Put to the Ultimate Test – Part 7: EMC Tests
During the development of our cables and wires, we vigorously test each product in our testing laboratories. In the seventh, and final, part of our series, we will explain our EMC testing process.
Electromagnetic compatibility (EMC) describes an electrical system's ability to function reliably in an environment with electromagnetic disturbances without, itself, disrupting other devices or components. Cables and wires are not just passive transmitters of signals and energy; they may also be the source of or be functionally impaired by disruptions. EMC disruptions occur quite often in industrial applications where frequency converters, motors, or control systems are in use.
This makes EMC therefore an important marker for quality in connection technology. After all, users want to be certain that the cables they're using won't turn out to be the weak link. The use of effective shielding is paramount, and HELU tests these in their highly modern, in-house testing center. Two properties are focused on in testing: the transfer impedance and the shielding attenuation.
Transfer impedance indicates how well a screen shields the internal conductor against high-frequency interference currents. It is measured in milliohm per meter (mΩ/m), where lower values indicate better shield performance. On the other hand, shielding attenuation refers to the strength of external electromagnetic fields that the cable can shield against. This is measured in decibels (dB), and the higher the value, the better.
HELU tests the transfer impedance according to EN 50289-1-6 and IEC 62153-4-3 using a triaxial method. This involves a standardised interference current being fed into the shield, during which the voltage on the inner conductor is measured. This allows the strength of the external field's influence on the interior of the cable to be precisely measured. Shielding attenuation is essentially measured in reverse. A specified, high-frequency test signal is applied to the cable, and the externally radiated signal is measured using a test instrument. The better the relationship between the signal being introduced and the signal being radiated, the more effective the shielding.
Both values are heavily dependent on the construction of the cable, especially the type of braid, the degree of coverage, and the material quality. This is why it's important to consult an expert when choosing cables and wires—especially for EMC-critical applications. Cables constructed according to customer-specific requirements can also help to safely and reliably overcome specific challenges related to electromagnetic compatibility.
Ask the Expert
What is the most common mistake made with regard to EMC when planning cables?
One common mistake is not paying enough attention to the grounding and shielding in a system. Often, a high-quality, shielded cable is used, but then not correctly grounded, which renders the advantages provided by EMC null and void. The mixing of signal and power paths combined with improper cable installation near sources of interference are frequent causes of EMC-related problems. It's essential to plan holistically.
Full screening or braided screening—which is better?
Full shielding (a shield with a solid surface) provides the best protection against very high frequencies as the transfer impedance is effectively zero. For moving applications, however, these cannot be used, as they're completely inflexible and break easily under bending loads. It is for this reason that this type of shielding is only found in permanently installed antenna cables. In industrial applications, a well-designed, braided shield typically suffices. The most important attributes are the angle of the braid, the degree of coverage, and the quality of the material. In our experience, "more" is not the answer, but rather the synergy between shield parameters.
You can find this article as well as many more exciting stories in our latest issue of POWER #18. Take a look now!