Emi notes

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EMI / EMC EMI is defined as the undesirable signal which causes unsatisfactory operation of a circuit or device.

EMC is defined as the ability of electronic and communication equipment to be able to operate satisfactorily in the presence of interference and not be a source of interference to nearby equipment.

EMS Electromagnetic susceptibility (EMS) is the capability of a device to respond to EMI.B.T.P.MADHAV

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B.T.P.MADHAVBasic Types of EMI:

These are of two types. They are

Intra-EMI:

EMI is said to be intra-EMI if the functional characteristics of one module within an electronic equipment or system is disturbed due to EMI from another module.

b) Inter-EMI:

EMI is said to be inter-EMI if the functional characteristics of one equipment is disturbed due to EMI generated by another equipment.

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B.T.P.MADHAVEMI SOURCESThese are divided mainly into two types.I. Natural andII. Man-madeI. Natural EMI sources are again of the followingtypes:Terrestrial and Extra-Terrestrial.Terrestrial SourcesThese are atmospheric thunderstorms, lightningdischarges and precipitation static.

Extra-Terrestrial SourcesThese are sun-disturbed & quiet, cosmic noise and radiostars.

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B.T.P.MADHAVThe common effects of EMI

(i) Annoying EffectsVery often, momentary and random disturbances inradio and television reception occur.

(ii) Disturbing EffectsUnwanted reset and change of status in settings incomputers and digital equipment is noticed due to EMI.The malfunctioning of computer key boards are noticed.

(iii) Catastrophic SituationsThe burning of electronic components, loss of data,change of threshold settings, improper or unwantedoperations and sometimes biological hazards occur veryoften.

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B.T.P.MADHAVBIOLOGICAL EFFECTS OF EMI / EMR

EM waves, light, heat, x-ray and gamma rays are all different forms of electromagnetic radiation. However, they differ in their wavelength. These radiations have hazardous effects on men and material. The effects can be divided into two categories.

Thermal Effects

2. Non-thermal Effects.

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B.T.P.MADHAVEMC STANDARDS

These are of two types

a) Military StandardsThese include emission and susceptibility standards. Emission standards specify emission limits in voltage or current, power or field strengths in specified frequency ranges. Susceptibility standards specify conducted spike or radiated field parameters.

b) Civilian Standards

The civilian EMC standards are applicable for equipments used for commercial, industrial and domestic applications. The emission standards are specified to protect the broadcast services from interference. These also take into account the physiological interference effects experienced by human beings.

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B.T.P.MADHAVMILITARY STANDARDS

MIL - STD - 461ATESTDESCRIPTIONFREQCE01Power Leads30 Hz-20 kHzCE02Control / Signal Leads30 Hz-20 kHzCE03Power Leads20 kHz-50 MHzCE04Control / Signal Leads20 kHz-50 MHzCE05Inverse Filter Method30 Hz-50 MHzCE06Antenna Terminal10 kHz-10 GHzCE07N/A

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MIL - STD - 461B/CTESTDESCRIPTIONFREQCE01Power / Signal Leads30 Hz-15 kHzCE02N/ACE03Power/Signal Leads15 kHz-50MHzCE04N/ACE05N/ACE06Antenna Terminal10 kHz-26 GHzCE07Power LeadsSpikes / Time Domain

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MIL - STD - 461DTESTDESCRIPTIONFREQCE101Power Leads30 Hz-10 kHzCE102Power Leads10 kHz-10 MHzCE106Antenna Terminal10 kHz-40GHz

MIL - STD - 461ETESTDESCRIPTIONFREQCE101Power Leads30 Hz-10 kHzCE102Power Leads10 kHz-10 MHzCE106Antenna Terminal10 kHz-40GHz

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CS01Power Leads20 Hz-50 kHzCS02Power Leads50 kHz-400MHzCS03Intermodulation15 kHz-10 GHzCS04Undesired Sig. Rejection15 kHz-10 GHzCS05Cross Modulation15 kHz - 10 GHzCS06Spikes, Power LeadsCS07Squelch CktsCS08Undesired Sig. Rejection30 Hz-10 GHzCS09N/ACS10N/A

