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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Diethard E. C. Moehr, I&S CTF EMC
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07.2003 Folie 2
Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Aims of EMC - EMC Marketing
The aim of EMC is to ensure that equipment and systems do not affect their surroundings to more than an acceptable extent and that they themselves can not be affected by interference from their surroundings.
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Areas-1
ImmunityImmunityEmissionEmission
EMCEMCEMCEMC
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
in complete devices
EMC requirements fordevices
in complete devices
EMC requirements fordevices
on PCB Level
PCB EMC requirement _
on PCB Level
PCB EMC requirement _
EMCEMCEMCEMC
EMC Areas-2
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EmissionEmission ImmunityImmunity
EMCEMCEMCEMC
conducted radiated
power mains
interconnectcabledata, signal
H-field E-field ESD RFI BURST SURGE
others
IEC 61000 - 4parts 2-6
Various 77A and CISPR standards
EMC Areas-3
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC / EMI always requires an emitter (source), a coupling medium and a receptor (receiver)
EMI sourcesEMI sourcesEMI sourcesEMI sources
• TV & radio transmitters
• Radar, Navigation• ITE & telecom equipment• local oscillators of receivers• power lines• switches• motors, engine ignition• computers and peripherals• fluorescent lights• electric heaters• arc welders• diathermy devices• natural sources: ESD noise,
lightning, galactic noise
• TV & radio transmitters
• Radar, Navigation• ITE & telecom equipment• local oscillators of receivers• power lines• switches• motors, engine ignition• computers and peripherals• fluorescent lights• electric heaters• arc welders• diathermy devices• natural sources: ESD noise,
lightning, galactic noise
Coupling mechanismCoupling mechanismCoupling mechanismCoupling mechanism
• Conductive
• inductive / capacitive
• radiation
• Conductive
• inductive / capacitive
• radiation
EMI receptorsEMI receptorsEMI receptorsEMI receptors
• computers & peripherals
• analog sensors and amplifiers
• industrial public controlsystems
• radio & TV receivers
• safety equipment
• military equipment
• humans (biological risks and hazards caused by
electromagnetic fields)
• computers & peripherals
• analog sensors and amplifiers
• industrial public controlsystems
• radio & TV receivers
• safety equipment
• military equipment
• humans (biological risks and hazards caused by
electromagnetic fields)
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Two pulses in time and frequency domain
-20dB/Decade
-40dB/Decade
t1 > t2 and tr1 > tr2
A B
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Shielded rooms; e. g. computer centreProblem: Emission Immunity
Emission of thecomputer system
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Shield Rooms
Transmitter;e. g. radio,television,intercom
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMI in a usual small computer system
INTRASystem EMC
CRTSJ
PRINTER
Mainframe Workstation
CC
RE RS
RE RS
RE RS
CE CSCS
CE
CSCS
CE
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB - EMI Emitters & Receptors
EmittersEmittersEmittersEmitters
• clock oscillators and clock signal lines
• data signal lines
• relays
• switched mode power supplies
• line drivers
• high voltage parts
(supplies)
• video and deflection amplifiers
• all fast data signal lines
• clock oscillators and clock signal lines
• data signal lines
• relays
• switched mode power supplies
• line drivers
• high voltage parts
(supplies)
• video and deflection amplifiers
• all fast data signal lines
ReceptorsReceptorsReceptorsReceptors
• analog amplifiers
• disc read heads
• write / read amplifiers
• logic circuits
(microprocessor, buffers, drivers)
• analog amplifiers
• disc read heads
• write / read amplifiers
• logic circuits
(microprocessor, buffers, drivers)
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC shielding
F1 - F4 Filters shielded cables non shielded cables
metal ormetalized box
complete integral shielding of every boxand all cables(compartment shielding)
plastic box
F1 F1
F2
F2
F3
F4F3
PCB2
PCB3PCB1
PS
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Integral shielding - Compartment shielding
disadvantagesdisadvantagesdisadvantagesdisadvantages
• not always possible
• design problems
• does not help against self-jamming
• not always possible
• design problems
• does not help against self-jamming
disadvantagesdisadvantagesdisadvantagesdisadvantages
• each sub-assembly (PCB, cables,
connectors) has to be shielded
• quite expensive
• each sub-assembly (PCB, cables,
connectors) has to be shielded
• quite expensive
advantagesadvantagesadvantagesadvantages
• internal shielding is not necessary
• cheap solution in the shielded box
• internal shielding is not necessary
• cheap solution in the shielded box
advantagesadvantagesadvantagesadvantages
• design of the complete device (housing cheaper)
• no self-jamming problems between
the sub-assemblies
• design of the complete device (housing cheaper)
• no self-jamming problems between
the sub-assemblies
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB with one connector - CASE 1
low frequency logic
medium frequency logic
high frequency logic
connector
Note: Use separate supplies for the logic families
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB with one connector - CASE 2
digital logic
interfaces lines drivers
analog logic
analog signal driver / receivers
connector
Note: Prevent supply layer overlaps (VCC / GND) between the analog and digital area.
