1

CHAPTER 1

AUTOMOTIVE SYSTEMS: EMI-EMC 1.1 INTRODUCTION

The scope of the present work is restricted to EMI- EMC studies

made on tracked vehicle to improve the system performance. This involves

identifying the causes of EMI and carrying out necessary hardening of the

electrical modules to meet the Military specification MIL STD 461 E. The

tracked vehicle in normal course of working has to ensure that systems

continue to give the desired performance without affecting an adjoin-

ing system.

1.2 EMI –EMC STUDY PURPOSE ON TRACKED VEHICLES

The present study is intended to identify, isolate EMI problems

encountered onboard that are inherent with defence vehicles and to enable

accomplishment of mission without degradation of performance.

There are a few countries in the world with manufacturing facili-

ties for making these vehicles. It was a challenging task to identify the root

of cause of malfunctions of the systems onboard, which are encountered in

the tracked vehicle. The vehicle encountered several EMI associated mal-

functions, degradation of performance and in a few cases complete failure

of equipment.

2

The EMI is a unique for tracked vehicles rarely seen normal au-

tomotive vehicles. The tracked vehicle houses several complex subsystems

in extreme close proximity space envelop of about 10 m3 . The vehicle has

sighting systems, communication systems, fire control systems, automotive

systems, navigation systems etc. The frequency band of operation of the

sub systems span from DC to several GHz. EMI was identified as primary

source of certain malfunctions during operation of the vehicle. The tracked

vehicle gets assembled in a complex manner and systems are very costly.

There are more than several hundred subsystems onboard. The identifica-

tion of EMI cause in a nightmare for EMC engineer, as the systems mod-

ules arrive from several manufacturing sources. The majority of the prob-

lem crop up only during integration in the vehicle. The constant subsystem

product upgradation causes inevitable EMI seen quite frequently in such

vehicles. Hence a problem solving approach methodology has been

adopted to tackle the EMI and ensure EMC successfully.

The specifications laid down for military environment are ex-

tremely stringent and qualification tests are rigorous. The vehicles are re-

quired to meet the laid down specifications of EMI-EMC such as MIL

STD 461C, MIL STD 5087, MIL STD 220A, and MIL STD1275A

standards (Military standards).

1.3 OBJECTIVE OF EMI –EMC STUDY

The main objective of the present study is based on the EMI

problems onboard that are likely to be encountered during the operation of

the tracked vehicle. EMI can be from the normal onboard events associated

with them along with power sources or due to external threats, which is re-

quired to be tackled to ensure EMC. The external causes are attributed to

3

occurrences of events such as lightning, NEMP (Braisy series, 1987) etc.

The EMI hardening of the vehicle resulted in better EMC performance, al-

so enhanced the reliability of entire system. Hence it was decided to study

the events, identify their causes, correlate them and provide necessary

counter measure to ensure EMC within vehicle.

The specific case studies include software modeling of external

EMI threats and the actual hardware modules testing was resorted to dur-

ing onboard studies. They are briefly discussed below.

a) Simulation studies on vehicle during deployment using fi-

nite element method of analysis ie., Ansoft, Pspice pack-

ages.

b) Study the effects of external threat and proximity to strong

fields such as Extra high voltage (EHV) transmission lines.

The fields generated on the surface of the vehicle with an-

tenna is of great importance for mounting of critical sensors.

c) Subsystems modeling of onboard modules such as Rotary

base junction along with the power distribution elements.

d) EMI- EMC performance evaluation for lightning using

hardware model is required to be carried out for the tracked

vehicle. The tracked vehicle is made of hard metal and has

critical sensors mounted on the surface that are essential for

the vehicle personnel.

e) To carry out transient analysis on power distribution ele-

ments, conducted as well radiated emission studies on the

4

complete vehicle in integrated form to ensure compliance to

the standards. This is required as the systems are in close

proximity, sub systems come from individual manufacturer.

h) To study the type of ideal grounding scheme, power supply

filtering required along with actual measurements for the

above purpose within the vehicle conforming the onboard

power quality.

f) EMC compliance on the complete vehicle is required to be

met after adopting the hardening techniques for the tracked

vehicles.

1.4 PROBLEM DEFINITION

A tracked vehicle has to work in a harsh environment that has

several subsystems modules working in close proximity. The various sub

systems are required to carry out certain specific function that spreads over

a broad frequency spectrum. The present study concentrates on the elec-

trical and communication systems modules as a part of work.

