International Biomedical AeroNO 2.0, Руководство по обслуживанию, Страница: 40 / 105

Part No. 715-0088, Rev. B - 37 -
3.10.8. Humidity Effects
Toxic gas cells use aqueous electrolytes, which, in conjunction with the porous
diffusion barrier, permit water vapor to be absorbed into the electrolyte under
conditions of high water vapor pressure, and allow the electrolyte to dry out at
very low ambient water vapor pressure. Normally, provided conditions are non-
condensing, the cell performance is relatively unaffected by humidity. However,
some sensors will show a transient response when rapid changes in humidity
occur. This should die away after about 20 - 30 seconds.
Continuous operation is possible between 15% and 90% RH over the full
operating temperature range without affecting sensor life or performance as,
under these conditions, the electrolyte will reach equilibrium with the external
water vapor pressure. It is possible to operate outside these conditions, but
water transfer may occur and must be taken into consideration.
3.10.9. High Humidity, High Temperature
Water will slowly diffuse in under continuous operation at high temperatures and
90 - 100% RH. If water uptake exceeds the free space available, then the
sensor becomes prone to leakage - increasingly so as more and more water is
taken up by the sensor. Lowering the humidity before leakage occurs will
gradually restore the sensor to its original condition and no permanent harm will
result from this exposure.
If a sensor is being affected by condensation, drying it with a soft tissue will
restore normal operation. Do not heat sensors above 40 C to dry them out.
3.10.10. Low Humidity, High Temperature
In continuous operation at 0 - 15% RH, water will diffuse out, only becoming a
problem when the volume of electrolyte has decreased by more than 40%. At
this point, the gas sensitivity of the sensor will be affected and the housing and
seals may be attacked by the very concentrated electrolyte. Exposure to a RH
above 15% will begin to restore the water balance, provided a sensor is not left
in this condition long enough for a reduction in the electrolyte to take place. A
medium sensitivity cell can operate for around six to seven weeks at 100% RH
and 40 C (continuous) and two to three weeks at 0% RH (continuous). In
general, low sensitivity cells will have slow water transfer rates, whereas high
sensitivity cells will have higher water transfer rates, and should be operated for
shorter periods of time in these conditions. The cells used in the AeroNOx
2.0 are towards the higher sensitivity end of the range.
3.10.11. Cell Handling
Toxic gas cells have a rugged design and are relatively insensitive to
mishandling. Following these few simple guidelines will ensure correct
operation in service:
Do not subject the cells to any pressure when clamping or handling.
Do not remove or puncture the protective mesh or the underside
slipcover over the capillary region.
The cell contains a small volume of strong mineral acid. In the unlikely
event of a leak, avoid contact with skin, eyes, and clothing. If exposed,
rinse contaminated parts thoroughly with water and consult a physician.