RKI Instruments GX-86 - Manual (Page 7)

Model GX-86 Instruction Manual Components and Controls • 3
CO and H
2
S sensors
The CO and H
2
S sensors are physically identical, except for their external labels. The
sensors are housed in a cylindrical plastic shell, with a bayonet-pin base for easy
replacement. The perforations at the end of the shell allow atmosphere to diffuse into the
sensor. The CO sensor also has a slip-on charcoal filter that covers the diffusion end. The
filter eliminates interference from H
2
S.
CO and H
2
S sensors - principle of operation
The CO and H
2
S sensors are electrochemical cells, consisting of two precious metal
electrodes in an acid electrolyte. A gas permeable membrane covers the cell and allows
gas in the atmosphere to diffuse into the electrolyte at a rate proportional to its partial
pressure. The gas reacts in the cell, producing a current proportional to the concentration
of gas. The current is amplified by the GX-86’s circuitry and converted to a measurement
of gas concentration. To maintain sensitivity and stability, the CO and H
2
S sensors are
exposed to a continuous bias current, even when the power is off.
Accessory Jacks
Two 2.5 mm accessory jacks are located at the bottom of the GX-86 on either side of the
diffusion head.
Buzzer jack
The buzzer jack is located to the right of the diffusion head. You can use this jack to
connect an extension buzzer.
Earphone jack
The earphone jack is located to the left of the diffusion head. You can use this jack to
connect an extension earphone.