ELECTRO-METRICS PCL-30
(PCL30-3)
3.2 Transfer Impedance And Sensitivity
The sensitivity of all measurements is dependent upon the value of the current probe
transfer impedance and the minimum voltage capable of being sensed by the detector or
voltmeter.
The transfer impedance is defined as:
ZT= E2/I1
Where:
E2is the output voltage of the current probe as measured by the detection
system (voltmeter, interference analyzer, oscilloscope).
I1is the current flowing in the conductor under test.
Each current probe is calibrated for ZTand serialized to prevent erroneous measurements.
The transfer impedance calibration is accomplished by passing a known current (I1) through a
test conductor and measuring the voltage E2developed across the input impedance of the
detector.
NOTE: 1) The calibration chart that accompanies each PCL-30
Current Probe is for E2developed across a 50resistive
load and is given in terms of transfer conductance GT
(GT= 1/ZT), in siemens.
2) If the user wishes to utilize the current probe on a
detector with an input impedance other than 50, the
probe must be recalibrated for that specific impedance.
The calibrated graph for GTthat accompanies each probe is shown in units of decibels
relative to one siemens, dB(S). This is defined as follows:
GT= -20 log[ZTohm/1 ohm]
As shown graphically; if GTis greater than one siemens, the plus sign applies and if less than one
siemens, the minus sign applies.
As an example of the sensitivity to which measurements can be made, assume that the
probe has a GTof one siemens and the detector sensitivity is 10 microvolts. The minimum
current that can be detected with these parameters is:
I1= GTE2
I1= 10 µV.1S = 10 µA
or in dB:
I1= 20 dB(µV) + 0 dB(S) = 20 dB(µA)
