RKI Instruments GX-82 - Manual (Page 7)

Model GX-82 Instruction Manual Components and Controls • 3
CO and H
2
S sensor
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 sensor - 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 circuitry of the GX-82 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.
Control Panel
The control panel is at the top of the GX-82 for easy access when you carry the GX-82. The
control panel contains the display, alarm lights, and buttons that control the many
functions of the GX-82. The buttons are touch-pads to reduce the possibility of accidental
activation or damage.
Table 2: GX-82 Button Functions
Button Function
POWER ON/OFF The POWER ON/OFF button controls power to the GX-82.
(Bias power for the electrochemical sensors is not affected by
the POWER button.)
BATT/DOSE The BATT/DOSE button displays the battery voltage and
the average level of H
2
S and CO exposure since the last time
the GX-82 was started.
PEAK HOLD The PEAK/HOLD button displays the highest reading for
exposure to LEL and H
2
S or CO, and the lowest reading for
O
2
exposure. It is also used (with the BATT/DOSE button)
to activate the GX-82’s Auto Zero function.
(All measurements are tracked since the last time the GX-82
was turned on.)
Alarm Lights Red light-emitting diodes (LEDs) labeled COMB, OXY, H
2
S,
or CO flash when the alarm for that gas is activated. The
alarm light automatically resets when the conditions fall
below (or rise above for O
2
) the alarm levels.