B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY

EMI/EMC

B.T.P.MADHAV

B.T.P.MADHAV

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.

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Basic Types of EMI:

These are of two types. They are

a)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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EMI 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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The 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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BIOLOGICAL 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.

1.Thermal Effects

2. Non-thermal Effects.

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EMC 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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MIL - STD - 461A

TEST DESCRIPTION FREQ

CE01 Power Leads 30 Hz-20 kHz

CE02 Control / Signal Leads 30 Hz-20 kHz

CE03 Power Leads 20 kHz-50 MHz

CE04 Control / Signal Leads 20 kHz-50 MHz

CE05 Inverse Filter Method 30 Hz-50 MHz

CE06 Antenna Terminal 10 kHz-10 GHz

CE07 N/A

MILITARY STANDARDS

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MIL - STD - 461B/C


CE01 Power / Signal Leads 30 Hz-15 kHz

CE02 N/A

CE03 Power/Signal Leads 15 kHz-50MHz

CE04 N/A

CE05 N/A

CE06 Antenna Terminal 10 kHz-26 GHz

CE07 Power Leads Spikes / Time Domain

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MIL - STD - 461DTEST DESCRIPTION FREQ



CE106 Antenna Terminal 10 kHz-40GHz

MIL - STD - 461ETEST DESCRIPTION FREQ



CE106 Antenna Terminal 10 kHz-40GHz

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CS01 Power Leads 20 Hz-50 kHz

CS02 Power Leads 50 kHz-400MHz

CS03 Intermodulation 15 kHz-10 GHz

CS04 Undesired Sig. Rejection 15 kHz-10 GHz

CS05 Cross Modulation 15 kHz - 10 GHz

CS06 Spikes, Power Leads

CS07 Squelch Ckts

CS08 Undesired Sig. Rejection 30 Hz-10 GHz

CS09 N/A

CS10 N/A

MIL - STD - 461A


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CS02 Power Leads 50 kHz-400 MHz

CS03 Intermodulation 15 kHz-10 GHz

CS04 Undesired Sig. Rejection 30 kHz-20 GHz

CS05 Cross Modulation 30 kHz - 20 GHz

CS06 Spikes, Power Leads

CS07 Squelch Ckts

CS08 N/A

CS09 Structure Common Mode Current 60 Hz-100 kHz

CS10 Damped Sinusoidal Transients (terminals) 10 kHz-100 MHz

MIL - STD - 461B/C


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CS103 Antenna Port-Intermod 15 kHz-10 GHz

CS104 Antenna Port-Rej. of Undesired Sig. 30 Hz -20 GHz

CS105 Antenna Port-Cross Mod. 30 Hz-20 GHz


CS103 Antenna Port-Intermod 15 kHz-10 GHz

CS104 Antenna Port-Rej. of Undesired Sig. 30 Hz -20 GHz

CS105 Antenna Port-Cross Mod. 30 Hz-20 GHz

MIL - STD - 461D


MIL - STD - 461E


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RE01 Magnetic Field 30 Hz-50 kHz

RE02 Electric Field 14 kHz-10 GHz

RE03 Spurious & Harmonic 10 kHz-40 GHz


RE05 Vehicle & Eng. Equipment 150 kHz-1 GHz

RE06 Overhead Powerlines 14 kHz-1 GHz

RS01 Magnetic Field 30 Hz-30 kHz

RS02 Magnetic Induction Powerline & Spike

RS03 Electric Field 14 kHz-10 GHz

RS04 Parallel Line Fields 14 kHz-30 MHz

RS05 N/A

MIL - STD - 461A


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RE03 Spurious & Harmonic 10 kHz-40 GHz

RE04 N/A

RE05 N/A

RE06 N/A

RS01 Magnetic Field, Equipment and Cables 30 Hz-50 kHz

RS02 Magnetic Induction, Equipment and Cables Powerline & Spike

RS03 Electric Field, Equipment and Cables 14 kHz-40 GHz

RS04 N/A

RS05 Electromag Pulse Field Transients

MIL - STD - 461B/C


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RE103 Antenna Spurious & Harmonics 10 kHz-40 GHz


RS103 Electric Field, Equipment and Cables 10 kHz-40 GHz

RS105 Transient Electromag Field Transients

CS109 Structure Current 60 Hz-100 kHz

CS114 Bulk Cable Injection 10 kHz-400 MHz

CS115 Bulk Cable Injection Impulse

CS116 Sine Transients - Cables, and Power Leads 10 kHz-100 MHz

MIL - STD - 461DTEST DESCRIPTION FREQ

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RE103 Antenna Spurious & Harmonics 10 kHz-40 GHz


RS103 Electric Field, Equipment and Cables 2 MHz-40 GHz

RS105 Transient Electromag Field Transients

CS109 Structure Current 60 Hz-100 kHz

CS114 Bulk Cable Injection 10 kHz-200 MHz

CS115 Bulk Cable Injection Impulse

CS116 Sine Transients - Cables, and Power Leads 10 kHz-100 MHz

MIL - STD - 461E


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ADVANTAGES OF EMC STANDARDS

The advantages are:

1. Compatibility, reliability and maintainability are

increased.

2. Design safety margin is provided.

3. The equipment operates in EMI scenario

satisfactorily.

4. Product life is increased.

5. Higher profits are possible.

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METHODS TO ELIMINATE EMI OR DESIGNMETHODS FOR EMC

The effective methods to eliminate EMI are

1. Shielding

2. Grounding

3. Bonding

4. Filtering

5. Isolation

6. Separation and orientation

7. Circuit impedance level control

8. Cable design

9. Cancellation techniques in frequency or time

domain

10. Proper selection of cables, passive components

11. Antenna polarization control

12. Balancing

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Filtering :

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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CLASSIFICATION OF EMI FILTERS

1)Low pass power line filters.

