
GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 13
identified
and
stored,
the
GDS
‐
68XP
enters
Recovery
mode
where
purge
air
flows
into
the
sample
flow
cell.
Once
the
sensor
output
drops
below
10%
of
scale
,
the
GDS
‐
68XP
transfers
the
stored
reading
to
the
4
‐
20mA
and
MODBUS
output.
In
the
event
that
an
overrange,
loss
of
flow,
peak
‐
find
algorithm
fault,
non
‐
return
‐
to
‐
zero
fault,
sensor
fault
or
calibration
fault
occurred
during
the
sequence,
a
specific
fault
indication
value
will
be
output
in
place
of
the
measured
value.
Finally,
the
GDS
‐
68XP
enters
Purge/Hold
mode,
during
which
purge
air
is
periodically
passed
across
the
sensor
to
prepare
it
for
the
next
sequence.
The
length
of
the
Purge/Hold
time
is
determined
by
the
SEQUENCE
switch
setting.
Figure 4-2: GDS-68XP Sample Timing
GDS
‐
68XP
Sequence
Timing
Condition
Sensor
Fixed
Delay
Sample
Charge
Sample
Read
Sensor
Recovery
Purge
/
Hold
Valve
opens,
sample
flows
to
sensor
Purge
air
applied
to
sensor
Valve
opens,
sample
flows
to
sensor
Sequencer
finds
and
stores
max
gas
reading;
valve
closes
Purge
air
applied
to
sensor
until
output
<
10%
of
scale
Purge
air
applied
to
sensor
(intermittent)
Fixed
5
‐
10
seconds
Fixed
5
minutes
Two
minutes
or
value
>
25%
Min:
2
seconds
Max:
5
minutes
Min:
1
second
Max:
10
minutes
Determined
by
sequence
switch
Figure 4-3: GDS-68XP Maximum Timing Values
Value or Fault indication transferred to Output
Condition
Sensor
Recovery
Purge
/
Hold
“RAW
SENSOR”
“
OUTPUT”
Delay
Charge
New
Cycle
Read