EMC Management & Lab AccreditationPoojita Rao BhattuEMC Test Engineer at Cisco Systems, Inc.
San Jose, CA, USA; Master Graduate in Electrical Engineering from [email protected] Abstract — EMC is the ability of equipment to functionsatisfactorily in its electromagnetic environment withoutintroducing intolerable disturbances into that environment orinto other equipment. The methods of couplingelectromagnetic energy from a source to a receptor can bedone in four categories – Conducted, Inductively, Capacitivelycoupled and radiated. Emphasis is placed upon an intersystemapproach to the improvement of the overall electromagneticenvironment. There are a plethora of tests which are doneunder EMC is Emissions and Immunity– Radiated &Conducted (PLCE and SLCE), Radiated & Conducted,Immunity, ESD (Electrostatic Discharge), EFT/B (ElectricFast Transient/Burst), Surge, VDI, Magnetic and Flickers.
This paper provides the overview of all the EMC testing’s,EMC Management, Laboratory Accreditation, Standards,different EMC Chambers and Legal issues of EMC. Keywords— EMC, RE (Radiated Emissions), CE(Conducted Emissions), ESD (Electrostatic discharge), EFT/B(Electric Fast Transient/Burst), PLCE (Power Line ConductedEmission), SLCE (Signal Line Conducted Emissions), VDI(voltage dips and Interruptions).INTRODUCTIONWhen we hear “EMC” or its longer version,”electromagnetic compatibility”, it suggests elaborate anechoicchambers with pretty tiles, highly-specialized antennae,sophisticated EMI receivers, copper and more copper, and athicket of regulations.
We all are concerned withelectromagnetic compatibility because we face specificproblems in our own specialized areas. In addition to this,natural environment, intentional electromagnetic threats arealso now emerging to which unprotected systems will bevulnerable. The environment itself is also a pertinent factorbecause its characteristics influence the electromagnetic energypresent within it. The fundamental work of strategic nature inEMC is required now to support emerging technologies andprevent new threats. A European technology Network onSustainable Electromagnetic Environments (ETN-SEE) hasbeen established to facilitate, coordinate, and accelerate thedevelopment and acceptance of technologies which will createan electromagnetic friendly and secure society in the future.Electromagnetic compatibility invariably has two aspects. Forany incompatibility to exist there must be a source ofinterference.
If either of these is absent, there is no EMCproblem. Electromagnetic Interference (EMI) has become amajor problem for circuit designers, and it is likely to become even more severe in the future. As circuitry has become smallerand more sophisticated, more circuits are being crowded intoless space, which increases the probability of interference.
Interference is the undesirable effect of noise. If a noise voltagecauses improper operation of a circuit, it is interference. Noisecannot be eliminated, but it can be reduced in magnitude. AnEMI filter is designed to attenuate one or more specificfrequencies in order to provide electromagnetic compatibilityof an electronic device while in the presence of anelectromagnetic emitter operating at the same or similarfrequencies.EMISSIONS AND IMMUNITY TESTSRadiated Emissions:Radiated Emissions testing involves measuring theelectromagnetic field strength of the emissions that areunintentionally generated by the system. The electromagneticwaves don’t extend out from the system in a spherical pattern.The emissions tend to be pretty directional, so in the test lab,we can just vary the height of the receiving antenna. Theantenna picks up both the signal direct from the system andfrom the ground.
The types of Antennas used for RadiatedEmissions are more than three types. Bilog Antenna (30MHz-1GHz), Horn Antenna (1-18GHz) and Fixed Gain HornAntenna (18-40GHz) are mainly used.Performing radiated emissions measurements is not asstraightforward as performing conducted emissionsmeasurements.
The complexity of the ambient environment isadded which could interfere with measuring the emissions froma DUT. There are some methods that can be used todiscriminate between ambient environment and signals fromthe DUT. Testing in a semi-anechoic chamber can simplify andaccelerate measurements because the ambient signals are nolonger present. Chambers are an expensive alternative to openarea testing.
If the device is placed on a turntable, rotate thedevice while observing a signal in question. If the signalamplitude remains constant during device rotation, then thesignal is more likely to be an ambient signal. Signals from aDUT usually vary in amplitude based on its position.Conducted Emissions:Conducted RF emissions are electromagnetic disturbances(noise voltages and currents) caused by the electrical andelectronic activity in an item of equipment and conducted outof that equipment along its interconnecting cables, such aspower, signal or data cables. The conducted disturbances in aconductor, emitted by one item of equipment, can coupledirectly into another item of equipment that is connected to thesame conductor. Conducted disturbances are also radiated fromthe conductors they travel along, as both electric and magneticwaves, and in this sense, the conductor is acting as an’accidental transmitting antenna’. A very common frequencyrange called out by conducted emissions standards is 150 kHzto 30 MHz. We have two different emission testing underConducted Emission Testing, they are – 1) PLCE (tested onpower ports) and 2) SLCE (tested on telecommunication ports).
