Section III
Paragraphs 3-80 and 3-81
Series Connection Measurements
Model 4342A
3-80.
Low Resistance Measurement.
3-81.
\lrhen measuring circuit is resonated
using a reference inductor, a resistor placed
in series with the reference inductor will
lower the indicated Q in proportion to the
resistance value of the sample.
This reduc-
tion of Q is utilized to measure the resist-
ance. To avoid a significant increment of
measurement error, the measurement should be
made for resistors within a reasonable range.
For low resistance,
the change in the indi-
cated Q should be greater than the Q meter
resolution, that is, 0.1 on AQ = 3 range, 0.3
on 10 range, 1 on 30 range and 3 on 100 range,
respectively. For high resistance, the indi-
cated Q should be higher than 10 when the
sample is connected. See Figure 3-5 for the
suitable sample value range.
To measure low resistances, proceed as
follows:
a.
Depress
the
appropriate FREQUENCY
RANGE button and set FREQUENCY dial
control for the desired measurement
frequency.
b.
Select a suitable reference inductor so
that relatively high resistances are
measured with a low tuning capacitance
and low resistances are measured with
a high tuning capacitance.
Connect
unknown resistor in series with the
reference inductor (between measure-
ment LO terminal 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 measure-
ment COIL terminals. Connect the
reference inductor to appropriate
terminals of the 16014A and unknown
resistor to 16014A series connection
terminals.
C.
Short-circuit the unknown (series con-
nection terminals) with a heavy (low
impedance) shorting strap.
d. Adjust L/C dial and AC dial controls
for a maximum Q meter deflection.
Note sum of the C dial and AC dial
readings as Cl and panel meter reading
as
Ql.
e.
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.
f.
Disconnect the shorting strap. Again
resonate the measuring circuit by ad-
justing L/C dial and AC dial controls.
Note sum of the C dial and AC dial
readings as C2 and panel meter as 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 = Ql - 42.
Note
This procedure (steps c, d and f)
permits the unknown component to be
physically connected even though it
is electrically out of the circuit,
and eliminates possible errors by
maintaining the relative positions
of the reference inductor and un-
known component.
22.
The resistance of unknown resistor is:
Cl
t 1
Rs= z
Ql
-
42
(a) . .
(eq. 3-42)
WCIQIQZ
Where,
w= 2~r times the measurement
frequency.
42 = Ql - AQ
If the unknown is purely .resistive
(C2 = Cl), the equation for resist-
ance reduces to:
Rs =
AQ
wClQlQ2
(Q) . . . . . . . . . (eq. 3-43)
If the unknown is also reactive, the
reactance is:
Xs = '",',;,~" (a) . . . . . (eq. 3-44)
3-26
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