Testing Systems and Installations

1. The EMC Directive

For non-radio products there are two ways of demonstrating compliance offered by the Directive; by the use of harmonised standards or by using a Technical Construction File (TCF). These approaches are generally acceptable for systems which are stand-alone and are of a size that would enable them to be tested on/in certified test facilities. However, for complex systems or installations, the method for showing compliance is less clear, particularly as current standards give examples of table-top equipment or a single rack system. For the designers, manufacturers and operators of such systems and installations as illustrated in the photographs, the compliance methodology is less well-defined.

2. The Commission's EMC Directive Guidelines

1. Systems: In normal usage, the word "system" is used to refer to an optional combination of several apparatus brought together by a manufacturer to perform a specific function, as defined by the manufacturer. This final system is seen by the EC as an apparatus, even though the apparatus can be physically large and complex. The major point brought out in the guidelines is that the "system" is capable of having free movement throughout the EEA. It must be designed and put together so as to comply with the essential requirements of the Directive and the compliance should take into account any reasonable foreseeable environment in which the system will be operated. A combination of apparatus is only considered as a system if the manufacturer advertises that the parts are intended to operate together as a system. Thus, if a manufacturer declares that the contents of an outside TV broadcast van is a system, then it would need to demonstrate compliance as a system. >

2. Installations: In their treatment of installations, the EC's approach is to consider whether the installation is fixed or moveable. In general, an installation should be considered as one which does not have free movement around the EEA, and as such follows the definition in the guidelines as one which is assembled from several systems, finished products and/or components at a given place to operate together in an expected environment to perform a specific task, but not intended to be placed on the market as a single functional unit. Thus, for example, powerstations, telecommunication switching centres, oil and gas platforms are installations which would not have free movement around the EEA.

3. Testing Complex Systems

The pragmatic approach is to define a worst case configuration of the complex system, This should be capable of being reduced in size whereby the configuration can be tested either by the manufacturer or a test house. From an EMC perspective, the configuration most likely to cause maximum disturbance is defined and this becomes the testable system. You may say, "how do I know if I have the worst case?". There is no easy answer to that question, but as designers of complex systems over a period of time, knowledge of the design parameters, operating speeds, measurements of harmonics of fundamental frequencies, and history of complaints when complex systems have previously been taken into service, will all help to determine the worst case configuration.

Having once defined a testable worst case system, applicable standards (e.g. the generics) can be used to demonstrate conformance. Note however, that you, the manufacturer, should define the compliance criteria for the worst case system, as only you have the knowledge of what is acceptable performance.

4. Testing Installations

Again, there is little help from the general run of standards as to how meeting the essential requirements should be approached. An in-situ testing standard has been proposed by CENELEC, but in-situ testing is no help as

• the test methodology is not well defined;
  
• it is expensive to install systems, test, and then find that a problem has to be solved before the installation can be taken into service.
  

5. EMC Management

• an EMC management control plan;
  
• control of design and manufacture;
  
• EMC management included in business procedures;
  
• EMC management as part of Quality Assurance;
  
• control of modifications, upgrades and enhancements;
  
• vendor assessment for EMC compliance;
  
• EMC maintenance procedures,
  

6. Conclusion

The photographs in this article appear by courtesy of BP Chemicals.