Datron 1061 - Page 9

2
'AcHf'
'
This
flattens
the
response
of
the
A'C'
ampli-
fier
used for
AC
voltage
measurement'
lt
should
only
be
used
when
a full calibration
i.e'
'7ero',
'Gain'
and
'AcHf'
is
carried
out.
As
with
'lb'the calibration
action
is iterative
and
requires several operations
of
the
key
to
complete'
'Lin'
'
This
is
an
important
calibration
operation
as
it
optimises
the basic
linearity
of
the
internal
measurement
circuitry
used
for all ranges
and
functions.
lt
must
be used
before any DC voltage or Ohms
calibration
is
carried out'
1.1.3.4'AUTOCAL'
usins'KEYBOARD'
This is
an extension
of
the
'AUTOCAL'
process
which is useful
when
using
a
calibration
source
set to a
nominal value but with known
errors.
This
means
for
example that
calibration
directly
to
a standard
cell
is
possible.
A
full explanation
of
the
procedure
is covered
in section 1.7.
1.1.3.5
'AUTOCAL'over the Bus
Each
of
the
five
calibration
operations
can be control-
led
using Option
50,
the IEEE
bus. This
means
that the
instrument can be
entirely calibrated
remotely
or under
program
control. As mentioned
in the
'Procedure
Outline'
for a
manual
calibration,
the
rear
panel
address
switch
should
be
set to 31,
i.e. all 1's.
When
a bus
calibration
is
required
the
address
switch
must
be
set to the
address
number assigned
to
the DVM
in the
system.
More details
of calibration
with the
bus
are included
in section 1.8.
1.2
DC
VOLTAGE
CALIBRATION
1.2.1
General
The
procedure in the table opposite
is all that
is
necessary
to
completely
'AUTOCAL'
the
DC
voltage
function. Steps
1 and
2 affect the accuracy
on all ranges
and should
therefore
be carried out even
if
just
one
range
is
being
calibrated.
On
each
range
a
'Zero'
and
'Gain'
calibration
is
required
for each
polarity
of input. The
two
'Zero'calibrat-
ions
are
included
to overcome a
possible
zero
difference
w¡th
the
polarity
setting
of the
DC
calibration
source.
lf
the
'DVM
Reading After
Calibration'
is not in
accordancr
with
the
table, repeat
operations
of
the same
'CALIBRATE'
key
are
permissible.
Where
no tolerance
is
shown
in this
column,
only
the
exact
reading
quoted
with
an
occasional
least
significant
digit
showing
is to be
expected.
1.1.3.6
'Er¡o¡
4'
lf during
calibration
'Error
4' is
displayed,
this
indi-
cates
that
the
Calibration
Source deviates too
far
from
the
calibration
span
of
the
instrument.
Under
these
circum-
stances,
the
calibration
memory
is not updated
and
the
instrument
goes
into 'Hold'
with the calibration
button
calibration
key
LED remains
on.
ln the case of
'Zero',
'Gain'
or
'AcHf'the Calibration
Source
should be checked and the same
'CALIBRATE'
key
repressed.
The
'Hold'
mode may be
released
any
time
and the instrument
will
free
run again.
lf
'Error
4'
follows
'Ib'
or
'Lin'or persistently
appears following
'Zero',
'Gain'
or
'AcHf'
then
an instrument failure
may
have
occurred.
Therefore either consult our Customer
Service
Sectíon
or the Servicing
Section
of this Handbook.
I
1.2.2
Equipment
Required
-
lMO'Lin'Source.
This
is a
1MO 5%
resistor in
parallel
with
a
1nF
capacitor,
shíelded
to reduce noise
i nte rfe rence.
-
10MO'Ib'Source'
This
is
a
10MO
5%
resistor
in
parallel
with
a
1nF capacitor,
shielded
to
reduce noise
i
nte rfe re
nce.
Datron
products,
number
400391
and
400392,
are
available
as
'Lin'
and
'Ib'
sources
and
are
recommended.
-
A
DC
Calibration
Source.
e'g':
Datron
4000/40004
Autocal Standard.
1.2.3
Checkíng
Accuracy
after'AUTOCAL'
To
check
the
accuracy
after
'AUTOCAL'the
'Specification
Verification'
section
of
the
User's
Handbook
will
be useful;
it
provides
tables
for
quick reference
of
accuracy
on all
ranges and
functions
in displayed
digits'
I
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