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Principle of a star supply system for PCBs
fast digital circuits
slow digital circuits
analogcircuits
interfaces and line driver circuits
+5V
OV
connector
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB with one connector - CASE 3
high
frequency
logic
low
frequency
logic
medium
frequency
logic
connector
Note:
• Use a “star” supply system for VCC / GND.
• Prevent loops in VCC / GND.
• Prevent loops in clock signal and data lines.
• Keep supply voltage paths for drivers short.
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB with several connectors
Note:
• Assign logic (interface logic)to the connectors.
• Sort logic according to its purpose.
• Separate logic families.
• Use separate supply systems.low freq. logic
high freq.logic
low freq. logic
mediumfreq.logic
mediumfreq.logic
high freq.logic
connector M1
connector E1
connector M2
connector E2
I / O circuits for interface 1
Interface 1 Interface 2
mother board
edge connectors
I / O circuits for interface 1
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
b
ld
d = thickness of the lineb = width of the linel = length of the linef = frequency
b = 1mm d = 0,03mm b = 3mm d = 0,03mm b = 10mm d = 0,03mm
f 10 30 100 300 l/mm 30 100 300 l/mm 100 300
10Hz 6m 17m 57m 172m 6m 19m 57m 6m 17m
100Hz 6m 17m 57m 172m 6m 19m 57m 6m 17m
1kHz 6m 17m 57m 172m 6m 19m 57m 6m 17m
10kHz 6m 17m 58m 174m 6m 20m 61m 7m 24m
100kHz 7m 24m 92m 311m 14m 62m 225m 44m 174m
1MHz 44m 173m 727m 2,6 131m 590m 2,18 440m 1,73
10MHz 437m 1,72 7,25 25,8 1,31 5,89 21,8 4,4 17,3
100MHz 4,37 17,2 72,5 258 13,1 58,9 218 44 173
1GHz 43,7 172 725 2,58k 131 589 2,18k 440 1,73k
Dependence of line impedance on length, widthand thickness of the line considering the pulse frequency
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
SummarySummarySummarySummary
• Use different areas for high, medium and low frequency logic.
• Use a “star” supply voltage system for VCC and GND.
• Use different areas for digital and analog logic.
• Assign interface logic to the connectors and keep connection as short as possible.
• Avoid parallel trace runs for interface signals and clock signals (cross talk problem).
• Consider cross talk between high, medium and low frequency signal lines.
• Use different areas for high, medium and low frequency logic.
• Use a “star” supply voltage system for VCC and GND.
• Use different areas for digital and analog logic.
• Assign interface logic to the connectors and keep connection as short as possible.
• Avoid parallel trace runs for interface signals and clock signals (cross talk problem).
• Consider cross talk between high, medium and low frequency signal lines.
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB Multilayer Guidelines - CASE 1
IL - Interconnect Layer
Advantage
• easy to repair
Disadvantage
• radiated emission from IL located outside of the PCB
IL 1
IL 2
VCC
GND
1
4
3
2
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Industrial Solutions and ServicesYour Success is Our Goal
EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB Multilayer Guidelines - CASE 2
Note:
Direction priority in IL 1 and IL 2 to avoid cross talk.
