Automotive EMI/EMC Pre-compliance Tests - Tektronix

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Automotive EMI/EMCPre-compliance TestsTektronix RF Automotive Test Solution––APPLICATION NOTE

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionIntroductionElectromagnetic interference (EMI) regulations are in placethroughout the world to provide improved reliability andsafety for users of electrical and electronic equipment. Theautomotive industry and individual automobile manufacturersare required to meet EMI standards specifically for automotivesystems.With the introduction of USB-based real-time spectrumanalyzers, pre-compliance EMI testing has becomesignificantly easier and more cost-effective for designers.This application note provides an overview of measurementAPPLICATION NOTEAUTOMOTIVE ELECTROMAGNETIC COMPATIBILITYSTANDARDSCISPR 12 and CISPR 25 are international standards containingprocedures and requirements for the measurement of radiodisturbances to protect off-board receivers and on-boardreceivers of automotive, respectively.CISPR 12 is a whole vehicle test rather than applying tosubassemblies. The goal is to assure that receivers are notaffected when the vehicle drives them. The test frequencyrange is usually from 30 MHz to 1 GHz. Only radiated tests arerequired.regulations and EMI pre-compliance procedures. Test setupsCISPR 25 measures the RF interference that is generated byfor both radiated and conducted emissions are shown usingthe vehicle and then picked up by vehicle mounted antennasthe Tektronix RSA306B with EMCVu software.(such as the AM/FM radio or GPS antenna). The test frequencyEMI Pre-compliance testingMost engineers employ good design practices to minimize thepotential for EMI problems. Still, to identify and address anypotential EMI issues before formal compliance testing, it isconsidered best practice to perform in-house pre-compliancemeasurements during the design and prototyping stages. Thisreduces the risk that the product will fail final compliance testsat the test house.Also, in the event of a failure during formal testing, the ability totest in your own lab gives you the time to methodically isolateproblem areas and test different corrections.bands are the operating bands of selected wireless standards(FM and TV broadcasting, cellular service, ).In addition to CISPR 12 and CISPR 25, most manufacturershave their own set of standards to augment the CISPRguidelines. For example, Ford Motor Company has their ownElectromagnetic Compatibility Specification for Electrical/Electronic Components and Subsystems (FMC1278). OtherOEMs have similar standards.Tektronix EMCVu pre-compliance software supports EMCstandards including CISPR, FCC and MIL-STD for many typesof devices. To automate testing, EMCVu provides a built-instandards table allowing you to choose the applicable standardfor your product and the region in which it will be sold.FIGURE 1. Affordable pre-compliance testing can easily be set up to uncoverpotential problems so that you can minimize test time in more expensivecompliance test facilities.FIGURE 2. EMI standard presets.2 TEK.COM

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTESELECTING ACCESSIORESSelecting accessories is one of the keys for EMI compliancetests. It is not unusual for the cost of accessories to exceed thecost of the spectrum analyzer itself. The required accessoriesdepend on the type of emission testing being performed.To help manage costs, there are low-cost accessoriesavailable. For example, the measurements shown Figure 1are being made with a very low-cost PC board log periodicantenna. One or two of these, along with a biconical antennacan often cover the required frequency range. The biconicalantenna is used for 20 to 200 MHz frequencies, since theFIGURE 3. Tektronix accessories for EMI pre-compliance tests.longer wavelengths require a larger antenna. In this examplethe antennas were mounted on an inexpensive tripod. AntennaFactors (AF) and cable loss can be input into the spectrumanalyzer software for field strength correction.To achieve better measurement accuracy and avoid accessorymismatches, Tektronix offers fully-validated accessoriesincluding antennas, Line Impedance Stabilization Networks(LISN) and pre-amplifiers. You can purchase accessoriesindividually, or in comprehensive accessory bundles forconducted and radiated tests. Characterization of accessoriesincluding gain and loss values are pre-loaded into EMCVu toprovide simple set-up and greater measurement accuracy.Measurements are corrected by negating the combined impactof all the accessories gains and losses.FIGURE 4. Tektronix near field probe set for trouble shooting.TEK.COM 3

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTEFIGURE 5. Accessory setup wizard in EMCVu.BETTER UNDERSTAND THE TEST ENVIRONMENT WITH ANAMBIENT SCANHowever, without a professionally built anechoic chamber,Most designers do not have access to a dedicated anechoictheir way to the front end of the spectrum analyzer and riskchamber, and must adapt to using less ideal testingimpacting measurements.environments. A good testing location should be roomy, andfree from powerful emitters such as Wi-Fi access points andnoisy electrical equipment. Basements, unused commercialspace, or parking garages may be good candidates.4 TEK.COMbackground noise and over-the-air broadcast signals will findThis makes it critical to have a better understanding the RFenvironment and establish a baseline in order to achieve usefulpre-compliance test results that approximate those expectedfrom a test house.

