Product Insights: Top Tips for Selecting EMC Chambers

1.  Selection of a chamber is determined by the standard being tested to. Some types of EMC Chambers are: Commercial, MIL STD/DO-160, CISPR 25 and Reverb.
2. Commercial chambers are used for IEC and CISPR standards for Emissions and Immunity testing. Typically, “Semi – Anechoic” and achieve CISPR16 (Emissions) and IEC 61000-4-3 (Immunity) chamber performance requirements.
3. Semi-Anechoic Chambers are strategically lined with absorber and ferrite to meet specifications without fully lining all surfaces.
4. Verification for CISPR 16 compliance is Normalized Site Attenuation (NSA) (26 MHz-1 GHz) and Site Voltage Standing Wave Ratio (sVSWR) (1-40 GHz). This verifies the chamber “Quiet Zone”. Quiet zones are normally equal to the turntable diameter. EUT’s can’t be larger than the quiet zone.
5. For compliance, variations in the quiet zone performance cannot exceed +/-4db for NSA and 6dB for sVSWR.
6. Verification for IEC 61000-4-3 is a field uniformity test. Typically, a 1.5m x 1.5m vertical plane consisting of 16 points spaced 0.5 m apart is the measured area. At least 12 Points must vary by <6dB.
7. MIL STD and DO-160 chambers can be Semi-Anechoic or Fully Anechoic. Standards require the absorber have a minimum absorption of 6dB from 80MHz to 250MHz and 10dB above 250Mhz. A table with a conductive top is bonded to the shield ground is used for testing the EUT.
8. CISPR 25 chambers are fully lined on walls and ceiling, contain a similar table with metal lining on top, and must pass the Long Wire Test or the Reference Site Method test to meet the Standard.
9. Reverb chambers rely upon the reflectivity of the walls and an internal movable paddle to reflect generated signals and increase the value of V/m generated from the transmit antenna.
10.   Information needed to design a reverb chamber is the lowest frequency, the test volume, maximum V/m, and standard to be tested to (MIL STD, DO, ISO).

This month’s Selection Tips are provided by Raymond EMC.

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