Datron 1061 Calibration And Servicing Handbook page 36

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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