Specifications
EMC-CS-2009.1
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February 11, 2010
Annex I (Normative): Method for Determining Correction Factor for CE 421
CE 421 requires voltage measurements similar to that required for CE 420, but at frequencies below that specified in CISPR
25. In order make these measurements, a correction factor (CF) must be applied. Although this correction factor accounts
for the insertion loss between the Artificial Network's DUT and measurement ports, it is not the same as insertion loss (e.g.
S21) values typically published by the manufacturer of the Artificial Network.
Figure I-1 illustrates the test setup for CE 421 using a standard CISPR 25 Artificial Network. At 100 kHz, the impedance
seen at the DUT connection of the Artificial Network is approximately 3 ohms. The resulting loss due to impedance
mismatch at the DUT connection port is approximately 20 db. This same loss is seen at the measurement port, which is the
insertion loss (e.g. S21) published by the manufacture of the Artificial Network.
At frequencies below 100 kHz, the impedance of the Artificial Network is proportionally lower
(impedance converges to the
DC resistance of the 5 uH inductor
) and the resulting mismatch loss increases. However, the loss at the measurement port
becomes greater than that seen at the DUT connection because of the increasing loss through the series capacitance at lower
frequencies. The correction factor (CF) represents this loss at frequencies between 10 kHz to 150 kHz.
The correction factor may be determined using the following procedure:
Step 1 (see Figure I-2):
a) Short the power supply connection port (A, B) using a 25 mm wide copper braided strap.
b)
Connect a 50 ohm termination resistor across Port (C, B)
c)
Connect Port (P, B) to the output of a 50 ohm signal generator and to the input of a 50 ohm measurement receiver.
Coaxial cables shall be use for these connections. Cable lengths shall not exceed 1000 mm in length.
d)
Measure and record the signal level ( P
OUT
(dBm) ) over the frequency range from 10 kHz to 150 kHz using
frequency steps per Table 9-1.
Step 2 (see Figure I-3):
a) Remove the 50 ohm termination from Port (C, B) and connect it to Port (P,B).
b)
Remove the measurement receiver from Port (P, B) and connect it to Port (C, B).
c)
Measure and record the signal level ( P
IN
(dBm) ) over the frequency range from 10 kHz to 150 kHz at the same
frequencies use to measure
P
OUT
in Step 1.
Step 3:
Calculate the correction factor (CF) at each test frequency (ref Table 9-1) using the measurement data from Steps 1 and 2 via
the following expression:
()
(
)
)() dBmPdBmPdBCF
INOUT
−=
Only the value of (CF) is applied when performing CE 421. The overall insertion loss of the Artificial Network as published
by the manufacturer shall not be used
when performing CE 421.