Advantage
• no radiated emission from signal and data lines
Disadvantages
• not easy to repair
• problems with very fast signals in the inner layers
VCC
GND
IL 1
IL 2
1
4
3
2
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
PCB Multilayer Guidelines - CASE 3
SH - Shield Layer
IL - Interconnect Layer
GND - Ground
VCC - Supply LayerSH
IL
VCC
GND
IL
IL
IL
IL
IL
SH
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
PCB Layout Guidelines
Location of decoupling capacitances
decoupling capacitance DC useless due to R and L in the current path
possible solution withlow R and L
optimal position of DC
Attn.: multi layer
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
Decoupling capacitances -the wrong and the right way
IC
+
-
+5V
OV
IC
IC
OV +5V
Decoupling capacitances
wrong long paths connecting the pins
introduce L and C
rightshort paths connecting the pins
minimize L and C
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
• EMC on PCB’s Part 1
•Generally you should take note of the following:Generally you should take note of the following:•Generally you should take note of the following:Generally you should take note of the following:
• avoid ground loops on the PCB
• avoid VCC loops on the PCB
• use a filter to avoid noise from the PCB being reradiated from supply data cables
• use completely shielded oscillators only
• connect the housing of used oscillators to the 0 volts of the PCB, locate a 0 volt area under oscillators to avoid other wires passing this area
• keep all clock traces as short as possible, the faster the signal is the shorter the trace has to be
• use decoupling caps for any chip (value 100 nF)
• traces from the decoupling capacitance's to the supply pins of the chips have to be as short as possible
• avoid ground loops on the PCB
• avoid VCC loops on the PCB
• use a filter to avoid noise from the PCB being reradiated from supply data cables
• use completely shielded oscillators only
• connect the housing of used oscillators to the 0 volts of the PCB, locate a 0 volt area under oscillators to avoid other wires passing this area
• keep all clock traces as short as possible, the faster the signal is the shorter the trace has to be
• use decoupling caps for any chip (value 100 nF)
• traces from the decoupling capacitance's to the supply pins of the chips have to be as short as possible
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
• EMC on PCB’s Part 2
• the faster the logic is the shorter the distance between the supply plug and the fast logic has to be
• use a “star” power (VCC / ground) supply, for instance, to separate analog and digital devices
• use a separate VCC / ground path for chips known to produce most of the noise
• don’t connect 0 volt and the shield
• ensure the possibility of placing a capacitor between 0 volts and the shield in case of ESD or radiation problems
• if using multi layer PCB’s take care to have shielding layers on the top and on the bottom
• put interconnecting layers inside
• ensure that the VCC / ground traces are as wide as possible in order to create low HF resistance and inductance
• terminate all inputs of gates to ensure better immunity of the device
• the faster the logic is the shorter the distance between the supply plug and the fast logic has to be
• use a “star” power (VCC / ground) supply, for instance, to separate analog and digital devices
• use a separate VCC / ground path for chips known to produce most of the noise
• don’t connect 0 volt and the shield
• ensure the possibility of placing a capacitor between 0 volts and the shield in case of ESD or radiation problems
• if using multi layer PCB’s take care to have shielding layers on the top and on the bottom
• put interconnecting layers inside
• ensure that the VCC / ground traces are as wide as possible in order to create low HF resistance and inductance
• terminate all inputs of gates to ensure better immunity of the device
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC on PCB’s Part 3
• avoid overshoots on any signal because they produce a broad frequency spectrum
• ensure that rising and falling slopes of used clocks are as slow as possible
• terminate all metal parts of the housing to the shield potential (not to 0 volts)
• don’t forget spark over problems caused by ESD discharges from persons and devices touching the surface (pay special attention to LED’s)
• use an electrolyte cap. (at least 10 µF) at the point where the supply voltage reaches every PCB (no tantalum cap)
• use the slowest system frequency possible
• especially for keyboards (and similar units): use the slowest scanning frequency possible
• use level dependent interrupters instead of slope dependent interrupts
• avoid overshoots on any signal because they produce a broad frequency spectrum
• ensure that rising and falling slopes of used clocks are as slow as possible
• terminate all metal parts of the housing to the shield potential (not to 0 volts)
• don’t forget spark over problems caused by ESD discharges from persons and devices touching the surface (pay special attention to LED’s)
• use an electrolyte cap. (at least 10 µF) at the point where the supply voltage reaches every PCB (no tantalum cap)
• use the slowest system frequency possible
• especially for keyboards (and similar units): use the slowest scanning frequency possible
• use level dependent interrupters instead of slope dependent interrupts
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC on PCB’s Part 4
• use a watchdog timer for monitoring the system
• fill unused ROM space with a restart command
• be careful with spike dependent units (flip flops and latches), level triggering, if possible
• use a watchdog timer for monitoring the system
• fill unused ROM space with a restart command
• be careful with spike dependent units (flip flops and latches), level triggering, if possible
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
Complete electronic system, e.g. example computer system:Complete electronic system, e.g. example computer system:Complete electronic system, e.g. example computer system:Complete electronic system, e.g. example computer system:
Question: What has to be done to meet the EMC requirements in order to get FCC / CE approval?
