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 meas-
urement path. This time–constant plays an important role in the resultant reading rate (measurement
time). The incremental times (or “sample times”) as well as the width of the “short apertures”, vary by
range, in order to minimize noise and increase reading accuracy.
For the best accuracy, take a zero null measurement with open probes, to null out the test lead capa-
citance, before connecting the probes across the capacitor to be measured (see Capacitance Meas-
urements for details).
Capacitance Measurement Considerations
Capacitors that have a high dissipation factor or other non-ideal characteristics will affect capacitance
measurements. Capacitors with high dissipation factors may exhibit a variance between the measured
value using the multimeter versus the single frequency method of some other LCR meters. The single fre-
quency method will also see more variation at different frequencies. For example, some inexpensive capa-
citance substitution boxes, when measured with the multimeter, are almost 5% different compared to the
same capacitance measured with the single frequency method of an LCR meter. The LCR meter will also
show different values at different frequencies.
Capacitors with long time constants (dielectric absorption) will result in slow measurement settling time,
and will take a number of seconds to stabilize. You may see this when first connecting a capacitor or when
the delay time to make a measurement is varied. A high quality film capacitor typically shows the least of
this and an electrolytic capacitor the most, with ceramic capacitors typically in between.
Measurement Tutorial
176
Keysight Truevolt Series Operating and Service Guide
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