Power Line Conducted Emissions – CE limit are imposedon power lines primarily to protect other equipment that sharesthe power lines. The ripple caused by emissions from multipledevices on the line can at times be additive. In the power lineconducted emission test, EUT is the interference resource andthe equivalent circuits of parallel transmission lines. Signal Line Conducted Emissions – CE limits on signallines apply to the entire cable bundle and are intended tocontrol low-frequency radiation produced by cabling harnesses.
Radiated and Conducted Immunity/Susceptibility: Radiated Immunity test is intended to see how well ourEUT performs when it is encountered with different types ofelectromagnetic field disturbances in normal usage. A signalgenerator feeds a modulated sine wave to a broadband RFpower amplifier. The output of the amplifier is connected to atransducer, which turns the varying conducted voltage into avarying radiated electromagnetic field. For RS test, we useLog periodic Antenna and Horn Antenna. The compliancetesting for radiated immunity for commercial products isbased on the international standard, IEC 61000-4-3, and isperformed from 80 to 1,000 MHz at e-field levels from 3 to 20V/m, depending on the production environment or application.The RF signal is generally modulated by a 1,000 HzAmplitude Modulation sine wave modulation set to 80% forcommercial testing, and short duration (as little as 1%) pulsedmodulation for military and aerospace testing. The modulationis designed to test for “audio rectification” issues.
Testing should be performed in a configuration, close toactual conditions in which the EUT will be used. A metallicgrounding plane is not required, but the EUT should be placedon a non-metallic, non-conductive material. The requiredwiring length required for the EUT is less than 3m, then thespecified length should be used. The required length is longer,a minimum of 1m of cable should be exposed to the RF field,and excess cables should be bundled in the center of the cablein lengths of 30-40cm.
Conducted Susceptibility is to test the immunity toconducted disturbances induced by radio-frequency fields. It isused to stimulate the normal voltage and current environmentof external power and signal cables. We can have bothcapacitive and inductive coupling when the cables are bundledtogether.
The different transducers that are used in CS test areCDNs, BCI Probe, EM Clamp and direct voltage injection.This test simulates adjacent cabling by injecting a common mode disturbance into your cabling using a transducer. Thecompliance testing for conducted immunity is based oninternational standard, IEC 61000-4-6, and it is performed totest the requirement of electrical and electronic equipment toelectromagnetic disturbances coming from intended RFtransmitters in the 9 kHz – 80 MHz frequency range.
Figure 1: Conducted Immunity Test Setup The frequency range is swept from 150 kHz to 80MHz,using the signal levels established during the settling process,and with disturbance signal 80% amplitude modulated with a1 kHz sine wave, pausing to adjust the RF signal level or tochange coupling devices as necessary. Where the frequency isswept incrementally, the step size shall not exceed 1% of thepreceding frequency value. The dwell time of the amplitudemodulated carrier at each frequency shall not be less than thetime necessary for the EUT to be exercised and to respond, butshall in no case be less than 0.5s. The sensitive frequenciesshall be analyzed separately. ESD (Electrostatic Discharge): An electrostatic discharge test is a common form of EMCimmunity test.
ESD involves in applying the discharges to anyareas of the EUT which are normally accessible to a humantouch. An ESD test has two discharge pins i.e.
1) Air and 2)Contact. In air discharge, the tip is blunt which is charged upto full voltage. When the air discharge tip is moved closer tothe conductive surfaces of the EUT with a sufficiently largepotential difference, a spark will arc across to the device.
Incontact discharge, the uncharged sharp tip gets in contact witha point on the EUT. When the trigger is applied to the ESDsimulator, the tip is charged that discharges the energy throughthe EUT. ESD can attack via two paths – conduction (direct)and electromagnetic radiation (indirect). The indirect effectsare real, and I’ve seen indirect ESD induced failures occur upto 20 feet away. These multiple paths often mean multipledesign fixes. For the direct effects, filters/transient protectionare used for vulnerable inputs/outputs, while ferrites or othercurrent limiting are used for power/ground paths.
For theindirect effects, high-frequency shielding is used. Damage iscommon when ESD is injected on an unprotected I/O pin –digital, analog, or even power. Circuits vulnerable to ESDdamage include I/O or any other lines directly connected tothe outside world. Circuits vulnerable to ESD upset includeresets, interrupts, and controls. Unwanted resets are verycommon with ESD — so common that we routinely addprotection to these devices. Even power circuits arevulnerable.
