Keeping up with the changing international EMI/RFI test regulations is like preparing for the Olympics: it requires consistent practice, attention to detail and the right equipment to be a winner. The training has to be appropriate and focused, and the equipment the latest design with all the finest features.
The same requirements are true for electronic manufacturers who sell products across international borders. They must keep up with the newest testing requirements and techniques, and the test equipment must be leading-edge technology to help correctly check products.
With the many changes and adjustments being made today in the EMI/RFI testing requirements in both the United States and abroad, keeping up to date is no easy task. For example, look at the major revisions–including the specification number change–made recently in the IEC immunity standard, a standard which significantly affects what test equipment you select to use. To understand the magnitude of some of the more important changes in this specification, see Table 1.
With IEC 1000-4-3, the 80% amplitude modulation (AM) requires that an RF amplifier supply a peak RF voltage 1.8 times the voltage required for continuous-wave operation. You can calculate the additional power needed to provide this increase in peak RF voltage by applying the logarithmic power ratio formula:
dB = 10 log (P2/P1)
P2 = Power required for 80% AM
P1 = Continuous-wave power level
And: P = V2/R
Substitute: dB = 10 log[(V2)2 /R2] ¸ [(V1)2/R1]
Assume R2 = R1
Therefore:
dB = 10 log(V2/V1) = 20 log(1.8/1) = 5.1
When a continuous-wave signal is 80% amplitude modulated, the peak RF power increases by 5.1 dB. To specify an RF power amplifier that meets the new IEC immunity requirements, determine the power required to generate a given continuous-wave E-field. If 80% AM is required, increase the power level by a factor of 3.24, which is determined by calculating the antilog of 5.1.1
Look for an amplifier with a broad range that easily serves your testing needs. It should provide a range from 10 kHz to 1,000 MHz to accommodate IEC testing, said Bernie Papocchia, Technical Support Engineer for Instruments For Industry (IFI). The wide frequency range provides a cushion as the specification evolves, he said.
Many manufacturers also offer an easy upgrade path for the inevitable change in test specifications. For example, if you purchased the PC6-288 Surge Tester from Haefely-Trench in 1986 to meet the IEEE 587 or draft standard of the IEC 801-5, you could upgrade to meet the requirements of today’s standards.
For the new power requirements, IFI offers a high-power series of amplifiers with single RF inputs and outputs which do not require cable switching. All you do is toggle a switch to go from a low band to a high band.
If you need more than an upgrade, several companies offer complete systems for diagnostic, precertification and final certification testing that include the amplifier, antenna, monitor, probe, cables and software. For example, the Tektronix 27120 EMI Measurement System for pre- and post-certification testing provides a quasi-peak detector and EMI filters, and optional antennas, tripods, cables, LISNs and probes. The software package allows you to define frequency bands, correction factors and specification limits as well as meet the new FCC Part 15 requirements, which changed from the 200 m V/m specification of Subpart J to 500 m V/m required by Subpart B.
The Cost of Immunity Testing
Because of the additional power requirements, immunity design and testing mandated by the European Union will be more expensive than the costs incurred for emission testing. However, this is not a completely accurate picture when you divide immunity into conducted and radiated testing, said Michael Cagney of Schaffner EMC.
“The greatest expense is associated with radiated testing, especially if the equipment under test requires an anechoic chamber. And the cost of equipment for radiated testing typically exceeds $80,000. For these reasons, many companies subcontract radiated immunity testing to outside labs,” he explained.
Conducted immunity testing usually is performed in-house because the capital expense is significantly less, continued Mr. Cagney. Prices typically range from $30,000 to approximately $100,000. The equipment also can be rented reasonably if purchasing does not fit into your budget.
While the move into immunity testing is expensive, help is available, said Dennis Handlon of Hewlett-Packard. “H-P offers a radiated immunity system that includes software for developing a uniform field for the required frequency range. This saves time and money because hand calculations of the signal power requirements for each frequency can be eliminated,” he said.
