Using Current Probes

When using current probes you should be aware of some common characteristics shared by current probes. All have some type of shielding to minimize the pickup of electrostatic fields radiating from the test conductor. Optimizing the design of the shield for maximum rejection has some compromises in other probe parameters. Thus, different vendors’ probes have differing ability to reject fast dv/dt signals in the test conductor. While the Teledyne LeCroy current probes have among the lowest voltage sensitivity in the industry you should still be aware of it. This means that wherever possible you should probe the circuit under test on the low voltage side of the circuit. When that is not possible a simple test can be used to quantify the electric field pick up in the actual circuit. Connect a short piece of wire to the test conductor. Do not terminate the opposite end. Place the jaw opening around the conductor and view the waveform. Because no current is flowing through the unterminated wire, any signal displayed in the waveform is due to the dv/dt coupling into the probe. Ideally, none of the voltage signal would be visible in the displayed waveform.

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