Radiocommunications Agency  EMC Awareness

Segregation

What this technique is used for

Segregation is sometimes called ‘system partitioning’ or ‘partitioning’ or ‘zoning’.

It simply consists of ensuring that electrically noisy items (i.e. those with high levels of emissions) are located in a separate place from sensitive electronic items (i.e. those with low levels of immunity). It is often beneficial to provide increased spacing between the segregated areas (or zones).

Although few textbooks or articles spend more than a few paragraphs describing it, segregation is one of the most powerful and lowest-cost EMC mitigation techniques if it is used early enough in a project.

Segregation is also an important mitigation technique for cable routing.

How this technique is used

Items of equipment are segregated to prevent the noisy ones from interfering with the sensitive ones.

For instance, at the end of a food processing line that is producing pre-packed food for a supermarket, the checkweigher (which is very sensitive) should usually be segregated from the plastic bag sealer (which uses dielectric heating with high levels of RF power) by several metres.

Where the separation distances between segregated items are insufficient to prevent radiated interference from occurring, one or both can be shielded.

Where the segregated items share the same power supply and conducted interference occurs, one or both can be filtered.

Key issues in employing this technique

EMC Directive compliance means little in practice

People often assume that if they purchase items that are CE marked, then they must be compliant with the EMC Directive and its emissions and immunity standards – and this means that they will not interfere with each other or with other equipment. This can be a dangerous assumption!

For low cost, segregation should be done at the earliest stage

Shielding and filtering cannot be used to protect a sensitive item from a noisy item – if the two items are not physically separated by a suitable distance.

For shielding, the distance needs to be sufficient to fit a complete metal barrier between the two. For filtering the distance needs to be enough to fit the filter and also to prevent induced and radiated coupling between the conductors on either side of the filter that would compromise its attenuation (may need to use shielding for this too).

If the appropriate amount of separation is not designed-in from the start, applying the segregation technique can involve moving the locations of large numbers of items and their conductors/cables, and this is usually very costly and time-consuming indeed.

It is much better to determine which items might need to be segregated from which other items, and to incorporate the required partitioning/zoning/segregation in the design at the earliest possible opportunity. This costs just a little extra effort in the early design stages, and is a well-known ‘good EMC practice’ which may be sufficient on its own but which allows shielding and filtering to be applied later on (if found to be necessary) with ease at relatively low cost.