Keysight E4981A - Selection Criteria of Parallel;Series Equivalent Circuit Models

Keysight E4981A 120 Hz/1 kHz/1 MHz Capacitance Meter 247
Technical Information
Basic Principles of Capacitance Measurement
Selection criteria of parallel/series equivalent circuit models
There are two equivalent circuit models used for capacitance measurement:
parallel mode and series mode, as shown in Table E-2. You must select one of
these before measurement, depending on the magnitude of reactance and the
effect of the equivalent parallel resistance (Rp) and equivalent series resistance
(Rs) on it.
• When capacitance is small:
When capacitance is small, reactance is large. Therefore, the effect of Rp is
greater than that of Rs. When Rs is small, its effect can be neglected
compared to capacitive reactance. In this case, use the parallel equivalent
circuit model shown in Figure E-6 (a).
• When capacitance is large:
When capacitance is large, reactance is small. Therefore, the effect of Rs is
greater than that of Rp. In this case, use the series equivalent circuit model
shown in Figure E-6 (b).
Figure E-6 Selection of capacitance measurement circuit model
Table E-2 Parallel/Series equivalent circuit models and measurement functions of the
E4981A
Circuit model Measurement function of E4981A Definition of D, Q, G
Parallel equivalent
circuit model
Cp-D, Cp-Q, Cp-G, Cp-Rp
D = 1/(|2ΠfCp|Rp)
Q = 1/D = |2ΠfCp|Rp
G = 1/Rp
Series equivalent
circuit model
Cs-D, Cs-Q, Cs-Rs
D = |2ΠfCs|Rs
Q = 1/D = 1/(|2ΠfCs|Rs)