Electromagnetic Interference Mitigation

Transcription

1 Electromagnetic Interference Mitigation Picture or Drawing 20.7 x 8.6 cm Frits J.K. Buesink, Senior Researcher EMC frits.buesink@utwente.nl Funded by the European Union on the basis of Decision No 912/2009/EC, and identified in the European Metrology Research Program (EMRP) as Joint Research Project (JRP) IND60 EMC ( ). Additional funding was received from the EMRP participating countries. The Current Boundary a provision to split loops (and shut out noise sources) (Mains cord 1) Unit 1 Situation in detector: practice AM-radio (I/O cable 1-2) Unit 2 (Mains cord 2) I cm (noise current) Ground 1 Ground 2 loop closes through ground Short circuit(s) check reduce loop area Create one or more inner-loops Ground 1 I cm Ground 2 loop closes through ground 2 1

2 Install current boundaries at natural interfaces edge of PCB, cabinet wall, basement of a building; one boundary per unit! Right Wrong Drawbacks: Current follows long path over equipment Loop area cannot easily be minimized I cm I cm 3 Examples of current boundaries on equipment wide conductors and low-resistance transitions (be careful with paint)! Short Wide No Paint! protect all units with a current boundary! (and check any conductor that passes it) check DC resistance with a milli- meter: < 1 m! 4 2

3 Use Current Boundary to protect existing pig-tail pig-tails can be acceptable as long as CM currents are kept away from it H-field lines Wide metal plate (Current Boundary) I cm EMC glands 5 If many Cables are Guided through Shielding Wall.. other options exist 6 3

4 Roxtec / Brattberg Glands 7 Special Gland System: Many Cables Through Wall all make good electrical contact in wall (< 10 m ) Wall of Equipment Room MIL-STD-1310G current boundary 3 Wall of Equipment Room 8 Injection Probe Monitoring Probe Amplifier Analyser w. Tracking Generator 4

5 Next: Separate Cables with Current Boundaries Category 1. Noisy (E) 2. Sensitive (I) 3. Indifferent (N) classify cables into categories red = source = Emission green = sensitive = Immunity blue = indifferent = Neutral E I I CM N Model 9 Model the Real System in CM loops Both sensitive (analog, various busses) and (polluted) power lines Process control system Power supply 10 kv/400 V power electronics relay s circuit breakers control bus Control equipment control bus control equipment PLC/PC/ C CPU bus pumps, fans, drives M 3~ pneumatic/ hydraulic valves machine structure Production process / machine I/O module sensors Industrial Environment Source: C.J. Post Lambda Engineering B.V. EMC of Large Systems PATO

6 Separating Cables with Current Boundaries use Neutral conductor to reduce loop area; then insert current boundary E N Steps: I N 1. herken recognize kring loop 2. reduce looparea 3. add boundary 11 Separating Cables with Current Boundaries neutral conductor in practical cases: never a wire, always a structure part cm Emission Neutral cross section: twin wires! (CM-) Transfer impedance of combination of two relatively thin conductors is too high (radiates fields) (does not work for high frequencies) 12 6

7 Separating Cables with Current Boundaries wide metal reduces fields i.e. the transfer-impedance of the cm-current loop cm Emission Neutral advantage: proximity & skin effects Wide sheet metal ( cable tray ) is far superior to the previous situation. The common-mode transfer impedance is much lower. Skin effect helps. 13 Separating Cables (Alternative) use structure metal parts to guide cables and insert current boundaries E I N Steps: 1. recognize loop 2. guide cables with metal strips or trays 3. connect current boundaries to strips 14 7

8 Separating Cables with Current Boundaries use (Ground-) Plane to reduce loop area; then insert current boundaries E Note: we are actually reducing CM-loop areas here, using wide metal short-circuits Plane could be metal mesh I N Steps: 1. recognize loop 1. herken kring 2. cover loop with metal (ground-)plane 3. connect current boundaries to plane 15 Experiment with Frequency Controlled Motor crosstalk between cables due to transfer-impedance PWM Controller Cable 1 (source) (twin wires) Plastic support DC Motor mode 50 AC supply Cable 2 (passive)

