Aspiration Psychrometer

The Aspirator Psychrometer FT3060 series are used for measuring the air temperature and the humidity. Two parallel mounted, equal mercury thermometers are used. The bulb of one thermometer (wet bulb thermometer) is covered by a wick, which must be moistened for a measurement. The bulb of the other thermometer remains without wick. Both bulbs are encased by two radiation tubes. In order to achieve an effective radiation shield the surface of the instrument is polished. Depending on the amount of water vapor in the ambient air the water evaporates more or less from the wick of the wet bulb thermometer. The evaporative cooling causes the mercury column of the wet bulb thermometer to drop. The dry bulb thermometer is indicating the true air temperature. From the difference in temperature of both thermometers results the psychrometric depression. From this, the relative humidity, the dew point temperature and the vapor pressure of the air may be computed or determined from tables. Both thermometer bulbs are ventilated during measurements by fan. The ventilating speed at the bulbs averages 3 m/s.