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
Main questions to be solved:Main questions to be solved:Main questions to be solved:Main questions to be solved:
• Which shielding system is necessary
(complete or compartment shielding)?
• Which filtering is necessary for the mains?
• Which cable shielding is necessary for internal system cables?
• Which connectors have to be used for internal system cables?
• What EMI hardening is necessary for other I/O ports
(telephone lines, etc.) ?
• How to keep EMI hardening cheap?
• Which shielding system is necessary
(complete or compartment shielding)?
• Which filtering is necessary for the mains?
• Which cable shielding is necessary for internal system cables?
• Which connectors have to be used for internal system cables?
• What EMI hardening is necessary for other I/O ports
(telephone lines, etc.) ?
• How to keep EMI hardening cheap?
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
Situation:Situation:Situation:Situation:
Reason:Reason:Reason:Reason:
Solution:Solution:Solution:Solution:
Choosing a filter by the manufacturer’s data sheet.
• filter performance from a manufacturer’s data sheet
• attenuation in the required frequency band (10 kHz - 30 MHz) looks high enough
• purchasing dept. orders 1000 filters
• filter is installed in the device and the system is taken to the EMI test site for compliance testing and
• the system fails the test because the filter does not work as promised
• filters are measured by the manufacturers acc. MIL STD 220 in a 50 / 50 Ohm system (50 Ohm source impedance / 50 Ohm load)
• real installation conditions vary widely (for instance for mains filters 1 Ohm / 103 Ohm not unusual)
• check any filter in the real installation condition before ordering
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
What to do and what not to do in filter mounting: What to do and what not to do in filter mounting: What to do and what not to do in filter mounting: What to do and what not to do in filter mounting:
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
What to do and what not to at cable entries: What to do and what not to at cable entries: What to do and what not to at cable entries: What to do and what not to at cable entries:
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
The performance of pigtail connections 1: The performance of pigtail connections 1: The performance of pigtail connections 1: The performance of pigtail connections 1:
Example: coaxial cable (braided shield) with two pigtails to connect the shield via a connector pin to GND
2 x 10 cm wire (~4 inches) with 1 µH /mZT = 10 mohm at 1 MHz 1 m longZTP = jL = 0,6 ohm at 1 MHz
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
The performance of pigtail connections 2:The performance of pigtail connections 2:The performance of pigtail connections 2:The performance of pigtail connections 2:
Voltage drop along the shield for:
I = 1 A (Ohm’s law)
U = I x (ZT + ZTP )
U = 1 A x (10-2 + 1,2 ) = 1,21 V
120 times the voltage drop as without pigtails.
Voltage drop along the shield for:
I = 1 A (Ohm’s law)
U = I x (ZT + ZTP )
U = 1 A x (10-2 + 1,2 ) = 1,21 V
120 times the voltage drop as without pigtails.
Conclusion:Conclusion:Conclusion:Conclusion:
• This shield is not an effective shield.
• Transfer impedance of the shield ZT can
be as low as possible, according to the
pigtails the whole impedance is too
high.
• Emission and susceptibility problems
can be expected.
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
Shielded cables and the performance of pigtails: Shielded cables and the performance of pigtails: Shielded cables and the performance of pigtails: Shielded cables and the performance of pigtails:
Transfer impedance ZT and shielding effectiveness as of the cable:
in db
for our example ZT = 1,21
as = 32 dB
Good coaxial cables have as 70 dB ( ZT ≤ 15 m )
Cable manufacturers are able to measure the as and ZT of a cable according to MIL STD 220.
