Shielded Cable Tray

Chalfant began supplying industry cable tray in 1948 and designed and developed its first RF Tray for NASA in 1960 when it became imperative to protect instrument and control cabling from EMI fields during missle launching. Over the past 30 years, Chalfant has developed both a Premium and an Ultra class RF Tray. The gasketed Ultra RF Tray has been successfully used at Sandia Labs, Los Alamos as well as military and other sensitive government facilities. Industrial and utility companies have found Chalfant's Premium RF Tray to be suitable because of the lower (long wave) EMI frequencies present in most of these applications.

RF Tray and Electromagnetic Compatibility
EMC is the technology of minimizing the electromagnetic interference caused by electromagnetic fields that are radiated or propagated along a conducting medium and reducing the susceptibility of these fields on electrical or electronic devices or systems. EMC is a coordinated systems design approach consisting of:

Reducing interference at the source.
Isolating the offending circuits by filtering, grounding or shielding cable in RF cable tray.
Increasing the immunity of susceptible circuits by distance or rerouting away from radiation sources such as power equipment or high voltage sources.

RF Tray often the answer
RF cable tray has become the solution when source radiation or rerouting of cables is difficult or impossible. They have saved industrial plants many man-hours of tracking and correcting offending circuits during plant or process start-up and shakedown.

In addition, properly grounded and shielded RF tray not only reduces the radiated EMI fields a sensitive circuit sees but also provides an isolated ground reference which effectively reduces internal and circuit part coupling and overall mode coupling.

Chalfant's answer to glitches and bad effects of EMI/RFI
The consequences of inadequate shielding of critical cable runs can include:

Computer 'glitches' (introduction and transmission of erroneous data).
Radio and television interference.
System malfunctions due to voltage variations. The longer the control cable run the more susceptible it is to EMI. Also the lower the control voltage, the higher the impedance and its susceptibility to induced interference. Typical operating voltages and current for process elements range between 100mV to 5K and 1mA to 50mA.
Stolen information through 'listening in' on unprotected, unsecured data lines.

Chalfant's tested RF Tray design plus Chalfant's proven field experience can minimize or reduce the 'bad' effects of EMI/RFI.

RF Cable Tray design considerations:
RF Trays are designed to either contain or exclude EMI/RFI. A perfect design would be a one-piece tray and seam welded covers. However, this design is impractical as easy access to cables is necessary. Straight sections, covers and fittings must also be designed for easy installation in the field.

Premium RF Tray
Low frequency magnetic fields are best attenuated by mass and material. Chalfants' Premium RF Tray has the capability to efficiently attenuate H fields in the 150 KHz - 10 MHz range from 70 to 83 dB.

E fields are effectively attenuated >114 to 90 dB at 1 MHz to 30 MHz. E fields below 1 MHz are attenuated over 100 dB. (See performance graphs.)

Ultra RF Tray
Chalfant's unique Ultra RF Tray has been designed with special cover clamps, splice plates, gaskets and foil. These features are essential for sealing and attenuating the plane wave frequencies 100 MHz through 1 GHz.

Special adjustable tension cover straps compress the cover seam gaskets for optimum shielding efficiency.

Chalfant RF Cable Tray - Easy to Install
Pre-galvanized steel (ASTM 653A, G90 Coating) has proven to be the most cost effective tray material. Its flat, smooth surface is formable, weldable and conductive. It has excellent corrosion resistance. Coatings or painted surfaces are not conductive and work against shielding effectiveness.

Surprisingly the overall shielding effectiveness of RF Tray is determined more from the elimination of seams or gaps than from the mass or thickness of the materials used.

Chalfant builds its RF Tray to close tolerances so surfaces are flat and mate tightly.

Tray is a one-piece construction without seams (18 gauge to 18" widths, 16 gauge @ 24" width).
Covers are designed to overlap at 90 degree angles (18 gauge to 18" widths, 16 gauge @ 24" width).
Fittings have long 3" tangents for tight fit with overlapped splice plates when joined with straight sections.
Splice Plates are wraparound with joint cover plates and special offset along with pressure bolted construction and 3" overlap over all seams.
Gaskets and Foil are made of exclusive conductive coated metal materials with pressure sensitive adhesive backing for easy field installation.
Cover Latches are wraparound snap-latch type with adjustable tension to 200 lbs. to assure positive pressure to compress cover gaskets.

Flatness, overlapping surfaces, tight tolerance and gasketing are the keys to Chalfant's proven RF Tray design.

Chalfant's RF tray: Field and Laboratory Tested to MIL STD 285
Chalfant retained the services of a major Radiation Testing Lab (widely recognized for Tempest Certification) to certify the performance and shielding effectiveness of Chalfant's Premium and Ultra RF Cable Tray. A complete series of tests were conducted to MIL STD 285 using a production run of RF Tray with the following components: two 12" wide straight sections; one 12" radius horizontal fitting with gasketed bottom; one blind end; two wraparound splice plates; one panel adaptor, with covers; cover gaskets and foil tape and adjustable cover staps. The results of these tests are shown below.

Chalfant also field tested a large Navy project to 60 dB at 1,000 MHz. Over six test set-ups were required. The on-site testing was done to MIL STD 285 by another highly respected testing company. Slight modifications were made to Chalfant's original design to eliminate variables of controlled laboratory conditions and small sample size to the actual conditions encountered on the job-site. The new improvements were incorporated and retested at 400 and 1,000 MHz.

Chalfant encourages comparision and believes you'll find theirs is the only tray company that offers a proven, tested system that results in attenuation levels far above any competitor.

Unmatched Shielding Effectiveness

Premium RF Tray (No cover gaskets)

Ultra RF Tray (With gaskets)

Caution: The foregoing test results can only be assured if the product is properly installed. Proper installation includes: providing of level supports, tightly butted joints, proper cleaming of contact surfaces, proper taping and/or installation of gaskets and proper adjustment of cover straps, all of which are the sole responsibility of others. If properly installed, the product will test as shown.

RF Tray Can be Supported to 12-foot Spans

Data plotted above based on NEMA VE-1 testing of 24"(610mm) wide, 4"(102mm) load depth RF Tray. Simple beam test.