I have seen ESD shut down power supplies due toESD upsetting power protection circuits. EFT/B, Surge, and VDI: The repetitive fast transient test with bursts consisting of anumber of fast transients, coupled into the power supply,control and signal ports of electrical and electronic equipment.Significant for the test are the short rise time, the repetitionrate and the low energy of the transients. EFT is done in twocoupling methods. They are – 1) Direct and 2) Capacitive.
Indirect coupling for power ports, the EFT disturbances areinjected directly onto the relevant signals with a carefullydefined source impedance. In capacitive coupling, the signalsare fed through a capacitive coupling clamp, which couplesthe disturbance to the cables. The International standard forEFT/B test is IEC-61000-4-4. Test voltages of up to 4 kV inpositive and negative polarities are applied to the A/C powerleads and up to 2 kV is applied to the I/O cables.
The testvoltages are at a 5 kHz pulse repetition frequency and appliedfor 60 seconds to each power supply terminal includingprotective earth and every combination of these terminals. Thecoupling clamp is used to apply up to 2 kV to the I/O cables. Surge is usually applied to AC (or DC) power input ports,but in some cases, it is also applied to the I/O ports. The surgepulses are coupled directly to the signals via defined sourceimpedance. The coupling network is usually contained insidean immunity test system along with a decoupling networkwhich helps to protect the power supply or auxiliaryequipment. Surge coupling mechanisms are described in twomodes: 1) Common mode 2/10 us, 6kV open-circuit voltage,100 amp short-circuit current.
(Longitudinal surge), 2)Differential mode 2/10 us, 1kV open-circuit voltage, 100 ampshort-circuit current (metallic surge). In common mode surge,all the conductors in the cable develop the same instantaneousvoltage with respect to earth ground. There is no voltagedifference between any two conductors in the cable. Themajority of surges that affect communication cables arecommon mode surges. Figure 2: Common surge mode When considering common mode surge, it is important tounderstand that if there is no path for surge current to exit theequipment, no surge current can flow.
Similarly, even if thereis a path that contains an isolation barrier that is stronger thanthe applied surge voltage, no current can flow, and thisstrategy particularly works very well for Ethernet ports. In differential mode surge, a surge voltage appearsbetween the individual conductors in a multi-conductor cable.The surge current will attempt to enter the equipment on oneof the cable conductors and exit the equipment on anotherconductor in the same cable. Figure 3: Differential surge mode VDI test is normally used to simulate voltage dips andshort brownouts on AC or DC power supplies. This test allowsus to know whether the EUT works properly with the powersupply fluctuations. IEC 61000-4-11 defines the immunity testmethods and range of preferred test levels for electrical andelectronic equipment connected to low-voltage power supplynetworks for voltage dips, short interruptions, and voltagevariations. This standard applies to electrical and electronicequipment having a rated input current not exceeding 16 A perphase, for connection to 50 Hz or 60 Hz A.
C. networks.Figure 4: Dips for a period in the order of a millisecond.
Voltage dips and short interruptions are caused by faults inthe network, in installations or by a sudden large change ofload. Voltage variations are caused by the continuouslyvarying loads connected to the network. The EUT is tested fortest levels of 30%, 60% and ;95% below the rated voltage forthe equipment. The duration of the dips/interruptions are10ms, 100ms and 5000ms respectively. Five dips areperformed for each test level at a rate of one dip per minute.The changes in supply voltage occur at zero crossing of thevoltage. A test level of 0% corresponds to a total supplyvoltage interruption.
Harmonics and Flickers: Flicker and harmonics testing are another forms ofemissions testing. These EMC tests are usually performed tothe EN61000-3-2 and EN61000-3-3 standards respectively. InEurope, these are considered to be 'horizontal' standards,which means that they apply to almost all types of electronicor electrical equipment that enter the EU. Harmonics iscurrent testing, which is usually associated with switch modepower converters and other non-linear loads. The harmonicsload on local power supplies is reduced, which helps to avoidoverheating and increases efficiency. The test setup formeasuring harmonic currents is very similar, only a senseresistor is added in series. By measuring the dynamic currentconsumption across the frequency range of interest, theanalyzer is able to calculate the current consumption of thepower supply harmonics.Figure 5: Harmonics Current measurement circuit.
Flicker is voltage testing that is caused arcing betweencontacts which in turn would cause nearby lamps sharing thesame power supply to flicker. In figure 6, all the analyzer ismeasuring the voltage across the EUT. There is a calibratedcomplex source impedance, so the analyzer can work out thevoltage fluctuations across a range of frequencies.
