Hello Robert, Martin,
As during emission testing and immunity testing cables act like antennas,
we should treat them like antennas. The efficiency of a wire antenna is a
sine function of its frequency and length. Therefore at a quarter wavelength
optimum emission/receiption takes place.
For emission testing cables longer then 2m50 meters (lowest F= 30 Mhz :: 10
meters wavelength) don't make sense. In immunity testing the same reasoning
is valid, but due to the limited uniform field area size only one meter or
less of it is effectively participating in picking up signal. In TEM and
GTEM cells this length is even shorter.
EN 55022 requires you to vary the length of the cables to maximise
emissions. This is most often
not practically realised. Instead max length cables (3 meters ore more)
are used.
For this reason the IEC decided in their new standard (IEC 1000-4-3) to
start immunity testing at 80 Mhz instead of 30. The frequency below 80 Mhz.
is extended to 150 Khz and is current injected into the cables using
coupling/decoupling devices. The philosophy is that at these lower
frequencies the contribution of cables is much higher as the enclosure
energy pickup.(IEC 1000-4-6)
For EFT and the clamp, the end of the cable should be the end near the
apparatus under test.
I believe that is what you meant to write. For mains voltage the EFT pulses
are galvanically coupled into the phase wires.
Regards,
Gert Gremmen Ing.
BTW is it standard or norm ; standardization or standardisation or
normalizing
I am not nativety speaking/writing this language (as you may have
remarked) so please
group, can someone shine some light on these linguistical topics. ?
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-----Oorspronkelijk bericht-----
Van: Robert F. Martin ITS/QS-Box <[email protected]>
Aan: [email protected] <[email protected]>; Francis L.
Fiedler <[email protected]>
Datum: donderdag 16 april 1998 18:21
Onderwerp: RE: Cable lengths needed
>It has been my philosophy is such cases, that a 3 meter length should be
>provided.
>
>During radiated emissions and immunity tests, a minimum of 1 meter
>should be exposed. In the case of immunity, the 1 meter should be in the
>'uniform' field area (even if you are not requiring the field uniformity
>test). The 3 meters then allows the cable to exit the enclosure.
>
>In the case of EFT, the standard specifies tests of cables >3 meters,
>and requires that the 1 meter coupling clamp be placed near the end of
>the cable. Using a 1 meter cable would be difficult because of the size
>of the clamp, and may also affect the results because of the potential
>for improved 'suppression' of the coupled transient via the support
>equipment.
>
>Bob Martin
>Sr. Technical Manager
>ITS - Northeast
>(978)263-2662
>[email protected]
>
>The opinions expressed are my own and not necessarily those of my
>employer.
> ----------
>From: Francis L. Fiedler
>To: [email protected]
>Subject: Cable lengths needed
>Date: Wednesday, April 15, 1998 6:24PM
>
>Greetings,
>
>Our equipment operates with cables that vary from two feet to two
>hundred feet in length. The length is dependent upon the customer's
>needs. Some cables are provided by the customer for their applications.
>We test our equipment to industrial environment using EN50081 and 50082.
>
>
>What length of cable do you think should be used for test purposes? The
>length of wire subjected to the test signal is usually one meter with
>additional 0.3 meters for positioning or decoupling purposes. Long
>length of wires can result in use of large areas and or bundling. Many
>test instructions specify not to bundle.
>
>
>All of your comments will be greatly appreciated. If you prefer to
>answer directly to me, your comments will be welcomed.
>
>
>Respectfully,
>
>
>Francis Fiedler
>
