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• EMC Part 1. Electromag...
Radiated emissions testing, also known as electromagnetic interference (EMI) testing, is a crucial process in electronics and electrical engineering. It is conducted to ensure that electronic devices comply with regulatory standards regarding the unintentional emission of electromagnetic energy.
When electronic devices operate, they emit electromagnetic radiation. If this radiation extends beyond certain limits, it can interfere with the operation of other nearby electronic devices, leading to potential malfunctions or disturbances. Radiated emissions testing aims to measure and evaluate the electromagnetic fields generated by the device under test to ensure that they fall within acceptable limits.
Preparation:
Set up the test equipment: Ensure that all test equipment including spectrum analyzer, EMI receiver, antennas, amplifiers, and any necessary accessories are properly set up and calibrated.
Preparation:
A tripod is used to support the antenna which is connected to an EMI receiver / spectrum analyzer to measure the radiated emission from the DUT.
Setup the EUT:
The Equipment Under Test (EUT) is placed on a non-conductive table of height approximately 0.8m which sits on a rotatable turntable. Ensure that it is positioned according to the requirements specified in the applicable standards or test plan.
Establish Test Conditions:
Power up the EUT: Apply power to the EUT and allow it to stabilize according to the manufacturer's specifications.
Configure the EUT: Set the EUT to operate in the appropriate test modes or operational states for the specific test being conducted.
Perform Pre-Test Measurements:
Background noise measurement: Use the spectrum analyzer to measure the ambient electromagnetic noise level in the test environment. This measurement is essential for establishing a baseline for comparison with emissions generated by the EUT.
Conduct Radiated Emission Testing:
The emissions from each face of the DUT are measured by moving the measuring antenna up and down from 1 to 4m. Both horizontal and vertical polarizations are measured.
Conduct Radiated Emission Testing:
The field strength in dBuV/m is captured by the EMI receiver at frequencies typically from 9kHz to 1GHz. The measured field strength is then compared to the limit line of CISPR22.
Mitigation and Remediation:
If emissions exceed acceptable limits, identify potential sources of interference and implement appropriate mitigation measures such as shielding, filtering, or redesigning circuitry.
Final Evaluation:
If the measured field strength is less than the limit line of CISPR22, the EUT has passed the radiated emission test requirement.
Conclusion
The electromagnetic waves don't extend out from your product in a nice spherical pattern.
The emissions tend to be pretty directional, so a test lab has to vary the height of the receiving antenna between 1 and 4 meters as well as rotate a turntable.
The receiving antenna picks up both the signal direct from the EUT, as well as a bounce off the ground. To increase measurement accuracy, the ground is covered with an electromagnetically reflective surface (aluminum, steel, wire mesh etc..) and this ground plane must be relatively flat.
The test lab will scan the frequency band of interest and look for emissions that are close to the limits. Using a process called 'maximization', the test lab focuses in on each of these emissions and quantifies the amplitude of the field strength.
28 сен 2024
