Collaboration Meeting at UCI, April 7-9, 2005

EMI Control System Design

Kurt Liewer

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 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

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 3

Main EMI box construction

frame is now stainless steel

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 4

Hardware within the main EMI box

ADU5

cPCI DC|DC converters

instrument power

cPCI crate

radiator plate

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 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

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 6

EMI enclosure to RFCM wiring

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 7

Box-within-a-box design for main box

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 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)

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 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

April 7, 2005 Collaboration Meeting at UCI, April 7-9, 2005 KML - 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