ATI Courses Professional Development Seminar Practical EMI Fixes by William Duff

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ELEMENTS OF EMI
SOURCES OF EMI
COUPLING
VICTIM OF EMI
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EMI CULPRIT AND VICTIM
EMI Source
CULPRIT
VICTIM
Signal Source
Signal Receiver
COUPLING PATH
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CONDUCTED OR RADIATED COUPLING

• SOURCE COUPLING VICTIM

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Historical EMI/E3-Related Incidents
Courtesy of Jose Reza
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• Shielding May Have Avoided
• Some of These Problems

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Proper Grounding May Have Avoided Some of These
Problems
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CONCEPTUAL ILLUSTRATION OF CONDUCTED AND RADIATED
EMISSIONS AND SUSCEPTIBILITY
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NARROWBAND AND BROADBAND EMISSIONS
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Filter Affects on a Pulse
Vin
V1
Tin
T1
Vin
F1
Tin
V1 F1TinVin T1 1/F1
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UWB PRF gt IFBW
Ai
Ao
Time Domain
t
t
RF Input
Output
Receiver
Ai
Ao
passband
f
f
f
Frequency Domain
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UWB PRFlt IFBW
Ai
Ao
Time Domain
t
t
RF Input
Output
Receiver
Ai
Ao
passband
f
f
f
Frequency Domain
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THREE-DIMENSIONAL GEOMETRY ILLUSTRATING GAIN OF
ANTENNA
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RECEIVER SUSCEPTIBILITY CHARACTERISTICS
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RECEIVER SPURIOUS RESPONSES
50 MHz 60 MHz 100 MHz 120 MHz
Mixer
I.F.
RF
10 MHz
L.O. 110 MHz 220 MHz 330 MHz
210 MHz 230 MHz 320 MHz 340 MHz
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RECEIVER INTERMODULATION

• RF AMP

100 MHz 101 MHz 102 MHz
R.F. Amplifier
100 MHz
fIM mf1 ? nf2
m 2 n 1 (-) m 3 n 2 (-) m 4 n 3
(-)
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INTERSYSTEM EMC DESIGN AND EMI CONTROL
Location Management
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Illustration of Common Mode Currents
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Illustration of Differential Mode Currents
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Illustration of Common and Differential Mode
Currents
Illustration of Common and Differential Mode
Currents
Illustration of Common and Differential Mode
Currents
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Common Mode Currents Resulting From Distributed
Capacitance to Ground
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Common Ground Impedance Common Mode EMI
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Controlling Conducted EMI
Source Power Supplies Motors Inductive
Loads High Level Analog Digital
Signals Transmitters EM Environment
Victim Analog Equipment Digital Equipment Video
Display Recorders Instruments Sensors Control
Systems Receivers
Conducted EMI
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WHAT IS GROUND ?

• SIGNAL RETURN?
• CHASSIS REFERENCE?
• SAFETY WIRE REFERENCE?
• EARTH REFERENCE?

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ELECTROMAGNETIC SHIELDING
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SHIELDING APPLIES TO ALL LEVELS

• Components
• Circuits
• Functional Stages
• Equipments

• Systems
• Cables
• Platforms
• Buildings

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CABLES, CIRCUITS AND COMPONENTS ACT
AS ANTENNAS
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REPRESENTATION OF SHIELDING PHENOMENA FOR PLANE
WAVES
Ey
Inside of Enclosure
Incident Wave
Transmitted Wave
A
Ey
Hz
Ey
B
H
Attenuated Incident Wave
Ey
Hz
Hz
Hz
Ey
Reflected Wave
Internal Reflecting Wave
Metal Barrier
Outside World
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REFLECTION LOSS
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REFLECTION LOSS (RdB) OF PLANE WAVES VS FREQUENCY
3kHz
30kHz
300kHz
3MHz
200
30MHz
300MHz
200
150
150
Copper
100
100
Iron
50
Hypernick
50
0
0
1kHz
10kHz
100kHz
1MHz
10MHz
100MHz
Radio Frequency
Valid for thickness gt 3 ? ? Skin Depth
Permeability assumed constant with frequency
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ABSORPTION LOSS, A
Current Density
?
t
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ABSORPTION LOSS VS FREQUENCY
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TOTAL SHIELDING EFFECTIVENESS
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PRINCIPAL BOX SHIELDING COMPROMISES
Holes or Slots for Convection Cooling
Screw Spacing Slot Radiation
Cover Plate for Access
Status Indicator Lamp
Forced Air Cooling
Panel Meter
Potentiometer
Connectors
Fuse
Switch
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SLOT AND APERTURE LEAKAGE
L
t
h
V. P. 20dB/dec.
SE (dB)
Log Frequency
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Shielded Enclosures

• Provide metal-to-metal contact at seams
• Use RF gasketing on access panels
• Use screws with lockwashers
• Use perforated grids or slots for opening

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EMI-Fix Matrix - Fixes vs. Coupling Paths, Part 1
PP
PP
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EMI-Fix Matrix - Fixes vs. Coupling Paths, Part 2
PP
PP
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