MIL - STD - 461ATESTDESCRIPTIONFREQ

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CS01Power Leads30 Hz-50 kHzCS02Power Leads50 kHz-400 MHzCS03Intermodulation15 kHz-10 GHzCS04Undesired Sig. Rejection30 kHz-20 GHzCS05Cross Modulation30 kHz - 20 GHzCS06Spikes, Power LeadsCS07Squelch CktsCS08N/ACS09Structure Common Mode Current60 Hz-100 kHzCS10Damped Sinusoidal Transients (terminals)10 kHz-100 MHz

MIL - STD - 461B/CTESTDESCRIPTIONFREQ

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CS101Power Leads30 Hz-50 kHzCS103Antenna Port-Intermod15 kHz-10 GHzCS104Antenna Port-Rej. of Undesired Sig.30 Hz -20 GHzCS105Antenna Port-Cross Mod.30 Hz-20 GHz

CS101Power Leads30 Hz-150 kHzCS103Antenna Port-Intermod15 kHz-10 GHzCS104Antenna Port-Rej. of Undesired Sig.30 Hz -20 GHzCS105Antenna Port-Cross Mod.30 Hz-20 GHz

MIL - STD - 461DTESTDESCRIPTIONFREQ

MIL - STD - 461ETESTDESCRIPTIONFREQ

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RE01Magnetic Field30 Hz-50 kHzRE02Electric Field14 kHz-10 GHzRE03Spurious & Harmonic10 kHz-40 GHzRE04Magnetic Field20 Hz-15 kHzRE05Vehicle & Eng. Equipment150 kHz-1 GHzRE06Overhead Powerlines14 kHz-1 GHzRS01Magnetic Field30 Hz-30 kHzRS02Magnetic InductionPowerline & SpikeRS03Electric Field14 kHz-10 GHzRS04Parallel Line Fields14 kHz-30 MHzRS05N/A

MIL - STD - 461ATESTDESCRIPTIONFREQ

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RE01Magnetic Field30 Hz-50 kHzRE02Electric Field14 kHz-10 GHzRE03Spurious & Harmonic10 kHz-40 GHzRE04N/ARE05N/ARE06N/ARS01Magnetic Field, Equipment and Cables30 Hz-50 kHzRS02Magnetic Induction, Equipment and CablesPowerline & SpikeRS03Electric Field, Equipment and Cables14 kHz-40 GHzRS04N/ARS05Electromag Pulse FieldTransients

MIL - STD - 461B/CTESTDESCRIPTIONFREQ

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RE101Magnetic Field30 Hz-100 kHzRE102Electric Field10 kHz-18 GHzRE103Antenna Spurious & Harmonics10 kHz-40 GHzRS101Magnetic Field, Equipment and Cables30 Hz-100 kHzRS103Electric Field, Equipment and Cables10 kHz-40 GHzRS105Transient Electromag FieldTransientsCS109Structure Current60 Hz-100 kHzCS114Bulk Cable Injection10 kHz-400 MHzCS115Bulk Cable InjectionImpulseCS116Sine Transients - Cables, and Power Leads10 kHz-100 MHz

MIL - STD - 461DTESTDESCRIPTIONFREQ

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RE101Magnetic Field30 Hz-100 kHzRE102Electric Field10 kHz-18 GHzRE103Antenna Spurious & Harmonics10 kHz-40 GHzRS101Magnetic Field, Equipment and Cables30 Hz-100 kHzRS103Electric Field, Equipment and Cables2 MHz-40 GHzRS105Transient Electromag FieldTransientsCS109Structure Current60 Hz-100 kHzCS114Bulk Cable Injection10 kHz-200 MHzCS115Bulk Cable InjectionImpulseCS116Sine Transients - Cables, and Power Leads10 kHz-100 MHz

