Model 4342A
Parallel Connection Measurements
Section III
Paragraphs 3-67 and 3-68
e.
Connect unknown inductor to measure-
ment CAPACITOR (HI and GND) terminals.
f.
Restore resonance by adjusting the L/C
and AC dial controls.
Note sum of the
C dial and AC dial readings as C2 and
panel meter AQ reading. If meter
pointer scales out at the left end of
the scale (AQ full scale), reset the
function for normal Q measurement.
The difference in Q is calculated from
the two Q values as AQ = Q1 - Q2.
EC.
Inductance of the unknown inductor is:
L=
1
w21c2 - Cl)
(H) . . . . . (eq. 3-17)
3-67.
Low Capacitance Measurement (<45OpF)
3-68. When the measuring circuit is reso-
nated using a reference inductor, a capacitor
placed in parallel with the tuning capacitor
will lower the tuning frequency.
To restore
resonance at the measurement frequency, the
tuning capacitance must be reduced as much as
the capacitance of the sample.
Hence, the
sample value can be determined by noting the
difference between the tuning capacitor dial
readings. After the sample is connected,
quality factor and equivalent parallel re-
sistance can be calculated from a reduction
of panel Q meter indication.
To measure a capacitance sample, proceed as
follows:
Where, W= 2~r times the measurement
frequency.
Q value of the unknown is:
Q
= 4142
CC2 - Cl)
AQCl
-‘--**‘-
(eq. 3-18)
Where,
AQ
=
QI
- 42
Equivalent parallel resistance is:
Rp = -QLQ- (52) . . . . . . . . . . (eq. 3-19)
wC1 AQ
h. The capacitance required to tune the
coil at the measuring frequency is
simply,
c = c2 - Cl . . . . . . . . . . . . . . . (eq. 3-20)
Note
If the measurement frequency is
higher than the self-resonant fre-
quency of the unknown inductor, the
unknown will not appear inductive
but capacitive,
and Cp will be less
than Cl.
Apparent capacitance of
the unknown in such frequency
region is:
Ca = Cl - CZ . . . . . . . . . . .
(es.
3-21)
and equivalent parallel conductance
is
a.
b.
C.
d.
e.
f.
Select a reference inductor which can
resonate at the desired measurement
frequency and connect it to measure-
ment COIL (HI and LO) terminals.
Set L/C dial control to desired tuning
capacitance and AC dial to zero. Note
the tuning capacitance Cl.
Note
If the approximate value of the
capacitor sample is known, select
a value for Cl such that the dif-
ference between Cl and the sample
value is 30 to 100pF.
Depress appropriate FREQUENCY RANGE
button and adjust FREQUENCY dial con-
trol for a maximum Q meter deflection.
Note frequency fl and panel Q meter
reading Q1.
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 func-
tion and recheck for correct reso-
nance. Again depress the AQ button
and recheck for AQ zero indication.
Connect the unknown capacitor to meas-
urement CAPACITOR (HI and GND) termi-
nals.
Restore resonance by adjusting the L/C
and AC dial controls. Note sum of the
L/C dial and AC dial readings as C2
and panel meter AQ reading.
If meter
3-19
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