Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Diethard E. C. Moehr, I&S CTF EMC

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 2 Industrial Solutions and Services Your 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.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 3 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Areas-1 Immunity Emission EMCEMC

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 4 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions in complete devices EMC requirements for devices in complete devices EMC requirements for devices on PCB Level PCB EMC requirement _ on PCB Level PCB EMC requirement _ EMCEMC EMC Areas-2

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 5 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions Emission Immunity EMCEMC conductedradiated power mains interconnect cable data, signal H-fieldE-fieldESDRFI BURST SURGE others IEC parts 2-6 Various 77A and CISPR standards EMC Areas-3

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 6 Industrial Solutions and Services Your 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 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 mechanism Conductive inductive / capacitive radiation Conductive inductive / capacitive radiation EMI receptors computers & peripherals analog sensors and amplifiers industrial public control systems radio & TV receivers safety equipment military equipment humans (biological risks and hazards caused by electromagnetic fields) computers & peripherals analog sensors and amplifiers industrial public control systems radio & TV receivers safety equipment military equipment humans (biological risks and hazards caused by electromagnetic fields)

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 7 Industrial Solutions and Services Your 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 t 1 > t 2 and t r 1 > t r 2 A B

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 8 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions Shielded rooms; e. g. computer centre Problem: Emission Immunity Emission of the computer system

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 9 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions Shield Rooms Transmitter; e. g. radio, television, intercom

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 10 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMI in a usual small computer system INTRA System EMC CRT SJ PRINTER MainframeWorkstation C C RE RS RE RS RERS CECS CE CS CE

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 11 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions PCB - EMI Emitters & Receptors EmittersEmitters 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 ReceptorsReceptors 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)

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 12 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC shielding F 1 - F 4 Filtersshielded cablesnon shielded cables metal or metalized box complete integral shielding of every box and all cables (compartment shielding) plastic box F1F1 F1F1 F2F2 F2F2 F3F3 F4F4 F3F3 PCB2 PCB3 PCB1 PS

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 13 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions Integral shielding - Compartment shielding disadvantagesdisadvantages not always possible design problems does not help against self-jamming not always possible design problems does not help against self-jamming disadvantagesdisadvantages each sub-assembly (PCB, cables, connectors) has to be shielded quite expensive each sub-assembly (PCB, cables, connectors) has to be shielded quite expensive advantagesadvantages internal shielding is not necessary cheap solution in the shielded box internal shielding is not necessary cheap solution in the shielded box advantagesadvantages 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 14 Industrial Solutions and Services Your 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 15 Industrial Solutions and Services Your 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 (V CC / GND) between the analog and digital area.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 16 Industrial Solutions and Services Your 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 analog circuits interfaces and line driver circuits +5V OV connector

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 17 Industrial Solutions and Services Your 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 V CC / GND. Prevent loops in V CC / GND. Prevent loops in clock signal and data lines. Keep supply voltage paths for drivers short.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 18 Industrial Solutions and Services Your 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 medium freq. logic medium freq. logic high freq. logic connector M1 connector E1 connector M2 connector E2 I / O circuits for interface 1 Interface 1Interface 2 mother board edge connectors I / O circuits for interface 1

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 19 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions b l d d = thickness of the line b = width of the line l = length of the line f = frequency Dependence of line impedance on length, width and thickness of the line considering the pulse frequency

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 20 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions PCB Layout Guidelines SummarySummary Use different areas for high, medium and low frequency logic. Use a “star” supply voltage system for V CC 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 V CC 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.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 21 Industrial Solutions and Services Your Success is Our Goal 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 V CC GND

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 22 Industrial Solutions and Services Your 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 V CC GND IL 1 IL

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 23 Industrial Solutions and Services Your Success is Our Goal 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 V CC - Supply Layer SH IL V CC GND IL SH

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 24 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions PCB Layout Guidelines Location of decoupling capacitances decoupling capacitance D C useless due to R and L in the current path possible solution with low R and L optimal position of D C Attn.: multi layer

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 25 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions Decoupling capacitances - the wrong and the right way

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 26 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC on PCB’sPart 1 Generally you should take note of the following: Generally you should take note of the following: avoid ground loops on the PCB avoid V CC 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 V CC 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 27 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC on PCB’sPart 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 (V CC / ground) supply, for instance, to separate analog and digital devices use a separate V CC / 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 V CC / 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 (V CC / ground) supply, for instance, to separate analog and digital devices use a separate V CC / 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 V CC / 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 28 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC on PCB’sPart 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 29 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC on PCB’sPart 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

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 30 Industrial Solutions and Services Your Success is Our Goal 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: Question:What has to be done to meet the EMC requirements in order to get FCC / CE approval?

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 31 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems 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?

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 32 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems Situation:Situation: Reason:Reason: 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 / 10 3 Ohm not unusual) check any filter in the real installation condition before ordering

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 33 Industrial Solutions and Services Your Success is Our Goal 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:

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 34 Industrial Solutions and Services Your Success is Our Goal 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:

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 35 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems 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 /m Z T = 10 mohm at 1 MHz 1 m long Z TP = j  L = 0,6 ohm at 1 MHz

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 36 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems The performance of pigtail connections 2: Voltage drop along the shield for: I=1 A(Ohm’s law) U= I x (Z T + Z TP ) 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 (Z T + Z TP ) U=1 A x (10 -2  + 1,2  ) = 1,21 V 120 times the voltage drop as without pigtails.Conclusion:Conclusion: This shield is not an effective shield. Transfer impedance of the shield Z T can be as low as possible, according to the pigtails the whole impedance is too high. Emission and susceptibility problems can be expected.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 37 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems Shielded cables and the performance of pigtails: Transfer impedance Z T and shielding effectiveness a s of the cable: in db for our exampleZ T = 1,21  a s = 32 dB Good coaxial cables have a s  70 dB ( Z T ≤ 15 m  ) Cable manufacturers are able to measure the a s and Z T of a cable according to MIL STD 220. Transfer impedance Z T and shielding effectiveness a s of the cable: in db for our exampleZ T = 1,21  a s = 32 dB Good coaxial cables have a s  70 dB ( Z T ≤ 15 m  ) Cable manufacturers are able to measure the a s and Z T of a cable according to MIL STD 220. a s = 20 lg 50  Z T

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 38 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems Summary 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.

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 39 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems Summary 2: 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, Al 2 O 3 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 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, Al 2 O 3 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 cm depending on the highest frequency. Sometimes additional shielding is required for special functional assemblies in the devices (turners, video amplifiers).

I:Moehr\Folien\B15-15_Des_Argentina_03_Logo_03-07.PPT Folie 40 Industrial Solutions and Services Your Success is Our Goal EMC Hardening for apparatus and special product EMC problems Common Technical Functions EMC Guidelines for complete systems Summary 3: 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 Services Your Success is Our Goal Thank you very much for your attention. Contact: Diethard Moehr I&S CTF EMC Schuhstraße 60 D Erlangen Phone: +49 (9131) Mail: