Table of Contents
Advertisement
Available languages
Available languages
31
3.
Service
data
3.1.
CIRCUIT DESCRIPTION
(see
fig.
25)
The
measuring
bridge
PM
6302
is
made
of:
—
a
switchable bridge
arrangement
—
a
switchable zero
indicator
—
a
supply
voltage generator,
1
kHz/100 Hz
and
1.5
V
d.c.
—
a
conversion
facility
for searching
and measuring
—
a
power
supply.
3.1.1.
Bridge
arrangements
There
are
three
selectable
measuring
ranges,
viz:
R
measurements,
C
measurements and L
measurements.
The
basic set-up
of the
arrangements
for
C
and L measurement
(for
reactances)
is
illustrated in
figure
7.
In this case,
the four bridge
parts,
the
supply source and
the
indicator are
illustrated
for
C
measurement
as far
as
the
potential
is
concerned.
The same
arrangement
applies for
L
measurement,
except
for the
fact
that
C515
and
R713
are
interchanged.
This
illustration
can be used
combined
with
fig.
8
for
R
measurement; assume
C515
and
R713
interchanged,
fixed
resistor
R634
instead
of
R713
and
bridge supplied
from
a
floating
d.c.
voltage source.
3.
1. 1.
1.
R
measurement
The
Wheatstone
bridge
(Fig. 8)
comprises
resistors
701-71
1
for
measuring
ranges
in
decade
steps.
They
determine
the coarse
measuring
range
and form
together
with
the
sample
(actual resistance)
one
arm
of the
bridge.
The
other
one
is
formed by components 634
and
71
3 + 636.
Fixed
resistor
634
is
adjusted with
635
and
658, while
the
initial
resistance of
potentiometer
713
is
adjusted
with
resistors
637
and
659
and
636.
Both
adjustments determine measuring
points
1
and 10
of
the
linear
scale.
The
bridge for
R
measurement
is
supplied with an
internal
d.c.
voltage.
The
diagonal voltage passes
through
a
dc-ac converter before entering the input of the
indicator amplifier.
Arrangement
in
searching
mode
for
R measurement,
see 3.1.4.
3.
1.
1.2.
C
measurement
The
dc Sauty-bridge
(Fig.
9)
comprises
the
same
measuring
range
resistors
701-711 and mostly
complex
sample
C
x
in
the
(left)
arm
of
the
bridge.
The
other
arm
comprises
components 713
+ (636//637//659)
and
515
in
series
with
712/A
or
712/B.
As
a
result
of
this
both
bridge
arms
are
made
of
RC
components which
divide
the
supply
voltage equally
and
in
the
same
phase,
provided the time constants
are equal.
The
diagonal voltage
between
P
and
earth
is
then
0
V.
The
results
in
adjusted
and
not
adjusted
state are vectorially
shown
in
figure
10b and
10c.
These
figures
apply
for loss-free
samples.
For
lossy
capacitances
a
phase adjustment
by
means
of
tandem
potentiometer
712/..
is
required.
This
adjustment
simulates an attenuation of adjusting capacitor 515.
For
correctly adjusted phase, the
simulated attenuation
equals that of the
sample
(Fig.
1
1-b)
and
its
angle
loss
and
tangent
values are equal;
potentials
0
(i)
and
P
compensate
each
other.
Tandem
potentiometer
712/..
is
marked
in
tan5
=D
values;
The
attenuation range
is
switchable
with
push-
button
D=
801/F.
The
end
values of the ranges
are
adjusted
with
resistors
633//712/A and
632//712/B.
The
frequency
of
supply
generator
312-314
is
converted
from about
1
kHz
to
about 100
Hz
by
depressing
button
D
(see
also
3.1.3.}.
The
calibration
of
712/..
in
D
values
depends on
the
frequency of
the
supply
voltage to the bridge;
therefore
pay
attention
to
this in
case of
checking
or external bridge supply.
The
calibration
of
adjusting
potentiometer
71
3
is
almost independent
of the
frequency
of the
supply
voltage.
Two
examples
of
a
not-adjusted
de Sauty-bridge
are
shown
in Fig.
11-c
by
dotted
and
chain-dotted
vectors.
The
other vectors
represent the voltage
division
of the bridge arm,
in
which
the
sample
is
present. In
the
first
case,
the simulated
losses
are
greater,
while
in
the second
case
they
are
smaller
than the
losses
(attenuation)
of the sample.
Advertisement
Table of Contents
