Signal Interference and Cable ShieldingA well-engineered cable is comprised of many crucial independent elements. Recently shielding has become just as critical as any other design element. The growing complexity of today’s communications and control systems, coupled with the increased distances signal and control communications are required to travel, have exponentially increased electrical interference (noise) related failures. Depending on the application, cables can be adversely affected by EMI/RFI/ESI (electromagnetic interference, radio frequency interference, electrostatic interference) also known as ‘signal interference.’ To combat the effects of signal interference proper shielding is vital.
According to industry technical data there are essentially four sources of signal interference.
Static Noise: Occurs when an electrical field distorts the signal and can be mitigated using continuous foil shields which offer 100% shielding efficiency and appropriate grounding techniques.
Magnetic Noise: Comes from large AC motors, transformers, and knife switches, and can set up current flows in opposition to the instrument. The simplest and best means of eliminating magnetic noise is through the use of twisted pair signal wiring.
Common Mode Noise: Results from current flowing between different potential grounds located at various points within a system. Solving this issue requires a carefully engineered and properly installed power and grounding system.
Crosstalk: Refers to the super imposing of the pulsed DC or standard AC signals between two or more nearby wires or cables. The most effective means of mitigation is individually shielded twisted pairs.
If one finds that noise will pose a problem it is then necessary to determine if the noise is low, medium, or high level.
The table below displays generalized noise levels:
After determining the type/level of noise one can better choose the most appropriate type of shielding.
Shielding surrounds the power carrying conductors of the cable and protects it by (1) reflecting signal interference as well as (2) picking up noise and conducting it to ground. Multi/Cable offers various shielding options and varying degrees of shielding effectiveness. When deciding on the type/amount of shielding required, consider the following factors:
Multi/Cable typically uses either foil or braid, or both foil and braid when shielding its cables.
Foil Shield: Good
Braid Shield: Better
MultiShield (Foil & Braid): Best
For more precise cable shielding information contact your friendly Multi/Cable sales or engineering associate.
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