ETS-Lindgren 94456 Current Probe (Archived) - Manual (Page 8)

Principles of Operation MODEL 94456 CURRENT PROBES
4 © EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265
be subject to damage. The load resistor must also be
protected from excessive line currents.
The influence of intermodulation on the current probe
output as measured with the EMI test equipment is
negligible for primary conductor power frequency currents
under 300 Amperes. For primary power currents above 300
Amperes, measurements taken by the EMI test equipment
generally will not be affected by intermodulation because
of its “averaging” characteristics for the Quasi Peak and
Peak functions, the readings will increase with current.
TRANSFER IMPEDANCE
The RF current (I
P
) in microamps in the conductor under
test is determined from the reading of the current probe
output in microvolts (E
S
) divided by the current probe
transfer impedance (Z
T
).
I
P
= E
S
/Z
T
Or, in dB
I
P
(dB
µµA) = E
S
(dB
µµV) – Z
T
(dB)
The typical transfer impedance of the current probe
throughout the frequency range is determined by passing a
known RF current (I
P
) through the primary test conductor
and noting the voltage, E
S
, developed across a 50 Ohm
load. Then,
Z
T
= E
S
/I
P
Archived 6/1/10