A highly accurate, long life, low cost gas sensor is disclosed, particularly
useful
for measuring carbon monoxide and other toxic gases in an environment. The gas
sensor has a first, sensing electrode and a second, counting electrode. Positioned
between the first and second electrodes is an ion conducting, solid electrolyte
membrane. In response to the presence of a toxic gas introduced to the first electrode,
an electric signal is produced between the first electrode and the second electrode.
The electric signal changes in response to changes in the concentration of the
toxic gas. Detection circuitry measures the electric signal to determine the concentration
of the toxic gas. An electrically conductive, hydrophobic top membrane electrically
connects the first electrode to the detection circuitry while preventing liquid
water from contacting the first electrode. An electrically conductive, hydrophobic
bottom membrane electrically connects the second electrode to the detection circuitry.
The top and bottom membranes, though hydrophobic, are preferably also microporous
so as to be gas permeable, including permeable to water vapor. Preferably the top
and bottom membranes are ion insulating as well. Optionally the sensor is provided
with a water reservoir to maintain constant relative humidity at the ion conducting
electrolyte membrane. The sensor may also have a heating element. Internal and
external self-diagnostic features to ensure that the sensor is functioning normally
are disclosed, as well as self-calibration features, so as to ensure sensor accuracy.