Compliance Testing
A precompliance system is designed to be low-cost, portable and easy to use even for the novice EMI test professional. While the precompliance system cannot guarantee the same accuracy as a compliance laboratory, the results normally will be close enough for you to know if the product is at least ready for formal testing, said Cliff Morgan, Product Marketing Manager at Tektronix. If precompliance testing shows that the product passes with a reasonable margin of safety, you can be fairly sure that the product will pass formal certification testing.
Precompliance testing can be performed indoors in a screen room constructed with inexpensive metallic cloth, continued Mr. Morgan. While the tests performed indoors may not yield the same results, they usually provide a close correlation.
To perform precompliance testing for radiated immunity, you can use very basic test equipment costing about $2,000, said Mr. Cagney. Or you can perform radiated field testing and relax the requirements for field uniformity to obtain similar results, he said.
If field uniformity constraints are relaxed, you may be able to use a semi-anechoic or even a nonanechoic screen room to significantly reduce the test-equipment costs. Precompliance testing for conducted immunity will require coupling devices for the RF generator and amplifier and will cost approximately $15,000, said Mr. Cagney.
When you are ready to buy precompliance test equipment, purchase a complete system, said Jim Ford, Applications Engineer at Wayne Kerr. Using equipment from various sources is acceptable, but make sure that they interact correctly because their interoperation is your responsibility. Typically this can be a minor inconvenience, but remember that precompliance testing is meant to reduce costs and design time–not increase them.
For certification testing, a full compliance laboratory uses a spectrum analyzer to perform prescans of the spectrum, said Mr. Morgan. Then, a CISPR-compliant receiver with a quasi-peak detector and CISPR bandwidths measures signals that approach or exceed the specification limit.
Because the front end is open to all signals present, the spectrum analyzer can be overdriven when used in high-ambient environments. Some manufacturers circumvent this problem by providing a tracking preselector or a bank of filters.
For example, the Tektronix 2706 Preselector is based on a bank of programmable bandpass filters which are switched by software control. This approach does not provide as much input protection as the tracking preselector but is approximately 20% of the cost.
Full compliance measurements rely on more than a receiver that conforms to CISPR requirements, said Mr. Handlon. They also require a characterized environment, such as an open-area test site (OATS). The OATS must meet the attenuation requirements in ANSI C63.4 Radio Noise Emissions From Low-Voltage Electrical and Electronic Equipment in the Range of 10 kHz to 6 MHz.
The final stage of testing occurs during production. The system used for production testing is similar to one used for precertification testing, said Mr. Morgan. The package includes quasi-peak detectors, EMC filters and various accessories.
The procedure consists of random tests on production samples to ensure that products continue to meet EMC requirements. If design changes were made during the life-cycle of the product, resubmit the product for formal testing, especially if the pre/post certification system showed appreciable change in the level of radiated or conducted emissions.
Production test needs equipment that is completely computer-controlled and offers fast test times, observed Mr. Cagney. The system also must detect failures automatically and provide flexible data gathering and reporting.
Most users have test applications that require integration of OEM test equipment not normally associated with EMI testing, such as DVMs and scanner cards. The production test platform must be flexible enough to allow such instruments to be integrated quickly and cost effectively.
Software can help ease the task, said Mr. Cagney. It should be able to perform the conductive immunity and emission tests, yet allow a wide range of commercial off-the-shelf test equipment to be integrated at a minimal cost.
Reference
1. Amplifier Selection Criteria Required To Achieve IEC 1000-4-3 Testing, Amplifier Research, Application Note 0026, May 1995.
EMI/RFI Test Equipment
Broadband Amplifier Provides
30-W Over Full Bandwidth
The Model 30W1000M7 RF Amplifier provides 30 W of power for susceptibility testing in the frequency range of 25 MHz to 1 GHz. It offers level output power over the test bandwidth and a front-panel gain control of 10 dB. The amplifier is immune to load mismatches and is not susceptible to fold-backs or shutdowns. $9,000. Amplifier Research, (215) 723-8181.
