EMC Introduction

 

Almost all electrical and electronic equipment is able to create ‘interference' in one form or another. The obvious example is radio interference, such as caused by electric drills or poorly suppressed motorcycle engines. These cause, at the very least, irritation and frustration for those listening to their favourite music or TV programme. At the other extreme they can interfere with emergency radio communication, aircraft navigation systems etc....

This interference not is necessarily just a ‘radiated' phenomenon, it may be transmitted from one product (the cause) to another (the victim) via the mains distribution wiring in a house or office block.

Another kind of interference is that caused by the power supply circuits in virtually every electronic product, including lighting systems. These circuits are well known for distorting the mains supply voltage by drawing ‘harmonic' currents off the mains. These harmonics are at frequencies which are multiples on the 50/60Hz supply and can lead to failures in the electrical distribution network.

All the above relates to ‘emissions' of one kind or another. The sum of all these creates a level of electrical noise in the environment. Some environments (such as industrial areas) will be worse than others, and some environments (for example, in the home) should be quieter.

All the phenomena all either electrical or magnetic or, (in the case of radio frequencies), both. They are all forms of electromagnetic emissions.

The other side of the coin is to ensure that products are able to work satisfactorily in the environment in which they are expected to be used. This is a measure of its susceptibility (or immunity) to electromagnetic noise. Again, there are several aspects to this measure. Not only are there radiated and conducted RF requirements, there is ESD, magnetic fields, mains power glitches, dropouts and brownouts. See later for the formal list.

 

 The aim of the EU directive (and FCC rules in the US) is to ensure that all emissions are kept low, and all immunity levels are kept high, thus creating a wide safety margin so ensuring problems are avoided. This is the principle of  ElectroMagnetic Compatibility (EMC). Products that are declared compatible with this principle are EMC Compliant.

In the EU, all electrical products fall within the scope of the EMC Directive. In the USA, consumer, IT and any products that use/generate RF must comply, in Australia/New Zealand, only the emissions are considered, but this applies to all electrical products. So it is important to check the rules that apply in the region in which the product is to be sold or used. In all cases, where EMC rules exist (and that means virtually the whole developed world), EMC compliance is mandatory and penalties, including withdrawal of all product, apply for non-compliance.

 

You have to ensure that your products are compliant and consistantly so. The best way to ensure this is obviously to measure the emissions and to test the immunity. If your product a low volume then a single example is tested, but if the product is in volume production a sample must be tested on a regular basis.

Your compliance strategy could be to use test labs to check your products, or do the testing yourself, or to use a combination of the two. The optimum route depends on the volume of product and number of different products to be tested. Generally, if more than five tests per annum will be required, self testing offers clear advantages in convenience, cost and timescale.

 

There are clear benefits in testing a product throughout the development cycle. Costly redesigns and the associated delays are avoided. Even if this aspect of the requirements is not required, the convenience of being able to test when you want and without having to book and travel to a test laboratory are significant.

But the basic truth is that the earlier you start to check the compliance of new product developments, the better. One failed test at the end of a product development cycle can be extremely expensive in terms of the effort required to redesign the product, plus there is the impact on 'time-to-market'.

 

Many standard test techniques require specialised test sites and/or test chambers. Laplace have researched and developed several unique techniques which enable you to test your product in your own environment with confidence. This means that you can test on your own site, in the office, factory or laboratory, without travelling to test labs or specialised sites.