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IV
volts
is
used as a
reference
for the
+
30
V,
+
5 V and
-
17V regulators.
The
-30V
regulator uses
-
17V
as a
reference. Ul02 in the
-
17 V
supply is operated
off raw
supply
thru
CR123
until
the
-30V
supply comes
up
after turn-on. It is then operated
off
-
30 V
thru CRl22.
The
-
5 V supply is zener
regulated from
the
-
l7V
supply. All supplies except
the
-
5 V
supply are voltage
regulated
and current
limited for
protection.
The output
of
each
supply is limited
by a
zener
diode to
protect
the
circuits
it supplies.
+I32. SELF.TEST FUNCTION.
+133.
Seven
tests,
which may be selected
by front
panel
switch
settings or
by optional remote control,
provide
internal
checks on the operation of
many of
the
3490A
circuits. Test
No. I checks
approximately 70%
of the logic
circuits,
and
the
other
six
check
analog
circuits as explained
in the following paragraphs
and
in
Table 4-3.
Model
3490A
4-134.
Logic
Test,
No. l.
4-135. A series of ten
readings,
shown
below,
provide
visible
indication
as
to
whether
the
display and certain
logic
circuits are
operating correctly. Note that the
instrument
autoranges
one
step
for each reading, uprang-
ing through all ranges,
then downranging through all
ranges. Note also
that the numerical
display
changes for
each
range.
In
logic
test, two
factors determine
the
Table
4-2. Polarity
in
Ratio
Measurements.
External
Reference
I nput
I nput
Signal
Ratio
Polarity
Signal
Displayed
Polarity
Measurement
Run-down
Reference
Required
Amplifier
Output
Used
+
+
+
HIGH
LOW
LOW
HIGH
HIGH
LOW
+
none
none
+
Invert. Amp.
Ext. Ref. Amp.
Ext. Ref. Amp.
Invert.
Amp.
Invert. Amp.
Ext. Ref. Amp.
Table
4-3.
Analog Tests.
T€sl
No.
Run-Up Run-Down
DC Amp.
Input
DC Amp.
Gain
DC Amp.
I nput
DC Amp.
Gain
2
J
4
5
6
7
Ground
+
Ref/- Ref
+
Ref
Ground
Input
x
0.01
o
Ref
x1
xl
xl
x 10O
x
100
x10
+
Ref/-
Ref
-
Ref/+ Ref
Input x 1
+
Ref/- Ref
+
Ref
+
Ref
x1
xl
xl
xl
x1
x1
FULL- WAVE
RECTI FIER
cRil9
-
t 20
RECT IFIER
REF
REGULATOR
Figure 4-17.
Power
Supply
Block
Diagram.
+lb,