RKI Instruments GX-94 - Manual (Page 12)

Page 11 GX-94 Operator’s Manual
diffusion screen and scrubs out H
2
S and most hydrocarbons which
cause a response on the CO sensor.
Sensors
The sensors are located inside the case in the top rear of the GX-94
behind the diffusion ports. A rubber sensor gasket is installed over the
sensors and forms a seal between the sensors and the inside of the
case to prevent any moisture or dirt which may enter the diffusion ports
from entering the inside of the GX-94.
Combustible Gas Sensor
The combustible gas (HC) sensor is contained in a cylindrical metal
shell with four connection pins at the base for easy replacement. The
flame arrestor on the top of the shell allows atmosphere to diffuse into
the sensor.
The HC sensor detects combustible gas and vapors in the atmosphere
with a catalytic platinum element. The reaction of gas with oxygen on
the catalyst causes a change in the resistance of the element, which is
converted by the GX-94’s circuitry into a reading of gas concentration.
Oxygen Sensor
The oxygen (O
2
) sensor is contained in a cylindrical shell, with two con-
nection pins at the base for easy replacement. The opening at the top of
the shell allows atmosphere to diffuse into the sensor.
The O
2
sensor is an electrochemical galvanic cell, which reacts to the
oxygen in the atmosphere, producing a voltage proportional to the oxy-
gen concentration. This voltage is converted by the GX-94’s circuitry
into an oxygen reading.
Toxic Sensors (H
2
S and CO Sensors)
The toxic sensors are physically identical, except for their external