My slides for the talk at HAWtech Automotive Summer School 2012, Berlin, Germany.

1. Electromagnetic Compatibility
Vesa Linja-aho – 2012-07-19

2. Me
 Senior Lecturer in Automotive Electronics at
Metropolia UAS
 Background: M.Sc. in Electromagnetics and
Circuit Theory, Helsinki University of Technology
 Worked as researcher, lecturer and journalist.
 Interested in Open Educational Resources and
Electric Work Safety.
2012-07-19 Vesa Linja-aho 2

3. Metropolia UAS
 In Finland, we have two kinds of institutions of
higher education
 University: Bachelor (3 yr), Master (2 yr), PhD
(3-4 yr)
 University of Applied Sciences (UAS): Bachelor
(4 yr) and Master (2 yr)
 Metropolia is the largest UAS in Finland
 Automotive engineering education:
 Formula Student –team
 Electric Raceabout (ERA)
2012-07-19 Vesa Linja-aho 3

4. Studying in Finland
 Metropolia unfortunately does not have
automotive engineering degree programmes in
English, unfortunately.
 But we have other interesting programmes:
http://www.metropolia.fi/en/
 In Finland, we do not have tuition fees (some
universities charge a tuition fee from non-EEA
citizens, but not Metropolia).
 The application time is at spring.
2012-07-19 Vesa Linja-aho 4

5. EMC = Electromagnetic Compatibility
 All electric and electronic devices should be
designed so that they
 will accept any normal interference
 won’t interfere other devices.
2012-07-19 Vesa Linja-aho 5

6. Everyday Examples?
2012-07-19 Vesa Linja-aho 6

7. Everyday Examples
 The ”GSM song”
 FM radio crackling when your neighbor drills a
hole on his wall.
 FM radio clicking when fluorescent tubes start.
2012-07-19 Vesa Linja-aho 7

8. Not-so-everyday Examples
 Electric wheelchair turns in the water when a
police officer pushes talk button in the police
boat radio.
 Piezoelectric cigarette lighter opens barrier at a
parking lot.
 Starting a welding transformer causes the
central computer to crash (in another building).
 The roof and central locking system react to
cellphone.
2012-07-19 Vesa Linja-aho 8

9. Electromagnetic Interference (EMI)
 Natural interference: cosmic radiation and
thunderstorm.
 Technical interference:
 Electrostatic discharge (ESD)
 Digital circuits
 Changes in the mains voltage
 Wireless communication
2012-07-19 Vesa Linja-aho 9

10. Coupling Mechanisms
 Conducting
 Capacitive coupling (via electric field)
 Inductive coupling (via magnetic field)
 Electromagnetic waves
2012-07-19 Vesa Linja-aho 10

11. Coupling Mechanisms
2012-07-19 Vesa Linja-aho 11

12. How to Fight EMI?
 Prevent the emergence of interference
 Cut the path of propagation
 Improve the tolerance for the interference
2012-07-19 Vesa Linja-aho 12

13. Countermeasures in Practice
 Layout design and position of the wires
 Symmetrical transmission
 Filtering
 Using digital electronics
 Using optical transmission
2012-07-19 Vesa Linja-aho 13

14. Brief Physical Background
 An electric charge creates an electric field.
 Electric current or changing electric field creates
a magnetic field.
 Changing magnetix field induces a voltage into a
wire.
2012-07-19 Vesa Linja-aho 14

15. Capacitive coupling = Coupling via Electric
Field
Countermeasures
 Metallic enclosing
 Increasing the distance between wires
 Positioning the wires near the ground plane
 Decreasing the impedance level
2012-07-19 Vesa Linja-aho 15

16. Inductive Coupling = Coupling via Magnetic
Field
Countermeasures
 Layout design
 Decreasing the impedance level
2012-07-19 Vesa Linja-aho 16

17. EMC is not a Separate Matter
 The risky way: design the product and fix the
EMC issues afterwards.
 The safe way: keep EMC in mind during the
whole design process
2012-07-19 Vesa Linja-aho 17

18. Common Mode vs. Differential Signal
 Common mode signal together with the ground
plane causes a large loop between circuits.
2012-07-19 Vesa Linja-aho 18

19. Three-level Protection
 Layout design
 Interface filtering
 Metallic enclosing
2012-07-19 Vesa Linja-aho 19

20. Do we need protection?
 In simple non-critical devices, the layout design
is often enough.
 Especially, if there are no cables to/from the
device.
 About 90 % of post-design EMC-problems are
caused by poor layout design!
2012-07-19 Vesa Linja-aho 20

