BK Precision 177/V-95 User Manual

CIRCUIT
DESCRIPTION
The
100 microampere
meter
movement
is connected
in the
plate
circuit
of
a
L2AU7
twin
triode
in
a balanced
bridge
arrangement.
The
zero
adjust
control
sets
up
a balance
between
the
two triodes
so that
with zero
voltage
applied
to
the first
grid,
the
potentials
on
each
plate
are
equal.
There
will
be no
voltage
drop
or
difference
in
potential
across
the meter,
and consequently
the meter
will
read
zero.
with
a
r,oltage
applied
to the first
grid,
the
balanced
condition
is
upset
causing
a difference
in
the
potentials
on
the two
plates
and consequently
across
the meter.
The
meter
will
then indicate.
The relationship
between
the
test
voltage
applied
to the
first
grid
and
the current
through
the
meter
is linear
and
therefore
the
meter
is
calibrated
with
a linear
scale.
one of
the advantages
of
a vacuum
tube
voltmeter
circuit
is the voltages
to be
measured
are
applied
to
the tube
and not
directly
to the meter.
since
the
amount of
current
a vacuum
tube
can
draw
is limited,
the
meter
movement
is
electronically protected.
The
maximum
test voltage
which is
applied
directly
to the L2AIJ7
is
approx_
imately
1.5 volts.
A voltage
divider
network
having
a total resistance
of
l0
megohms
reduces
voltages
higher
than 1.5
volts.
An
additional
isolating
resist-
ance of
1 megohm,
located
in
the test
probe,
is used
in
the DC
position,
making
it
possible
to
take measurements
in
circuits
with
R-F
components
with
a
min-
imum
disturbance.
AC measurements:
D3
and
D4
are used
to rectify
the test
voltages
providing
a DC
voltage proportional
to
the
applied
AC.
The DC
voltages
is
then
applied
through
the voltage
divider
network
to
the input
grid
of
the
L2ALJ7
balanced
bridge
circuit
causing
the meter
to indicate.
The
AC voltage
scales
are
calibrated
to read
both
RMS
and Peal<-to-Peak
'alues.
The
0-1.5v
and 0-5.0V
RMS
low
AC
scales
have
been
especially
calibrated
to improve
the
accuracy
of
the meter
on
these low
ranges.
stray
pickup
reduces
the
accuracy
of
any highly
sensitive
vrvM
on
the lower
AC
ranges.
with
this
special scale
you
have
improved
accuracy
that
many
other
instruments
do
not have.
In
the
0-1.5,
0-50,
and 0-1b0
volt
ranges,
the full
AC voltage
being
measured
is
applied
to
the diode
rectifier.
A voltage
divider
network
reduces
the voltage
on
the
0-500,
and
0-1500
voltage
ranges
to limit
the voltage
applied
to
the diode
to
a
safe
level.
when
the instru-
ment
is
used
properly,
it is
not
possible
to
apply more
than
150 volts
to the
diode.
when measuring
any
unknown
voltage,
always
make it
a
habit
to start
on
the highest
range,
and then switch
down
to
a
more
appropriate
range.
For
measuring
resistances,
a 1.5 volt
DC supply
is
connected
through
a series
of multiplier
resistances
and
the external
resistance
to be
measured.
This forma
a voltage
divider
circuit
consisting
of
the
l.s volt
supply
in
series
with one
or
more
multiplier
resistors
and
the resistance
under
test.
The voltage
across
the
unknown
resistor
is then
proportional
to its resistance
This
voltage
is
supplied
to the input
grid
of
the 12AU7
balanced
bridge
circuit
which
produces
an ohm-
meter scale
reading
proportional
to the
unknown
resistance.
rn
the
"off"
position
the meter
movement
is
automatically
shorted
to
preven,t
damage
in
transit.
II

BK Precision 177/V-95 Specifications

General

Brand	BK Precision
Model	177/V-95
Category	Measuring Instruments
Language	English