Is your preferred EMC test lab calibrating and performing theIEC 61000-4-3 Radiated Immunity test correctly?
When your product standard, such as the Medical Devices EMC Standard (EN 60601-1-2), requires a 3 or 10V/m radio field (RF) immunity test, the IEC 61000-4-3 Radiated Immunity test procedure is referenced.
The IEC 61000-4-3 EMC standard has gone through a number of changes over the years, with the biggest change being in the Calibration Level and the Verification that the amplifier is not in saturation for each frequency.
The biggest concern for your product under test is that the calibration level is set at a higher level such as 18V/m using the Carrier Wave (CW) for a 10V/m field with the AM modulation applied.
The primary reason for this is to ensure that the RF field is always above 10V/m for each frequency when the modulation is active. This calibration level is also required to ensure that the amplifier is not in saturation during tests with AM modulation.
Saturation is a significant concern since this is where the peaks of the modulation are being “clipped” due to the amplifier not having enough power, resulting in under testing at the desired frequency.
Clipping will also result in higher levels of Harmonic frequencies being transmitted. This can result in misleading test results where you product may appear to be failing at 100MHz when it is actually failing at the harmonic frequency such as 500MHz.
As a general rule, for the frequency range 80MHz to 1GHz, the EMC test lab needs to have a 200W amplifier to get to an 18V/m field with most antenna’s positioned at 3 meters from the Equipment Under Test (EUT).
Depending on their setup, the size of the chamber and their antenna, getting to 18V/m is often only achieved without any attenuators and a short cable between the amplifier and the antenn.
The amplifier will have a lower power output to the antenna if they are using an attenuator or a long cable so that the amplifier can be outside of the chamber. They may be using an attenuator to reduce amplifier VSWR errors or alarms in the amplifier. As an example, for every 3dB of attenuation reduces your power output by ½. If a lab is underpowered, they will often move the antenna closer to achieve the required test levels.
IEC 61000-4-3 prefers that all tests be performed with the antenna positioned at 3meters or further and the calibration should be a 16point calibration to cover a test area of 1.5meter wide by 1.5m high.
The reason for this is to ensure that the typical product or rack, including the cables, can be tested in one antenna position.
You are required to test the EUT as well as 1 meter of cable so you need to expose a minimum of 1meter area. If the lab has calibrated using a 4 point calibration of 0.5meters, they will need to perform a minimum of 2 tests instead of 1 test per side in order to expose a product and cables that is 1 meter wide.
What this also means is that they have to run a separate calibration for each antenna position.
Due to these changes, when Labtest updated it’s radiated immunity test lab, Labtest purchased 1000Watt amplifiers to meet your needs and reduce your testing time.
You can ask us at LabTest, we have the data to prove it.
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