
GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 28
7
CALIBRATION
CALIBRATION
OVERVIEW
Calibration
is
critically
important
to
ensure
correct
operation
of
the
GDS
‐
68XP.
The
GASMAX
CX
built
‐
in
CAL
MODE
function
is
designed
to
make
calibration
quick,
easy
and
error
free;
a
successful
ZERO
and
SPAN
calibration
requires
only
four
keystrokes.
It
is
important
to
note
that
a
GASMAX
calibration
should
only
be
performed
during
Purge/Hold
mode
.
During
each
sample
sequence,
the
GDS
‐
68XP
sequencer
checks
for
a
number
of
different
error
conditions,
including
overrange,
sensor
fault,
sample
peak
identification
fault,
and
sensor
non
‐
return
‐
to
‐
zero.
Since
the
sequencer
expects
a
valid
output
from
the
GASMAX
at
all
times,
if
the
GASMAX
CX
is
placed
in
CAL
MODE
at
any
time
during
the
sample
sequence,
a
CAL
ERROR
is
generated.
Always
check
to
be
sure
that
the
L2
(GREEN)
indicator
LED
is
flashing
before
performing
a
GASMAX
calibration
procedure.
Calibration
can
be
performed
in
one
of
three
ways.
If
certified
calibration
gas
is
available,
the
Cal
Port
Sample
calibration
technique
is
the
fastest
and
most
convenient
method.
If
a
three
‐
way
valve
is
installed
in
the
sample
stream
inlet,
the
Inlet
Port
Sample
calibration
technique
is
preferred,
as
the
calibration
gas
passes
through
the
filter,
regulator,
control
valve,
flow
switch
and
flame
arrestors,
more
closely
simulating
the
path
taken
by
the
actual
sample
gas.
Finally,
if
calibration
gas
is
not
available,
but
the
stream
contains
a
known
amount
of
target
gas,
the
Stream
Sample
calibration
technique
is
available.
In
all
cases,
the
GDS
‐
68XP
should
be
calibrated
at
least
once
every
three
months.
Furthermore,
during
the
initial
six
months
of
operation,
the
GDS
‐
68XP
should
be
checked
more
often
to
verify
that
the
sensor
is
operating
properly
and
that
some
component
of
the
sample
gas
mixture
has
not
damaged
the
sensor
or
change
the
sensor’s
response
to
the
target
gas
compound.
IMPORTANT:
FOR
MAXIMUM
ACCURACY,
USE
CALIBRATION
GAS
WITH
A
CONCENTRATION
VALUE
THAT
IS
GREATER
THAN
25%
OF
FULL
SCALE
AND
LESS
THAN
75%
OF
FULL
SCALE.
Before
beginning
calibration,
make
sure
you
have
the
following
items:
A
cylinder
of
calibration
gas,
fixed
flow
regulator
and
a
length
of
flexible
tubing.