ETS-Lindgren 94606-6 Current Probe - Manual (Page 34)

34 | Principles of Operation
Core Saturation and Intermodulation
The magnetizing effects of a primary conductor carrying large currents at power
line frequencies can saturate the current probe core material. Core saturation
produces non-linear transforming action and can result in:
• A decrease in the current probe RF output for a given RF current input.
• Modulation of the RF output by the power line frequency.
The specified pulse duty cycle should not be
exceeded or the current probe internal load
resistor (if applicable) may 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 due to the 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
dBμA E
S
dBμV Z
T
dB