RKI Instruments GX-2001 Manual - Manual (Page 11)

Model GX-2001 Operator’s Manual Description • 6
Oxygen Sensor
The O
2
sensor is a galvanic type of sensor. A membrane covers the cell
and allows gas to diffuse into the cell at a rate proportional to the partial
pressure of oxygen. The oxygen reacts in the cell and produces a voltage
proportional to the concentration of oxygen. The voltage is measured by
the Model GX-2001’s circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
CO and H
2
S Sensors
The CO and H
2
S sensors are electrochemical cells that consist of two
precious metal electrodes in an acid electrolyte. A gas permeable
membrane covers the sensor face and allows gas to diffuse into the
electrolyte. The gas reacts in the sensor and produces a current
proportional to the concentration of the target gas. The current is amplified
by the Model GX-2001’s circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
Scrubber Filters/Sensor Cover
Charcoal Filter Disk
The charcoal filter disk is located in the CO sensor diffusion port of the
sensor retainer. It is black, has a woven texture, and is impregnated with an
H
2
S absorbing material. It fits into a recessed area of that port. The CO
sensor will respond if exposed to H
2
S and certain hydrocarbon gasses.
The charcoal filter scrubs these gasses out of the gas sampled to avoid
false CO readings. The H
2
S absorbing material added to the charcoal filter
extends it’s H
2
S absorbing life. If false or elevated CO readings are
noticed, especially in the presence of H
2
S, change the charcoal filter disk.
NOTE: One H
2
S removal filter disk is used over the charcoal filter as an
additional guard against false CO readings as described below.
H
2
S Removal Filter Disks
The H
2
S removal filter disks are used in two locations. One H
2
S removal
filter disk is located in a recessed area of the combustible gas sensor
diffusion port in the sensor retainer. One is also used over the charcoal
filter disk in the CO diffusion port to extend the life of the charcoal filter. The
H
2
S removal filter disks are white when new. They scrub H
2
S out of the gas
sampled to increase the life of the combustible sensor and the charcoal
filter disk. They darken as they absorb H
2
S and must be changed when
they turn to a dark brown color. The recommended replacement frequency
will depend on how often the unit is exposed to H
2
S and the concentration.
Check the condition of the H
2
S removal filter disks quarterly.