Figure 6: Flicker measurement circuit.Pass/Fail Criteria: When performing all the EMC Immunity tests, we have toevaluate whether the product passes or fails each EMCimmunity test. They need to monitor your equipment duringand after each test and watch for any changes to the behavioror operation.
The performance of the product usually falls intocategories A, B, C, and D.? Criteria A: It is considered perfect, which means ourproduct performs normally and within specifications,usually in the product manual, during and after thetest. So essentially nothing bad happens to theproduct.? Criteria B: The product may have a temporary loss offunction of performance which ceases after theapplied disturbance ceases. So after the test finishes,the equipment under test recover to its normalperformance without operator intervention. ? Criteria C: It is the same as Criteria B, but theoperator intervention is required. So maybe the EMCphenomena reset the device and we need to power itback on manually.? Criteria D: There is a loss of degradation ofperformance which is not recoverable, owing todamage to the hardware or loss of data.
So basicallyin some way the test has trashed the product. It mighthave fried some components or caused corruption ofsome data.EMC MANAGEMENT AND METHODOLOGIESTo facilitate assurance of achieving compatibility, an EMCmanagement lifecycle for every project is required. Each phaseof the project lifecycle can be termed Definition, Requirement,Tendering, Design, Manufacture, Installation, Commissioning,and Operations ; Maintenance.A.
Definition PhaseIn this phase, the potential impact of EM interferencebetween different electrical and electronic systems in the pre-defined electromagnetic environment is accessed andidentified.B. Requirement PhaseIn this phase, the general EMC management and specificEMC technical requirements applicable to the project isformulated.C. Tendering PhaseDuring this stage, EMC competence of the tenders isassessed based on their technical abilities to comply with thespecific EMC requirements. Upon completion of the EMCassessment, the relevant project leaders should be advised ofthe results to enable them to finalize their overall assessment.D. Design PhaseIn the Design phase, EMC design progress, and compliancewith requirements of each sub-system should be monitored.
The design submissions include EMC Management Plan, EMCTest Specification, EMC Test Reports or Certificates and EMCDesign Review.E. Manufacture PhaseAll EMC design should be completed with each systemwith the compliance requirements.
Based on the provendesigns, manufacturing of the system hardware is commenced.F. Installation PhaseTo make certain system design integrity, good EMCinstallation is practiced.
G. Commissioning PhaseDuring this phase, the identification of all necessary EMCinterface and integration tests for each component of thesystem should be carried out.H. Operation ; Maintenance PhaseThe operators ; maintainers monitor the performance ofthe system.
Enhancement of the EMC Compliance Matrixshould be revised which will facilitate the preparation of theEMC specifications for the future system upgrade. EMC management mode enables the interpretation of roledefinition and the management required in each phase of theproject is to manage the EMC assurance in a large-scaleproject. LABORATORY ACCREDITATIONSince 1990, the accreditation of EMC laboratories hasbecome increasingly important in many parts of the world. Thecompliance of most of the electronic products with nationaland international electromagnetic compatibility (EMC)requirements is to be determined and documented. Qualifiedtest laboratories can help reduce the test and approval periods,especially when regulatory authorities accept test data andreports documented without further evaluations. For example,in the US, an EMC test laboratory is accredited by A2LA(American Association for Laboratory Accreditation), NVLAP(National Voluntary Laboratory Accreditation Program).
A2LAworks with government and industry to serve as a resource onissues of quality and competence, provides technical expertiseand recommendations on approaches to oversight, and helps toensure conformance with established policies and requirementsthrough accreditation. Accreditation of US EMC test laboratories to the foreignstandards serves as a basis for their recognition by the foreignregulatory authority as a conformance assessment body (CAB).Accreditation provides a formal recognition to competent EMCtesting laboratories based on the authentication of theenforcement of a quality system in the laboratory (inaccordance with ISO/IEC 17025) and the determination of aminimum level of technical proficiency to perform the EMCtests. There are four distinct groups that benefit fromaccreditation in general: EMC laboratories, users of laboratorytesting services, regulatory authorities (private and publicentities that require quality test data to operate), and the public.Accreditation has a positive impact on the public bystimulating higher standards of quality within EMC testinglaboratories. Manufacturers also gain efficiency because ofaccreditation as they do not have to perform their own on-siteassessments.
