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EMI/EMC. B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY. CHAPTER-I. EMI ENVIRONMENT. EMI / EMC • EMI is defined as the undesirable signal which causes unsatisfactory operation of a circuit or device.

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

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B t p madhav lecturer dept of ece kl university

EMI/EMC

B.T.P.MADHAVLecturer, Dept.of ECEKL UNIVERSITY

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

CHAPTER-I

EMI ENVIRONMENT

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • Basic 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

EMI SOURCES

These are divided mainly into two types.

I. Natural and

II. Man-made

I. Natural EMI sources are again of the following

types:

Terrestrial and Extra-Terrestrial.

Terrestrial Sources

These are atmospheric thunderstorms, lightning

discharges and precipitation static.

Extra-Terrestrial Sources

These are sun-disturbed & quiet, cosmic noise and radio

stars.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

The common effects of EMI

(i) Annoying Effects

Very often, momentary and random disturbances in

radio and television reception occur.

(ii) Disturbing Effects

Unwanted reset and change of status in settings in

computers and digital equipment is noticed due to EMI.

The malfunctioning of computer key boards are noticed.

(iii) Catastrophic Situations

The burning of electronic components, loss of data,

change of threshold settings, improper or unwanted

operations and sometimes biological hazards occur very

often.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

  • Thermal Effects

  • 2. Non-thermal Effects.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

EMC STANDARDS

These are of two types

a) Military Standards

These 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

MILITARY STANDARDS

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

CHAPTER-II

EMI CONTROL TECHNIQUES

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

METHODS TO ELIMINATE EMI OR DESIGN

METHODS 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

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Filtering :

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

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • CLASSIFICATION 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

  • π-section filters

  • T-section filters

  • High pass filters

  • Band pass filters

  • Band reject filters

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

EFFECT OF IMPROPER GROUNDING

Lightning stroke current from radio tower

Side flash because of long load grounding lead

i

Radio equipment cabinet

equipment cabinet

VL

L di/dt

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Vc = ( Vpg + Vng )/2

Vd = (Vpg - Vng )/2

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Ground loop

Signal wire

Circuit-I

Circuit-II

Ground wire

Ground loop

VG1

VG2

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

Flux

Circuit-I

Circuit-II

Ground loop

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Transient suppressing devices

  • 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.

Transient and surge suppressing devices

  • There are two categories of transient suppression devices are there

  • Gas discharge tubes.

  • Semiconductor devices.

  • The nature and shape of the transient interference signal waves change during propagation through transmission lines.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Gas – Tube surge suppressors

Fuse

L

Gas tube

Surge current

supply

Load

G

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • METAL OXIDE VARISTORS

  • Metal oxide varistors in which metal oxide semiconductors are used to exhibit voltage dependent resistance.

Fuse

L

supply

Load

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.


B t p madhav lecturer dept of ece kl university

  • ADVANTAGES.

  • Low cost

  • High transient energy absorption

  • DISADVANTAGES

  • Low average power dissipation.

  • Progressive degradation with repetitive surges

  • APPLICATIONS

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


B t p madhav lecturer dept of ece kl university

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

CHAPTER-III

EMC DESIGN GUIDELINES

AND

CHOICE OF PASSIVE COMPONENTS FOR EMC

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

TYPICAL SYSTEMS IN ELECTRONIC EQUIPMENT

  • Transmitters.

  • Receivers

  • Antennas

  • Power supplies

  • Motors

  • Control devices

  • Digital circuits

  • Computers

  • Integrated circuits

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Receivers : -

RF Amplifier

Mixer

IF Amplifier

Demodulator

AF 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

INDUCTORS

An inductor or a reactor is a passiveelectrical component that can store energy in a magnetic field created by the electric current passing through it.

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.

  • Guide lines for inductors :-

  • Core losses ---- -----Causes Energy losses

  • Eddy 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Capacitors :

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 ------

  • Electrolytic Capacitors

  • Paper Capacitors

  • Mica and Ceramic Capacitors

  • Polystyrene Capacitors

  • Feed – through Capacitors

  • Impedance of the Capacitor is

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

  • 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 and

  • the desired frequencies are allowed to pass the filter.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Resistors :-

  • 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.

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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

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


B t p madhav lecturer dept of ece kl university

  • 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

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

  • Analog and video signals.

  • High current switching signals

  • AC and unfiltered dc main signals.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

Wires 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 other

Distance 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.

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

CHAPTER-4

OPEN AREA TEST SITES

B.T.P.MADHAV

DEPT.OF ECE

KL UNIVERSITY


Open area test sites

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


B t p madhav lecturer dept of ece kl university

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.

EUT

calibrated receiver/ field strength meter

Power line filter

Power source

Power source


B t p madhav lecturer dept of ece kl university

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.

EUT

Power line filter

Transmitter

Power line filter

Power source

Power source


Test antennas

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.


Measurement precautions

Measurement Precautions

1) 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 lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


B t p madhav lecturer dept of ece kl university

B.T.P.MADHAV


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