2)Low pass telephone line filters.

3)High pass data line filters.

4)Band pass communication filters.

5)Band reject filters.

lumped element low-pass filters(capacitive and inductive filters).

L-section filters

π-section filters

T-section filters

High pass filters

Band pass filters

Band reject filters

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Shielding :

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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Grounding :

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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Radio equipment

cabinet

equipment cabinet

Lightning stroke current from radio tower

VL

L di/dt

Side flash because of long load grounding lead

i

EFFECT OF IMPROPER GROUNDING

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The 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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Bonding :

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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ISOLATION TRANSFORMERS

The 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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The 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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Ground loop

Circuit-I Circuit-II

Ground loop

VG1 VG2

To obtain noise immunity, the ground loop must be broken. This can be done using transformers, optical couplers etc.

Circuit-I Circuit-II

Ground loop

Signal wire

Ground wire

Flux

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Electrical surges are short duration transient waves of current, voltage, or

power on low voltage power supply lines i.e (<1000v rms )

Such transients produce EMI in the practical operation of equipment.

The energy delivered by a surge to a receptor is W =∫ V(t).i(t) dt

The transient that travels along well protected power supply lines and due to

this input stages of the receptors may damage.

There are two categories of transient suppression devices are there

1)Gas discharge tubes.

2)Semiconductor devices.

The nature and shape of the transient interference signal waves change

during propagation through transmission lines.

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Surge current

Gas tube

Fuse

supply Load

L

G

Gas – Tube surge suppressors

1. The 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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Applications

Because 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

It’s response time is slow and it can’t be used for fast rise time surges.

The tube remains in the conducting state even after the surge is removed.

Semiconductor Transient suppressors

Semiconductor transient suppression device maintain a constant voltage at a

desired level across a device by offering variable resistance when transient

voltages are present.

1. METAL OXIDE VARISTORS

Metal oxide varistors in which metal oxide semiconductors are used to exhibit

voltage dependent resistance.

supply

Load

Fuse L

G

• 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.

1) Low cost

2) High transient energy absorption

DISADVANTAGES

1) Low average power dissipation.

2) Progressive degradation with repetitive surges

APPLICATIONS

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

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Component selection

The selection of components can be classified into three categories:

A) Components that affect the RELIABILITY and FUNCTIONALITY .These

Components 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 EMI

MODERATE.

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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Signal 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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TYPICAL SYSTEMS IN ELECTRONIC EQUIPMENT

1) Transmitters.

2) Receivers

3) Antennas

4) Power supplies

5) Motors

6) Control devices

7) Digital circuits

8) Computers

9) Integrated circuits

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Transmitters:-

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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Receivers : -

RF Amplifier

MixerIF

AmplifierDemodulat

orAF

Amplifier

Local Oscillator

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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Objective :-

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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INDUCTORS

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 losses

1)Eddy currents ------- Amount of energy loss increases with the area inside the

loop of current.

2)Hysteresis ---------- Materials with low coercivity have narrow hysteresis loops

and so low hysteresis losses.

3)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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Capacitors 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 ------

Capacitors :

1.Electrolytic Capacitors

2.Paper Capacitors

3.Mica and Ceramic Capacitors

4.Polystyrene Capacitors

5.Feed – through Capacitors

Impedance of the Capacitor is )1( CjwR

RjwlRZ

p

pSC

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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Incoming 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

& mixed

Wire-wound Low noise Composition Noise is more.

Film type Noise is in Between wire-wound and composition.

Resistors :-

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.

TRANSFORMERS

Used for voltage and current transformation or level shifting, impedance matching, power transfer and Isolation process

This allows noise coupling through the transformer. This coupling can be

eliminated by providing an electrostatic or Faraday shield

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Conductors :-

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

1.Digital & Low current, filtered & regulated power signals.

2.Analog and video signals.

3.High current switching signals

4.AC and unfiltered dc main signals.

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1. Wires of different types are not be bundled together.

2. Wire bundles of different types of signals should be physically separated from

each other.

3. Minimum separation is to be 6-8cm.

4. The area of current loops on PCBs and board interconnections should be

minimum.

5. Maximum loop area should be 4cm2.

6. Divide larger loops with smaller loops.

7. Loops and wires should cross at right angles to each other

8. Distance between twisted pairs should be atleast 1.5 times the twist length.

9. Multiple ckts with common return should be twisted as group.

10.Wires between units should follow the most direct route.

OPEN AREA TEST SITES

B.T.P.MADHAVDEPT.OF ECEKL UNIVERSITY

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 AREA TEST SITE MEASUREMENTS

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

MEASUREMENT OF RE

• EUT is switched on

•The 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.

calibrated receiver/ field strength meter Power line

filter

EUT

Power source Power

source

MEASUREMENT OF RS

• 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 filter

EUT

Power source

TransmitterPower line filter

Power source

Test Antennas

A 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 Type Frequency, MHz

Rod antenna 1 - 30

Loop antenna 1 – 30

Biconical antenna 30 – 220

Dipole antenna 30 - 1000

Log periodic antenna 200 -1000

Conical log spiral 200 – 10000

Wave guide horn Above 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 scatters

One 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 connections

The power needs used to energize the EUT, receiver and transmitter

should also pass through filters to eliminate the conducted

interferences carried by power lines.

B.T.P.MADHAV

B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY

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