14 • Instrument Description
Gas Tracer Operator’s Manual, CSA Version
PPM Sensor (SH-8641)
The ppm combustible sensor detects combustible gas in the ppm range. It is used
in Leak Check Mode. It is a combination catalytic/MOS type sensor with a
current output. The current is amplified by the Gas Tracer’s circuitry, converted to
a measurement of combustible gas concentration, and displayed on the LCD.
%Volume Sensor (TE-7561)
The % volume sensor detects combustible gas in the % volume range. It uses a
thermal conductivity (TC) element for detection. The presence of combustible gas
cools the element causing a change in the resistance of the element which affects
the current flowing through it. The current is amplified by the Gas Tracer’s
circuitry, converted to a measurement of combustible gas concentration, and
displayed on the LCD.
Oxygen Sensor
The O
2
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 Gas Tracer’s circuitry,
converted to a measurement of gas concentration, and displayed on the LCD.
CO Sensor
The CO sensor is an electrochemical cell 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 Gas Tracer’s circuitry, converted to a measurement
of gas concentration, and displayed on the LCD.
