Wednesday 23 November 2011

Reproducible emissions measurements

Teseq has introduced a new line termination clamp as required by CISPR test methods.

Reproducible emissions measurements require a defined line termination for the frequency range where connected lines provide a significant influence on the emissions. The key parameter is the asymmetrical impedance (common-mode impedance) which can be seen as the common-mode impedance to the reference ground.

Line impedance stabilisation networks (LISNs) are commonly used for conducted emission measurements. As well as providing the coupling function for the measurement receiver LISNs provide the line termination and decouple the equipment under test (EUT) from the mains or auxiliary equipment.

In the past a suitable line termination was not available for radiated emissions measurements above 30 MHz. LISNs are typically used for this application but they are undefined above 30 MHz.

The new TESEQ CMAD (Common Mode Absorption Device) is specified in CISPR 16-1-4 and its use will be defined in the forthcoming version of CISPR 16-2-3. It improves the asymmetrical line termination in the frequency range 30 MHz to 200 MHz and improves measurement reproducibility. The CMAD needs to be clipped on lines leaving the test chamber. No more than three CMADs should be used for one setup.

Teseq’s CMAD 20A conforms to the new requirements of CISPR 16-1-4. It replaces the existing CMAD 20 series, which were developed for CISPR 22 Edition 4.0 2033, but do not conform to CISPR 16-1-4.

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