5 • Description
03 Series Operator’s Manual
Sensor Gasket, Sensor Membrane, and Charcoal Filter
The sensor membrane is a paper-like filter disk that is held in place by the
sensor gasket and fits into a recessed area on the inside of the front case.
The sensor membrane covers the diffusion port and protects the sensor
from dirt and moisture. The sensor membrane should be inspected
periodically and replaced if contaminated by dirt or moisture. See
“Replacing the Sensor Membrane and Charcoal Filter” on page 68 for
sensor membrane replacement instructions.
The CO-03 includes a charcoal filter disk which is located in the sensor
gasket. The charcoal filter disk removes gases from the sampled air that
will cause a response on the CO sensor such as H
2
S and certain
hydrocarbons. If false or elevated CO readings are noticed, especially in
the presence of H
2
S, change the charcoal filter disk. See “Replacing the
Sensor Membrane and Charcoal Filter” on page 68 for replacement
instructions.
Sensor
The 03 Series uses either an oxygen, CO, or H
2
S sensor. The sensor is
protected by the white sensor membrane which is held in place by the
sensor gasket. The sensor membrane allows ambient air to diffuse past it
to the sensor. The three sensors used in the three 03 Series models use
different detection principles as described below.
Oxygen Sensor
The oxygen 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 03 Series’ 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 sensors that consist of two
precious metal electrodes in an 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 03 Series’ circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
LCD
The LCD is visible through the front case. When the 03 Series is in
Measuring Mode, the target gas concentration, battery condition, and
alarm indications are displayed on the LCD. Various other items are
