Datron 1061 - A3.3.4 High Frequency Compensation; A3.3.5 Frequency Detection A29; Test

A29
:.
. .
The
buffer
output
voltage
(3.12V
full
range)
is
developed
across
R52-R56
and R7ò,
referred
to
Output
Common
at
M4
input.
Log-feedback
stage
M4/M3
closes
the
'square-Root'
loop,
pro-uiOing
feedback
current
for
the
RMS computation
in
M I
l.
When
the
AC,
or
DC-coupled
AC option
is
selected,
03 connects
the
buffer
output
to
the
Analog.to.Digital
converter.
Test
links
TLC,
D,
E and
F are
selectively
removed
at
manufacture
to set
the
correct
output
level.
M15
M17
M1?
Fig.
43.24
SIMPLIFIED
DIAGRAM
OF AC
FILTERS
#
i1
I
43.3.4
High Frequency Compensation
M20
fo RMS
3.crbñ
I
s
o
L
A
T
I
o
N
B
A
n
Â
I
E
ß
Fig.43.26
SIMPLIFIED
DIAGRAM
OF
AC HIGH
F REOUËNCY
COMPENSATION
CALIBRAfION
MEMOñY
MrcRoPhocESsoft
The calibration
is carried out
at
one
H.F.
frequency
but since
it flattens the AC
amplifier
response, the correction
is valid
for all
specified
frequencies. lt should be noted
that the
calibration
routine
is iterative
since
the
varicap
is non-linear.
43.3.5
Frequency
Detection
(430552
sheet 2l
The
sígnal
frequency
is monitored
by M10 which is
set so that
a signal
frequency
greater
than
2kHz causes
a
logic'1',
(0
volts) on
Ml9-4. This
signal
indicates
to the
Digital
Board via M18,
M2
(Drawing
No. 430328
sheet 5)
which
one of
the two sets
of
specificatíons
should
be
used
for calculating
the measurement
uncertainty
when
the
Spec
key
is depressed.
43.3.6
Test
During
the
self-test
routine
(actuated
from
the front
panel
or
remotely
programmed)
the
AC assembly
is
checked
for correct
operation.
The
circuitry
is
placed
into
the
,lV
range as described
in Section
3'2'1.3.
F'E.T. O31 is
'closed'
from M7-13
causing
a
signal
of 0.08
volts
DC to be
injected into
the
preamplifier.
Thus
a signalof
approximately
3.14 volts
is
output
from the RMS
section
and applied
to
the A
-
D
converter
situated
on the
Analog assembly.
This
signal
is then measured
and
compared
with a stored
value.
lf the measured
sígnal
is within
*6% of the stored
value,
the test continues
with
a
1V range check.
During
the
calibration
cycle,
the
microprocessor
notes
and
stores
the
high
frequency
(HF)
error
of
each
range.
When
AC
volts
is
selected the
compensation
inform-
ation
for
a
particular
range
is recalled
by
the
micropro.
cessor,
transferred
across
the
isolation
barrier
and
latched
on
to
Ml3,
M14
(Drawing
No.430328
sheet
5),
see Fig.
3,26.
The
output
from
the
latches is
applíed
to
a
digital.to-
analog
converter,
AN2'
The voltage
produced
is
fed
to
the
Ác
converter
via
connector Jî
pin
'11
and
applied
to
varicap
D14.
The
varicap
is thus
adjusted
to
give
the
amplifier
chain
a
flat
freguency
response.
Range
.t
1
Output
from RMS section
+3.14
volts
+0.314
volts