Electromagnetic Compatibility

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

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Electromagnetic Compatibility

  1. 1. Electromagnetic CompatibilityVesa Linja-aho – 2012-07-19
  2. 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. 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. 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. 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. 6. Everyday Examples?2012-07-19 Vesa Linja-aho 6
  7. 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. 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. 9. Electromagnetic Interference (EMI) Natural interference: cosmic radiation and thunderstorm. Technical interference:  Electrostatic discharge (ESD)  Digital circuits  Changes in the mains voltage  Wireless communication2012-07-19 Vesa Linja-aho 9
  10. 10. Coupling Mechanisms Conducting Capacitive coupling (via electric field) Inductive coupling (via magnetic field) Electromagnetic waves2012-07-19 Vesa Linja-aho 10
  11. 11. Coupling Mechanisms2012-07-19 Vesa Linja-aho 11
  12. 12. How to Fight EMI? Prevent the emergence of interference Cut the path of propagation Improve the tolerance for the interference2012-07-19 Vesa Linja-aho 12
  13. 13. Countermeasures in Practice Layout design and position of the wires Symmetrical transmission Filtering Using digital electronics Using optical transmission2012-07-19 Vesa Linja-aho 13
  14. 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. 15. Capacitive coupling = Coupling via ElectricFieldCountermeasures Metallic enclosing Increasing the distance between wires Positioning the wires near the ground plane Decreasing the impedance level2012-07-19 Vesa Linja-aho 15
  16. 16. Inductive Coupling = Coupling via MagneticFieldCountermeasures Layout design Decreasing the impedance level2012-07-19 Vesa Linja-aho 16
  17. 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 process2012-07-19 Vesa Linja-aho 17
  18. 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. 19. Three-level Protection Layout design Interface filtering Metallic enclosing2012-07-19 Vesa Linja-aho 19
  20. 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. 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. 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. 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. 24. Rule of thumb for grounding < 1 MHz: Single-point grounding > 10 MHz: Multi-point grounding2012-07-19 Vesa Linja-aho 24
  25. 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. 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. 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. 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. 29. Interfaces and filtering Most devices are interconnected to other devices via a cable.2012-07-19 Vesa Linja-aho 29
  30. 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. 31. 2012-07-19 Vesa Linja-aho 31
  32. 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. 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. 34. SwitchesSwitches cause disturbance in two ways: Arcing Bouncing   Use RC snubber2012-07-19 Vesa Linja-aho 34
  35. 35. Relays RC snubber + protective diode2012-07-19 Vesa Linja-aho 35
  36. 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. 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. 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. 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. 40. EMC Testing EMI immunity EMI emissions2012-07-19 Vesa Linja-aho 40
  41. 41. EMC Testing Case Example: Electric Raceabout
  42. 42. Name surname 42
  43. 43. Thank you!www.metropolia.fi/en/www.facebook.com/MetropoliaAMKfirstname.surname@metropolia.fi

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