A fast thermocouple psychrometer is described. The sensors, which are constructed from head-on welded chrome-alumel junctions of 50 μm diameter wire, are mounted verti-cally.
The vick is a fine polyester thread covering the
thermocouple wires over a length of about 20 mm. The wet junction is supplied with water by droplets falling along the wick with a frequency of about one per minute.
The falling drop method ensures a reliable vetting of the wet bulb. Moreover, accumulation of dirt on the wick is avoided.
The response times of the wet bulb and the dry
bulb have been measured by means of wind tunnel experiments.
At a wind speed of 4 m a-1 the response time of the wet bulb is 0.3 s, that of the dry bulb 16 0.05 s.
A study has been made of several possible error sources. The effect of radiation is a few tenths of a degree Celsius for both bulbs.
The wet bulb may be influenced by electrochemical voltages unless deionized or destillated water is used. The instrument has been used with several measuring campaigns and proved to work reliably.
W. Kohsiek and W.A.A. Monna. A fast response psychrometer
KNMI number: WR-80-04, Year: 1980, Pages: 37