
GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 33
FAULT
AND
OVERRANGE
CONDITIONS
The
GDS
‐
68XP
contains
multiple
microprocessors
that
monitor
flow
rates
and
sensor
readings
to
detect
problems.
In
the
event
that
a
fault
occurs
during
a
sample
sequence,
the
4
‐
20mA
output
will
indicate
one
the
following
fault
condition:.
POWER
UP
Immediately
after
power
‐
up
the
GDS
‐
68XP
outputs
0mA
(FAULT)
for
8
seconds
and
then
4mA
(“0”)
until
the
first
reading
is
successfully
recorded.
This
allows
a
remote
device
to
determine
if
the
GDS
‐
68XP
was
forced
to
restart
as
a
result
of
a
power
failure.
INPUT
OVERRANGE
FAULT
To
protect
the
electrochemical
sensor
in
the
event
of
an
over
‐
range
condition
during
a
sample
measurement
sequence,
the
sample
valve
will
automatically
and
the
purge
air
pump
will
be
activated
to
force
fresh
air
into
the
sensor
cell.
SENSOR
RECOVERY
FAULT
After
the
sensor
output
is
monitored
for
a
prompt
return
to
zero.
If
the
output
does
not
return
to
a
value
of
less
than
10%
of
full
scale
during
the
recovery
interval,
the
sensor
may
be
saturated
with
sample
gas
and
the
GDS
‐
68XP
will
indicate
a
“recovery
fault”
PEAK
ALGORITHM
FAULT
–
During
the
sample
sequence,
the
GDS
‐
68XP
looks
for
a
level
peak
value.
If
no
level
peak
is
found,
the
GDS
‐
68XP
will
indicate
an
“algorithm
fault”.
SAMPLE
OR
PURGE
AIR
FLOW
FAULT
If
the
sequencer
senses
a
lack
of
flow
for
more
than
10
seconds
during
the
sample
sequence,
the
GDS
‐
68XP
will
indicate
a
“flow
fault”.
CALIBRATION
FAULT
–
If
the
sensor
output
higher
than
10%
of
scale,
or
lower
than
‐
10%
of
scale
when
a
sequence
starts
the
GDS
‐
68XP
will
indicate
a
“calibration
fault”.
The
GDS
‐
68XP
will
also
indicate
a
“calibration
fault”
if
the
GASMAX
is
placed
in
Cal
Mode
at
any
time
during
a
sample
sequence.
SENSOR
FAIL
FAULT
If
the
sensor
is
removed
or
fails
in
such
a
way
as
to
cause
a
channel
1
sensor
FAULT
reading
during
a
sample
or
sequence,
the
GDS
‐
68XP
will
indicate
a
“sensor
fault”.
FAULT
REASON
%
OF
SCALE
OUTPUT
(MA)
RANGE:
0
‐
3.00
RANGE:
0
‐
100
OVER
‐
RANGE
INPUT
EXCEEDS
MAX
RANGE
VALUE
105%
21MA
“3.15”
“105”
RECOVERY
FAULT
SENSOR
FAILS
TO
DROP
BELOW
10%
‐
15%
1.6
MA
“
‐
0.45”
“
‐
15”
PEAK
FIND
FAULT
PEAK
FIND
ALGORITHM
TIMES
OUT
‐
17.5%
1.2
MA
“
‐
0.52”
“
‐
17.5”
FLOW
FAULT
GAS
OR
PURGE
AIR
FLOW
DISRUPTED
FOR
>
10
SECONDS
‐
20%
0.8
MA
“
‐
0.60”
“
‐
20”
CALIBRATION
FAULT
GASMAX
CAL
DURING
SEQUENCE
OR
SENSOR
INPUT
>
10%
OR
<
‐
10%
OF
SCALE
AT
START
OF
CYCLE
‐
22.5%
0.4
MA
“
‐
0.67”
“
‐
22.5”
SENSOR
FAULT
SENSOR
BAD
OR
IN
FAULT
‐
25%
0.0
MA
“
‐
0.75”
“
‐
25”
Figure 8-1: Fault Conditions