Datron 1061 - Page 36

28
I
I
.
I
I
I
l
:
I
I
I
I
t
I
i.
I
i
I
I
ì
t
r
I
t
t
ç
3.3.3
RMS Convertet
(430402sheet
2)
The
RMS converter
takes
the scaled
AC signal
from
the
preamplifier
and
converts
it to an
equivalent
DC signal
suitable
for Analog'to-Digital
conversion.
The
conversion
technique
is
electronic
true
RMS
sensing
as
shown
in the
simplified
block
diagram
Fig. 3'25.
MB
and
l\49
form a
summing type,
full wave recti-
fier. The
output
of
M8,
a
precision
half-wave
rectifier
inverter,
is summed
with
the
non-inverted signal
with
a
weighting
of
2:
1at
the
input of M9' This forces a full-
wave
rectified
current
to
flow
in
RMS module
M6'
Potent'
iometer
R50
balances
the
rectifier to
provide
the same
output
for
non-inverted
or
inverted asymmetric
waveforms.
The
output
current
from
the RMS
module
passes
into
filter-buffer
M1
and
is converted
to a nominal
5
volts
for a
full range
signal.
01
and
02 switch
in additional
capacitors
when
FILTER
is selected,
to operate
down to
45H2.
M2
is
a
voltage
to current
converter
providing
a
feedback current
to
the
RMS
module
proportional
to
the
output
voltage.
R90
is the
zero adjustment
for the half
wave
rectifier
Mg
and
R35
is the
high crest
factor
gaín
adjustment.
R75
is adjusted
for optimum
linearity.
The
output
of
Ml
(TP2)
is
fed to
a resistor
chain
R1
-
R7,
to
provide
an output
of
3.14
volts
by the
selection
of
resistors
R2
-
R5.
03
is turned
on
when
AC
is selected
and switches
the
output
of
the AC
converter
into the
Arralog-to-Dig¡tal
Converter
(Drawing
No.
430328
sheets 3
and
4).
F¡G.3.23
SIMPLIFIED
DIAGRAM
OF
THE
AC
PREAMPLIFIER
SCALING
R95
R110
8109
R114
RL5
RL6
RL4
1KV
c57
RL3
R96
Rl1
10v
100v
RL3
io FrequencY
Compensation
Sect¡on
o30
1O0mV
015.016
O20
to
O24
O32 ro O34
R
123
to
R
126
Log
Anti
-
Log
Log
Log
FIG.3.25
BLOCK DIAGRAM OF RMS
CONVERS¡ON
TECHNIOUE
Vf
vx
log