length and electrode structure. This in-
ductance resonates with the capacitance of
the capacitor at a high frequency.
At this
self-resonant frequency, the impedance of the
capacitor is minimum owing to the series
resonance which occurs in the capacitor it-
self. Hence, its self-resonant frequency
determines the upper limit of the useable
frequency for the capacitor.
Usually the
self-resonant frequency of electrolytic,
tantalum,
film, mylar capacitors and others
which are within a capacitance range of about
5nF to 1nF can be measured with a Q meter.
When the capacitor self-resonates, the imped-
ance is minimum and purely resistive.
This
characteristic is utilized to determine the
self-resonant frequency and the equivalent
series resistance at this frequency.
The
measurement procedure to determine the self-
resonant frequency of a capacitor is similar
to that for an inductor (described in para-
graph 3-46). Proceed as follows:
a. Depress a trial FREQUENCY RANGE
button.
Note
For high capacitance samples, se-
lect either the 22k - 70k or the
70k - 220k range and, for a rela-
tively low capacitance samples,
select the 220k - 700k or the
0.7M - 2.2M range, respectively.
b.
Select a reference inductor which
allows the measuring circuit to reso-
nate with a tuning capacitance of
approximately 400pF. Connect unknown
capacitor in series with the reference
inductor (between measurement LO ter-
minal and low potential end of the
reference inductor) and to measurement
COIL (HI and LO) terminals.
Note
If 16014A Series Loss Test Adapter
is available, attach it to meas-
urement COIL terminals.
Connect
the reference inductor to appro-
priate terminals of the 16014A
and unknown capacitor to 16014A
series connection terminals.
C.
Short-circuit the unknown (series con-
nection terminals) with a heavy (low
impedance) shorting strap.
d.
Adjust FREQUENCY dial control for a
maximum panel Q meter deflection.
Model 4342A
Section III
Series Connection Measurements
e.
Disconnect the shorting strap. Again
resonate the measuring circuit by ad-
justing the L/C dial control.
If L/C
dial control has to be rotated in the
direction of higher capacitance, in-
crease the measurement frequency. If
it has to be rotated towards a lower
capacitance, decrease the frequency.
f.
Repeat steps c, d, and e until the in-
fluence of the test capacitor to tun-
ing condition is non-existent (indi-
cated Q value may change).
Note
If such condition can not be ob-
tained on the selected frequency
range even though the L/C dial
control is set to maximum, change
FREQUENCY RANGE setting to upper
range. If the L/C dial control
must be reduced to less than 200pF,
change FREQUENCY RANGE setting to
a lower range. Replace reference
inductor with another trial in-
ductor and repeat steps a through
f until the adjustment in step f
succeeds.
g.
Note sum of C dial and AC dial read-
ings as Cl and dial freauencv reading
as-fo. This frequency is identical
with the self-resonant frequency of
the unknown capacitor.
h.
Connect the shorting strap (if not
already connected). Depress AQ
button and adjust AQ ZERO (COARSE and
FINE) controls so that meter pointer
indicates zero (full scale) on AQ
scale.
Note
Press AQ button to release AQ
function and recheck for correct
resonance. Again depress the AQ
button and recheck for AQ zero
indication.
1.
Disconnect the shorting strap.
Note
panel Q meter AQ reading.
If meter
pointer scales out at the left end of
the scale (AQ full scale), reset the
function to normal Q measurement. The
difference in Q is calculated from the
two Q values as AQ = Q1 - Qz.
.
7.
Equivalent resistance of the capacitor
at the resonant frequency is:
Rs =
AQ
JJJCIQIQZ
PI
. . . . . . . (eq. 3-41)
Where, w = 27rfo.
3-25
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