Datron 4708 User Handbook Manual page 139

remains connected for both
AC
and
DC
nulling the
Thermal
Transfer Standard.
Otherwise
the
procedure
is
similar to that for
DC
Voltage
Calibration.
Alternative
Current
Calibration
(Using Calibrated Standard
AC
Current Shunts)
This
method
required
Standard Current Shunts
which have been
designed
to
give a
flat
frequency response.
Each
current
range
requires
its
own
specific
value of shunt, calibrated
to
develop
either
IV
or
lOOmV
Full
Range
at
LF
and HF.
An
AC
DVM
is
standardized to the
appropriate voltage,
and
the
Current range
is
calibrated
when
the
voltage across
its
shunt
is
correct.
The
method
is
detailed in
Appendix
1
to this
section (page 8-19).
Standardization
To
'Standardize* all
Ranges:
The Voltage procedure
is
used,
but
pressing
STD
instead
of
SET
on
the
1
V/IOV
Range.
CAUTION! Do
not 'Standardize' unless
it
is
necessary for
the
reasons
quoted on page
8-2.
GENERAL NOTES
Remote Sense
is
available
as
follows:
IV lOV lOOV lOOOV
-
Local/Remote Sense
ImV
lOmV lOOmV
-
Local Sense only
All current ranges
-
not applicable
(Local:
2-wire sense.
Remote: 4-wire sense)
Output must be
OFF
to
change sense connection (except that
Remote
changes
automatically to
Local
when
switching
to
Millivolt
Ranges).
Upranging
-
OUTPUT OFF
Default
The 4708
cannot
enter
High-Voltage
state
(>75V
RMS)
with
OUTPUT
ON.
Consequently,
when
ranging-up, the
operating
system allows
the
upranging to occur, but defaults to
OUTPUT
OFF
for
two
specific cases:
a.
When
upranging
to the
lOOOV
Range,
b.
When
altering the output
on
the
lOOV Range
to
a voltage of
75V
or
more.
Otherwise,
OUTPUT
remains
ON
when changing
OUTPUT
RANGE
(refer to
Section
4,
pages 4-8
to 4-9).
High Frequency
Calibrations
Several passes
may
be required
to
achieve satisfactory calibra-
tion,
particularly if
the
initial
errors are large or
the calibration
takes
longer than required
by
the
Transfer
System
in use.
Repeat
procedure
as required.
1000V Range
Calibration
Sequence
LF
calibration
must be completed
first.
However HF1/HF2
bands may,
if
the user requires,
be
calibrated in
reverse
order.
SET mode
must be used
for
700V/HF2.
SPOT Memory
Erasure
To
prevent
unwanted
calibrations
at
obsolete spot frequencies,
it
is
possible to
'Uncalibrate'
any
spot frequency
on any
range.
The
procedure
is:
Select
Zero Output,
set
Output
ON
and
Press
CAL.
When
the
CAL ENABLE
/RUN
switch
is
set to
RUN,
any
selection
of that particular
Spot
F
will
cause the uncalibrated
message
'SEX
—
'
to
be
shown on
the
MODE/FREQUENCY
display.
Preparation
Before any
calibration is
carried out,
prepare the
4708
as
follows:
1
.
Turn on
the
instrument
to
be checked and allow mini-
mum
of 2 hours
to
warm
up
in the specified
environment
2.
Ensure
familiarity
with
normal operation of the
4708
described
in this
Handbook.
3.
Refer
to
'Equipment Requirements'
in
Section
7;
the
same equipment and techniques
used
for verification are
also applicable to calibration.
4.
Consult
the
manufacturer's
handbooks before connect-
ing
and operating the
Thermal Transfer
Std,
DC
Voltage
Std.,
Inductive
Voltage Divider,
AC DVM,
and Thermal
Transfer Standard Current Shunts.
5.
Interconnection
and Guarding: Refer
to
Section
4,
pages
4-1 to 4-3.
6.
Cancel any
MODE
keys,
ensure
OUTPUT
set to
OFF.
7.
IEEE 488 Address
switch:
Set
to
ADD
mil
(Address 3
1)
unless the
4708
is to
be
calibrated via the
IEEE
488
interface.
8.
CALIBRATION ENABLE
key
switch:
Insert
Calibration
Key
and
turn
ENABLE.
9.
Set
the Calibration Interval
Switch
to
24
hr.
WARNING
During
the Full
range voltage
is
present
at
the
Thermal
Transfer Standard input terminals.
On
lOOOV
checks
this
voltage
is
potentially lethal,
so
EXTREME
CAUTION
must
be observed
when making
adjustments
to
the
Thermal
Transfer Standard
sensitivity.
8-12