9 Experiment with Frequency Controlled Motor crosstalk between cables due to transfer-impedance PWM Controller Cable 1 (source) (twin wires) Plastic support DC Motor mode 50 AC supply Metal cable tray Cable 2 (passive) Cable distance is important once a cable tray is used for protection D closer cable catches more flux H proximity effect 18 9

10 Separating Regions using Current Boundaries enclosures with current boundaries form individual environments Region N Top level ( outside ) Region 0 Region N+1 19 Three Types of Current Boundary Short Circuit for Common-Mode Sources Environment Region 0 1. Connector Plate Environment Region 1 Enclosure / EMC Cabinet / Shielded Room 3. Completely Shielded Enclosure 20 10

11 Regions/Environments can be Nested prepare for current boundaries on every module interface 21 Only Limited Shielding can be achieved per Enclosure [db]; but it can be applied recursively! In EMC terms, sometimes referred to as: Multipoint Grounding 22 11

12 Regions are defined Electromagnetic Environments (example) region 0: MIL-STD-464A, region 1: bridge, region 2: below deck Aim: use commercial equipment in region 2 (susceptibility level 10 V/m) Shielding between successive regions: db (factor 10 to 100) Define where EM zones will be Define the EM levels per region Use adequate current boundaries between regions 23 Multipoint Grounding hierarchy of current boundaries Cabinet with Back-plane PCB with ground plane current boundary 1 current boundary 2 Connector Plate on Cabinet Wall 24 12

13 Multipoint Grounding separating rooms in a ship is called Zoning (partitioning into EM-Regions) Cabinet Wall current boundary 2 Wall of Equipment Room current boundary 3 PCB PCB 2 backplane 1 cabinet 1 room wall cabinet 2 20 db per boundary: = 100 db! backplane 2 25 Try to stick to the Low Frequency Approach use current boundaries to restrain sizes to way below half-wavelength Large Scale Low Frequencies Small Scale High Frequencies 26 13

14 Systems Designers Heaven independent building blocks with abstract behaviour Object Oriented realise complex from simpler behaviour make assemblies independent solve undesired as low as possible System EMC Principal Laws No high frequencies Do not transport them Use adequate boundaries Software Modules Hardware Components 27 Product Development/Program Support systems EMC requirements are set by the environment it is intended for Industry Ground Based Airborne At Sea Domestic [Tests to cover] Small Medium Large 28 14

15 EMC is achieved during the design process when problems appear during testing, we are too late! many M$$ Available Mitigation Options Requirements Bankruptcy Measures Repair/redesign Check bonding Cost of Modification 0 Concept Design Manufacture Test Operational phase in the lifecycle 29 0 Example of a Large Organization: Thales aerospace, defense, information technologies In terms of EMC: How to keep the same quality standards all over the world? 30 15

16 Four Key Elements of EMC implementation in large organizations 1. Awareness 2. Network 3. Rules & Guidelines 4. Program support 31 Product Development/Program Support perform engineering & qualification tests

17 EMC approach through the Knowledge Cycle insert electro magnetic behavior up front Problem definition: desired behavior Test Validation/Verification Validated models Research/Analyses Development Support Behavioral Model Knowledge Transfer & Education 33 EMC Rules and Guidelines a lot of information on EMC engineering can be found on the internet 34 17

18 EMC Rules and Guidelines or: buy a book! ISBN End of Part II 36 18

19 Relation of MIL-STD-461E tests to Phenomena survey of test identifiers CE102 RE101 RE102 RE103 CS101 CS114 CS116 RS101 RS103 RS105 Conducted Emissions, Power Leads, 10 khz to 10 MHz Radiated Emissions, Magnetic Field, 30 Hz to 100 khz Radiated Emissions, Electric Field, 10 khz to 18 GHz Radiated Emissions, Antenna Spurious and Harmonic Outputs, 10 khz 40 GHz Conducted Susceptibility, Power Leads, 30 Hz to 150 khz Conducted Susceptibility, Bulk Cable Injection, 10 khz to 200 MHz Conducted Susceptibility, Damped Sinusoidal Transients, 10 khz to 100 MHz Radiated Susceptibility, Magnetic Field 30 Hz to 100 khz Radiated Susceptibility, Electric Field, 2 MHz to 40 GHz Radiated Susceptibility, Transient Electromagnetic Field (NEMP) 37 19