HP 400D, Инструкция по эксплуатации и обслуживанию

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2-1 CONTROLS AND TERM1NALS
ON
This toggle switch closes the primary circuit of
the power transformer. With the switch ON, the
red pilot lamp will glow.
This rotary switch connects the proper multiplier
resistors into the circuit for the desired voltage
range. The position of the switch indicates
1)
the
full scale voltage of the range in use and 2) the db
level, when the meter pOinter is at zero on the
DECmELS
scale. Limits of each range are shown
in
Table 1-1.
INPUT AND OUTPUT TERMINALS -
The two binding posts designated INPUT are con­
nected to the input circuit
of
the instrument. The
two biirling posts deSignated OUTPUT are the output
terminals for the amplifier. The lower binding post
in
each pair, designated
G
is
connected to the chassis.
The binding posts will accommodate either a banana
p
\
ug or wire, and are so arranged that any double
banana plug with a
3/4
inch spaCing may be used.
CAUTION
The maximum voltage (the sum of the dc voltage
and ac peak voltage) applied to the input terminals
of
the instrument must not exceed 600 volts. Higher
voltages will break down the capacitors in the input
system of the instrument.
FU
S
E
-
The fuseholder, located on the back of the instru­
ment, contains cartridge fuse, which is in the power
transformer primary circuit. Heplacement fuses
must be of the" Slo-Blo" type as speCified in the
Table of Replaceable Parts.
Sect. II Page 1
SECTION 11
OPERATING INSTRUCTIONS
2-2 OPERATION
NOTE
When the Mcxiel 400D or 400H is turned off the meter
pointer should indicate zero.
If
it does not, refer
to the correct zero adjustment procedure inSecUonN,
paragraph 4-2.
The Model 400L Meter pOinter adjustment screw
is
not connected to anything. The proper adjustment
is made by the meter movement manufacturer.
After the Model 400D or 400H is turned on, the
meter pointer may show an indication of as much
as two scale divisions, principally on the one milli­
volt range. This
effect is
normal and does not
impair the accuracy of the instrument.
On the lowest three ranges of the instrument the
high input impedance coupled with the gain of the
amplifier causes the meter needle to be forced
against the right-hand stop of the meter when the
input terminals are unshielded. This condition is
normal
and
Is caused by stray voltages
in
the vicinity
of
the instrument.
If
measurements are made from a high-impedance
source, hum pick-up can affect the meter indication
because of the high impedance of both the source
and the voltmeter. Shielded leads will reduce pick­
up, although they will cause an increase in the
capacity shunted across the source, with the pos­
sibility of excessive circuit loading.
In
order to maintain accuracy of measurement,
it must be kept in mind that the instrument Is an
average-responding device but that the meter is
calibrated in terms of the rms voltage of a pure
sine wave. If the waveform
of
the voltage being
measured contains appreciable harmonic voltages
or other spurious voltages, the meter indication
will deviate from the true rms value on the order
indicated by Table 2-1.