Electromagnetic Interference (EMI) IBEX 2011 Speakers: David - - PowerPoint PPT Presentation

IBEX 2011

Speakers: David Gratton- Martek-Palm Beach, FL Johnny Lindstrom- Westport Shipyard, WA

Electromagnetic Interference (EMI)

Property of the NMEA. Shall not be copied or re-distributed.

Seminar Overview

• EMI Troubleshooting
• EMI Prevention with Proper Cabling & Terminations
• Lightning Protection
• Corrosion
• Grounding

Property of the NMEA. Shall not be copied or re-distributed.

Electromagnetic Interference

• Unwanted Periodic Signal/Energy

– “One person’s signal is another person’s EMI.”

• Interrupts, Obstructs,

Degrades, or Limits Equipment Performance

Property of the NMEA. Shall not be copied or re-distributed.

Electromagnetic Interference

• Radiated Emissions – RF Energy That Reaches

Susceptible Equipment via Broadcast

• Conducted Emissions – RF Energy That Reaches

Susceptible Equipment via Common Connections

Property of the NMEA. Shall not be copied or re-distributed.

EMI Propagation

• Radiated Emissions –

– Signals/Energy that Reaches Susceptible Equipment via Broadcast – Radiated Power Decreases by Distance Squared

• Conducted Emissions –

– Signals/Energy that Reaches Susceptible Equipment via Common Connections

• Combined Modes –

– Signals/Energy that Propagates via Cable Connections that then Become Signal Radiators

Property of the NMEA. Shall not be copied or re-distributed.

EMI Sources

• AC Units
• Alternators
• Battery Chargers
• Blower fans
• Engines
• Generators
• Inverters
• Propeller Shafts
• Radars
• Wiring

Property of the NMEA. Shall not be copied or re-distributed.

EMI Recipients

• Electronic Compasses
• AV Systems
• Multifunction Displays
• Just about any Electronic Device

Property of the NMEA. Shall not be copied or re-distributed.

Identifying EMI Sources

• Trial-and-Error Process of Elimination

– Turn off All Equipment Except for Affected Device – Turn on a Device and Check for Symptoms – Repeat Until Interference Symptoms Return

• Additional Testing May Be Required to

Determine If Interference Is Radiated or Conducted

• Interference May Be Radiated from Cables

Connected to Interference Source

Property of the NMEA. Shall not be copied or re-distributed.

Avoiding EMI Problems

• Layout and Space Planning

– Identify Potential EMI Radiation Sources – Identify Potential EMI Conducted Sources – Avoid Potential Hot Spots

VHF Radio Auto- pilot F RF Transmission Line Rudder Feedback Signal

Parallel cable runs are not desirable

Property of the NMEA. Shall not be copied or re-distributed.

Mitigation Is Application Dependent

Internal High Frequency Signal DC Power Supply Leads Signal Output Stage AC/RF Output

RF Output to Antenna (AC Signal Wave Form)

Property of the NMEA. Shall not be copied or re-distributed.

Mitigation for Unintended Signals

• Objective: Block the Signal

– Prevent Signal Transmission on Cables – Prevent Signal Transmission through Enclosure

• Shielded Enclosure with Attached Ground
• Input and Output Cables

– Active Filters- usually BandPass or Notch – Ferrites – Best Practice is to attempt to solve problems within the “offender” rather than the “offended”.

Property of the NMEA. Shall not be copied or re-distributed.

Ferrites as an EMI Suppressor

• Ferrites Composed of Ferrous Oxide and One
• r More Powdered Metals
• Composite Material Resists Imposed EMI

Fields by Suppressing Electron Movement

• Variable Sensitivity to Frequency

– Lower Frequencies Pass without Significant Loss – Above Resonant Frequency Signal Becomes Coupled to Ferrite, Causing a High Impedance

• Increasing Turns Increases Effectiveness

Property of the NMEA. Shall not be copied or re-distributed.

Ferrite Geometry

Property of the NMEA. Shall not be copied or re-distributed.

Mitigation for Signal Cables

• Objective: Preserve Signal on Cable; Prevent

Radiation to Other Cables and Devices

• Balanced Signals Cancel Radiation
• Shielding Captures Radiation and Diverts

Signal to Ground (not applicable to coax).

• Find it with troubleshooting

Type Coverage Conductivity Flexibility Foil 100% poor poor Braid 85-95 % good good

Property of the NMEA. Shall not be copied or re-distributed.

Eliminating Interference: Power cables

• Shielded Cables – Connect One End of Shield to

RF Ground

• Grounding – Connect Case to RF Ground

– Better to Connect Source’s Case – Less Desirable to Connect Affected Device’s Case

• Filters – Install in Power Leads of offender first
• Ferrites – Effective for Conducted and Radiated

Noise

Property of the NMEA. Shall not be copied or re-distributed.

Other Mitigation

• Relocate Cable Runs
• Relocate Equipment Displays
• Relocate Antennas

– Consider Antenna Radiation Patterns

• Consider Cable Lengths

– Avoid Multiples of ¼ Wave Length with power & data cables – This is not an issue with coax cables

Property of the NMEA. Shall not be copied or re-distributed.

Signal Loss Calculations

Total Loss = Cable Loss + Connector Losses (Depends on Type) Cable Loss = Loss in dB per 100 ft. x Cable Length / 100 Connector Loss = Number of Connectors x 0.5 dB

Property of the NMEA. Shall not be copied or re-distributed.

