- 9 -
A large capacitance has a small reactance, i.e. low impedance, which makes the influence
of serial resistance Rs on the measurement far larger than that of parallel capacitance Rp,
thus Rp can be neglected and measurement circuit provides a serial equivalent circuit mode.
Fig.9 Small capacitance Eig.10 Large capacitance
(Parallel equivalent circuit mode) (Serial equivalent circuit mode)
(3) The measurement circuit mode is determined according to impedance value of a capacitor to
be measured, which is switched at about 10
in relation to internal impedance of LCR meter.
The relationship between capacitance and impedance is shown in Fig.11. The
“
Electric
Capacitance
”
(4.7) and
“
Dielectric Dissipation Factor
”
(4.8) sections of the public standard
JIS C 5101-1-1998 define measurement frequency to 1kHz for 10
F or lower capacitance
and to 120Hz for capacitance higher than 10
F. Therefore, the impedances of all these
capacitance values become 10
or greater, which are measured by the parallel equivalent
circuit mode. However, for a capacitance exceeding 10
F, the serial equivalent circuit mode
is used, as its impedance is lower than 10
F.
Fig.11 Relation between Capacitance and Impedance
High impedance)
Low impedance)
