Transcript Electro Magnetic Compatibility.
Electro Magnetic Compatibility.
A new approach for finding solutions for interference problems.
Ir. W.J. Vogel – www.mate.nl
May 20 ir. W.J. Vogel - www.mate.nl .
1
Fundamentals of EMC: Units and Symbols.
Duality between Electricity and Magnetism.
Electric field strength E V/m or N/C Electric charge Q C or As Electric Voltage U V or J/C Capacitance C F or C/V Electr. Charge density D C/m 2 Electr. Permittivity ε F/m U = - dΦ/dt V or Wb/s Energy density = ½ D.E J/m 3 Vacuum Permittivity ε 0 = 8.85 pF/m 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/m 2 Magn. Permeability µ H/m Current density J A/m 2 Magnetic pole strength q m Am I = dQ/dt A or C/s Energy density = ½ B.H J/m 3 Vacuum Permeability µ 0 = 1.26 µH/m Light velocity (vacuum) c 0 = 3.10
8 c 0 2 = ( µ 0 ε 0 ) -1 Wave impedance in free space: Zo = ( µ 0/ / ε 0 ) 0.5
= 120 p ( Ω) m/s May 20 ir. W.J. Vogel - www.mate.nl .
2
Fundamentals of EMC: Coupling paths.
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.
May 20 ir. W.J. Vogel - www.mate.nl .
3
Electric Field (1).
Electric field lines between two conductors with equal and opposite electric charge.
May 20 ir. W.J. Vogel - www.mate.nl .
4
Electric Field (2).
Electric field lines between the plates of a flat capacitor (side effects not considered).
May 20 ir. W.J. Vogel - www.mate.nl .
5
Magnetic Field (1).
Magnetic fieldlines around a straight current carrying wire.
May 20 ir. W.J. Vogel - www.mate.nl .
6
Magnetic Field (2).
Magnetic field lines through a round current carrying loop.
May 20 ir. W.J. Vogel - www.mate.nl .
7
Magnetic Field (3).
Magnetic field lines through a current carrying solenoid.
May 20 ir. W.J. Vogel - www.mate.nl .
8
Impedance of EM fields.
Flat wave in free space: Impedance = (E/H) = 120 p ( W ) ( far field; r >> l ).
For the near field, other rules apply !
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.
May 20 ir. W.J. Vogel - www.mate.nl .
9
Impedance of EM fields.
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.
May 20 ir. W.J. Vogel - www.mate.nl .
10
Power and fieldstrength.
Flat wave in free space: Impedance = (E/H) = 120 p ( W ).
Power per m 2 : S = E x H ( W/m 2 ).
Surface of a sphere around an isotrope antenna = 4 p r 2 =>> E = (30 P) 0.5
For a dipole antenna: E = 7 . (P) 0.5
/ r .
/ r .
May 20 ir. W.J. Vogel - www.mate.nl .
11
When occurs interference between two EM systems?.
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 ] May 20 ir. W.J. Vogel - www.mate.nl .
12
When occurs interference between two EM systems?.
[ 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.
May 20 ir. W.J. Vogel - www.mate.nl .
13
Types of Electro Magnetic Interference between two systems.
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.
May 20 ir. W.J. Vogel - www.mate.nl .
14
Generating Interference and being interfered……..
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.
May 20 ir. W.J. Vogel - www.mate.nl .
15
Generating Interference and being interfered……..
Narrowband: Most transmitters, Oscillators.
Wideband: Spark bridges (ignition systems), SMPS, Collectormotors, Thermostats, Frequency control systems, Power control systems, Dimmers.
May 20 ir. W.J. Vogel - www.mate.nl .
16
Generating Interference and being interfered……..
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.
May 20 ir. W.J. Vogel - www.mate.nl .
17
Detection of Interference.
Equipment: Signal generator.
E-field probe.
H-field probe.
Oscilloscope.
Spectrum analyzer.
EMI test receiver.
May 20 ir. W.J. Vogel - www.mate.nl .
18
Reciprocity.
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.
May 20 ir. W.J. Vogel - www.mate.nl .
19
Properties of probes.
Dimensions are small compared to the wavelength of the signal.
E-field probe is high impedant (short whip).
H-field probe is low impedant (small loop).
May 20 ir. W.J. Vogel - www.mate.nl .
20
Kirchhoff’s laws
Currents to a node: S i = 0 .
Voltages in a closed loop: S u = 0 .
Real: S u = - d F / 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.
May 20 ir. W.J. Vogel - www.mate.nl .
21
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.
May 20 ir. W.J. Vogel - www.mate.nl .
22
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.
ir. W.J. Vogel - www.mate.nl .
23 May 20
How to find solutions for Electro Magnetic Interference.
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).
May 20 ir. W.J. Vogel - www.mate.nl .
24
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).
May 20 ir. W.J. Vogel - www.mate.nl .
25
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.
May 20 ir. W.J. Vogel - www.mate.nl .
26
Practical Examples (2).
May 20
Solving a whistle problem at MW in a radio receiver by using 4 extra components at the PCB.
ir. W.J. Vogel - www.mate.nl .
27
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.
ir. W.J. Vogel - www.mate.nl .
28 May 20
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.
May 20 ir. W.J. Vogel - www.mate.nl .
29
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.
ir. W.J. Vogel - www.mate.nl .
Solution: Increase the distance between the inductors at the PCB.
30 May 20
Practical Examples (5b).
ir. W.J. Vogel - www.mate.nl .
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 Frequency/ Hertz 10M 20M 40M 100M 400M 1G 31 May 20
What’s the trend (1)?
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.
May 20 ir. W.J. Vogel - www.mate.nl .
32
What’s the trend (2)?
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 !
May 20 ir. W.J. Vogel - www.mate.nl .
33
What’s the trend (3)?
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 !
May 20 ir. W.J. Vogel - www.mate.nl .
34
What’s the trend (4)?
The switching times of semiconductors are becoming shorter !
Example: SMPS.
=> The interfering sources will produce more power at higher frequencies !
May 20 ir. W.J. Vogel - www.mate.nl .
35
Conclusion:
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 !
May 20 ir. W.J. Vogel - www.mate.nl .
36
Contact information:
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.
May 20 ir. W.J. Vogel - www.mate.nl .
37