RKI Instruments GX-3R Pro - Sensors and Filters

GX-3R Pro Operator’s Manual Chapter 2: Description • 16
Sensors
The GX-3R Pro uses four sensors to monitor up to 5 gases simultaneously. The sensor retainer
and bottom cover hold the sensors in place. The sensors use different detection principles, as
described below.
Combustible Gas Sensor
The combustible gas sensor detects combustible gas in the % LEL range using 2 catalytic
elements: a standard element and a poison-resistant element that is resistant to sensor poisons like
silicone. The element’s resistance changes based on the reaction of gas with oxygen. The change
in resistance affects the current flowing through the element. The GX-3R Pro’s circuitry amplifies
the current, converts the current to a gas concentration, and displays the concentration on the
LCD.
The standard calibration for the combustible gas sensor is to methane but the sensor will still
detect and respond to a variety of combustible gases.
O
2
/CO/H
2
S/Super Toxic Sensors
The O
2
, CO, H
2
S, and super toxic 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 GX-3R Pro’s circuitry amplifies the
current, converts the current to a gas concentration, and displays the concentration on the LCD.
There are 4 different types of CO and H
2
S sensors available:
• CO only (ESR-A13P-CO): A single electrochemical cell that detects CO.
•H
2
compensated CO (ESR-A1CP-CO-H): A single electrochemical cell that detects CO.
This sensor does not respond to or responds minimally to hydrogen (displays H2 RICH
once H
2
concentration reaches 2000 ppm).
•H
2
S only (ESR-A13i-H2S): A single electrochemical cell that detects H
2
S.
•CO/H
2
S (ESR-A1DR-COHS): A combination electrochemical cell that detects both CO
and H
2
S.
IR Sensors
The infrared sensors detect CO
2
in the ppm and % volume ranges. Gas enters the sensor through
an opening on its face. Infrared light shines through the gas and into an infrared detector. The
intensity of the infrared light changes with the gas concentration and this change is converted to
an electrical signal. The GX-3R Pro’s circuitry converts the signal into a gas concentration and
displays the gas concentration on the LCD.
Dummy Sensors
A dummy sensor is installed in any units that have less than 4 sensors. Dummy sensors are factory
installed. The flat side of the dummy sensor faces away from the GX-3R Pro and the hollow side
faces toward the GX-3R Pro.