CISPR standard up for a vote
Make compliance measurements below 1 GHz with a spectrum analyzer.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 11/1/2009 1:00:00 AM
The preview of Edition 3 of CISPR 16-1-1—the international standard covering EMC (electromagnetic compliance)—is now available. If approved, the standard will allow engineers to make compliance measurements below 1 GHz with a spectrum analyzer that does not offer preselection. The current version—Edition 2—requires you to use an EMI (electromagnetic interference) receiver that meets all the standard’s requirements. Edition 3 is open for voting by the national committees until November 20, 2009. If approved, CISPR 16-1-1 Ed. 3.0 (Ref. 1) should be published on or about February 28, 2010.
Werner Schaefer of Cisco Systems, the project leader for Edition 3, explained that spectrum analyzers have advantages over EMI receivers and usually are less expensive, which is one reason why EMC engineers want to use them. But Edition 3 specifies that spectrum analyzers used for CISPR 16-1-1 compliance must have certain features. “If a spectrum analyzer has the proper average and quasi-peak detector (down to 20 Hz), and meets all other stated requirements, then you can use it below 1 GHz,” he said. “In addition, you must also demonstrate that the EUT [equipment under test] doesn’t emit signals with repetition rates of 20 Hz or less to use a spectrum analyzer. Otherwise, you must use a fully compliant EMI receiver.”
Schaefer explained that EMI receivers were required in earlier versions of the standard because they have preselection (filters) on their front ends to provide adequate dynamic range for quasi-peak measurements of low-repetition-rate signals and to prevent broadband signal overload to a large degree. You can, though, get results with a spectrum analyzer similar to those from an EMI receiver if you use spectrum analyzers properly. You must take care when using spectrum analyzers on high-amplitude signals and on broadband signals to avoid overloading the analyzer’s front end.
Schaefer also noted that spectrum analyzers may sweep across a frequency spectrum more rapidly than traditional EMI receivers, which scan a spectrum in discrete frequency steps. Thus, emissions tests may take less time with a spectrum analyzer, especially if you can use pre-scan measurement results to perform the final measurements only at frequencies with amplitudes close to or above the applicable limit.
“Spectrum analyzers let you see the entire swept-frequency range and they let you see how the EUT behaves,” said Schaefer. “EMC engineers typically use a spectrum analyzer anyway to find the settings and cable layouts that produce the highest emissions. So, why not use it for compliance measurements?”
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