GDS-68XP Operation & Maintenance Manual, Revision 3.4
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4
OPERATION
OVERVIEW
The GDS-68XP uses low cost, reliable electrochemical sensors to detect hydrogen sulfide, mercaptan, THT
and other trace gases in process streams that contain little or no oxygen. As electrochemical sensors
require oxygen to operate, the GDS-68XP alternatively exposes the sensor to the process flow and then
purges the sensor with ambient air to maintain the sensor in a sensitive, oxygenated state.
Figure 4-1: GDS-68XP Flow Diagram (Pressure)
At the beginning of each sequence, the GDS-68XP performs
Conditions the Sensor
by allowing a small
sample of gas to enter the sensor flow cell, followed by a fixed 5 minute delay. The 68XP then enters
Sample
Charge
during which sample gas flows into the sensor flow cell for two minutes, or until sensor
output exceeds 25% of scale. Once sample pre-charge is complete, the sequencer enters
Read
mode
where the sequencer processor attempts to identify a stable peak value. Once the sample value is
Purge Air
Pump
Flow
Switch
Cal Gas Inlet
Sample
Inlet
Flow Meter
Sample Outlet
Sensor
Flow Cell
Run / Cal
Valve
3-Way
Valve
Pressure
Regulator
Purge Air
Inlet
Filter
RAW SENSOR
(Ch 1)
PPM OUTPUT
(Ch 2)