The concept of Earthing/Electromagnetic Compatibility (EMC) in industrial plant design

A Challenge for Industrial Automation

Faults, error messages or machine outages: these are some of the problems caused by Ethernet and bus data transmission networks in production plants. But what is the origin of network communication errors? Users often blame the performance of the cables and wires. This white paper explains why this is too narrow a view on the matter, and why inadequate electromagnetic compatibility (EMC) in plants can result in data transmission errors.

Possible Causes of Plant Failure

There are a number of factors that are likely to cause disruptions in plants: the failure to follow wiring instructions during the construction of cable ducts, the use of excess cable lengths, the incorrect selection of cable types and/ or connectors, the installation of too many connectors and the presence of magnetic fields. The latter is a risk to plant disruption when the concept of earthing is not implemented in an optimum way. It is, therefore, particularly important that plant operators apply earthing concepts that not only are correct but, even more significantly, that are tailored to their needs. With this, disruptions, outages and lost sales due to inadequate electromagnetic compatibility of an entire plant can become a thing of the past.

More Power and Higher Frequencies in Smaller Spaces

In the early 2000s, electromagnetic compatibility was rarely an issue in plant machinery. Production facilities were often located in huge factories where individual machines and robots had plenty of space and operated at large distances from each other. The flow of data was easily controlled, reducing disruptions related to inadequate electromagnetic compatibility.

Today ‘s plants are designed to be more compact and efficient. Time and space savings are important to companies as both have major impacts on costs and profits. Modern, high-performance industrial robots are now located close to each other and work more quickly, precisely, and efficiently than ever before. Moreover, their tasks are becoming increasingly complex and extensive. To do their work properly, today’s robots require more data and higher transmission speeds. This data increase, in turn, requires wider and higher frequency bands. The resulting magnetic fields inevitably induce noise currents and volt- ages. Whereas bus lines used to operate in the 500 kilo-hertz to 16 megahertz frequency band, industrial Ether- net uses frequencies ranging from 1 to 600 megahertz, depending on the category. Even frequencies as high as 4 gigahertz can be used these days for Single Pair Ethernet (with MultiGig BASE-T1). As a rule of thumb, the higher the usable frequency range of a cable, the more susceptible a plant is to electromagnetic interference and hence the better the shielding must be.

However, the more complex the cable’s shielding, the more inflexible, expensive, and thicker its construction becomes. The same also applies to the downstream assembly processes, such as connecting the cable to the plug. The solution is therefore to minimize magnetic fields from the outset and to protect the cables from these fields. But how? The answer is the implementation of the correct earthing concept which includes earthing straps (for further information click HERE), EMC glands, stranded conductors (class 2 or 5) and high-grade shielded cables.

A Summary of the Effects on Machine Operation

  • New, state-of-the-art plants operate with larger volumes of data, higher acceleration values and faster rates of travel. Faster data transmission requires more power.
  • More power and faster rates of travel mean the drives need to be more performant and draw more current
  • Higher currents, in turn, increase the electro- magnetic radiation released into the environment.
  • The closer machinery and robots are to each other, the greater the radiation because distance is also an influencing factor in electromagnetic interference. Hence, magnetic field interference can be reduced by increasing the separation distances.

Example of a Plant Earthing Concept (click HERE)

Helukabel products for Earthing Concept (click HERE)

 

By URKUNDE, 24-08-2022