EMC Pre-Compliance Testing to Reduce Time To Market and Save $$ Photo Goes Here Jason Chonko Applications Engineer, Rigol Technologies USA
What is Compliance testing? - Check radiated and conducted emissions from a product Must be below legal limits specific to end product type and usage - Optional: Check radiated and conducted susceptibility - Well defined test geometry, instrumentation, configuration, and setups - Equipment can be expensive to rent or purchase and requires expertise - Typical compliance testing runs from $2-3k a day.. Costs build quickly if a product needs to continually be retested.
What is Pre-compliance testing? - Measuring your product using techniques that provide insight into the radiated and conducted electromagnetic performance of the product such that you are more likely to pass compliance tests the first time - This insight can be used to alter the design such that it is more likely to pass compliance testing - Make design changes earlier in the development process design and test to ensure you pass compliance earlier
Why Pre-compliance? - Your product failed compliance testing - You are concerned that your product may fail
Common Pre-Compliance Tests - Conducted Emissions - Radiated Emissions - Near Field Emissions - Cable emissions
Pre-Compliance Starters Have your failed compliance report handy.. - Extremely useful information. It provides a direct link to the areas that need investigation. - What frequencies fail? - What is the root cause for these frequencies? - Switching power supply? - Digital communications? - It s ok if you don t have a fail report. There is still a lot that you can learn on your own.
Pre-Compliance Starters Test Identical Products - If you failed your first compliance test, make sure that the product you are using for your pre-compliance tests matches the failed test product EXACTLY. - Everything matters.. cable routing/connections, component type/placement, panels/seals/gaskets, and the test environment - Correlation is difficult, but it becomes nearly impossible if you are not testing identical products
Pre-Compliance Starters For example, a customer was testing an assembly that included power line filtering on the mains power input for their product. The power line filter that was used during the failed compliance testing was not identical to the power line filter on the product they were using for pre-compliance. They continued to struggle until they matched the product exactly.
Pre-Compliance Starters Take good notes.. Including all of the equipment used in the test and the settings. This will make increase repeatability and build a consistent library of data on a design which could help with future revisions or products.
Conducted Pre-Compliance Physical Setup Measure the RF reflected down the power line by the EUT RF on the power line can cause unwanted interference with AM broadcasts
Pre-Compliance Tools: The Spectrum Analyzer The eyes of a pre-compliance system.. Used for radiated, conducted, and near-field pre-compliance measurements. Main function is to measure and display input frequency vs. amplitude Lower noise floor is better (DANL of -120 dbm or more) Upper frequency range of 1GHz (minimum) for FCC subpart 15 Optional Tracking Generator (internal sweeping RF source) helpful for testing filters and discrete RF components Instruments available for $500 - over $10k. Many options are around $2k.. Less than a day at the compliance lab.
Conducted Pre-Compliance Tools: Additional hardware LISN Line Impedance Stabilization Network.. Its job is to separate the AC Mains noise from the conducted noise being generated by the Equipment- Under-Test (EUT). Select a LISN that has the proper voltage, current, and frequency ranges for your equipment-under-test. Required for Conducted tests New cost $200-$2000. Can build your own as well.
Conducted Pre-Compliance Tools: Additional hardware A few 50 ohm attenuators (10dB) to help minimize power delivered to analyzer input for unknown inputs $100-$500
Conducted Pre-Compliance Tools: Additional hardware Transient Limiter Protects analyzer input from unexpected or high voltage spikes - $200-$500
Conducted Pre-Compliance Connect transient limiter and attenuator to analyzer input (recommended) Connect Equipment-Under-Test (EUT) LISN Power On/enable power to the EUT.. THEN connect to analyzer.. Minimizes transients to the analyzer (especially with any EUT with motors or other inductive loads that can draw a large current on start up)
Conducted Pre-Compliance The horizontal and vertical ground planes are typically sheets of metal with surface areas twice the dimensions of the EUT. The horizontal and vertical ground planes should be electrically bonded to each other. Equipment placed on insulated table over the horizontal ground plane. No equipment or cabling should run below the equipment. LISN electrically bonded to the horizontal ground plane. Do not coil cables. You want to minimize inductive loops by laying cabling out smoothly. The spectrum analyzer should be placed some distance away from the horizontal ground plane. Typically, it is a few feet away.