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTESpurs mainly from the air, because themath trace shows smaller readoutsSpurs mainly from the DUT, because themath trace shows larger readoutsRed: Violations of the limit lineBlue: Could be from the ambienceFIGURE 6. Using ambient scan and math trace (ambient minus peak scan) to separate the spurs from DUT and spurs from environment and spectrum analyzer.An ‘Ambient scan’ tool in Tektronix EMCVu software helpsThe example in Figure 6 shows a CISPR 25 radiated emissionestablish an ambient EMI baseline by capturing emissionstest. After the recalling the standard preset, EMCVu displays acaused by environment or equipment. Before an ambient scanpeak scan with the trace with yellow color. The magenta traceis done, the DUT (device under test) must be switched off,is the ambient scan measured when the DUT is turned off. Theor completely removed from the setup. After performing anpink trace is the math trace presents the difference betweenambient scan with the DUT turned off, and then performingthe ambient and peak scan. From the math trace, it is easy toa scan with the DUT activated, a math trace can be used totell the spur #1 is from the environment, because peak scanobserve the difference between the ambient signals and theand ambient scan have almost the same value. The spur #2,spurs from the DUT.#3, and #6 are likely from the DUT, because the math traceCONDUCT A QUICK SCAN WITH PEAK DETECTORSThe quasi-peak detector specified in many EMI standardsindicates the ambient scan is little compared to the peak scan.In the emission results table, the spots with ambient effects areflagged in blue.takes significant time to scan over wide frequency ranges. Tosave time, you can perform a quick scan using a peak detector,instead of a quasi-peak detector. The scan using the peakdetector will give a set of “worst case” measurements, and youcan perform quasi-peak measurements to dig deeper into outof-limit conditions.TEK.COM 5

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTERE-MEASURE OVERLIMIT SPOTS WITH CISPR QUASI-PEAKDETECTOROnce you have identified potential trouble areas within thespectrum, you can apply long dwell time detectors, such asquasi-peak, to only those frequencies that have exceededlimits.EMCVu offers three measurement methods for most standards Pre-scan Manual Spot - A quick pre-scan followed bychoosing spots from the results table and re-measuringthem with detectors recommended by the standard (orthose of your choice). Pre-scan Auto Spot - A pre-scan followed by anautomated re-measurement for a chosen number of spotsfail the test criteria. The maximum number spots can beset for re-measurement. Complete Scan - A complete scanwith detectors recommended by the standard – this couldbe time consuming if detectors such as CISPR Quasi Peakor CISPR Avg are chosen.FIGURE 7. Three measurement methods in EMCVu.Remeasured results with CISPR Quasipeak and average detectorRemeasured results withCISPR PK, QPK, and AVGFIGURE 8. Re-measure the selected over limit spurs with CISPR quasi-peak and average detectors.6 TEK.COM

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTEFIGURE 9. Complete report preview and generation.GENERATING A TEST REPORTAfter taking pre-compliance measurements, the results mustbe recorded and documented for future use. Creating a reportsimilar to the certification lab report may help you discoverpotential issues and gain confidence before the formalcertification tests.Whereas making notes on a general-purpose spectrumanalyzer may be challenging, PC-based test and analysissoftware simplifies the report generation process. A “reportwizard” in EMCVu simplifies report generation by allowing youto specify the information to include in the report, and allowingyou to merge multiple test results. Reports may be output inseveral formats, including PDF, MHT, XLSX and several imageformats.FIGURE 10. Report Generation wizard.TEK.COM 7

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTETroubleshooting and debugging withreal-time spectrum analysis technologyOnce issues have been found in pre-compliance tests, what’snext? You need to troubleshoot the issues and locate thesources of RF emissions. The real-time DPX technology inTektronix spectrum analyzers can help you to discover themost difficult, hard-to-find problems. It enables you to see RFcharacteristics that are practically invisible to a conventionalspectrum analyzer.Figure 11 shows a near-field probe being used to locateemission sources in the near-field. Figure 12 shows both theDPX spectrum and the regular spectrum displays. The DPXspectrum indicates regularly occurring spurs, even though theyFIGURE 11. The DPX real time spectrum analysis with a near filed probe helpsyou discover and locate the transient emission sources.are hidden below wideband noise.Low power spurs under wideband noiseFIGURE 12. The DPX real time spectrum analysis vs regular swept spectrum analysis. DPX can detect transient signals, and helps users to gain insights of co-channelinterference.8 TEK.COM

Automotive EMI/EMC Pre-compliance Tests Tektronix RF Automotive Test SolutionAPPLICATION NOTESummaryEMI compliance testing for automotive components andsubsystems is an important part of the design process, and itusually occurs quite late. Pre-compliance testing can take helpmitigate stress on your project and by taking the right steps,you can have higher confidence that your design will passat the test house. New, relatively low-cost instruments andsoftware are available to help you minimize testing expenseand achieve schedule commitments while getting yourproducts EMI certified.TEK.COM 9

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Automotive EMI/EMC Pre-compliance Tests - Tektronix RF Automotive Test Solution Summary EMI compliance testing for automotive components and subsystems is an important part of the design process, and it usually occurs quite late. Pre-compliance testing can take help mitigate stress on your project and by taking the right steps, you can have higher confidence that your design will pass at the .

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