Measurement Testing

Mjr · Site Admin Joined: 13 Jul 2005 Posts: 294

What are labs are doing for immunity test setup verifications.

For instance, the Radiated Immunity test standard, 61000-4-3, calls
for a check with the field probe in the empty chamber, at 2 or 3
positions. (How many labs do that? and what is the go/no-go
criteria?) What is done for the conducted immunity test?

Since some tests require the use of a current probe for feedback, we
normally use the probe during tests, even when using a CDN. The
value is recorded and plotted, which is good information when there
is a failure since an unusually high reading indicates a possible
cable resonance. It can also indicate a possible problem with the
test setup, but it is not a reliable means due to the affect of the
EUT circuit impedance. One may think about coming straight out of the
CDN to the ground plane, through the current clamp, which would not
only test the RF generation equipment, but the measuring and
feedback setup as well, including the software and correction
factors, etc.

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For Radiated Immunity, a particular lab may verify the set-up prior to testing by
placing a field probe at one of the 16 points used during field
uniformity testing and then play back the calibration file. The
field probe should measure greater than or equal to the requested
field from 80 - 1000 MHz.

To verify the conducted immunity setup, the lab may do a calibration into a
50 ohm fixture and then play back the calibration file using a
second calibration fixture attached the to first fixture with a
measurement probe installed. The measurement probe should read
within 1 dB of the calibration current at each test frequency. Both
ends of each fixture are terminated in 50 ohms. This usually works out
for audits where a test artifact was not available.

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Another lab has a procedure for radiated immunity, in which they run the probe in three positions, and had to be +/- 2db. The lab has software written that would does this automatically. The +/- 2dB seemed to
please the auditors. If it were -0 +4 dB, then it might make sense to do the calibration 2dB above the required field.

For the conducted immunity tests, does one hit all of the calibration
frequencies, or some smaller representative numbers? Also, from the
description above, this sounds like the lab is doing a bulk-current injection test, not a CDN, is that correct?

Answer: Yes -- Most of this lab's testing is GR-1089 or automotive so they use BCI. They usually run a verification accross the entire test range since it usually takes less than an hour.