GX-2012 Operator’s Manual Instrument Description • 7
Combustible Gas Sensors
% LEL/ppm Sensor (NC-6264A)
The % LEL/ppm sensor detects combustible gas in the % LEL and ppm
range. It uses a catalytic element for detection. The reaction of gas with
oxygen on the catalyst causes a change in the resistance of the element which
affects the current flowing through it. The current is amplified by the GX-
2012’s circuitry, converted to a measurement of combustible gas
concentration, and displayed on the LCD.
%Volume Sensor (TE-7561)
The % volume sensor detects combustible gas in the % volume range. It uses
a thermal conductivity (TC) element for detection. The presence of
combustible gas cools the element causing a change in the resistance of the
element which affects the current flowing through it. The current is amplified
by the GX-2012’s circuitry, converted to a measurement of combustible gas
concentration, and displayed on the LCD.
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 GX-2012’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 a dilute 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 GX-
2012’s circuitry, converted to a measurement of gas concentration, and
displayed on the LCD.
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