Transfer impedance ZT and shielding effectiveness as of the cable:
in db
for our example ZT = 1,21
as = 32 dB
Good coaxial cables have as 70 dB ( ZT ≤ 15 m )
Cable manufacturers are able to measure the as and ZT of a cable according to MIL STD 220.
as = 20 lg as = 20 lg 50
ZT
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EMC Hardening for apparatus and special product EMC problems
Common Technical Functions
EMC Guidelines for complete systems
Summary 1Summary 1::Summary 1Summary 1::
• All metal surfaces which are expected to have a good metal conducting contact to each other have to be protected against corrosion (for instance Sn coating on steel or aluminium surfaces).
• Metal or metalized surfaces where contact may arise during operation or normal service of a device should never be floated but connected to GND or safety potential where available.
• Connections between metal surfaces have to be solid; no accidental connections allowed; enforced contacts recommended.
• Shields of cables have to be connected 360° with metal or metalized connectors.
• All metal surfaces which are expected to have a good metal conducting contact to each other have to be protected against corrosion (for instance Sn coating on steel or aluminium surfaces).
• Metal or metalized surfaces where contact may arise during operation or normal service of a device should never be floated but connected to GND or safety potential where available.
• Connections between metal surfaces have to be solid; no accidental connections allowed; enforced contacts recommended.
• Shields of cables have to be connected 360° with metal or metalized connectors.
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Common Technical Functions
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• Bodies of connectors have to be connected with metal or metalized PCB frame if available; with connections between logic GND and the shield potential take special care.
• Main filters have to be connected with the metal or metalized housing of the device at the place of cable entry in a solid way.
• Anti-corrosive coatings, paint, Al2O3 and chromate coatings are not conductive even if they sometimes look like metal (remember to be aware of ESD problems).
• Moving parts such as doors have to be contacted by finger stock systems every 10 - 20 cm depending on the highest frequency.
• Sometimes additional shielding is required for special functional assemblies in the devices (turners, video amplifiers).
• Bodies of connectors have to be connected with metal or metalized PCB frame if available; with connections between logic GND and the shield potential take special care.
• Main filters have to be connected with the metal or metalized housing of the device at the place of cable entry in a solid way.
• Anti-corrosive coatings, paint, Al2O3 and chromate coatings are not conductive even if they sometimes look like metal (remember to be aware of ESD problems).
• Moving parts such as doors have to be contacted by finger stock systems every 10 - 20 cm depending on the highest frequency.
• Sometimes additional shielding is required for special functional assemblies in the devices (turners, video amplifiers).
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Common Technical Functions
EMC Guidelines for complete systems
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• Radiation sources cannot be placed behind slots for ventilation; also pay attention to signal lines behind slots.
• Prevent ESD from sparking directly into PCBs.
• In case of a plastic housing connect the shielding of cables also via metal or metalized connectors to metal or metalized PCB frames where available and via these frames to logic ground or better safety ground.
• If possible always ensure the separation of logic ground (GND) and safety ground (G/Y wire), only one conductive connection in a complete system is allowed.
• Always remember: HF current always takes the path of lowest impedance; this path can often be unusual; in case of different path in parallel the HF current uses only the path with the lowest impedance.
• Radiation sources cannot be placed behind slots for ventilation; also pay attention to signal lines behind slots.
• Prevent ESD from sparking directly into PCBs.
• In case of a plastic housing connect the shielding of cables also via metal or metalized connectors to metal or metalized PCB frames where available and via these frames to logic ground or better safety ground.
• If possible always ensure the separation of logic ground (GND) and safety ground (G/Y wire), only one conductive connection in a complete system is allowed.
• Always remember: HF current always takes the path of lowest impedance; this path can often be unusual; in case of different path in parallel the HF current uses only the path with the lowest impedance.
Industrial Solutions and ServicesYour Success is Our Goal
Thank you very much for your attention.
Contact:
Diethard MoehrI&S CTF EMCSchuhstraße 60D-91052 ErlangenPhone: +49 (9131) 7-27210
Mail: [email protected]