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EMI Control System Design

EMI Control System Design

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EMI Control System Design

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  1. EMI Control System Design Kurt Liewer Collaboration Meeting at UCI, April 7-9, 2005

  2. EMI reduction philosophy • Goal is attenuate all locally generated interfering signals by ~100 dB • both radiation and conduction paths to be protected • All electronics are enclosed with EMI enclosures • exceptions are telemetry and GPS antennas, rotator and PV arrays • enclosures have copper (or copper plated) walls and soldered or gasketed joints • connectors are either coax or circular connectors with backshells and 360° shielding (mil 33999) • non-coax connectors have additional box-within-a-box filtering and use shielded twisted pair wire • Noisy components (power supplies) within the main enclosure will also be within EMI enclosures • power will, to the extent possible, have a single ground point that is connected to ground (the gondola) at a single point • the antennas and RF amps prevent this from happening for the RF 12 V supply Collaboration Meeting at UCI, April 7-9, 2005

  3. Main EMI box construction frame is now stainless steel Collaboration Meeting at UCI, April 7-9, 2005

  4. Hardware within the main EMI box cPCI crate radiator plate cPCI DC|DC converters instrument power ADU5 Collaboration Meeting at UCI, April 7-9, 2005

  5. Box-within-a-box concept • example of box-within-a-box filtering applied to the RFCM • Any signal on the wires or leaking through the connector must pass through the filter • discrete filter components allows leakage past the filter • Filter feedthrus would be implemented at both ends of the cable • with >65 dB of filter attenuation less than 35 dB of rejection is required in the cable and connector Collaboration Meeting at UCI, April 7-9, 2005

  6. EMI enclosure to RFCM wiring Collaboration Meeting at UCI, April 7-9, 2005

  7. Box-within-a-box design for main box Collaboration Meeting at UCI, April 7-9, 2005

  8. Wiring • RF cable • minimal change in attenuation across band • high attenuation of inside to outside fields • candidates • heliax (outside of EMI box) • LMR-400 (outside of EMI box) • semirigid, mini-bend or Coaxicon ultraflex (inside) • multiconductor cable • candidate • Alpha 45295 • twisted pairs • foil/braid • > 40 dB rejection (estimated) • Belden 88641 (for AD590 temperature sensors) • shielded (foil) twisted pair • > 40 dB rejection (estimated) Collaboration Meeting at UCI, April 7-9, 2005

  9. AD590 wiring • The AD590 outside of the EMI box will have the configuration shown in the diagram • The connectors may change from LEMO to something else • Shield of twisted pair is connected to the AD590 enclosure but not to the circuit return • Resistors are chosen to match the cable impedence Collaboration Meeting at UCI, April 7-9, 2005

  10. Concerns • Very difficult to know if the design will provide the necessary protection without testing • The testing is very difficult until the final configuration is in place Collaboration Meeting at UCI, April 7-9, 2005