RKI Instruments GasWatch 2 Manual - Manual (Page 11)

GasWatch 2 Operator’s Manual Description • 6
Sensor
The GasWatch 2 uses either an oxygen, CO, or H
2
S sensor. The sensor is
protected by the white sensor cover which is held in place by the sensor
cap and sensor gasket. The sensor cover allows ambient air to diffuse past
it to the sensor. The three sensors used in the three GasWatch 2 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 GasWatch 2’s 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 GasWatch 2’s circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
LCD
The LCD is visible through the top case. Target gas concentrations, the
time, battery condition, and alarm indications are displayed on the LCD.
When either of the control buttons is pressed, the LCD backlight comes on
for 20 seconds.
Control Buttons
Below the LCD are the two control buttons. They are POWER/MODE and
AIR. They turn on the power to the GasWatch 2 and turn it off. They control
what is displayed on the LCD, including time, gas concentrations, peak,
TWA, and STEL readings, as well as other messages. They also allow you
to perform a fresh air adjustment, change alarm points, change the time,
and calibrate the instrument. The functions performed by the control
buttons are summarized in the following table: