Gert, et al
For our tests, we use the AC mains cable shipped with the product. If there
is none shipped, we select a "representative" AC mains cable.
The AC mains cable's 7 uH core impedance does not have the same impedance as
50 uH. It has the same impedance as the LISN. The LISN's impedance
consists of 50uH in PARALLEL with 50 ohms (whether that is the spectrum
analyzer or a dummy load). At around 1 MHz the AC cable's core inductive
reactance is 50 Ohms.
Sometimes an 8 foot cable, or an AC mains cable that is made differently,
moves the "resonance" of the EUT (due to the interaction between the AC
cable's core reactance and the EUT's parasitic capacitance to the room) in
the spectrum to cause the EUT to fail, yet the 6 foot cable allows the EUT
to comply.
- Robert -
PS: The 7-10MHz "hump" (sometimes this hump is just starting at 30MHz) one
usually sees is caused by the AC mains cable's core inductance resonating
with the test setup. As one takes the EUT from test site to test site, it
is reasonable to see this peak at different frequencies and therefore create
a much larger variation in measurements in this range than one would
otherwise expect, especially if the peak is just starting near 30MHz.
-----Original Message-----
From: Gert Gremmen <[email protected]>
To: Robert Macy <[email protected]>; Muriel Bittencourt de Liz
<[email protected]>; Lista de EMC da IEEE <[email protected]>
List-Post: [email protected]
Date: Wednesday, February 23, 2000 11:57 PM
Subject: RE: conducted emissions test setup
>Robert, Muriel and group,
>
>Therefore it is essential that the mains wire is short and limited
>to 50 cm ( < 2 feet) or even less. The transformer model I can see
>( 3 longitudal straight "windings" , sharing the same magnetic field= def.
>of transformer)
>I don't see however, how 6 uH can have the same impedance as 50 uH ?
>
>Please explain in detail.
>
>Regards,
>
>Gert Gremmen, (Ing)
>
>ce-test, qualified testing
>
>===============================================
>Web presence http://www.cetest.nl
>CE-shop http://www.cetest.nl/ce_shop.htm
>/-/ Compliance testing is our core business /-/
>===============================================
>
>
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