21. Good layout design
 Split the system in parts
 Think the ground plane as a large current
conducting path.
 Choose grounding points well and minimize the
grounding impedance.
 Remember that every conducting part can carry
interfering currents!
2012-07-19 Vesa Linja-aho 21

22. Splitting the system in parts
 Decide which parts are critical vs. non-critical.
 Place the parts which are neither sensitive nor
sources for interference, into separate locations
even on their own circuit boards.
 For example, linear power supplies, non-clocked
logic circuits and power amplifiers are usually
immune to interference.
2012-07-19 Vesa Linja-aho 22

23. Grounding
 The ground plane is non-ideal. The correct
grounding style depends on the circuit.
 Single-point grounding is common in switching-
mode power supplies. It prevents interfering
voltages caused by currents through common
impedances.
 But: on large frequencies, the wires act as
transmission lines!
 Multi-point grounding. Works well on large
frequencies. Each circuit has its own ground,
and the grounds are interconnected with short
wires.
2012-07-19 Vesa Linja-aho 23

24. Rule of thumb for grounding
 < 1 MHz: Single-point grounding
 > 10 MHz: Multi-point grounding
2012-07-19 Vesa Linja-aho 24

25. Using a ground plane
 If you use a multilayer PCB, using a ground
plane is possible and recommended.
 With RF circuits and fast digital circuits using the
ground plane is practically mandatory.
 What is the purpose of the large ground plane?
2012-07-19 Vesa Linja-aho 25

26. The purpose of the ground plane
 The main purpose is to provide low grounding
impedance.
 The secondary purpose is to act as a shield.
2012-07-19 Vesa Linja-aho 26

27. Crosstalk
 Two wires on the PCB are – unfortunately –
connected to each other capacitively and
inductively.
 In practice, there is no cross-talk if the distance
between wires is larger than 1 cm.
 Dropping the impedance and using the ground
plane will reduce crosstalk.
2012-07-19 Vesa Linja-aho 27

28. Design Checklist
 Avoid long wires on the PCB board.
 Sensitive and interfering components should not
be placed near each other.
 Do not place sensitive parts near the edges of
the ground plane.
 Split the circuit in parts very carefully.
2012-07-19 Vesa Linja-aho 28

29. Interfaces and filtering
 Most devices are interconnected to other devices
via a cable.
2012-07-19 Vesa Linja-aho 29

30. Ferrite chokes
 Very common in data cables.
 Adds series inductance to cable.
 Effective on frequencies 1-1000 MHz
(approximately).
 Disadvantage: relatively low attenuation (10-20
dB).
 Advantage: easy to add afterwards.
 Ferrite choke attenuates also fast transients
caused by ESD.
2012-07-19 Vesa Linja-aho 30

31. 2012-07-19 Vesa Linja-aho 31

32. Mains filtering
 Example: an electric shock from computer
chassis.
 Maximum leak current 0,5 mA. (EN 60601-1-1)
2012-07-19 Vesa Linja-aho 32

33. Cables
 Coaxial cable
 Twisted pair
 Shielded twisted pair
 The shield should be connected evenly – avoid
the pig tail mistake!
2012-07-19 Vesa Linja-aho 33

34. Switches
Switches cause disturbance in two ways:
 Arcing
 Bouncing
  Use RC snubber
2012-07-19 Vesa Linja-aho 34

35. Relays
 RC snubber + protective diode
2012-07-19 Vesa Linja-aho 35

36. Electric motors
 Motors cause strong magnetic fields.
 If the motor has commutator or brushes, the
arcing causes wide-spectrum RF interference.
 Inverter-driven permanent magnet machines are
more EMC-safe.
2012-07-19 Vesa Linja-aho 36

37. ESD protection
 Have you ever destroyed anything with ESD.
 What precautions you should take when handling
and installing an expensive graphics card to your
computer?
 MOSFET components are the most sensitive part
to ESD.
 The main method for ESD protection is
protective diodes.
2012-07-19 Vesa Linja-aho 37

38. Legislation and Standards
 Harmonized by European Union
 EMC-directive 2004/108/EY
 Radio and telecommunications equipment
1999/5/EC
 Automotive EMC-directive 2004/104/EC.
 European standards and national laws.
2012-07-19 Vesa Linja-aho 38

39. There are Plenty of Standards
 Many device types have their own standard.
 If there is no standard available, the general
standard is to be applied.
2012-07-19 Vesa Linja-aho 39

40. EMC Testing
 EMI immunity
 EMI emissions
2012-07-19 Vesa Linja-aho 40

41. EMC Testing Case Example: Electric Raceabout

42. Name surname 42

43. Thank you!
www.metropolia.fi/en/
www.facebook.com/MetropoliaAMK
firstname.surname@metropolia.fi