Manufacturers who have in-house EMC testingcapabilities can reduce or eliminate the overhead costs by usingexternal accredited laboratories with the assurance of technicalproficiency. Laboratory accreditation uses criteria andprocedures specifically developed to determine technicalcompetence. Qualified technical assessors conduct a thoroughevaluation of all factors in a laboratory that affects the production of test or calibration data. Very often these criteriaare based on ISO/IEC 17025, which is used for evaluatingEMC test laboratories throughout the world. Mutual recognition arrangements (MRAs), are crucial inenabling test and calibration data which are accepted by thecountries.
MRAs rely on accreditation as a basis forestablishing technical competence and building regulatorconfidence. The accreditation bodies are responsible foraccrediting competent conformity assessment bodies (CABs)in accordance with international standards and to the importingparty’s technical requirements. In the United States, NIST(National Institute of Standards and Technology) currently listsA2LA, ANAB (ANSI-ASQ National Accreditation Board) , andNVLAP as acceptable for use by MRAs for EMC andtelecommunications test laboratories (ISO/IEC 17025). BothA2LA and ANSI are recognized through the NationalVoluntary Conformity Assessment Systems Evaluation(NVCASE) Program as accreditors of certification bodies(ISO/IEC Guide 65). ISO/IEC 17025 allows laboratories toimplement a sound quality system and demonstrate that theyare technically competent and produce valid and reliableresults.The accreditation of EMC test laboratories around theworld becomes more important with the globalization of tradeand the proliferation of electronic and electric products in allaspects of life. Regulatory authorities in many countries havechanged product approval processes for various productcategories and now allow manufacturers to determine anddeclare product compliance with applicable standards.Qualified EMC test laboratories can now test products inaccordance with foreign requirements/standards and preparetest reports that serve as the basis for product approval inforeign markets.
EMC test laboratories must demonstrate theirtechnical proficiency to perform these tests and also establish aquality framework that allows testing under repeatable andconsistent conditions. The laboratory accreditation process(applied by recognized accreditation bodies), based on thegenerally accepted standard ISO/IEC 17025, allows testlaboratories to obtain this independent determination anddocumentation of technical proficiency in the technical field ofEMC.From my experience, few things that I can share about ISO17025 Accreditation. ISO 17025 is mainly applicable fortesting and calibration laboratories. Normally the process ofISO 17025: 1) Scope, 2) Normative References, 3) Terms andDefinitions, 4) Management Requirements and 5) TechnicalRequirements. In Scope, meet general requirements alaboratory has to meet to be considered competent. InNormative references, general terms and their definitionsconcerning standardization and other quality systems likeinstallation, designing and development are done.
Terms andDefinitions are for the purpose of International standards suchas shall, should, policy, procedure, documents, quality systemand recording of the product is done in the process or not.Quality control data shall be analyzed where they are found tobe outside pre-defined criteria, the planned action shall betaken to correct the problem and to prevent incorrect resultsfrom being reported. Under Management Requirements weensure that the quality system, document control, review ofrequests, tenders, service to the client, purchasing services andsuppliers, correction, prevention and management reviews areperformed. Finally, under technical requirements,environmental conditions.
Test methods, validations, sampling,traceability and reporting the results are completed. Therefore,the ISO 17025 pass level is 80%. The newer version ofISO/IEC 17025 calls out requirements for impartially statingthat the laboratory management must commit to impartiallyand that the laboratory must ensure impartially in all itsactivities and not allow commercial, financial or otherpressures to compromise impartially. Impartially is theprinciple that decisions are based on objective evidenceobtained during the performance of the laboratory’s activities,not on the basis of bias or prejudice caused by the influence ofdifferent interests of individuals or other involved parties. EMC STANDARDS Standards were created to provide a method of testingproducts so that different test facilities could compare testdata.
Without standards, each test lab or manufacturer wasperforming testing of products to their own methods andlimits. The major worldwide standards for the EMC sector areIEC (International Electrotechnical Commission) standardsand CISPR (Comité international spécial des perturbationsradioélectriques) standards. IEC standard defines the inputfrom the country organizations as they are trade consensus.CISPR addresses at 9 KHz and also 18-40GHz.
CISPR is thestandard that presents several test methods, with suggestedlimits, to evaluate the level of radiated emissions from acomponent designed for installation. CISPR is subdivided intothree categories. They are 1) Basic standards 2) Genericstandards 3) product standards. The basic standards tell uswhat actually the procedure is, but, it doesn’t explain at whichlevel the product should be tested.
Generic standards areapplied when the product doesn’t have its specific standardsbut, explains how to perform the test. Product standards arethe product group’s i.e. medical, household equipment’s andexplains which test should be performed t what level on eachequipment. CISPR 11 is widely used international standard forEMC within Europe for electromagnetic emissions ordisturbances from Industrial, Scientific, and Medical, ISM,Equipment.
