Voltech AT360, User Manual

Page: 306 / 470

T
ESTS AND
T
EST
C
ONDITIONS
P
AGE
7-8 V
OLTECH
AT
I
U
SER
M
ANUAL
circumstances, any measurement instrument may report negative inductance
values and measurement errors. Should these symptoms be observed, reduce
the test frequency to avoid problems.
The frequency at which the inductive impedance equals the capacitive
impedance (X
L
= X
C
) is known as the self resonant frequency (SRF) of the
component. At this point, the phase angle of the impedance (which can be
measured using the ANGL test) is zero. At test conditions where the frequency
is low enough for problems with capacitive impedance to be negligible, the
phase angle will be positive and close to 90 degrees. Therefore an ANGL test
can be used during program development to confirm if measurement problems
are due to the chosen test frequency approaching the SRF of the part under
test. If the angle is significantly less than 90 degrees, consider reducing the
test frequency.
Note that stray fixture capacitance will add to the capacitance of the
component and reduce the SRF. Performing compensation will remove the
effect of stray fixture capacitance on the measurement of capacitance, but
cannot remove its effect on SRF.