Test - Datron 1061 Calibration And Servicing Handbook

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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
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1
CALIBRATION
MEMORY
MICBOPBOCESSOR
D-A
019
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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