CISPR 11 applies to a very wide variety ofequipment including everything from Wi-Fi systems, andmicrowaves through to arc welders, all of which fall into theindustrial, scientific and medical category that can use theISM license-free bands like 2.4 GHz. CISPR 16 is a series of fourteen publications specifyingequipment and methods for measuring radio disturbances andimmunity of voltages and currents in the frequency range 9kHz to 1GHz. CISPR 16 is split into four distinct parts with anoverall number of fourteen different elements i.e.
CISPR 16-1,CISPR 16-2, CISPR 16-3 and CISPR 16-4. CISPR 16-1consists of five parts which specify voltage, current, and field measuring apparatus. CISPR 16-2 specify the methods formeasuring high-frequency EMC phenomena.
It addresses bothEMC disturbances and immunity. CISPR 16-3 is basically atechnical report rather than a standard and it contains specifictechnical reports and information on the history of CISPR.CISPR 16-4 consists of five parts and contains informationrelated to uncertainties, statistics and limit modeling . CISPR22 is widely used standard for electromagnetic compatibilitywithin Europe for Information Technology Equipment, ITE.
CISPR 22 differentiates between Class A and Class Bequipment and it gives figures for conducted and radiatedemissions for each class. CISPR 22 requires certification overthe frequency range of 0.15 MHz to 30 MHz for conductedemissions. CISPR 22 has no specified limits for frequenciesabove 1.0 GHz, and CISPR limits are provided in dBµV, whilethe FCC limits are specified in µV. In terms of similarities, theconducted and radiated emission limits specified in CISPR 22and FCC Part 15 are similar.The tables below give a summary of the field strength limitsfor conducted and radiated emissions of CISPR 22 standard.Table 1: CISPR 22 CLASS A Conducted EMI Limit:Thefrequency ofEmission(MHz) Conductedlimit(dBuV) Quasi-peak Average0.
15-0.5079 660.50-30.073 60Table 2: CISPR 22 CLASS B Conducted EMI Limit:The frequencyof Emission(MHz) Conductedlimit(dBuV) Quasi-peak Average0.15-0.50 66 to 56 56 to 460.50-30.
0 56 465.00-30.0 60 50Table 3: CISPR 22 CLASS A 10-meter Radiated EMI Limit:The frequency ofEmission (MHz) Field StrengthLimit (dBuV/m)30-88 3988-216 43.5216-960 46.5above 960 49.5Table 4: CISPR 22 CLASS B 3-metre Radiated EMI Limit:The frequency ofEmission (MHz) Field StrengthLimit (dBuV/m)30-88 4088-216 43.
5216-960 46above 960 54FCC Part 15 is a Code of Federal Regulations, Title 47, Part15, 47 CFR 15. Title 47 regulates everything from spuriousemissions to unlicensed low-power broadcasting in the USA.Part 15 of the FCC Title 47 is often just called FCC part 15and it relates to EMC. The FCC Part 15 rules and regulationshave been designed to align with the European CISPRregulations.The scope of FCC Part 15 is split into three sections asfollows:? FCC Part 15A: This section sets out the regulationsunder which an intentional, unintentional, orincidental radiator may be operated without anindividual license. It also contains the technicalspecifications as well as the administrativerequirements and other conditions relating to themarketing of FCC Part 15 devices.? FCC Part 15B: This covers the operation of anintentional or unintentional radiator that is not inaccordance with the regulations in this part must belicensed according to the provisions of section 301 ofthe US Communications Act of 1934.
? FCC Part 15C: Unless specifically exempted, theoperation or marketing of an intentional orunintentional radiator that is not in compliance withthe administrative and technical provisions, includingprior FCC authorization or verification, asappropriate, is prohibited under section 302 of the USCommunications Act of 1934.There are two classes of the device for FCC Part 15:? Class A digital device: Within FCC Part 15, a Class"A" digital device is one that is used in a commercial,industrial or business environment.? Class B digital device: Within FCC Part 15, a Class"B" digital device is used in a residential or domesticenvironment. Examples of devices in this categorymay be personal computers, calculators, and similarelectronic devices that are marketed for use by thegeneral public. One of the major elements of this was the EMC Directive -89/336/EC.
EMC standard applied to all equipment that wasplaced on the market of users within the EC. The EMCDirective from the EC (European Commission) was ground-breaking in terms of EMC standards and legislation as it wasthe first time that limits had been placed on the immunity ofthe equipment to interference as well as its emissions. TheEMC Directive has moved onwards and is now a well-established EMC standard. EMC CHAMBERS A Chamber is used for EMC and RF (Wireless) testing. Theword ‘anechoic’ more or fewer means ‘without echo.’ Ananechoic chamber is designed to absorb reflections of waveswithin the chamber rather than have them bounce off the wallswhich can cause echo. If these chambers are designed andassembled correctly, they can keep the waves entering fromthe chamber i.
e. they provide shielding from outsideinterference. There are many types of anechoic chambers thatare designed for different applications.
