Teledyne T200, Руководство по эксплуатации, Страница: 300 / 425

Principles of Operation Teledyne API
– T200 NO/NO2/NOx Analyzer Operation Manual
298
transfers water through a relatively slow diffusion process, per-evaporation is a simple
kinetic reaction. Therefore, the drying process occurs quickly, typically within
milliseconds.
Because this chemical reaction is based on hydrogen bonds between the water molecule
and the Nafion
®
material most other chemical components of the gas to be dried are
usually unaffected. Specifically, the gases of interest for the T200, NO and NO
2
, do not
get absorbed and pass the dryer unaltered.
On the other hand, other small polar gases that are capable of hydrogen bonds such as
ammonia (NH
3
) can be absorbed this way, too. This is an advantage since gases such as
NH
3
can cause interference for the measurement of NO
x
, NO and NO
2
(see Table 13-1).
Figure 13-10: T200 Sample Dryer
To provide a dry purge gas for the outer side of the Nafion tube, the T200 returns some
of the dried air from the inner tube to the outer tube. This means that any time the
analyzer is turned on after having been OFF for 30 minutes or more, the humidity
gradient between the inner and outer tubes is not very large and the dryer‟s efficiency is
low. Since it takes a certain amount of time for the humidity gradient to become large
enough for the Sample Dryer operate efficiently, in such cold start cases the O
3
Generator is not turned on until 30 minutes has passed in order to ensure that it is not
operating until its air supply is properly dry. During this 30 minute duration the O3 GEN
OVERRIDE menu displays “TMR” on the front panel screen.
Note
When rebooting the instrument within less than 30 minutes of power-down, the
generator is turned on immediately.
The Sample Dryer used in the T200 is capable of adequately drying ambient air to a dew
point of ≤ -5˚C (~4000 ppm residual H
2
O) at a flow rate of 1 standard liter per minute
(slpm) or down to ≤ -15˚C (~1600 ppm residual H
2
O) at 0.5 slpm. The Sample Dryer is
also capable of removing ammonia from the sample gas up to concentrations of
approximately 1 ppm.
06858E DCN7057