EMI for the tracked vehicle due to external threats levels were

studied using the software packages, while the onboard EMI investigation

were made using actual hardware. The present software studies include the

effects lightning impulse levels, derivation of equivalent circuit diagrams,

coupling matrices, with the mechanical inputs such as material properties

etc. The input impulses (source) were assigned on computer model of

tracked vehicle; this resulted in the anticipated outputs. The onboard power

supply studies made on the vehicle includes

5

a) Quality power supply: Power supply is the primary cause of

coupling of EMI into any system. Hence the decision to in-

vestigate sources of interferences and improve the quality

of power supply in the tracked vehicle under all load condi-

tions. This vehicle has primary 24 V battery bank that works

in parallel with a 20 kW generator to supply all system with-

in the vehicle.

b) Communication system: To ensure secure and necessary

communication under different threat levels from few MHz

to several hundreds of MHz.

c) Conformity of threshold levels as per army limits: The elec-

trical and electronics modules are interconnected with power

loads via cables and control harnesses. EMI conducted le-

vels were investigated for their permitted threshold levels.

d) Post Integration EMI-EMC levels: It is observed that the

though individual modules meet the specification, malfunc-

tion is seen after integration in the vehicle. The malfunction

in some cases has resulted in resetting of computers, failure

of internal components. These items fielded are electronics

intensive, extremely costly that have failed during normal

operation, though individual elements are defence qualified.

e) Protection Schemes for the Modules: The adoption of ap-

propriate protection scheme for the tracked vehicle and to

know the design limits of threat levels using simulation.

6

f) Grounding Schemes and countermeasures: The grounding a

plays important role for impulse performance. The vehicle

grounding schemes is required to be checked for tracked

mobile vehicle application. Similarly proper EMI counter-

measures taken for EMC compliance is met by the modules

and vehicles as a integrated system.

Hence it was challenging task to make thorough investigation on

the cause of failure, isolate the failures attributed to EMI. The transient le-

vels were monitored during the operation of equipment during failure

mode and after adopting EMI hardening techniques. The results were

found to comply with the stipulated standards with enhanced system re-

dundancy. The preliminary investigations on EMI related malfunctions

have been taken up as a part of this research work.

1.5 METHODOLOGY ADOPTED

The specific case studies were restricted to certain areas due to

complex nature of the systems. The complete investigation has been split

to software modeling of vehicle using finite element method package such

as Ansoft and studies based on hardware. The computer based studies were

made to simulate electric and magnetic field in devices with a uniform

cross section or full rational symmetry

The software modeling were carried out for the vehicle deployed

in field areas to know the field levels generated on vehicle surface in the

presence of strong interfering fields. The computer modeling is good tool

to understand the interference process without using any hardware, thereby

7

saving on prototype cost. Ansoft enables us to designate wide range of ma-

terials with varied physical properties, assign time dependent or constant

sources to the model. The different solvers can be effectively utilised to

solve complex situations before arriving at optimum solutions, quiet com-

monly encountered by the vehicle .This can be used to simulate situations

that can be impossible in practice such as NEMP.

The hardware modeling studies are made onboard the vehicle for

EMC performance. The lightning at field areas has caused havoc to critical

subsystems leading to complete mission failure (Hasse, 1992). This has

been taken in the present case as part of the investigation carried out on the

vehicle.

The real time analysis of transients onboard is limited to the elec-

trical power distribution system. The EMI though power supply to mod-

ules being the prime cause of conducted interference within the vehicle

.The studies also included the performance of the shielding and filtering

systems due to system generated EMI and due to external interferences.

1.6 BRIEF DESCRIPTION ON PRESENT EMI-EMC STUDY

Chapter 1 discusses the EMI-EMC aspects of the electrical sys-

tem for tracked vehicles, its functional requirement, safety aspects of the

vehicle. The vehicle encounters malfunctions, degradation of performance

and other problems due to the close proximity of critical subsystems result-

ing into near field interference problem of various automotive systems.

