3-1
GENERAL
The circuit of this vollmeler includes a two-step
voltage divider in the input. a stabiiized broadband
amplifier, a ret.:Hfier and meter circuit, and a
regulated power
supply. A
rrangcment of the circuit
is shown in block diagram form in Figure 3-1. and
in detail on the schematic diagram.
The voltage under measurement is applied to the
vollmeter at the input terminals. On the lower ranges
the voltage is coupled directly to the grid of a cathode
follower, the cathcxie of which is cOlUlccted as a volt
a�e divider tapped for six outputs.
On
the higher
ranges the voltage is reduced to a thousandth of its
value at INPUT before it is applied to the grid of
the cathode follower.
011
of
the six-tap divider the
voltage is coupled to
a
four-stage amplifier. The
outfAlt
of
the :lmpllflp.r feP.ds into a full-wave rectifier
bridge with a dc milliammeter across its midpOints,
and
a current proportional to the input voltage flows
through the .meter movement. The meter is so
calibrated that the resulting deflection indicates
Sect.
III
Page
1
SECTION '"
THEORY OF OPERATION
the rms value of a sine-wave voltage applied at
INPUT.
The circuit of the voltmeter is discussed in greater
detail in the following paragraphs.
3-2
INPUT VOLTAGE DIVIDER
The input voltage divider consists of a 1000:1 re
sistive voltage divider feeding into the grid of tube
VI,
and
a six step resistance voltage divider feeding
into the first stage (V2) of the amplifier. The
6
step
voltage divider is connected into the cathode circuit
of VI, which is arranged
as
a cathode follower. Con
nections to both resistive dividers are set up by the
DB
VOLTS switch,
by
means of which the circuit
may be arranged to operate on anyone of twelve
ranges.
a.
1000:
I Voltage Divider -
the
VOLTS
switch on anyone
of
the six lower ranges (.001 volt to .3 volt), section
VOLTAGE
AMPLIFIER
RECTI FIER
115 -230V
50 -1000'"
POWER
SUPPLY
V6
DIVIDER
VI
V2,V3,V4,V5
_
_
___
_
.--,._._._._J
--+--
VOLTAGE
REGULATOR
V7 ve V9
Figure 3-1.
ModeI400D/H/L Block Diagram
AND
METER
UT
�
REPRO