MIL - STD - 461ETESTDESCRIPTIONFREQ

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B.T.P.MADHAVMETHODS TO ELIMINATE EMI OR DESIGNMETHODS FOR EMCThe effective methods to eliminate EMI are1. Shielding2. Grounding3. Bonding4. Filtering5. Isolation6. Separation and orientation7. Circuit impedance level control8. Cable design9. Cancellation techniques in frequency or timedomain10. Proper selection of cables, passive components11. Antenna polarization control12. Balancing

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B.T.P.MADHAVFiltering :

These are used to filter out conducted EMI. The filtering effectiveness is expressed by Insertion loss (IL). It is defined as

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B.T.P.MADHAVCLASSIFICATION OF EMI FILTERS

Low pass power line filters.Low pass telephone line filters.High pass data line filters.Band pass communication filters.Band reject filters.

lumped element low-pass filters(capacitive and inductive filters). L-section filters -section filters T-section filters High pass filters Band pass filters Band reject filters

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B.T.P.MADHAVShielding :

The main objective of shielding is to restrict radiations to a specified region to prevent it from entering into susceptible devices.

The quality of shielding is expressed in the form of shielding effectiveness of the material.

The shielding of materials can be solids, screens and braids. They can be in the form of boxes, partitions, cables and connector shields.

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B.T.P.MADHAVGrounding :

Grounding provides a conducting path between electronic devices and ground. The ground is nothing but some reference point. It is a circuit concept. The ideal ground is characterized by zero potential and impedance.GROUNDING is a technique that provides a low resistance path between electrical or electronic equipment and the earth or common reference low impedance plane to bypass fault current or EMI signal.

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B.T.P.MADHAVEFFECT OF IMPROPER GROUNDING

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B.T.P.MADHAVThe types of grounding techniques are

a) Floating Ground : It isolates circuits from a common ground plane. It may be hazardous some times.The ground plane is in the form of wire or a conductive rod.b) Single point Grounding : It reduces the effects of facility ground currents. This is used to control EMP energy.c) The multiple point grounding : It reduces ground lead lengths.

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B.T.P.MADHAVBonding :

It provides a low-impedance path between two conducting surfaces. It is a part of grounding and represents its physical implementation.It creates homogeneous structure for current flow and suppresses the creation of potentials between two metallic parts.Bonding is useful to protect against the effects of shocks, protect circuits from current return paths. They reduce potential difference between the devices and carry large faulty currents.The bonding is of two types.

Direct bonding is made by metal-to-metal between the connected elements. Indirect bonding is made by contact using conductive jumpers.

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B.T.P.MADHAVISOLATION TRANSFORMERSThe isolation transformers are used to suppress the common-mode and differential mode interferences.CM is the unwanted electrical p.d b/w any current carrying conductor and the reference ground.DM is the unwanted p.d b/w any two current carrying conductors.Transformers are used to isolate ground current loops.

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B.T.P.MADHAVThe shield facing the primary side is connected to the primary neutral to suppress DM interference. The shield facing the secondary side is connected to the reference ground to suppress CM interference.

Vc = ( Vpg + Vng )/2

Vd = (Vpg - Vng )/2

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B.T.P.MADHAVGround loopVG1VG2To obtain noise immunity, the ground loop must be broken. This can be done using transformers, optical couplers etc.Circuit-ICircuit-IIGround loopSignal wireGround wireFlux

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B.T.P.MADHAVGas Tube surge suppressorsThe gas discharge tube can handle very large transient currents ( >10KA), when the tube is connected between the line and the ground.

2. When the transient EMI voltage in line exceeds the striking voltage of the tube, an arc discharge occurs and the ionized gas produces a low impedance from line to ground to shunt surge current.

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B.T.P.MADHAVApplicationsBecause of high current handling capability gas tube surges suppressors are used in AC power distribution lines and in telecom lines as lightning and other high energy surge or transient arrestors.

Drawbacks Its response time is slow and it cant be used for fast rise time surges.The tube remains in the conducting state even after the surge is removed.Semiconductor Transient suppressorsSemiconductor transient suppression device maintain a constant voltage at a desired level across a device by offering variable resistance when transient voltages are present.

