User manual

Operator Information
Probe Shielding
The P6022 probe
is shielded to minimize the effect of external magnetic fields.
However, strong fields can interfere with the current signal being measured. If you
suspect that an external field is interfering with your measurement, remove the
probe from the conductor, but keep it in the same location a s when you made the
suspect measurement. If a signal still appears on the oscilloscope, try to m easure
the conductor current at a point farther from the location of the magnetic field.
If you must measure current in the presence of a strong magnetic field, you can
minimize its interference by using two current probes and a differential-input
oscillosc
ope. To do so, follow these steps.
1. Connect the probes (with termination) to the positive and negative inputs of
the oscil
loscope.
2. Clamp one probe around the conductor whose current you wish to measure.
3. Place the other probe as close as possible to the first. Ensure that its slide
switch is completely closed, without a conductor inside it.
4. Set the oscilloscope to subtract the component of the signal that is common to
both probes.
5. Adjust the positions of the probes for best results. It may be difficult to
eliminate the undesirable signal completely, due to differences between the
probe
s or their terminations.
Droop
The flat-top response of any AC current probe displays a certain amount of droop.
This is caused by probe inductance loading the source impedance, causing an L/R
exp
onential decay. For short pulse widths, the response looks nearly flat. The
amount of droop can be calculated from the following relationship:
%D
roop = 200 (π)Tf
where:
T = pulse duration
f = lower 3 dB frequency of probe
8 P6022 Instruction Manual