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3.10
MEASUREMENT O F GROUNDED COMPONENTS.
If the component to be measured i s connected
directly t o ground, the comp0nen.t may be measured
with the c a s e of the 1650-B floating off ground.
Either unknown terminal of an unknown capaci-
tor may be grounded.
Grounding the low terminal tol-
erates large capacitance from the c a s e t o ground, but
increases sensitivity t o hum.
However, most of the
hum can be removed by the internal 1-kHz filter in the
amplifier.
Grounding the other unknown terminal de-
c r e a s e s sensitivity t o hum, but a capacitance of 1000
p F from the c a s e t o ground c a u s e s a 1% capacitance
error (paragraph 4.6).
If the unknown i s an inductor, the LOW terminal
should be grounded.
Even when the bridge is floating, the bridge
panel can be used a s a guard terminal for three-termi-
nal or remote measurements.
3.11
USE O F THE TYPE
1650-PI
TEST JIG.
3.1 1.1 GENERAL.
T h e Type 1650-P1 T e s t Jig (Figure 3-11) provides
a means of making quick connections t o the bridge with
a pair of conveniently located c l i p terminals. When the
1650-B is s e t u p for limit measurements (paragraph
3.12), the combination facilitates the rapid sorting of
electrical components.
The jig is a l s o useful for measurements on small
capacitors because of i t s small zero capacitance and
because the unknown component is positioned and
shielded t o make repeatable measurements possible.
3.1 1.2 INSTALLATION.
The t e s t jig i s connected t o the bridge UN-
KNOWN terminals by means of the shielded Type 274
Connector attached t o the jig.
A three-terminal con-
nection is necessary. The third connection is made by
means of the screw, located directly below the UN-
KNOWN terminals, and the lug on the shield of the con-
nector.
T h i s screw makes the ground connection t o
the jig and a l s o holds the connector in place.
The leads of the t e s t jig may be brought around
in back of and underneath the bridge s o that the jig
may be located directly in front of the bridge without
interference from the leads.
Figure
3
-
11.
T y p e
1650-P
1
T e s t Jig.
3.11.3 RESIDUAL IMPEDANCES OF THE TEST JIG.
The residual resistance of the leads i s about 80
m n (total) and the inductance i s about 2 pH. The zero
capacitance, when the leads are connected to the
bridge, is negligible (=0-2 pF).
The shielded leads
c a u s e a capacitance t o ground of about 100 p F each.
Corrections may be necessary for the residual resis-
tance and inductance when measurements are made on
low impedances (paragraph 4.10).
The capacitance t o
ground c a u s e s no error for capacitance measurements,
but can c a u s e a D (1/Q) error up to about 0.007 for in-
ductance measurements (paragraph 4.6).
3.12
LIMIT TESTING.
The Type 1650-B may be s e t up to provide a go-
no-go indication useful for component testing.
The
panel meter i s used a s the indicator.
The setup pro-
cedure is a s follows:
a. Balance the bridge with one of the components
to be measured (preferably one within tolerance).
b. Offset the CGRL d i a l by the desired tolerance,
if the tolerance i s symmetrical, or by one half of the
total allowable spread if unsymmetrical.
c .
Adjust the SENSITIVITY control for a five-
division meter deflection.
d. Set the CGRL d i a l t o the center value (the
nominal value if the tolerance is symmetrical).
e . Connect each component t o the bridge (or Type
1650-P1 T e s t Jig). I f the meter deflection i s l e s s than
five divisions, the component i s within limits.
When the unknown has a tolerance greater than
g o % , the limits may be in error by more than 1% if the
abbve method i s used.
A sure method i s t o s e t the
CGRL d i a l s o that unknown components a t both limits
give the same deflection.
S P E C I A L MEASUREMENTS
3-7
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