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METAL OXIDE VARISTORSMetal oxide varistors in which metal oxide semiconductors are used to exhibit voltage dependent resistance.supplyLoad Fuse LG When connected between line and common point , these devices present very high resistance at normal operating voltage levels. when high voltage spikes appear in the AC or DC line the terminal voltage exceeds the switch on voltage and the resistance decreases rapidly.

ADVANTAGES.Low costHigh transient energy absorption

DISADVANTAGESLow average power dissipation.Progressive degradation with repetitive surges

APPLICATIONS1) Due to high peak current, they used at equipment power input stage.

B.T.P.MADHAVComponent selection

The selection of components can be classified into three categories:

A) Components that affect the RELIABILITY and FUNCTIONALITY .TheseComponents are marked as RELIABILITY CRITICAL components or components that MODERATELY affect RELIABILITY.

B) Components that affect the EMI PERFORMANCE are marked as EMI CRITICAL and EMIMODERATE.

C) Components that affect the AUDIO PERFORMANCE, e.g. Signal to Noise Ratio are marked as AUDIO CRITICAL and AUDIO MODERATE.

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B.T.P.MADHAVSignal control

Shielding uses conductive material to wrap up the EMI completely to ground. In this way, electromagnetic energy is kept inside the system. It also gets harder for an external signal to cause EMI into the system. It is useful to both conducting EMI and radiated EMI.

Generally this is an expensive way to protect the sensitive part of the system, and it takes space. It works well for higher frequencies. For clock frequencies or edge rates lower than 100 MHz, EMI is coupled from the clock signal onto the shield and the shield itself does the radiating. In this case, shielding has very little effect.

Good decoupling and careful layout can reduce conducting EMI better than shielding, in most cases. Bypassing or "decoupling" capacitors on each active device (connected across the power supply or ground, as close to the device as possible) help to guide the clock or any other high-frequency signal component directly to ground instead of interfering other signals.

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B.T.P.MADHAVTransmitters.ReceiversAntennasPower suppliesMotorsControl devicesDigital circuitsComputersIntegrated circuits

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B.T.P.MADHAVTransmitters:-The physical design of the transmitter should be so as to achieve input-output isolation. Thus high power stages are physically removed from low level signal stages. Interstage shielding will help to achieve isolation where physical isolation is not feasible due to space constraint. Grounding measures should be applied considering multipoint grounding. Lumped or distributed constant filters should be used at required source of interference. The undesired RF paths should be decoupled by the use of bypass capacitors and series inductors.

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B.T.P.MADHAVReceivers : -

RF Must be low noise amplifier. Use AGC circuits to maintain Constant output By maintaining the perfect Isolation Between blocks. By maintaining the high of RF amplifier, sensitivity is also high. Selectivity is to be High. Fidelity ---- Ability of the receiver to reproduce all frequencies.

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B.T.P.MADHAVObjective :-

To study the behavior of passive components such as resistors, capacitors, inductors and transformers at various frequencies.

To know the factor affecting the choice of components for high frequency applications

Passive components, such as resistors, capacitors, and inductors, are powerful tools for reducing externally induced interference when used properly.

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B.T.P.MADHAVINDUCTORS

An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it.Guide lines for inductors :-Core losses ---- -----Causes Energy lossesEddy currents ------- Amount of energy loss increases with the area inside the loop of current. Hysteresis ---------- Materials with low coercivity have narrow hysteresis loops and so low hysteresis losses. Non-linearity -------- E.g.... Intermodulation.An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic material.

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B.T.P.MADHAVCapacitors are used for charge storage, timing, filtering, blocking, control of rise and fall times and to provide low impedance paths for high frequency signals.

