GASMAX CX Operation & Maintenance Manual, Revision 1.0
Page 26
6
CALIBRATION
CALIBRATION
OVERVIEW
Calibration
is
critically
important
to
ensure
correct
operation
of
the
GASMAX
CX.
The
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.
During
CAL
MODE
zero
and
span,
the
sensor
output
is
disconnected
and
the
GASMAX
CX
transmits
a
fixed
mA
value,
called
the
CAL
MARKER,
to
notify
the
receiving
device
that
a
calibration
is
in
progress.
During
the
following
CAL
PURGE
DELAY
time,
the
GASMAX
CX
transmits
a
fixed
4.0
mA
signal
to
prevent
external
alarms
during
calibration.
In
the
case
of
local
or
remote
Oxygen
sensors,
during
CAL
PURGE
DELAY
the
output
simulates
a
typical
atmospheric
reading
of
20.8%.
CAL
MODE
automatically
exits
if
no
keystrokes
are
detected
after
5
minutes.
Follow
these
GASMAX
CX
calibration
guidelines:
Calibration
accuracy
is
only
as
good
as
the
calibration
gas
accuracy.
GDS
Corp
calibration
gases
are
traceable
to
NIST
(National
Institute
of
Standards
and
Technology).
Never
use
calibration
gas
that
has
passed
its
expiration
date.
Check
the
SPAN
GAS
VALUE
setting
and
make
sure
it
matches
the
calibration
gas.
(See
Fig.
6
‐
2)
Always
use
a
GDS
Corp
calibration
cup
that
completely
surrounds
the
sensor
head.
Be
sure
to
use
ZERO
AIR,
a
mixture
of
21%
oxygen
and
79%
nitrogen,
as
a
zero
reference
unless
you
are
certain
that
no
target
gas
exists
in
the
area.
Ambient
gas
may
result
in
an
‘elevated
zero’
condition
that
will
cause
a
FAULT
to
occur
once
the
ambient
gas
is
no
longer
present.
Always
calibrate
a
new
sensor
before
depending
on
the
device
for
personnel
or
equipment
safety
Calibrate
on
a
regular
schedule.
GDS
Corp
recommends
a
full
calibration
every
3
months,
with
periodic
‘bump
tests’
on
a
more
frequent
basis
to
ensure
that
the
sensor
has
not
been
affected
by
temperature
extremes
or
the
presence
of
incompatible
gases.