4/9/98
A-4
Application of the Hygrometer (900-901D1)
Pressure
GE Panametrics hygrometers can accurately measure dew points
under pressure conditions ranging from vacuums as low as a few
microns of mercury up to pressures of 5000 psig. The calibration
data supplied with the moisture probe is directly applicable over
this entire pressure range, without correction.
Note:
Although the moisture probe calibration data is supplied
as meter reading vs. dew point, it is important to
remember that the moisture probe responds only to water
vapor pressure.
When a gas is compressed, the partial pressures of all the gaseous
components are proportionally increased. Conversely, when a gas
expands, the partial pressures of the gaseous components are
proportionally decreased. Therefore, increasing the pressure on a
closed aqueous system will increase the vapor pressure of the
water, and hence, increase the dew point. This is not just a
mathematical artifact. The dew point of a gas with 1000 PPMv of
water at 200 psig will be considerably higher than the dew point
of a gas with 1000 PPMv of water at 1 atm. Gaseous water vapor
will actually condense to form liquid water at a higher
temperature at the 200 psig pressure than at the 1 atm pressure.
Thus, if the moisture probe is exposed to pressure changes, the
measured dew point will be altered by the changed vapor pressure
of the water.
It is generally advantageous to operate the hygrometer at the
highest possible pressure, especially at very low moisture
concentrations. This minimizes wall effects and results in higher
dew point readings, which increases the sensitivity of the
instrument.
Содержание PM880
Страница 1: ...PM880 Portable Hygrometer ...
Страница 38: ...August 2003 2 18 Initial Setup Keypad cont Figure 2 8 The PM880 Keypad ...
Страница 150: ...August 2003 8 4 Servicing the PM880 Printing Reports cont Figure 8 3 Printout of a Typical Drive Report ...
Страница 237: ...5 August 2003 Index cont K K PPMv 3 17 Keypad Description 2 17 Key Description 2 17 Keys Description 2 17 ...