Transcript Electro Magnetic Compatibility.

Electro Magnetic
Compatibility.
A new approach for finding
solutions for interference
problems.
Ir. W.J. Vogel – www.mate.nl
July 15
ir. W.J. Vogel - www.mate.nl .
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Fundamentals of EMC: Units and Symbols.
Duality between Electricity and Magnetism.
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Electric field strength E
Electric charge
Q
Electric Voltage
U
Capacitance
C
Electr. Charge density D
Electr. Permittivity
ε
V/m or N/C
C or As
V or J/C
F or C/V
C/m2
F/m
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U = - dΦ/dt
V or Wb/s
Energy density = ½ D.E
J/m3
Vacuum Permittivity
ε0= 8.85 pF/m
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Magnetic field strength H A/m or N/Wb
Magnetic flux
Φ Wb or Vs
Electric current
I A or J/Wb
Inductance
L H or Wb/A
Magn. Flux density
B Wb/m2
Magn. Permeability
µ H/m
Current density
J A/m2
Magnetic pole strength qm Am
I = dQ/dt
A or C/s
Energy density = ½ B.H
J/m3
Vacuum Permeability
µ0= 1.26 µH/m
Light velocity (vacuum) c0= 3.108 m/s
c02= (µ0 ε0) -1
Wave impedance in free space:
Zo = (µ0/ / ε0) 0.5 = 120 p (Ω)
July 15
ir. W.J. Vogel - www.mate.nl .
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Fundamentals of EMC:
Coupling paths.
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Through common electric conductors.
Direct radiation from/to the outside world.
(E/H) = 120 p ( W ).
[ far field, flat wave in free space ].
Capacitive (E-field) coupling.
Inductive (H-field) coupling.
Transmission line (E- + H-field) coupling.
July 15
ir. W.J. Vogel - www.mate.nl .
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Electric Field (1).
Electric field lines
between two
conductors with equal
and opposite electric
charge.
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Electric Field (2).
Electric field lines between the plates
of a flat capacitor (side effects not
considered).
July 15
ir. W.J. Vogel - www.mate.nl .
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Magnetic Field (1).
Magnetic
fieldlines around
a straight current
carrying wire.
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Magnetic Field (2).
Magnetic field
lines through a
round current
carrying loop.
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ir. W.J. Vogel - www.mate.nl .
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Magnetic Field (3).
Magnetic field
lines through a
current carrying
solenoid.
July 15
ir. W.J. Vogel - www.mate.nl .
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Impedance of EM fields.
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Flat wave in free space: Impedance =
(E/H) = 120 p ( W ) ( far field; r >> l ).
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For the near field, other rules apply !
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If (E/H) >> 120 p (W), then it is a highimpedant field.
If (E/H) << 120 p (W), then it is a lowimpedant field.
July 15
ir. W.J. Vogel - www.mate.nl .
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Impedance of EM fields.
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If (E/H) >> 120 p (W), then it is a high-impedant field.
If (E/H) << 120 p (W), then it is a low-impedant field.
High-impedant fields are found near high-voltage
circuits.
Coupling will be mainly capacitive.
Low-impedant fields are found near high-current
circuits.
Coupling will be mainly inductive.
July 15
ir. W.J. Vogel - www.mate.nl .
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Power and fieldstrength.
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Flat wave in free space: Impedance =
(E/H) = 120 p ( W ).
Power per m2: S = E x H ( W/m2 ).
Surface of a sphere around an isotrope
antenna = 4 p r2
=>> E = (30 P)0.5 / r .
For a dipole antenna: E = 7 . (P)0.5 / r .
July 15
ir. W.J. Vogel - www.mate.nl .
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When occurs interference
between two EM systems?.
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When there is a source of interference.
When there is a device which is susceptible
for interference.
When there is a coupling path.
[ SOURCE => COUPLING PATH =>
SUSCEPTIBLE DEVICE ]
July 15
ir. W.J. Vogel - www.mate.nl .
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When occurs interference
between two EM systems?.
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[ SOURCE => COUPLING PATH => SUSCEPTIBLE
DEVICE ]
To prevent EMC problems, sufficient margins have
to be realized for all three subjects.
=> Margins following the law requirements.
=> Margins following the user requirements.
July 15
ir. W.J. Vogel - www.mate.nl .
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Types of Electro Magnetic
Interference between two systems.
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Degradation of performance.
Missing functions of the system.
Components becoming defect.
=> Consequences for the quality and
the safety of the product => Can lead
to claims from the end-user of the
product.
July 15
ir. W.J. Vogel - www.mate.nl .
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Generating Interference and
being interfered……..
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Sources of interference can have a
narrowband (sine) or a wideband
(pulse or noise) characteristic.
Sources of interference can cause
problems inside and outside the
frequency range of the susceptible
device.
July 15
ir. W.J. Vogel - www.mate.nl .
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Generating Interference and
being interfered……..
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Narrowband: Most transmitters,
Oscillators.
Wideband: Spark bridges (ignition
systems), SMPS, Collectormotors,
Thermostats, Frequency control
systems, Power control systems,
Dimmers.
July 15
ir. W.J. Vogel - www.mate.nl .
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Generating Interference and
being interfered……..
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Inside the frequency range of the
susceptible device: main cause is direct
radiation or coupling into the device.
Outside the frequency range of the
susceptible device: main cause is
rectification of the interfering signal (LFD =
Low Frequency Detection).
The function of a device is disturbed when
the output of the device deviates more than
what’s expected from the own noise of the
device.
July 15
ir. W.J. Vogel - www.mate.nl .
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Detection of Interference.
