Datron 1062 - Page 8

1
SECTION
1
CALIBRATION
1.1
INTRODUCTION
1.1.1
General
The
purpose
of
calibration
is
to
take
account
of
any
long-term
drifts
in
the
components
of
the
instrument
and
to
restore
the
accuracy,
traceable
to
a
known
standard.
The
period
between
calibrations
depends
upon
the
accuracy
performance
required
from
the
instrument
and
for
guidance,
guaranteed
accuracies
for
24
hours,
90
days
and
1
year
are
quoted.
The
calibration
procedures
presented
in
the
following
pages
should
cater
for
most
calibration
situations.
If,
how-
ever,
a
special
problem
arises,
please
contact
our
Customer
Service
Section.
1.1.2
The
Essentials
for
Good
Calibration
Temperature
-
So that
the
instrument
can
meet
its
specification
over
the
quoted
temperature
range,
the
temp-
erature
environment
should
be
stabilised
at
230C
±1oc.
In
addition,
temperature
gradients
around
the
instrument
should
be
considered,
therefore
calibrate
the
instrument
in
its
normal
operating
position
and
allow
plenty
of
room for
ventilation.
Warm
up
-
It is
essential
that
the
instrument
has
fully
temperature
stabilised
if
the
best
results
from
cali-
bration
are
to
be
achieved.
Therefore,
at least
a
2 hour
warm-up
period
is
recommended
during
which
time
the
line
supply
or
the
covers
should
not
be
removed
even
for
a
short
period.
In
addition,
if
the
covers
have
been
removed,
make
certain
that
they
are
correctly
fitted
and
that
the
leaf
contacts
to
the
Earth
and
Guard
Shields
are
in
good
shape.
Calibration
Source
-
To
perform
a
useful
calibration
the
accuracy
of
the
source
should
always
be
at least
four
times
that of
the
instrument
being
calibrated.
In
most
cases,
examples
of
likely
sources
are
given
for
each
cali-
bration
function.
With
some
calibration
sources,
the
output
may
take
several
seconds
to
settle
to a
final
value,
therefore
unless
a
shorter
settling
time
is
assured,
a
period
of
10
seconds is
'ecommended
before
each
calibration
operation.
Guarding
-
It
is
preferable
to
arrange
for
the
DVM
to be
calibrated
with
'Local
Guard'
selected.
Furthermore
to arrange
for
the
'Lo'
terminal
of
the
DVM
to
remain
at
'earth'
throughout
and
let
the
calibration
source
float.
If
a
'Remote
Guard'
connection
is
necessary
then
examples
are
shown
in
the
Operating
Manual.
1.1.3
The
'AUTOCAL'
Process
1.1.
3.1
General
The
Datron
'AUTOCAL'
process
means
that
complete
calibration
of
AC,
DC,
Ohms
and
Current
on
every
range
can
be
carried
out
from
the
instruments
own
front
panel.
In
the
process,
an
internal
non-volatile
memory
stores
calibration
constants
for
each
function
and
range
as
deter-
mined
when
the
instrument
takes
a series
of
16
readings
of
the
applied
calibration
source.
Internally,
each
of
the
readings
is
deviated
by
one
sixteenth
of
a digit
and
when
an
average
is
taken,
the
instrument
is
able
to
resolve
to
better
than
one least
significant
digit
displayed.
Access
to
the
non-volatile
memory
is
gained
using
a
key
inserted
into
the
rear
panel.
When
calibration
is
complete,
the
key is
removed,
therefore
preventing
acci-
dental
or
unauthorised
use
of
the
calibration
routine.
1.1.
3.2
Procedure
Outline
-
Select
the
'FUNCTION'
and
'RANGE'
to be
cali-
brated
and
cancel
any
'MODE'
or
'COMPUTE'
buttons.
Insert
the key
into the
'CALIBRATE
ENABLE'
keyswitch
on
the
rear
panel
and
turn
to the
'CAL'
position.
(The
'cal'
legend
will
be
displayed
on the
front
panel.)
If
the
instrument
is
fitted
with
Option
50
IEEE
Bus,
set the
rear
panel
address
switch
to
31 i.e.
all 1
's.
-
Connect
the
calibration
source
to the
input
terminals
and
operate
the
keys
shown
in
the
tables in
the
following
pages.
When
a
'CALIBRATE'
button
is
operated,
its
assoc-
iated
L.E.D.
indicator
will
light
and
extinguish
when
the
calibration
operation
is
executed.
-
When
all
calibration
is
complete
turn
the
keyswitch
to
'RUN'
and
remove
the
key.
1.1.
3.3
The
Five
'AUTOCAL'
Keys
'Zero'
-
This
takes
account
of
offsets
in
the
instrument
and in
the
calibration
source.
'Gain'
-
This
sets
a scaling
factor
for
each
range
and
function.
Ib
-
This
nulls
the
input
bias
current
of
the
DC
voltage
measurement
circuits
to
around
lOpA.
Therefore
it
only
has
a significant
effect
on the low
DC
voltage
ranges
and
high
resistance
Ohms
ranges.
It
can
be
operated
as
often
as
required
and
independently
of
other
calibration
operations.
It will
be
seen
that
successive
operations
of
'Ib'
approach
the
final
nulled
value
of
current
iteratively.