Shielding

Shielding

Use of shields Shielding is required if susceptible equipment and sources of interference cannot be sufficiently distanced through room rearrangements.

Shield

A shield is a metal component that is placed between the source of interference and the susceptible equipment. It influences the distribution between source and the equipment. The coupling is minimized this way.

Shielding types There are several different types of shield that can be used:  Cable shield  Chassis as shield  Room shielding  Partition panel as shield

Shielding effectiveness The effectiveness of the shield depends on its mutual impedance The mutual impedance must be as small as possible in order to achieve good shielding effectiveness. The smaller the mutual impedance is, the greater the leakage current can be.

Mutual impedance of different cable shields The following diagram shows the mutual impedance of different cable shields depending on the frequency:

Shield grounding The shield is connected to ground to dissipate the currents. Sufficiently large cross sections are required for current dissipation since the current discharge can be very large with expanded plant systems.

Double shielding Shielding can be improved by using double shielding. The additional shield is connected to ground at a suitable point.

Driven shield Shielding can be improved by using a driven shield. This maintains the shield at the potential of the signal voltage. You can achieve this for example, by back coupling a repeater output. This also means capacitive interference currents between the conductor and the internal shield are avoided.