However, the problem is that the lamps are used at distances much closer
than the standard measurement distance. Certainly they are a problem in the
design lab when trying to make sensitive measurements, and also a problem
in the home where a radio and fluorescent light may often be found close to
each other.
Don Borowski
Schweitzer Engineering Labs
Pullman, WA, USA
John Woodgate
<[email protected]
o.uk> To
Sent by: [email protected]
[email protected] cc
Subject
09/11/2007 11:57 Re: Fluorescent light noise
PM
In message <[email protected]>, dated Tue, 11 Sep 2007, Doug
Smith <[email protected]> writes:
>The results are surprising in the amplitude observed at 48 kHz. Go to
>http://emcesd.com . The picture of the scope probe and fluorescent
>light is the link to the article.
Presumably the lamp manufacturer claims that the lamp meets CISPR 15/EN
55015?
This points up the importance of 'measurement distance' in EMC. Limits
for radiated interference are based on a standard distance between
source and measuring antenna (although the measurements may be made at a
different distance and 'referred' to the standard distance by applying a
factor (often of doubtful accuracy, since everything is in the near
field where true corrections for distance are complex in the extreme).
Your measurements are all made much closer to the source that the
standard distance. Also, you have looked at the electric field, but the
emissions are probably substantially magnetic (because the dimensions of
the lamp are very much smaller that the wavelength it is a very
inefficient electric radiator), and many receivers in the low and medium
frequency ranges have magnetic antennas.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
There are benefits from being irrational - just ask the square root of 2.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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