  In spectral studies of water vapor under laboratory conditions (determination
of molecular constants, measurement for spectral transmission functions), the
amount of water vapor in the time of the measurements is one of the most
essential parameters, which should be determined accurately. We discuss the
application for this purpose of polymer sensors of humidity manufactured by
Praktik-NC (Moscow) and used in the Pulkovo VKM-100 multipass vacuum cell.
These sensors were examined in the laboratory of Lindenberg Meteorological
observatory (Germany) by comparison between their readings and those of
standard measuring devices for various values of relative humidity, pressure,
and temperature. We also carried out measurements of relative humidity in boxes
with saline solution, in which the relative humidity that corresponds to a
given solution is guaranteed with the accuracy of several tenths of percent.
The analysis of the results of the laboratory examination of the sensors and
extended sets of measurements made with the Pulkovo cell made it possible to
conclude that in measurements in the interval of relative humidity 40-80%, the
~5% accuracy of the measurements for the water vapor content is reached.
Further paths are indicated for the increase of the accuracy of measurements
and extending the interval of the relative humidity, in which accurate
measurements may be carried out.
