GDS-68XP Operation & Maintenance Manual, Revision 3.4
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
