GX-2003 Operator’s Manual Instrument Description • 13
Sensors
The GX-2003 uses up to five sensors to monitor combustible gas,
oxygen (O2), carbon monoxide (CO), and hydrogen sulfide (H
2
S)
simultaneously. The sensors are located inside the GX-2003 and are
held in their sockets by the flow chamber. The sensors use different
detection principles, as described below.
Combustible Gas Sensors
% LEL Sensor (NC-6264AT)
The % LEL sensor detects combustible gas in the % LEL 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-2003’s circuitry, converted to a measurement of combustible gas
concentration, and displayed on the LCD.
NOTE: The % LEL sensor can not be used in instruments that utilize
Bar Hole Mode or Leak Check Mode.
LEL/PPM Sensor (NC-6264ALB)
The LEL/ppm combustible sensor is a specialized version of the %
LEL sensor. It is used instead of the % LEL sensor in instruments that
are intended for use in Bar Hole Mode or Leak Check Mode. The
LEL/ppm sensor can also be used for detection in Normal Mode.
%Volume Sensor
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-2003’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 Model GX-2003’s circuitry, converted to a
measurement of gas concentration, and displayed on the LCD.
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