Conducted Pre-Compliance: First scan Configure analyzer FCC subpart 15: Scan from 150kHz 30Mhz Set analyzer RBW to 9kHz or as close as your analyzer will allow Add correction factors for LISN, cabling Correction factors mathematically adjust the input signal to remove insertion loss, gain, etc. Use Positive Peak detector This will show worst case conditions Quasi-Peak detector is not critical, but can help adjust for intermittent sources of RF If available, enable limit lines on your analyzer to have visual indication of the limit
Conducted Pre-Compliance: Analyze Failed Peaks After the first scan, note peaks that are above or within 5dB of the limit line Make sure failed peaks are real analyzers can show false peaks due to mixing products.. Add attenuation. The peaks and the noise floor amplitudes should drop the same amount as the added attenuation. If they do, the peaks are likely real.
Conducted Pre-Compliance: Analyze Failed Peaks Note the frequency value of each failed peak Rescan each failed peak.. Set center frequency = failed frequency peak and span 2x the RBW setting Optional: Use the Quasi-Peak detector on these zoomed scans to get more accurate representation of data Make changes to the design until all peaks are below the limit
Radiated Compliance Physical Setup Measure the RF radiated by the EUT Requires expensive enclosure to minimize environmental RF (WiFi, Radio, etc) and reflections
Radiated Pre-Compliance Physical Setup Without an anechoic/semi-anechoic chamber, repeatable and useful measurements can be tricky Physical location and orientation of the EUT, antenna, and elements in the test environment (desks, chairs, people, etc..) need to be consistent for any hope at correlation Minimize metal (desks, chairs, etc) that can cause reflections
Radiated Pre-Compliance Tools: Additional hardware Antenna(s) and non-conductive stand/holder (fiberglass, graphite, PVC, etc..) Calibrated antennas come with correction factor tables (gain vs. frequency) but cost more New cost $2-$5000+
Radiated Pre-Compliance Tools: Additional hardware (Optional) EMI Enclosure Minimizes environmental RF effects Reflections are still an issue. Test Geometry (location and orientation of everything in the enclosure) is critical to repeatability New cost $500-$10,000+
Radiated Pre-Compliance Tools: Additional hardware Aluminum foil Not just for hats anymore! Can wrap EUT Effectively eliminates radiated EMI.. Just peel away areas near possible radiators (ribbon cables, display boards, USB/Communications connectors) to isolate specific areas Conductive tape Can use to create temporary EMI shields and EMI gaskets to seal holes in enclosures New cost $1-$100+
Radiated Pre-Compliance: First scan Configure analyzer FCC subpart 15: Scan from 150kHz 1GHz or higher Set analyzer RBW to 9kHz or as close as your analyzer will allow Add correction factors for antenna, cabling Correction factors mathematically adjust the input signal to remove insertion loss, gain, etc. Use Positive Peak detector This will show worst case conditions If available, enable limit lines on your analyzer to have visual indication of the limit Scan with EUT OFF to get environmental RF.. And retest this periodically to note any environmental RF changes
Radiated Pre-Compliance: Analyze Failed Peaks After the first scan, note peaks that are above or within 5dB of the limit line Make sure failed peaks are real analyzers can show false peaks due to mixing products.. Add attenuation. The peaks and the noise floor amplitudes should drop the same amount as the added attenuation. If they do, the peaks are likely real.
Radiated Pre-Compliance: Analyze Failed Peaks Note the frequency value of each failed peak Rescan each failed peak.. Set center frequency = failed frequency peak and span 2x the RBW setting Optional: Use the Quasi-Peak detector on these zoomed scans to get more accurate representation of data Make changes to the design until all peaks are below the limit
Near Field Probing Near field probes pick up the magnetic (H) or electric (E) field created by unshielded currents.. Read out amplitude vs. frequency on a spectrum analyzer Unlike a broadband antenna (Radiated testing), need to be close to source of RF. Less susceptible to environmental RF Can use a preamp to help boost low level signals Commercially available ($400-$2000) or make your own using semi-rigid RF cable
Near Field Probing Scan cutouts in the enclosure and along seams Display ribbon cables and LCD panels can be loud Use probes to find leaks, and then create temporary gaskets with conductive tape or foil You can also use a test fixture to hold the probe at a specific fixed distance from EUT.. This helps repeatability
Cable Emissions Testing Cables (USB, VGA, Power, etc..) can act as antennas Current clamp probes surround cables and pick up common mode (unbalanced) currents flowing through cables Commercially available or homemade (spilt RF choke with wire wrapping) $10-$1500
Cable Emissions Testing Power up EUT and attach cables Clamp probe around cable and measure output on a spectrum analyzer Check cable terminations and shields.. Incomplete shielding at the connector is usually a big issue Grounding of connector to the chassis can also be inadequate
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