Hi Brian
I am forwarding this response by Chase EMC as they have been having
problems axcessing this system! Hope it helps!
Message:
1000-2-6 is simply trying to provide a repeatible method for radiated
immunity testing at frequencies below 80MHz. Becasue of the problems
associated with low frequency radiated immunity testing in semi-anechoic
chambers the IEC developed this standard to simulate the induced voltage
found on cables while exposed to a radiated RF field. As we all know the
cables are typically the coupling mechanisim for most RF fields into the
EUT. This type of conducted immunity testing has been going on in the
military arena for several years via Mil-Std-461.
1) The EN 50082-1 or -2 requires this test to be performed on AC, DC
inputs/outputs and I/O cables. The 3 meter clause only applies to I/O
cables. This 3 meter rule comes from the wavelength of the frequencies
being applied. If your standard PC parallel port interface cable is less
than 3 meters than it would NOT qualify to be tested.
2) If the EUT only has an AC mains, the return path would be the stray
capactance between the EUT chasis and the ground reference plane (GRP).
The
correct common mode current is developed because the EUT chasis is 10cm
above the GRP, the I/O cables are 3-5 cm above the GRP and the CDN loop
impedance is 150 (300)ohms. With this in mind, the RF unmodulated current
should be 33mA or 66mA for 3 or 10 volts, respectively.
2b) We have used five CDN's as the rule of thumb. Meaning if your EUT
configuration yields greater than five I/O cables we recomend the use of
BCI
or EM Clamp. We have found that ground loops can exsist with multiple
CDN,s
thereby creating a possible RF short circuit condition.
3) If no ground exsists with the EUT than do not add one, simply use a M-2
CDN (two line).
3) CDN-T2 Telephone
CDN-S1 Shielded Cable
CDN-M1 Chasis ground of cabinet enclosure or EUT
4) Yes the clamp can be used on shielded cables but great care must be
taken
so that you do not exceed the current limit of the standard. This is done
by monitoring the unmodulated current with an additional current probe
located between the clamp and the EUT. See section 7.3 of the standard.
5) Most EMC labs and consultants agree that CDN's should be used for AC
mains unless the AC current exceeds 50-100 amps. But to answer your
question, the clamp can be used to test AC mains provided you monitor the
resultant current per section 7.3 of the standard. The 30cm strap you
refered to is used for reducing the antenna effect of the clamp by
grounding
the shield of the coax.
Please feel free to contact me directly to discuss this standard in more
detail.
CHASE EMC
(973) 252-8001
Joe Heins
Sr. EMC Application Engineer