Unit Reproduces Voltage
Perturbations on AC Mains
The PLINE 1610 Voltage/Dips Tester reproduces voltage perturbations, including interrupts, dips and variations on the AC power mains, in accordance with the IEC 1000-4-1 specification. The unit provides a motor transformer to adjust the incoming voltage and another transformer to create the desired disturbance at the desired location and for the required duration on the AC mains sine wave. A built-in microprocessor aids programming and storage of the disturbances. The unit stores 18 voltage disturbances in 18 programs. $18,950. Haefely-Trench, Inc., (703) 494-1900.
Automated EMC Analyzer
Speeds Precompliance Testing
The HP 8590EM Series Analyzers, covering 9 kHz to 1.8, 2.9, 6.5 or 22 GHz, have two operational modes: EMI analysis and spectrum analysis. Automated features include setup keys linking predefined CISPR parameters, antenna/amplifier cable corrections, limit lines and predefined routines that automatically measure all signals over specified frequency ranges. Swept-tuned receivers ensure that intermittent signals are not overlooked, and continuously adjustable spans optimize signal evaluation. Swept measurements are performed on multiple signals and up to 230 signals can be saved. From $16,300. Hewlett-Packard Co., (800) 452-4844.
Wideband Amplifier Suited for
Radiated and Conducted Tests
The SMX 100 Wideband Amplifier provides the capability to perform radiated and conducted immunity testing ranging from 0.01 MHz to 1,000 MHz. It supplies 75 W of linear power and 100 W of saturated power, and generates electrical fields in excess of 10 V/m. The unit features 40 dB of gain control and automatic electronic leveling to keep the signal within a ±0.6-dB range. Internal circuitry provides voltage standing wave ratio protection, and the unit automatically powers down if the input/output signals exceed tolerances. $24,000. Instruments For Industry, Inc., (800) 467-7705.
Instrument Measures EMI,
Meets CISPR 16 Requirements
The AME 5000 EMI Test Receiver performs conducted and radiated emission testing, agreement testing as well as autocertification, and complies with CISPR 16 and VDE 0876 specifications. The instrument features a 7″ color display and a built-in 486 PC. It performs simultaneous measurement of peak, quasi-peak and average values, and provides a 9-kHz to 1.2-GHz frequency range. The software enables automatic measurements without the need to write application software. $26,500 Schaffner EMC Inc., (800) 367-5566.
Certification System Meets
FCC, VDE, VCCI Requirements
The 27120 EMI Measurement System combines the instruments and devices necessary for testing to FCC, VDE, VCCI and European Union requirements. The system includes the company’s 9-Hz to 1.8-GHz 2712 Spectrum Analyzer with EMC bandwidth filters, a 2706 Stepping RF Preselector, a transient limiter, a line impedance stabilization network, biconical and log-periodic broadband antennas, an RF probe set and an EMI software package. $25,120. Tektronix, Inc., (800) 426-2200.
System Examines Conducted
And Radiated Emissions
The EASY 1 Emissions Assessment System examines conducted and radiated emissions from electronic equipment. The system includes the SSA 1000A Spectrum Analyzer, Windows-compatible software, a GPIB card, a near-field probe kit, an LISN and a broadband antenna. The antenna allows open-field testing from 30 MHz to 1 GHz. The near-field probe helps pinpoint the source of emissions. LISNs, ranging from 9 kHz or 150 kHz to 30 MHz, connect to the spectrum analyzer and measure conducted emissions. $12,990. Wayne Kerr, Inc., (800) 933-9319.
Broadband Antenna Aids in
Testing From 25 MHz to 1 GHz
The LPB-2513 Broadband Antenna for emission and immunity testing from 25 MHz to 1 GHz combines the electrical properties of biconical and log-periodic antennas. A broadband matching network helps maintain radiated symmetry. An insulated mast for tripod mounting and a polarization adjustment joint are standard. The antenna measures 38″ x 51″ x 28″ when horizontally polarized. The rear elements can be removed for storage. $2,980. Antenna Research Associates, Inc., (301) 937-8888.
Was Now
IEC 801-3 IEC 1000-4-3
Frequency 27 MHz to 500 MHz 80 MHz to 1,000 MHz
Modulation None 80% amplitude modulation
Distance of DUT 1 meter 3 meters
from Antenna
Copyright 1995 Nelson Publishing Inc.
October 1995