8

Chapter 2 discusses estimation of EMI using finite element me-

thod based on computer simulation. The main software’s used on desktop

PC include Ansoft (Ansoft, 1995) FEM, Pspice package (Pspice, 1996) for

the present case study. The finite size of object related to the frequency of

concern makes Ansoft package an ideal choice for electrical analysis. The

overvoltage is a prime cause of failure in majority of cases and hence they

need to be studied more closely (Daniel 2000). This is basically intended

for electrical parameter extraction, using separate solver under different

operating conditions of system or module, to enable for further analysis in

Pspice. The Ansoft 2D (Ansoft 1996) electrostatic, magnetostatic and AC

conduction solvers were used in the present case. The analyses were car-

ried out on the vehicle and its sub-system slipring that transfers power

from the static to rotating member where special systems are located. A

theoretical study was made in the Ansoft and the results were in concur-

rence with measured values.

Chapter 3 discusses a practical model of the antenna integrated

lightning arrestor for the evaluation using impulse generator under simu-

lated conditions of lightning within laboratory. The impulse voltage

studies were carried out on a hardware model successfully for such an

application.

Chapter 4 discusses the importance of grounding for automotive

systems. The improvement schemes and techniques available is also dis-

cussed in details. The measurements made in situ within the vehicle con-

firm the various parameters that meet the laid down specifications for

automotive systems.

9

Chapter 5 discusses the simulation study carried out on a model

of lightning arrestor to protect the vulnerable vehicle systems from the ex-

ternal lighting disturbances. The fighting vehicle may be subjected to vari-

ous external disturbances like lightning, ESD, (Symposium ESD 1998) etc.

during its normal operation. However hardening may be required to meet

the threat due to EMP fields.

Chapter 6 discusses the onboard EMI-EMC post integration mea-

surements carried out on the vehicle after identifying the probable interfer-

ing source within the vehicle. The necessary counter-measures to bring

down the same have also been discussed in this chapter. The present sys-

tem configuration layout is found to meet the stringent requirement of the

fighting vehicle. The system designer has to incorporate the required pro-

tection system, follow laid out standards and procedures in his own expe-

rience and wisdom so as to ensure EMC within the vehicle. The modules

have to confirm to the relevant standards while carrying out normal in-

tended functions within vehicle.

1.7 EMI –EMC DEFINITION

Electromagnetic Interference (EMI) (US Army 1979) is a situa-

tion where the signals produced by a system intentionally or unintentional-

ly causes malfunction, degradation of performance or complete failure of

another system working in close proximity in the same environment.

The capability of a system to operate well with its specification

even in a electromagnetic environment is called as Electromagnetic Com-

patibility (EMC) (Donald white et al 1988). This indicates that presence of

10

unwanted signals produced by allied system do not interfere with the sys-

tem under consideration.

Electromagnetic Interference can be defined as undesirable noise

that causes some malfunction performance degradation or system failure.

Electromagnetic susceptibility is the capability of a system to respond to

the spurious noise (conducted & radiated). The conducted emission indi-

cates the transfer of spurious signals through metallic paths or conductor

(or common impedance) where as in radiated emission the coupling takes

place through free space (Kaeser 1987 ).

1.8 SOURCES OF EMI ON AN AUTOMOBILE SYSTEM

The EMI sources can be classified into two groups-natural and

man-made. Natural causes include atmospheric noise, lightning electrostat-

ic discharge etc. The intentional transmission made by man through televi-

sion, radio, radar etc are major causes of electromagnetic interferences.

The military environment (US ARMY handbook 1974) also has to harden

its equipment against the nuclear electromagnetic pulse (NEMP) (Conrad

1978) caused by nuclear explosion that creates electromagnetic interfe-

rence in most severe form.

1.9 NATURAL SOURCES 1.10 COSMIC NOISE It is known that hot atmospheric bodies like stars, galaxy, pulsars, sun etc emit radiation towards the earth. These are attributed to random motion of charged ions resulting from thermal ionization at very high tem-

11

perature. The emissions have continuous as well as discrete distribution. Galaxy normally emits broadband noise. The potential discrete emission is from sun, moon, Jupiter etc.

1.11 LIGHTNING SURGE The natural lighting causes sharp impulse wave form generally

causes havoc to the equipment exposed to such high intense fields (Coo-ray1998), (Clay 1978). The lightning causes catastrophic damage to the modules exposed externally. The partial coupling of this energy to the in-ternal system may cause malfunction performance degradation which damages critical modules (David 1991). 1.12 ELECTROSTATIC DISCHARGE PULSE (ESD) The ESD is attributed to accumulation of charge or static electric-ity acquired by an object above surroundings. This results in potential dif-ference between the object to the ground. The accumulated charge depends on humidity, properties of the materials, temperature, etc. The accumulated charges may get discharged in a short duration of time in the form of pulse of the order of pico sec. The EMI from electrostatic discharge (ESD) cov-ers entire electromagnetic spectrum from D.C to several giga hertz (Jorden 1992). The pulsed EMI characteristics of the various waveforms are shown in Table 1.1.

