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2.4.3 1-KC RESISTANCE AND CONDUCTANCE MEAS-
UREMENTS.
2.4.3.1 Procedure.
a. Set the GEN LEV control fully clockwise.
b. Set the BRIDGE SELECTOR to:
Rs - if series resistance is desired, and the resistance
of the unknown is between 0 and 1 MD or if the unknown
is inductive.
Gp -
if
parallel conductance is desired, and the conduc-
tance of the unknown is between 0 and 1 mho or if the
unknown is capacitive.
(Note: Any resistor small enough to require use
of the R s bridge because of value will be induc-
tive; likewise, any resistor large enough to re-
quire use of'the Gp bridge will be capacitive.
In the range between 1
.0
and 1 MD the phase of
the resistor will determine which bridge is re-
quired unless Q is small enough to permit use of
either bridge. R s may be calculated from Gp, and
vice versa, from the formula R s
=
_.-L
1
_
(1
+
Q2) G p
c. Set the function switch to INT
At.
d. Connect the unknown resistor to the UNKNOWN
terminals.
e. If the proper range setting of the FULL SCALE
RANGE is not known, set the concentric CGRL controls
for a reading somewhere near 5000, adjust the DET
SENS control for an upscale meter reading and set the
FULL SCALE RANGE switch for a minimum meter de-
flection.
f.
Adjust the concentric CGRL controls and the
three Q controls for the best minimum meter deflection.
The DET SENS control may have to be readjusted to give
greater sensitivity as balance is approached.
g. The resistance or conductance of the unknown
isindic~ted directly on the counter readou~ with the dec-
imal point and unit illuminated.
The Q of the unknown
is read directly on the Q readout. and is inductive or ca-
pacitive as indicated by the lights (unless the Q balance
is less than 0, in which case the opposite is true). Note
the decimal point in the first· (coarsest) adjustm'ent,
which makes major divisions on the vernier dial steps
of 0.001.
The meaning of an X indicator is explained
in paragraph 2.2.
2.4.3.2 Accuracy. The accuracy of the R or G reading
is ±0.1% of the reading ±0.005% of full scale (which is
±1/2 of the last digit) on all but the lowest R and high-
est G ranges where the accuracy is ±0.2% of the reading
±0.005% of full scale.
On the lowest R range the residual resistance of
the bridge (approximating 0.9 mD) should be subtracted
OPERATING PROCEDURE
from the measured resistance.
Use short, heavy leads
to connect the unknown resistor, measure the resis-
tance of these leads by connecting the free ends to-
gether, and subtract this value from the measured value.
Residual inductance and capacitance affect only
the Q of the resistor. Corrections for these effects are
given in Table 2-5.
When resistors with high Q's are
measured, an additional error term of O.I%Q is added to
the specification (refer to paragraph 1. 5. 3).
This term
is practically negligible when Q is less
th~n
0.2.
2.4.4
MEASUREMENTS USING INTERNAL GENERA-
TOR AT FREQUENCIES OTHER THAN 1 KC. If <tn os-
cillator-detector tuning unit other than the l-kc unit
usually supplied is· used, the operating procedure is the
same as for l-kc measurements, but the accuracy
speci~
fications and D and Q ranges are the same as those for
an external generator at the same frequency (refer to
Section 2.5).
The plug-in unit gives the DQ multiplier
required for the various bridges so that it does not have
to be calculated (refer to paragraph 2.5.1).
2.4.5 NOTES ON AC MEASUREMENTS.
2.4.5.1
Capacitance to Ground.
The Type 1608-A Im-
pedance Bridge generally measures "ungrounded" com-
ponents, since neither UNKNOWN terminal is connected
directly to the panel, which should be grounded except
for measurements on grounded components (refer to· para-
graph 3.5).
Capacitance from the LOW UNKNOWN ter-
minal is placed directly across the detector (see Figure
2-3) and does not cause an error, but can, if large
enough, cause a reduction in sensitivity.
Capacitance
from the other UNKNOWN terminals shunts an arm of the
bridge and therefore causes an error which can be signi-
ficant if the stray capacitance is large enough.
Table
2-6 gives the error caused by a stray capacitance for
each quantity measured.
Note that for the capacitance bridges stray capa-
citance causes a small capacitance error.
Since Ct is
0.15 Ilf, it takes a stray capacitance of 150 pf to cause
D
Figure
2-3.
Capacitance and inductance
bridge diagrams, showing capacitances
to ground.
15
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