How do I correctly enter and use the correction factors for a current probe such as the 11967A/B with an E7400A Series EMC
Current Probes such as the 11967A or 11967B are used as the transducer for many military conducted emission tests. The probe, which is clamped around the wire of interest, is exposed to the magnetic field produced by the current in the wire. The resultant output voltage of the probe is proportional to the current level, frequency, and probe characteristics such as permeability, cross-sectional area and number of turns.
To determine the current level associated with a particular voltage the transfer impedance (ZT) of the probe must be known. By subtracting the transfer impedance (dBΩ) from the voltage (dBµV) measured on the EMC analyzer the equivalent current (dBµA) can be calculated, as shown below.
Transfer Impedance (ZT) = Vout / Icond
I (dBµA) = V (dBµV) - Z (dBΩ)
The transfer impedance values for the particular current probe being used should be provided by either the manufacturer of the probe or the calibration service provider. To use these values with the D7400A Series EMC, you will need to enter them into the Antenna Correction Factors table in the analyzer. (You will find information on how to do this in the EMI Receiver Mode User’s & Programmer’s Reference in chapter 4).
There is one other step that needs to be taken in order to read the correct values for your measurement. As noted above, the transfer impedance correction values need to be applied to the measured dBµV values, which then become dBµA values. The problem is that the analyzer will only work in one amplitude unit at a time. This can be handled in one of two different manners:
- Use the instrument with the amplitude units set to dBµV and read the values as though they were dBµA, ignoring the on-screen units.
- Change the amplitude units to dBµA and add the proper conversion factor to the data by means of one of the other correction factor tables. The correction factor for this is -33.98dB. For example, if you were using an 11967A, which has a frequency range of 15KHz to 50MHz, you could enter just the low and high end frequencies both with the -33.98dB correction value into the "Other" or "User" correction table.