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hlodcl4 12A
SECTION 111
0
PER
AT1 N
G
3-1. INTRODUCTION.
3-2. The
-lip- Model 412A/AR DC Vacuum Tube
Voltmeter nieasures dc voltages from 1.0 mV full scale to
lo00 V full scale with an accuracy of
1%
of full scale.
Current measurement ranges are from 0.001 mA full scale
to
1000
mA full scale, with accuracy of 2% of full scale.
The Model
41
2A/AR makcs resistaricc measurements from
1.0 ohm center scale to 100 megohms center scale.
Resistance measurenicnt accuracy is
5% of
reading between
.3 and 3
on
the ohms scale.
A
dc amplifier output is also
provided.
Voltage
gain of tlic amplificr is from
-1000
to
+1000,
depending
on
range selcctcd. Amplifier output is
1 . O V
at full scale. and maxinium current load is
1
. O mA.
3-3.
LOW-LEVEL ELECTRICAL PHENOMENA.
34. Stray low-level electrical phenomena may cause error
in low voltage measurements. When using the lower voltages
of the Model 412A, consider the possibility of low-level
voltages produced by thermoelectric effects, residual
charges on capacitors, battery action, or flexing of coaxial
cables,
3-5.
The voltagc probe, currentlresistance lead, and
common lead of the Model 412A/AR are all designed t o
have a very low thermoelectric effect with copper, the most
commonly used conductor. However, some component
leads such as transistors and reed relays may have leads
made of such alloys as nickel-iron, which produce a
thermoelectric voltage when joined with copper. Whenever
possiblc, connect tlic
412A
leads to copper. If this is not
possible, the voltage probe and common lead should both
I n : conncctcd
to
the
smic
kind of inctal compncnt lead,
and both connection points maintained at the same
tc
111
pcra t urc.
3 4 . To minimize tlic possibility of battery action when
making
low
voltage mcasurcments, make sure the 412A
probe tip and common lcad alligator clip are clean. Also be
surc tlic component leads or other points of connection are
clean. The prcsence of sonic chemicals such as solder flux
niay cause noticeable nieasiirement error due to battery
action.
NOTE
Operating the Model 412A/AR without
grounding the third (power line ground)
wire of the power cable will result in a
zero offset of the meter and oscillation of
the pointer.
IN
STRU CTiO
NS
3-7. TURN-ON PROCEDURE.
Section 111
BEFORE CONNECTING PRIMARY
POWER, MAKE SURE THE REAR
PANEL 115/230 V SLIDE SWITCH
IS SET TO THE POWER LlNE
V O L T A G E
T O
B E
USED.
INCORRECT
SETTING MAY
RESULT IN DAMAGE TO THE
INSTRUMENT.
a. Make sure the proper fuse is installed for operation
with the power line voltage t o be used. A
0.6 A
slow-blow fuse should be used for I
IS
V
operation, and a
0.4
A slow-blow fuse for 230 V
operation.
b. Connect to ac power and turn instrument ON.
Allow a S-minute warm-up period.
3-8. VOLTAGE
MEASUREMENT.
a.
Set
FUNCTION switch t o VOLTS, and select
proper polarity.
b. Set RANGE switch t o desired range.
If
in doubt,
set
switch t o high range and downrange as
necessary.
c. Connect VOLTS and
COM
leads across circuit or
component, and read voltage.
DO
NOT
OVEKLOAD THE
INSTRUMENT.
MOMENTARY
OVERLOADS UP TO TEN TIMES
FULL SCALE WILL NOT DAMAGE
THE INSTRUMENT; HOWEVER,
C U R R E N T
S H U N T S , AND
I N T E R N A L
R E S I S T A N C E
S T A N D A R D S
A R E
N O T
PROTECTED FROM EXTREME
OVERLOAD.
33. CURRENT MEASUREMENT.
a. Set FUNCTION switch t o MA.
b. Set RANGE switch t o desired range.
If in doubt,
select high range and downrange as necessary.
00 1
29-5
3-1
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