Connector Selection

Connector Type Maximum Frequency Impedance Permitted Uses

UHF (PL-259) 300 MHz 50-Ohm VHF, SSB, DGPS, Stereo BNC 4.0 GHz 50-Ohm VHF, SSB, DGPS, Cell, GPS TNC 2.5 GHz 50-Ohm VHF, SSB, DGPS, Cell, GPS, MINI-M N 11.0 GHz 50-Ohm VHF, SSB, DGPS, Cell, GPS F 2.0 GHz 75-Ohm TV, GPS Mini UHF 2.5 GHz 50-Ohm Cell SMA 12.0 GHz 50-Ohm SAT Phone SMB 4.0 GHz 50-Ohm FME 200 MHz 50-Ohm VHF, SSB

Property of the NMEA. Shall not be copied or re-distributed.

Cable Bend Radius

Cable Type Bend Radius (inches)

RG58U 2.0 RG8X 2.4 RG8U 4.5 RG213 5.0 LMR240 0.75 LMR400 5.0

Better to route coax cables using gentle S-curves (green) than tight right-angle turns (yellow) when possible.

Coax Cables

• Attenuation

– Transmission Losses (dB per ft.) – Connector Losses (dB) – Impedance Mismatch (Avoidable) 50 Ω - 75 Ω – Also affected by installation

• Cable Length

– Minimum Length Necessary (Most systems have no “tuned” length)

• Equipment Connections

– Match Application and Cable Type

• Extensions –beware of the allowed loss

Cable Selection

RG58U RG8X RG8U RG213 LMR240 LMR400 Nominal O.D.

3/16" 1/4" 13/32" 13/32" 1/4" 13/32”

Conductor (AWG) 20 16 13 13 15 9 Impedance (Ohms) 50 50 52 50 50 50 Impedance Match within  2 Ohms

Property of the NMEA. Shall not be copied or re-distributed.

Shielding Connections of Power

• Shields Connected to RF Ground System
• Effectiveness Dependent on Low Impedance

to Ground

• Best Ground Path for High Frequency EMI

signals is via Copper Foil

– #8 AWG Stranded Copper Wire Acceptable

Property of the NMEA. Shall not be copied or re-distributed.

Lightning Strikes- GOOD LUCK!

• Direct Strike – Direct Hit on a Part of the

Vessel, Such as an Antenna or Mast.

• Conductive Strike – Strike on a Utility Line

and Conducted Aboard Through the AC Power Cord

• Inductive Strike – Nearby Strike Causing a

Large Magnetic Field, Which in Turn Induces a Voltage in the Vessel’s Wiring

• There is no sure way to prevent damage from

any type of strike.

Refer to ABYC TE-4 — Lightning Protection for more information

Lightning Protection:

Two schools of thought

• Conductive and Inductive

– Commercially Available Surge Protection Products

• Direct Strikes

– Air Terminals Connected to Properly Sized Conductors, with Relatively Straight Paths to Ground – Towers Grounded Port and Starboard

Refer to ABYC TE-4 — Lightning Protection for more information

Property of the NMEA. Shall not be copied or re-distributed.

Corrosion

• Electrolysis – Chemical and/or Electrochemical

Change Due to Electric Current

• Galvanic Corrosion – Corrosion from Electric

Current Flow between Connected but Dissimilar Metals in the Same Electrolyte

Refer to ABYC E-11 — AC & DC Electrical Systems on Boats for more information

Other Corrosion Sources

• Stray Current Corrosion – Electric Current Flow Caused

by an Outside Source. (In a Marina).

• Velocity Corrosion – Electric Current Flow Caused by

Strong Water Currents

• Selective Corrosion – Electric Current Flow Caused by

Areas with Different Composition within the Same Alloy

• Oxygen Starvation – Electric Current Flow Caused by

Trapped Electrolytes Making Adjacent Surfaces More Positive to the Remaining Metal Surface

Refer to ABYC E-11 — AC & DC Electrical Systems on Boats for more information

To Bond or Not to Bond Age Old Debate!

• Decision Is Vessel Dependent
• Bonding Is Fairly Common in the Industry
• Aluminum Is Less Noble Than Almost

Everything Else

• Always Isolate From Bonding System And/or

Bond by Itself to a Sacrificial Anode Selected Especially for Aluminum

Refer to ABYC E-2 — Cathodic Protection for more information

Property of the NMEA. Shall not be copied or re-distributed.

DC Common Grounding System

• Shorts Stray Potentials to

Ground

• May Provide Cathodic

Protection

• Usually Main Connection

between Vessel and Earth Ground

Refer to ABYC E-11 — AC & DC Electrical Systems on Boats for more information

Property of the NMEA. Shall not be copied or re-distributed.

Grounding System Interconnect

• Objective: Single Point with No Current Flow
• Practical: Few Interconnections with No Common Currents

Refer to ABYC E-11 — AC & DC Electrical Systems on Boats for more information

Vessel Grounding Systems

System Type When Required DC Ground or Negative Reference All Vessels with DC Systems AC Neutral Reference Vessels with AC Shore Power, Generator, or Inverter Installed AC Grounding (Safety) Safety RF Ground Performance Vessels with Electronics Equipment Installed Single Side Band (SSB) Ground Performance Vessels with SSB Transceiver Installed DC Grounding Reference Lightning Ground Safety

Refer to ABYC E-11 — AC & DC Electrical Systems on Boats for more information

Property of the NMEA. Shall not be copied or re-distributed.