Different Types of Capacitors are ------

Electrolytic CapacitorsPaper CapacitorsMica and Ceramic CapacitorsPolystyrene CapacitorsFeed through CapacitorsImpedance of the Capacitor is

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When a bypass capacitor is connected from the signal to ground, the capacitor impedance decreases as the frequency increases.Since noise is a high frequency phenomenon, and the impedance is minute at high frequencies, the capacitor will channel the noise directly to ground, eliminating it from the circuit.At lower desired frequencies the capacitor appears as an open circuit andthe desired frequencies are allowed to pass the filter.

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B.T.P.MADHAVIncoming noise is converted to heat and dissipated in the resistor. But note that a fixed resistor does produce thermal noise of its own. Resistors are grouped into 1) wire-wound 2) Film type 3) Composition-carbon & mixedWire-wound Low noise Composition Noise is more. Film type Noise is in Between wire-wound and composition.

Series Resistors Also among the most important and cheapest of protective elements. Properly selected according to resistance and power dissipation, they can replace more costly elements, with comparable results.

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TRANSFORMERSUsed for voltage and current transformation or level shifting, impedance matching, power transfer and Isolation processThis allows noise coupling through the transformer. This coupling can be eliminated by providing an electrostatic or Faraday shield

B.T.P.MADHAVConductors :-

conductors exhibits intrinsic or internal inductance due to thermal magnetic flux an ac resistance due to skin effect.

Conductors exhibit external inductance giving rise to external magnetic flux.

The external inductance of conductor with diameter d located at distance h above ground plane is L = 0.2 ln (4h/d) H/m

Wiring Guidelines :-

For the purpose of wiring & signal connection the signals can be divided into

Digital & Low current, filtered & regulated power signals.Analog and video signals.High current switching signalsAC and unfiltered dc main signals.

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B.T.P.MADHAVWires of different types are not be bundled together.Wire bundles of different types of signals should be physically separated from each other.Minimum separation is to be 6-8cm.The area of current loops on PCBs and board interconnections should be minimum.Maximum loop area should be 4cm2.Divide larger loops with smaller loops.Loops and wires should cross at right angles to each otherDistance between twisted pairs should be atleast 1.5 times the twist length.Multiple ckts with common return should be twisted as group.Wires between units should follow the most direct route.

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CHAPTER-4

OPEN AREA TEST SITES

The measurements of radiated emissions and radiated susceptibility of apparatus , equipment constitute two basic electromagnetic interference and electromagnetic compatibility measurements.

The purpose of radiation susceptibility testing is to determine the degradation in equipment performance caused by externally coupled electro magnetic energy.Open site measurement is most direct and universally accepted standard approach for measuring radiated emissions from an equipment or the radiation susceptibility of a component or equipment

EUT is switched onThe receiver is scanned over the specific frequency range It measures electromagnetic emissions from the EUT It determine the compliance of these data with the stipulated specifications. Power line filterEUTPower sourcePower source

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EUT is placed in an electromagnetic field created with the help of suitable radiating antenna.The intensity of the electromagnetic field is varied by varying the power delivered to the antenna by the transmitter amplifier performance of EUT are then observed under different levels of electromagnetic field intensity.Power line filterEUTPower sourceTransmitterPower line filterPower source

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Test AntennasA convenient approach to illuminate an equipment under test with known field strengths is to used exact half wave length a long dipoles at fixed frequencies.This arrangement is superior when compared to connecting a test antenna to a signal source using co-axial cable that might distort the field pattern.

Antenna TypeFrequency, MHzRod antenna1 - 30Loop antenna1 30Biconical antenna30 220Dipole antenna30 - 1000Log periodic antenna200 -1000Conical log spiral200 10000Wave guide hornAbove 1000

Measurement Precautions1) Electro magnetic environment According to American national standards describes that is conducted and radiated ambient radio noise and signal levels measured at the test site with the EUT deenergized, be at least 6 db below the allowable limit of the applicable specification or standard.2) Electro magnetic scattersOne method fro avoiding interference from underground scatters is to use a metallic ground plain to eliminate stror reflections from under ground sources such as buried metallic objects.3) Power and cable connectionsThe power needs used to energize the EUT, receiver and transmitter should also pass through filters to eliminate the conducted interferences carried by power lines.

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