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urements are made, the effects of lead resistance and in-
ductance should be considered (see Table 2-5).
3.4 USE OF TYPE 1650-Pl TEST JIG.
3.4.1 GENERAL. The Type 1650-Pl Test Jig provides
a means of making quick connections to the bridge with
a pair of conveniently located clip terminals. When the
Type 1650-A is set up for limit measurements (refer to
paragraph 3.6), the combination facilitates the rapid sort-
ing of electrical components.
.
The jig is also useful for measurements on small
capa'citors because of
its
small zero capacitance and be-
cause the unknown component is positioned and shielded
to
make repeatable measurements possible.
3.4.2 INSTALLATION. The test jig is connected to the
bridge UNKNOWN terminals by means of the shielded
Type 274 Connector attached to ·the jig.
A three-ter-
minal connection is necessary. The third connection is
made by me.ans of the screw, located directly below the
UNKNOWN terminals, and the lug on the shield of the
connector.
This screw makes the ground connection to
the jig and also holds the connector in place.
The leads of the test jig can be routed through
cable clamps secured by the fluted panel screws so that
the jig can be located directly in front of the bridge with-
out interference from the leads.
3.4.3
RESiDUAL IMPEDANCES OF TEST JIG.
The
residual resistance of the leads is about 80 milliohms
(total) and the inductance
is
about 2 flh. The zero ca-
pacitance, when the leads are connected to the-·bddge,
. is approximately 0.2 pf.
The shielded leads cause a
capacitance
to
ground of about 100 pf each. Corrections
may be necessary for the residual
resi~tance
and induc-
tance when measurements are made on low impedances
(see Table 2-5).
The capacit"ances to ground cause an
error of 0.07% for capacitance measurements, but can
1
cause a D
~Q)
error up to about 0.004 for inductance
measurements (see Table 2-6).
3.5 MEASUREMENTS ON GROUNDED COMPONENTS.
If the component to be measured
is
grounded, the
cabinet of the Type 1608-A must be disconnected from
ground.
To do this, open the link between the rear ter-
minal labeled 3RD WIRE GROUND and the adjacent ter-
minal tied to the chassis.
The 3RD WIRE GROUND
should be grounded externally if an ungrounded, two-wire
power cord
is
used (refer to paragraph 2.1. 2).
If the LOW UNKNOWN terminal
is
grounded there
is no error due to the capacitance of the bridge to
ground, but there is a residual meter deflection due to
internal hum pickup in the bridge as well as external
hum pickup to the bridge chassis which can usually be
removed by grounding of nearby equipment.
This hum
pickup can become very large when high-impedance
components are measured.
SPECIAL MEASUREMENTS
There
is
less hum pickup in the measurement of
high-impedance components if the other (unlabeled) UN-
KNOWN terminal
is
grounded.
However, the internal
capacitance of the bridge. chassis to ground (approxi-
mately 300 pf), plus any external capacitan"ce from the
chassis to ground, will shunt one arm of the bridge,
causing an error given in Table 2-6.
Even
when the bridge is floating, the bridge
chassis can be used as a guard terminal for three-ter-
minal or remote measurements.
3.6 LIMIT TESTING.
The Type 1608-A can be set up to provide a go-no-
go indication useful for component setting.
The panel
meter is used as the indicator.
The procedure is as
follows:
a. Balance the bridge with one of the components
to be measured (preferably one within tolerance).
b.
Offset the CGRL setting by the desired toler-
ance, if the tolerance is symmetrical, or by one half of
the total allowable spread if unsymmetrical.
c.
AJ.just the DET SENS control for five-divi-
sion meter deflection.
d.
Set the CGRL dial to the center value (the
nominal value if the tolerance is symmetrical).
e. Connect each component to the bridge (or Type
1650-Pl Test Jig).
If the meter deflection is less than
five divisions, the component
is
within limits.
When the unknown has a tolerance greater than
±1O%, the limits may be in error by more than 1% if the
above method is used.
A sure method is to set the
CGRL dial so that unknown components at both limits
give the same deflection.
3.7
MEASURING RESONANT FREQUENCY AND RE·
SONANT IMPEDANCE OF TUNED CiRCUITS.
The resonant frequency of a series or parallel run-
ed circuit can be found with the use of an external vari-
able-frequency oscillator. Either the G p or R s bridge may
be used (depending upon the desired quantity). Connect
the
~xternaI
generator to the _EXT GEN terminals and
set the function switch to EXT AC.
Set the Q balance
adjustment to zero, and null the bridge using the con-
cefl.tric CGRL controls and the frequency adjustment on
the oscillator.
.(\t null the bridge reads
th~
effective R s or G p of
the tuned circuit at that frequency where the tuned cir-
cuit is resistive.
The resonant frequency is indicated
by the variable-frequency oscillator.
The accuracy of
the R s or G p reading depends on the test frequency
(refer to paragraph 2.5.5) and the accuracy of the re-
sonant frequency depends on the Q of the tuned circuit,
and
is
limited to the frequency change that would give a
measurable change in the bridge
Q
adjustment (±0.0005
f
1 kc' above 1 kc).
27
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