18 • Chapter 2: Description
GX-6000 Operator’s Manual
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-6000’s circuitry, converted to a measurement of gas concentration, and displayed on
the LCD.
PID Sensor
Two types of PID sensors can be used with the GX-6000, a low range (higher sensitivity)
sensor and a high range (lower sensitivity) sensor (see Table 1 for specifications).
The PID sensor is a cylindrical sensor with a diffusion opening on the front and 3 pins on
the back. It is installed in a white housing that has three sockets on the bottom that mate
with the GX-6000 instrument. The PID sensor must always be installed in the first smart
sensor position which is located in the top left corner of the sensor block.
The standard calibration for a PID channel is to isobutylene. A PID channel can be factory
setup for and calibrated to other gases. Regardless of the calibration gas, the PID channel
will still detect and respond to a variety of volatile organic compounds (VOCs). Consult
RKI Instruments, Inc. for other available PID configurations and to specify the desired
PID configuration when a unit is ordered.
Dummy Sensors
Any unit that has less than 6 sensors will have a dummy sensor installed in one or more
unused sensor positions. Dummy sensors are factory installed. The flat top of the dummy
sensor should face up and the bottom hollow side should face down.
Filters
An H
2
S removal filter disk is placed into a recess in the sensor gasket over the %LEL
sensor. It prevents H
2
S in the ambient air from reaching the unit’s combustible gas sensor.
Removing H
2
S that is present in the monitored air prolongs the life of the sensor. The H
2
S
filter disk is dark red in color and although it may darken over time, its color is not
indicative of remaining filter life. The H
2
S filter disk can absorb H
2
S for 33 ppm hours
and should be replaced after that much exposure. With this many ppm hours of absorption,
the H
2
S filter disk should be replaced after 80 minutes of exposure to 25 ppm H
2
S. This
equates to replacing the H
2
S filter disk after 40 2-minute calibrations with a cylinder
containing 25 ppm H
2
S. If H
2
S exists in the monitoring environment, the H
2
S filter disk
will have to be replaced more frequently.
A charcoal filter is placed into a recess in the sensor gasket over the CO sensor. The
charcoal filter is black, has a woven texture, and is impregnated with an H
2
S absorbing
material. The CO sensor will respond if exposed to H
2
S and certain hydrocarbon gases.
The charcoal filter disk scrubs these gases out of the sample to avoid false CO readings. If
false or elevated CO readings are noticed, especially in the presence of H
2
S, change the
charcoal filter.