12

Table 1.1 Pulsed EMI Characteristics

ESD EFT Surge EMP Waveform rise time

Rise time

Energy

Duration

Peak Vol-tage (into high impedance)

Peak Current (Into low impedance )

Sources

extremely fast rise time

less than 15 nslow (m J )

ns

up to about 15kV me-dium

few amps

accumula-tion of static electricity

fast rise time repetitive pulses

~ 5 ns

medium (mJ)

ns & repeating

kV

Low (A)

activation of gaseous dis-charge / breaking elec-trical circuit

slow rise time large energy

high (J)

Several kV

High (kA)

lightning power switching

very fast pulse, high rise time, high energy in 1-5 ns very High (MJ) Very high 250

several 50 kV order of kA Nuclear deto-nation high Energy is concentrated below 10MHz where magnet-ic Field effects predominate

ESD - Electro Static DischargeEFT - Electrical Fast Transients LEMP - Lightning Electromagnetic Pulse NEMP - Nuclear Electromagnetic Pulse

13

1.13 NUCLEAR ELECTROMAGNETIC PULSE (NEMP)

INDUCED VOLTAGE

The radiation from a high altitude EMP can be approximated as a

Plane wave in the vicinity of a Power transmission line near the surface of

earth (Louie 1992). Kodali et al (1999) has indicated that the nuclear elec-

tromagnetic pulse can be represented as an exponential waveform given by

E (t) = Eo e-

1.14 SOURCES OF EMI

Electromagnetic Interference takes place due to presence of

source, transmission path and response of a system. The ‘conducted’ EMI

propagates through metallic path including lumped components such as

capacitors and transformers. The various causes of intrasystem and inter-

system EMI is listed in Tables 1.2 and 1.3 respectively.

TABLE 1.2 INTRASYSTEM EMI CAUSES

Emitters SusceptorsAutomobile Ignition Power Supply SystemsComputers Generators Radar TransmittersRadio TransmittersFluorescent Lights

Display Devices Relays Navigation Instruments ComputersRadar Receivers Radio Receivers Ordinance

14

TABLE 1.3 INTERSYSTEM EMI CAUSES

Emitters Susceptors

Radio TransmittersMicrowave relayBroadcast Aircraft Shipboard Land MobileRadio ReceiversLocal oscillatorRadar TransmittersPower Lines Lightning StrokesMotorsFluorescent Lights

Radio Receivers Microwave relayBroadcast AircraftShipboard Land mobile Radio Transmitters Low-level circuit Radar ReceiversHeart pacers ComputersNavigation Instruments Industrial controls

Radiated is the term used to characterize non-metallic path even

though the transfer mechanism may be the ‘Near Field’ or ‘Induction’ ra-

ther than radiated field of an antenna. EMI reaches from one system to

another system (Path) either by means of conduction emission (CE) or ra-

diated emission (RE), refer to Figure 1.1.

RE: Radiated Emission

CE: Conducted emission

Figure 1.1 EMI Transmission Paths

E(Emitter)

S(Susceptor)

RE RE

CE

15

1.15 LITERATURE SURVEY AND EMC PRACTICES

EMI phenomena is discussed in great detail by Roger (1961),

Hasse (1992) has discussed issues pertaining protection of low voltage sys-

tems.Don white (1987) has done extensive pioneering work to ensure

EMC. Similarly repetitive transients and random noise can be analyzed to

show their power spectral density versus frequency (Arrillaga et al 1995).

The specific EMI literature has been referred at appropriate chap-

ters during the present study is listed as ‘References’ in the end.

The coupling can be conductive, capacitive (electric), or inductive

(magnetic) (kaeser 1987). The important parameter of the electrical trans-

mission is the frequency spectrum. Each periodic waveform can be ana-

lyzed into one on more spectral components. Aperiodic waveforms is also

called as one shot transients; can be analyzed to show their spectral content

in the form of energy density as a function of frequency.

The purpose of EMC practices is to ensure system to enable

EMC compliance of each sub system to meet the anticipated EMI threats.

This can be achieved by adopting proper shielding techniques, filtering

mechanism, grounding methods. The other methods such as layout, parti-

tioning etc. helps in reducing EMI level further ( Tront 1984).