Some of the mostcommon uses and types are for things like audio recording,radiated emissions testing, radiated immunity testing, wirelesstransmitter (RF) testing, antenna testing and specificabsorption rate (SAR) testing. Audio chambers are the oddman out here because they deal with absorption of soundwaves rather than electromagnetic energy which is common toall the other types of chambers. Semi-Anechoic Chamber: An anechoic chamber is an RFshielded room whose walls and ceiling have been coveredwith microwave absorbers and ferrites.
Ferrites are used forlow frequencies for continuous matching between theimpedance of interior of the chamber and the impedance of theshielded walls. The most common type of EMC testingchamber by far is the semi-anechoic chamber. The word ‘semi’indicates that it’s only partially able to absorb electromagneticenergy and one of the reasons for that is, the floor of thechamber is reflective rather than absorptive. The test distancefor the semi-anechoic chamber is 3m, 5m, and 10m. A semi-anechoic chamber is a room where sound reflections onlycome from the floor because the walls and ceiling areabsorbent. The solid floor makes this room much easier towork in than the anechoic chamber because equipment can bestood on the solid floor. We often put absorbent material onthe floor to reduce floor reflections.
Figure 7: Semi-Anechoic Chamber Full-Anechoic Chamber: The main purpose of a fullyanechoic chamber is to perform full compliance measurementsof radiated emission and immunity. The full anechoic chamberis a multi-functional EMC test facility for commercial andtelecom testing. The combination of the pan-type 2mmgalvanized panel system, parallel closing RF shielded doorsand polystyrene hybrid absorbers on the walls, floor andceiling create a high performance controlled electromagneticenvironment that complies with international immunity andemission test standards. The FAR test volume is measured atthree levels, bottom, middle and top, with a fixed position forthe receive antenna. The two methods for FAR validation arethe reference site method (RSM) for path lengths of 3 and 5meters and traditional NSA for 5 and 10-meter distances. TheRSM is required in the shorter paths in order to reducecoupling or near-field effects related to biconical receiveantennas.
Figure 8: Full-Anechoic Chamber OATS (Open Area Test Site): In OATS is preferable to theSAC because there are no walls in the vicinity of themeasurement area. Even with plenty of absorbing material onthe walls of a SAC, there will still be a portion of the waveenergy that gets through the absorber and reflects back off themetallic surface of the chamber wall. An Open Test Area Siteis a 3m and 10m emissions test range. The receivingmeasurement antenna, in that case, picks up the wave comingfrom the equipment under test (EUT), the reflection off thefloor and the partial reflection off one or more walls.Figure 9: OATS (Open Area Test Site) GTEM (Gigahertz Transmissive Electromagnetic cell ):GTEMs are used to measure radiated emissions for FCC part15B and 18 devices (with some caveats) and perform radiatedimmunity testing according to IEC61000-4-3. The two maindownsides of a GTEM are the limited EUT size and themeasurement error at lower frequency ranges (approximatelyunder 200 MHz). The GTEM cell is a frequency extendedvariant of the traditional TEM (Transverse Electro-Magnetic)cell. It is designed for EMC applications, calibration ofantennas/field probes, test and measuring of mobile phonesand screening measuring of material.
Figure 10: GTEM cell Reverberation Chamber: An electromagneticreverberation chamber (RVC) is a chamber which is made toresonate. They are predominantly used as a cavity resonator toperform radiated immunity testing. Due to the high Q-factor ofthe chamber and the almost complete reflectivity of the wallsand floor, an electromagnetic field of a given strength can becreated using a much smaller power amplifier compared tothat needed in a SAC.Figure 11: Reverberation Chamber RF Shielded Room: An RF shielded room forms the basisfor a semi-anechoic chamber. It is a well-sealed metal boxwhich offers electric and magnetic field shieldingeffectiveness over a given range of frequencies. RF Shieldedrooms provide RF quiet environment in which to conductdifferent application tests such as EMC, wireless technologyon automotive or military vehicles, MRI scans, etc. Theserooms are built with Smart shield TM modular RF shielding,electromagnetic pulse protection EMPP shielding, TEMPEST(secure communications) shielding and architectural shieldingfull systems. Figure 12: RF Shielded RoomLEGAL EMC ISSUESTraditionally, EMC and EMI issues are solved in the EMClab, often without getting a full understanding of theunderlying effects.
