Datron 1061 - Test

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3.3.4
High
Frequency
Compensation
During
the
calibration cycle,
the
microprocessor
notes
and
stores
the
À;gh
lr"q;"cy
(HF) error
of
each
range.
when
AC volts
is
ielected
the
compensation
inform-
at¡on
for
a
particular
range
is recalled
by
the
micropro-
cessor,
transferred
u.ror,
ti.
isolation
barrier
and
latched
on
to
M13,
M14
(Drawing
No.
430328
sheet
5),
see
Fig'
3.26.
As
in
the
case
of tñe lnput
Current
Compensation
(section
3.2.2.s|,
the
output
from
trre
latches
is
applied
to
a
digital-to-analog
converter,
AN2.
The
voltage
produced
is
3.3.5
Frequency
Detection
(430402
sheet
2)
The
signal
frequency
is monitored by M10 which
is
set
so
that
a
signal
frequency
greater
than SkHz
causes a
logic
'1',
(0
volts)
on
Ml0
-
4. This signal indicates
to
the
Digital
Board
via
M18,
M2
(Drawing
No. 430328
sheet
5)
which
one
of
the
two
sets
of specifications
should
be
used
for
calculating
the
measurement uncertainty
when
the
SPec
keY
is dePressed'
fed to
the
AC
converter
via
connector
Jl
pin
1
1
and
applied to varicap
D11.
The
varicap
is
thus
adjusted
to
give
the
amplifier
chain
a flat
frequency
response.
The
calibration
is
carried
out at one
H.F.
frequency
but
since it
flattens
the
AC
amplifier
response,
the
correc-
tion
is valid
for
all
specified
frequencies.
lt should
be
noted
that the calibration
routine
is
iterative since
the
varicap
is non-linear.
3.3.6
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 .tV
range
as described
in
Section
3'2.1
.3. Filter is
selected
and
F.E.T.
O31
is
'closed'from
M5
-
13 causing
a signal
of
0.08
volts
DC
to
be
injected
into the
preampli'
fier. Thus
a
signal
of
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 meas'
ured
and
compared
with
a
stored
value.
lf the
measured
signal
is
q¡i1þi¡
+67o
of
the
stored
value, the
test continues
with
a 1V
range
check.
Output
from RMS
section
+3.14
volts
+0.314
volts
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Range
.1
1
CALIBRATION
MEMORY
MICBOPBOCESSOR
D-A
019
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A
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SIMPLIFIED
DIAGRAM
OF AC
HIGH
FREOUENCY
COMPENSATION
I
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M11
FtG.3.26
o
From
To
RMS
Section