1.16 CONDUCTED INTERFERENCE

Conducted interference is the interference that propagates

through a metal conductor such as wire or any metallic structure. This in-

cludes coupling by means of capacitors, inductors, transformer etc. The

sources of conducted interference may be intentional or non – functional

(Table 1.4). The non-functional sources are often associated with Electro

16

mechanical equipment such as commutation, heater circuits, fluorescent

lamps, static power devices, etc.

Table 1.4 Sources of Conducted Interference

Source Spectrum MagnitudeHeater Circuit (Contact Cycling) Fluorescent Lamps Mercury Arc Lamps Computer Logic BoxCommand Programmer Sig-nal lines Power lines Multiplexer Latching ContractorCoil Pulses Contact cyclingTransfer SwitchPower Supply SwitchingCircuitPower ControllerPower Transfer ControllerConstant noiseTransients Magnet Armatures Circuit Breaker Cam Con-tactsCoronaVacuum Cleaner

50 kHz to 25 MHz 0.1 to 3 MHz (peak at 1 MHz)0.1 to 1.0 MHz50 kHz to 20 MHz 0.1 to 25 MHz1 to 25 MHz 1 to 10 MHz 1 to 25 MHz 50 kHz to 25 MHz0.1 to 25 MHz0.5 to 25 MHz 2 to 15 kHz 10 to 25 MHz 50 kHz to 25 MHz2 to 4 MHz 10 to 20 MHz 0.1 to 10 MHz0.1 to 1.0 MHz

20 to 300 V/kHz 8000 V/kHz 20 000 V/kHz(250 V transient spike) 100 V/kHz3000 V/kHz

17

1.17 AUTOMOTIVE SOURCES

A conducted interference exists on automotive vehicles during

the normal use of systems as generator, solenoids ignition coil system,

heating etc. This is of both transient and a steady state nature.

1.18 TRANSIENT TYPES

The generator load is disrupted abruptly, the current being sup-

plied by generator/battery, there is a drop in bus voltage accompanied by

voltage spike with amplitude of the order of 125 V. It has a rise time of the

order of 100 s and a decay time ranging from 0.1 to 5 s resulting in dam-

aged components. The inductive load-switching transient occurs during

vehicle operation whenever an inductive accessory is turned off. Its severi-

ty depends upon the magnitude of the switched load as well as the line im-

pedance. This type of transient has a peak as great as 200 V to 80 V, dura-

tion of the order of 300 s resulting into EMI problems. Heater Voltage

transients of the order of 600 V may result from the simultaneous occur-

rence of the inductive switching of solenoid & generator decay transients

(CVRDE 1999).

1.19 FUNCTIONAL SOURCES

Functional interference results when the normal functioning of

one part of a system directly interferes with normal functioning of another

part. The EMI can be classified as ‘Narrow band’ and ‘Broad band’ related

to the bandwidth of the instrument used to measure the corresponding sig-

nal or noise. The waveform plays an important role in the EMI, sharper

the rise time, the wider the band occupied. In general the lower frequency

18

content in the spectrum results from the amount of area under the pulse;

while the higher frequency contents depends upon the number and steep-

ness of the slopes in the pulse. The Gaussian shaped pulse is the most eco-

nomical (Roger 1961).

1.20 RADIATED INTERFERENCES

Radiated interference is any interference transferred through a

medium by an electromagnetic field. The electromagnetic field constitutes

energy that actually escapes from a source and spreads out in space accord-

ing to the laws of wave propagation. The electromagnetic radiation can es-

cape from the equipment in a variety of ways viz. through component case;

components case discontinuities, where the case is discontinuous to pro-

duce EMI.Inadequate case grounding inter-connecting cables attached to

components, unusual condition such as corroded surface, corona dis-

charges (Kuffel et al 1984) build up between components and insulation

breakdown, inadequately installed connectors, leakage through braided

shield wires are other causes for the radiated interference in a fighting ve-

hicle (Edward 1978).

1.21 CONCLUSION

The EMI EMC is a complex phenomenon and definitely needs to

be studied for a modern tracked vehicle, as electronics product account for

up to 35-40 percent of the vehicle cost. The tracked has several onboard

sources of EMI .The external threats cause necessitates use of techniques

to mitigate the phenomena of EMI. The tracked vehicle as integrated sys-

tem has to comply with the EMC standards.