Technical Support - Teledyne Lecroy HVD3000 Operator's Manual

Operator's Manual
Differential Mode and Common Mode
Differential probes sense the voltage difference that appears between the + and – inputs.
This is referred to as the Differential or Normal Mode voltage. The voltage component that
is referenced to earth and is identical on both inputs is rejected by the amplifier. This is
referred to as the Common Mode voltage and can be expressed as:
Differential Mode Range and Common Mode Range
Differential Mode range is the maximum signal that can be applied between the + and -
inputs without overloading the amplifier, which otherwise would result in clipping or
distorting of the waveform measured by the oscilloscope.
The Common Mode Range is the maximum voltage with respect to earth ground that can
be applied to either input. Exceeding the common mode range can result in unpredictable
measurements. Because the Common Mode signal is normally rejected, and not displayed
on the oscilloscope, be careful to avoid accidentally exceeding the common mode range.
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