2
'AcHf'
-
This flattens the
response
of the A.C.
ampli-
fier used for
AC
voltage measurement.
It should only be
used when a full
calibration i.e. 'Zero',
'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. It must be used
before any DC
voltage or Ohms
calibration is carried
out.
1.
1.3.4
'AUTOCAL' using
'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
with
the polarity
setting
of the DC
calibration
source.
If
the 'DVM
Reading
After Calibration' is not in
accordance
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
'Error
4'
If 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.
In 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. If
'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
Section or the
Servicing
Section of this Handbook.
1.2.2
Equipment
Required
-
1M12 'Lin'
Source.
This is
a
IMfi 5%
resistor in
parallel with a
InF capacitor,
shielded to reduce
noise
interference.
-
10MJ2
'Ib'
Source.
This is a lOMfi 5%
resistor in
parallel with a
InF capacitor,
shielded
to
reduce
noise
interference.
Datron products,
number 400391 and
400392,
are
available as 'Lin' and 'Ib'
sources
and are recommended.
-
A DC
Calibration
Source, e.g.:
Datron
4000/4000A
Autocal Standard.
1.2.3
Checking 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.
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