Shielding Services for Facilities

Shielding Services for Facilities

(Did You know?)

Shielding Services:

Washington Laboratories has more than 25 years of experience in the management and control of interference phenomena with particular expertise in:

  • Radio Frequency note abatement
  • Lightning Protection
  • EMF Measurements
  • RF Shielding and Systems Design
Engineering for Architects and Space Planners
Electromagnetic Interference(EMI) can cause system malfunction, communications interruptions, loss of data and erroneous measurements. With the increased quantity and mobility of RF threats, EMI management has become a critical issue in facilities design. Protection in an urban environment, where systems and users are in close proximity to potential threats, requires an understanding of the coupling and physics to find the most effective solutions.Washington Laboratories has over 25 years of experience in the management and control of interference phenomena with particular expertise in Radio Frequency noise abatement, Lightning Protection, EMF Measurements, RF Shielding and Systems Design.
Customers include the following: Examples of interference sources in the urban environment include:
  • Military and Government Agencies
  • Banks and Financial Institutions
  • Industrial/Commercial Companies
  • Research and Medical Facilities
  • TV/Radio and communications transmitters
  • WiFi and Wireless communications systems
  • Rail and subway systems
  • Motors, lighting and electrical equipment
  • Power distribution
Managing these threats takes an understanding of the interaction between the sources and the potential victims.

Protection

Protection for Systems Data, communications, voice, video and broadband services require protection against Electromagnetic Interference (EMI). Shielding systems are often employed in building facilities to protect sensitive systems from radio frequency sources in the urban environment. Communications security must be robust and free from eavesdropping or disruption.
Protection in the Laboratory Research hospitals, biotechnology and life sciences organizations deal with extremely sensitive sensors and systems during research and development. The small signals that are detected in animal-cell activities are measured in billionths of amperes, which can be overwhelmed by intruding signals from mobile networks, WiFi access points, TV/AM/FM broadcast and other sources of man-made noise.
Protection in the Workplace Electromagnetic Fields (EMF) are a concern for worker safety and health, as well as potentially interfering with sensitive electrical equipment. High-amplitude AC power currents can generate low frequency magnetic fields that are difficult to control and to reduce. Shielding is one of the options to reduce these fields.

A System Approach

Washington Laboratories takes a systems-level approach to the problems of radiated interference. Our objective is to find the most cost-effective methods of controlling interference. A complete design methodology must take into account the following factors:

  1. Quantifying the threat
  2. System sensitivity and probability of interference
  3. Reduction and control of potential sources
  4. Prudent space configuration to minimize interference coupling
  5. Specifying appropriate materials and construction methods
  6. Quantifying the performance

interferenceDesign Considerations and Methodology

The potential for interference depends on the level of interference and the level of susceptibility. To solve an interference problem, one may suppress the source or harden the victim. Our approach is to specify a degree of both, as appropriate for the situation.For many installations, it is not possible to predict the possibility of interference; however, based on judicious selection of equipment and an appropriate level of appropriate shielding, a high degree of confidence can be achieved.

 

Source of Interference and Mitigation

There are two primary considerations when considering “low-noise” design for facilities. The two concerns are based on frequency and nature of potential threats to equipment operations and accurate measurements.

It is important to separate the two concerns because the nature of the design and mitigation techniques are different.

Magnetic fields


Magnetic fieldsMagnetic fields are primarily generated
by 60Hz AC power currents. The major sources are from long conductors, particularly distribution cabling. From experience, the major source of magnetic fields are from legacy wiring that has may have multiple ground conductors and are not in compliance with current codes that require single-point-grounding.In addition, older equipment may have significant “leakage current” that causes ground currents to flow along presently uncontrolled return paths.To mitigate this type of situation often requires expensive and extensive shielding. For new installations, compliance with NEC requirements often preempts this source of interference. In addition, newer equipment is more likely to have low leakage current because safety standards are more strict than in the past. Higher leakage currents constitute a safety risk as well.

  • Other methods of construction can be implemented to reduce the potential for magnetic fields, including separation and placement of equipment with respect to potential interference sources.
  • Avoid the use of bus duct risers. Use conductors in conduit risers in electrical distribution. The close bundling of phase conductors results in a net cancellation of the fields that radiate from current-carrying conductors.
  • Locating high-current conductors as far as possible from sensitive equipment.
  • Locate power distribution transformers as far away as possible from sensitive equipment

With the above technique in place, it is possible that magnetic field threats may be entirely mitigated without special measures. However, the exact arrangement equipment and systems needs to observe critical noise-reduction measures, such as proper shielding of cables, equipment grounding and minimization of pickup loops.

Radio Frequency Fields


High frequency interference
is of concern in urban environments. The potential for applying shielding around the space is a consideration. The exact determination will be made after measurements of the existing fields are performed.

A shield system that would be adequate to protect the equipment may involve a foil-based shield material up to frame and panel designed installations. There are several possible options for achieving the necessary attenuation. The ultimate level is dependent on an assessment of the existing field levels and the sensitivity of the equipment.

Shielding Effectiveness is used to describe the amount of reduction offered by a shield to an impinging source. The levels are normally specified in terms of decibels (dB) over some frequency range. Proper shield design must take into account the following electrical and mechanical penetrations:

  • Electrical outlets, lights and switches
  • Air handling units, HVAC
  • Plumbing
  • Structural members
  • Fire Alarm Systems
  • Floor/wall/ceiling interfaces
  • Communications cabling
  • Doors, window and other ingress/egress

A complete and comprehensive study and review of a facility is recommended for cost-effective and practical design to protect electrical and electronic systems from Electromagnet Interference.

Did You Know? Shielding

Did you know that the shielding effectiveness is determined by (effectiveness – leakage)?

Often a facility or enclosure specification calls out an overall shielding effectiveness stated in dB of attenuation and we are seeing where the requirements are based on a particular material’s spec sheet.  That seems like the two elements agree but the problem is that the leakage part of the equation is not considered.  Any gap or penetration in the shielding material can present a potential for leakage.  Doors are one of most difficult issues presenting a dis-continuity in the shield design – even shielded doors present gaps around the frame and hinges.  Wiring and plumbing items that penetrate the shield may present a means for signals to conduct through the shield presenting a leakage.  Details of shielding design have to consider the complexity or material and maintaining the integrity of the design – as well as the ability for integrating into the overall facility construction. – Questions or more information – contact us.

 

Article Reference ID: DYK00007

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