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SECTION
2
OPERATING
2.1 INSTALLATION.
2.1.1 POWER CONNECTIONS. Connect the bridge to a
suitable power source as indicated on the plate above
the power receptacle on the rear of the instrument (115
or 230v, 50-60 cps).
A three-wire power cord is sup-
plied.
2.1.2 GROUNDING. The bridge should generally be op-
erated with the bridge chassis grounded except in spe-
cific cases where the unknown component or a de bias
supply should be grounded (refer to paragraphs 3.1. 5 and
3.5).
The ground connection is made through the three-
wire power cord to the 3RD WIRE GROUND terminal on
the rear of the instrument. This terminal should be con-
nected to the adjacent CHASSIS terminal unless the
bridge must be ungrounded.
If
the three-wire power cord
is not used, this connection should be made externally.
2.1.3 MOUNTING. The instrument is available as either
the Type 1608-AM, for bench mounting, or Type 1608-AR,
for relay-rack mounting.
The bench-mounting model is
equipped with aluminum end frames, while the Type
160B-AR
includes mounting brackets for relay-rack in-
stallation.
I~structions
for assembly accompany these
brackets, which may be ordered separately (Type ZSU-6-7)
to convert from bench to rack use.
Type ZSU-6-7 mounting brackets are of a unique
General Radio design which permits the instrument to be
pulled out on slides for service. Eith"er chassis or cabinet
can be removed from the rack independently of the other.
2.2
INTERPRETATION OF ·X· IN READ-OUT.
The main CGRL indication consists of up to five
digits displayed in an in-line read-out.
Th~
three left-
hand digits are controlled by the larger of the two con-
centric CGRL controls; the two right-hand digits are
controlled by the smaller (vernier) control.
To provide
an overlapping transition from full-scale vernier reading
(99) to the next higher coarse step, the vernier read:out
extends beyond 99, up to 106. To avoid the ambiguity of
two digits on the same counter, an X is used in place of
the number 10.
To interpret a reading containing an X,
simply substitute 0 for the X and add 1 to the digit
im-
mediately to the left of the X.
For example, 102X3 :::
10303; 99X2 :::10002.
The letter X is also used on two of the three Q
OPERATING PROCEDURE
dials used with the R s and G p bridges. Here again, sub-
stitute 0 in place of the X and add 1 to the digit to the
left of the X.
For example, .IX4 :::.204; .2XX:::.310.
Users may find it helpful to record measurement
data exactly as it appears on the bridge read-out, in-
cluding any X's that appear.
In that way, any possible
error in the interpretation of the X can be rechecked.
2.3
DC RESISTANCE MEASUREMENTS.
2.3.1 PROCEDURE.
a.
With the function switch (1, Figure 1-1) off,
check the NULL meter mechanical zero position, and,
if necessary, center the pointer with the screw-driver
adjustment on the meter.
b.
Turn the DET SENS control almost fully
counterclockwise.
c.
Set the BRIDGE SELECTOR switch to R s for
resistance measurements from 0 to 1.1
MD
and G p for re-
sistance measurements above 1
MD
and for conductance
measurements from 0 to 1.1 mho.
d. Connect the resistor to be measured to the UN-
KNOWN terminals.
e. Turn the function switch to !NT DC.
NOTE
As the function switch is rotated from OFF to
INT DC, it passes through an undetented posi-
tion where the circuit is operative but the
meter sensitivity is greatly reduced.
A pre- "
liminary balance may be made with the switch
in this position instead of with the DET SENS
control turned down.
f.
Adjust the FULL SCALE RANGE switch and
the
concentric CGRL balancing controls for a zero
(center) reading, and adjust the DET SENS and GEN
LEV controls for increased sensitivity as necessary.
A meter deflection to the right indicates that the un-
known is larger than the indicated CGRL dial setting.
For greatest accuracy the" reading should have at least
four digits showing. If not, turn
to
the next lower range.
g. The value of the UNKNOWN is read directly on
the counter with the decimal point correctly located and
the unit illuminated above. The meaning of an X indica-
tor is explained in paragraph 2.2.
9
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