116 34410A/11A/L4411A User’s Guide
4 Measurement Tutorial
An Illustration of the response curve while charging is shown below:
Capacitance is calculated by measuring the change in voltage (DV) that occurs over a
“short aperture” time, (Dt). This measurement is repeated at two different times during
the exponential rise that occurs. An algorithm takes the data from these four points, and
by linearizing that exponential rise over these “short apertures”, accurately calculates the
capacitance value.
The measurement cycle consists of two parts: a charge phase (shown in the graph) and a
discharge phase. The time–constant during the discharge phase is longer, due to a 100
kΩ protective resistor in the measurement path. This time–constant plays an important
role in the resultant reading rate (measurement time).
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