Hi All,
I read the standard EN 61000-4-3:1996 with amendments to gather a deeper
understanding of the requirement and the procedure. It appears the
procedure is at odds with the requirement. Please allow me to explain.
The requirement is to establish 75% of the field points to be within -0 dB
to +6 dB. Exploring the uniformity by means of constant field strength
invokes Clause 6.2 a, d, e, f, and h. I have trouble with clause e.
Paraphrasing for simplicity,
- take the data
- find the mean in V/m
- throw out the worst 25%
- the remaining points shall lie within +/-3 dB
- use the lowest of the remaining points as reference.
The 4th step does not make sense to me. I can still maintain a -0, +6 dB
spread without invoking a +/- 3 dB window about the median.
As an illustration, suppose I have data that establishes a spread from -15
dB to +4 dB about the mean. My worst 4 points are -15, -14, -13, -12 dB.
So these points are clearly further from the mean than +4 dB and are
deleted. The remaining points are clustered between +1 and +4 dB. Step
"e" says the remaining points shall remain within +/- 3 dB, so the point at
+4 dB is considered non-compliant, even though it is only 3 dB away from the
lowest point. Step "f" says to make the lowest point the reference for -0,
+6 dB. This being the case, my non-compliant point, originally identified
as +4 dB from the mean is now well within the -0, +6 dB range of the
reference, but is considered non-compliant.
I realize the standard allows up to 3% of points to fall between +6 and +10
dB, but that is not the issue. This point should not have been identified
as non-compliant in the first place, but clause "e" requires it to be
identified as non-compliant.
Does anyone know the rationale to clause "e"? What am I missing? Are
there any committee members out there who can shed some light on this?
Kind regards,
Don Umbdenstock
TEPG -- Sensormatic
561 912 6440
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