Detcon P-1000 - Manual (Page 7)

P-1000
Portable Model 1000 H2S Analyzer Rev. 1.0 Page 3 of 24
1.2 Principle of Operation
Sample gas is fed into the unit via the Process Sample Inlet port on the side of the unit. The flow of the gas is
regulated by the Rotameter, and passed through the coalescing filter to remove moisture and condensation.
The nominal flow rate should be 500cc/min. with a minimum flow rate of 200cc/min. and a maximum of
1000cc/min. The gas enters the ISM via the Flow-through Chamber where it is read by the sensor, and vented
to the atmosphere via an Activated Carbon Scrubber to the Vent Port. H
2
S gas diffuses through the capillary
diffusion barrier of the cell where detection is made by an electrochemical reaction at the surface of an
electrode called the sensing electrode. The controlling circuit maintains a small external operating voltage
between the sensing and counter electrodes of the proper bias and magnitude so that no current flows to or
from the reference electrode while its potential is maintained at the correct fixed voltage — usually ground.
The electrochemical reaction creates a change in current flow from the counter electrode to the sensing
electrode. This change in current is proportional to the gas concentration and is reversible. The quick
response of the sensor results in continuous and reliable monitoring of H
2
S Concentration.
Process Sample Inlet
Port
Span/Zero Gas Inlet
Port
12VDC
Battery Charger Port
Vent Port
Figure 4 Gas Ports
Data from the sensor is exported by a HOBO Data Logger via a USB Port. The incorporation of the
HOBOware™ Software and a PC or Laptop complete the unit and allow the user to record the data in graphic
format that can be viewed via the HOBOware™ software. For more information, refer to the HOBOware™
Users Guide.
During Calibration the 3-way valve is placed in the CALIBRATE position and Cal Gas is fed to the sensor via
the Sample Gas Inlet Port.
1.2.1 Interference Data
UniTox™ Model 200 series electrochemical H
2
S sensors are subject to interference from some gases. This
interaction is shown in Table 1 as the relation between the amount of the interfering gas applied to the sensor,
and the corresponding reading that will occur. All measurements are in ppm unless otherwise noted.
Table 1 Gas Interference
Gas Name Symbol Cross Gas Name Symbol Cross
Acetyldehyde C2H3O n/d Hydrocarbons C-H’s n/d
Acetylene C2H2 n/d Hydrocarbons (unsat.) C-H’s (u) n/d
Acrylonitrile C3H3N n/d Hydrogen H2 1%=<5
Alcohols Alcohols n/d Hydrogen Bromide HBr n/d
Amines Amines n/d Hydrogen Chloride HCL 5=0