Document No. 715-7000
Revision E
Page 30 of 63
Sensors
The
AeroNOx
is supplied with one
nitric oxide
sensor and one
nitrogen dioxide
sensor in the
delivery & analysis module. AeroNOx
sensors are designed to provide trouble-free use for
about twelve (12) months. Lifetime of the AeroNOx
sensor will depend entirely on the
concentration of NO or NO
2
being analyzed. The normal lifetime is about 1000 hours of
continuous use when exposed to 100 ppm NO and 10 ppm NO
2
respectively.
The AeroNOx
sensors must have a bias voltage going to them at all times. The battery must
be charged in order to maintain this “bias voltage”. The AeroNOx
maintains this voltage even
when the power button is in the “off” position. This means that the battery is being drained even
when the unit is powered off. For this reason, it is recommended that the AeroNOx
be plugged
in whenever possible to avoid the possibility of draining the battery to the point where it can no
longer maintain the “bias voltage” necessary to keep the sensors in a ready state.
Unbiased sensors will need up to 48 hours to fully bias. This applies to the installation of new
sensors as well as to sensors which have lost their bias due to a loss of battery power.
Unbiased sensors will read a value greater than zero when exposed to room air. This value will
continue to drop as the sensor biases. Once the value has dropped to zero, the AeroNOx
must
be re-calibrated prior to use.
CAUTION!
The NO
2
sensor may easily be damaged by inadvertent high levels of
NO
2
. Use nitrogen or air to flush the system after high levels of NO
(> 100 ppm) or NO
2
(> 20 ppm) have been introduced to the sensor.
CAUTION!
Condensing humidity will impair the function of the AeroNOx
sensors. Use only “NO WORRIES” sampling line (P/N 415-0004)
which utilizes
Nafion
tubing to prevent condensing humidity from
reaching the sensors.
In the unlikely event that the sensor(s) gets wet, turn the unit on and
sample dry room air to allow the
AeroNOx
delivery & analysis
module
to dry out.
Once dry, the AeroNOx
sensors will function
normally.
Analysis
Electrochemical sensors in the AeroNOx
measure NO and NO
2
concentrations in parts per
million (ppm). NO values are displayed to the nearest ppm while NO
2
values are displayed to
the nearest tenth (0.1) parts per million. The electrochemical sensors operate by allowing NO
and NO
2
molecules to diffuse across a membrane located on the top of the sensor. Once inside
the cell, these molecules react in an electrolyte solution augmenting an electrical current
between an anode and a cathode. The augmented current is proportional to the NO or the NO
2
concentration. The AeroNOx
also samples oxygen % for added safety.