Equipment:
Signal generator.
E-field probe.
H-field probe.
Oscilloscope.
Spectrum analyzer.
EMI test receiver.
July 15
ir. W.J. Vogel - www.mate.nl .
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Reciprocity.
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Passive probes are usable in two directions:
1. For detection of signals.
2. For inducing of signals.
Active probes are not reciprocal; these are
only usable in one direction as detector.
July 15
ir. W.J. Vogel - www.mate.nl .
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Properties of probes.
Dimensions are small
compared to the
wavelength of the signal.
E-field probe is highimpedant (short whip).
H-field probe is lowimpedant (small loop).
July 15
ir. W.J. Vogel - www.mate.nl .
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Kirchhoff’s laws
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Currents to a node: S i = 0 .
Voltages in a closed loop: S u = 0 .
Real:
S u = - dF / dt because the loop area is not equal to zero!
Electric field generated by a time-varying magnetic field;
(a) dΦ/dt > 0 ; Σ u < 0.
(b) dΦ/dt < 0 ; Σ u > 0.
July 15
ir. W.J. Vogel - www.mate.nl .
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How to find solutions for
Electro Magnetic Interference.
Position the PCB in an EM
field.
Look for the frequencies at
which the interference is at
its maximum.
Localize the susceptive or
the generating devices by
using H-field en E-field
(inductive and capacitive)
probes.
Example: locating a whistle problem in a radio receiver.
July 15
ir. W.J. Vogel - www.mate.nl .
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How to find solutions for
Electro Magnetic Interference.
Try to minimize the problem by using
decoupling capacitors and damping
resistors or ferrite beads.
Investigate the signal paths and the
return paths.
Example: The effect of resonance in a
series tuned circuit.
July 15
ir. W.J. Vogel - www.mate.nl .
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How to find solutions for
Electro Magnetic Interference.
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Parallel connection of capacitors: NOT ALWAYS OK!
Cause: Self-inductance of the conductors (PCB
tracks) between the capacitors.
Better solution: Connect impedances (ferrite beads)
in the power line when the signals have been
referred to ground (GND).
July 15
ir. W.J. Vogel - www.mate.nl .
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How to find solutions for
Electro Magnetic Interference.
Try to minimize the problem by
using a better DC operating
point for the semiconductors in
the circuit.
Investigate the consequences
for battery consumption, noise
properties, bandwidth, etc.
Diode characteristics (1N4148).
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (1).
Sensor for outdoor lighting
system causes interference in
Mediumwave radio receivers.
Root cause: Wrong application of
the product.
Solution: Use the sensor in
combination with a conventional
light bulb or use another sensor
type in combination with an
energy-saving lighting system.
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (2).
Solving a whistle problem at MW in a radio receiver
by using 4 extra components at the PCB.
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (3).
In a repaired TV set the
teletext function is missing.
Root cause: Other H-field
pattern due to another
Horizontal Output
Transformer type.
Solution: Mount an extra
ground wire connection
between the control PCB and
the teletext PCB.
Above: Common ground wire.
Below: One-point grounding system.
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (4).
PCB on which a certain IC becomes
regularly defective.
Root cause: Signal path and return
path (ground) are covering a large
area.
Solution: Mount extra ground
connections at the PCB.
Above: Improved one-point grounding system.
Below: Multiple-point grounding system.
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (5a).
PCB on which the two
inductors right below are
coupling due to
mounting close together.
FM Band reject filter
characteristics are now
dependant of the phasing
of the inductors:
coupling may become
positive or negative.
Solution: Increase the
distance between the
inductors at the PCB.
July 15
ir. W.J. Vogel - www.mate.nl .
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Practical Examples (5b).
Influence of the phasing of
the inductors:
Red: Coupling = + 5%
Blue: Coupling = - 5%
0
-10
-20
?
-30
-40
-50
-60
-70
-80
100k 200k 400k
1M 2M 4M
10M 20M 40M 100M
400M
Frequency/ Hertz
July 15
ir. W.J. Vogel - www.mate.nl .
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1G
What’s the trend (1)?
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Frequency range of EMC is increasing !
Examples:
GSM (cell) phones (900 MHz => 1800 MHz).
Magnetrons (2450 MHz).
=> Extra investments are necessary for
good EMC measurement set-ups.
July 15
ir. W.J. Vogel - www.mate.nl .
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What’s the trend (2)?
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The current consumption of
semiconductors is decreasing; the
number of semiconductors in a circuit
is increasing !
=> The susceptibility for RF sources is
becoming more worse !
July 15
ir. W.J. Vogel - www.mate.nl .
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What’s the trend (3)?
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The dimensions of the circuits are
becoming smaller due to
miniaturization, SMD technology and
integration !
=> The susceptibility for RF sources is
shifting to higher frequencies !
July 15
ir. W.J. Vogel - www.mate.nl .
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What’s the trend (4)?
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The switching times of semiconductors
are becoming shorter !
Example: SMPS.
=> The interfering sources will
produce more power at higher
frequencies !
July 15
ir. W.J. Vogel - www.mate.nl .
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Conclusion:
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Recognizing EMC problems and finding
solutions is more actual than it ever
was before !
A good EMC product design from the
begin of the product development will
save additional costs through the
whole product life cycle !
July 15
ir. W.J. Vogel - www.mate.nl .
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Contact information:
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Website: www.mate.nl .
Ir. W.J. Vogel - consultancy
E-mail: [email protected]
Kramersstraat 2, 5612 NV Eindhoven
Tel. +31 40-7850345, GSM +31 6-29393856.
July 15
ir. W.J. Vogel - www.mate.nl .
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