The root causes of electromagneticresonance, effects the product, enabling fast design cycles andhigh product quality. To reduce the EMC issues, powerchokers are used with inverters. In general, one choke is usedfor each phase of an inverter. Currents flowing through thesechokes are in the range of a few amps. Electric and magneticlosses lead to heat generation, and this heat can affect theperformance and reliability of inverters. The denser theindividual components of an inverter are packed together, themore critical heat management is. AC Inverters use a fastswitching PWM (Pulse Width Modulation) technique to createa variable frequency AC Output to the connected motor. Thefast switching of the output of the drive when connected withlong motor cables results in a reflected voltage at the motorwhich can be up to three times the AC supply voltage.
Outputchokes help to reduce this peak voltage, and increase the risetime, to reduce the stress applied to the motor insulation andprevent damage. Currents flowing through these chokes are inthe range of a few amps. Electric and magnetic losses lead to heat generation, andthis heat can affect the performance and reliability ofinverters. The denser the individual components of an inverterare packed together, the more critical heat management is.Some EMC issues are caused by poor grounding and shieldingi.e.
quieting the sources of interference, inhibiting couplingpaths and hardening the potential victims. The issues withshielded enclosures are when the longest dimensionapproaches half wavelength. There are three main issues ofconcern for wound (inductive) components which controlstray magnetic fields, the variability of their parameters withcurrent and temperature, and their resistivity. Whileperforming EMC tests, the test setup, including the layout ofthe equipment, the cable used, cable length, supportingequipment, etc. shall follow the relevant EMC standards.Sometimes, we need to maintain the exact length of the cablesthat are connected to the system to simulate the actualoperating conditions of the equipment in its applications.FUTURE EMCToday, the trends of the past 20 years are continuing.Computing devices are getting denser, faster, more complexand more pervasive, creating new challenges for the EMCengineer.
At the same time, advances in electromagneticanalysis and available design possibilities are revolutionizingthe methods used to ensure compliance with EMCrequirements. Newer technologies are more likely to cause anEMI disruption that could cause functional degradation toanother system with low levels of immunity protection.Mixed-signal components (digital and analog) are both usedon printed circuit boards, yet during the design processhardware engineers are concerned with functionality as permarket specifications. Digital devices may emit EMI thatcould interfere with the operation of other electrical devices and systems. Newer technologies are in general more likely tocause an EMI disruption or induce an event that could causefunctional degradation to another system with low levels ofimmunity protection. Government and industry conventions, the test proceduresrelated to electromagnetic compatibility continue to beintroduced and updated on a regular basis.
Nevertheless, therapid pace of technical innovation basically ensures thatregulations alone will never be sufficient to guarantee thesafety and compatibility of electronic systems. This makes itmore important than ever to address electromagneticcompatibility issues early in the design, rather than “fixing” aproduct after it fails to meet a given requirement.Understanding the nature of EMI in a real-life environment andhow to deal with it can help users to make their processes andequipment much more effective and error-free, and theirsensitive devices better protected from EMI-caused electricaloverstress. EMC engineers should be educated in HazardBased Safety Engineering (HBSE) which addresses functionalsafety along with hazard and risk assessments.
As of today,only a few engineers are aware of a new HSBE standard (IEC62368-1) that may eventually replace certain UL, CSA, IECand EN product safety standards.ACKNOWLEDGMENTI would like to express my deep gratitude to my Professorsand Colleagues, for their patient guidance, enthusiasticencouragement and useful critiques of this paper. Finally, Iwish to thank my parents for their support and encouragementthroughout my study.REFERENCES1 Electromagnetic Compatibility Engineering by Henry W.Ott.2 Electromagnetic Compatibility of Integrated Circuits:Techniques for Low Emissions and Susceptibility bySonia ben dhia , Mohamed ramdani , Etienne sicard J. 3 Woodrow W.
Everett, JR, Member of IEEE, and R.Powers, Member of IEEE “ElectromagneticCompatibility: A Position Paper,” IEEE Transl. Volume:EMC-8, Issue:3 , pp. 161-168, 1966 8 th NationalSymposium.
4 EMC standards and legislation from Electronic Notes 5 COMTEST Engineering6 EMC FastPass, by Andy Eadie.7 https://incompliancemag.com/article/designing-ethernet-cable-ports-to-withstand-lightning-surges/8 CST – Computer Simulation Technology webinars.9 www.
a2la.org/regulators .10 In Compliance Editorial Team.
11 Interference Technology.12 Electro Magnetic Test Inc. – EMC Testing, Standards etc