come in with a rather simple – but sometimes difficult in practice – idea. Don’t run simulations in order to check that a system can handle ideal values, instead measure reality. Jan has thrown himself into the deep end of this topic and Detectus – now a part of Pendulum – have developed several measuring systems with which designers can measure the intensity and location of a radiation source down to a component level.
Jan Eriksson will hold a presentation during the Evertiq Expo Tampere about how electromagnetic fields from electronic devices can behave inside shielded boxes and leak out if you are not aware of the issue. For more information, visit our Evertiq Expo site.
