Whirling Hygrometer (also known as Sling Psychrometer) – wet and dry bulb.
The whirling hygrometer also known as a sling psychrometer is made out of two thermometers mounted on a frame which rotates around a handle, so it can be whirled in the air by hand.
One thermometer is covered with a tight-fitting muslin sock which is kept wet by preferably with distilled water. This type of thermometer is known as the wet-bulb thermometer. The other is the dry-bulb thermometer and exposed to the atmosphere directly.
Whirling Hygrometer (sling Psychrometer)
- Made in accordance with BS2842.
- Housed in a yellow plastic case with folding Handle.
- Available in Red Spirit.
- Supplied with Hygrometric tables, spare wick and instructions
- No electronics and therefor great for us in mines.
How does a Whirling Hygrometer work?
The psychrometer is whirled to let air past the bulbs which in turn makes water evaporate from the muslin cloth, This in turn cools down the wet bulb temperature. The amount of cooling that occurs dependant on the amount of relative humidity. With high relative humidity the wet bulb will cool less than in dryer air where the water in the muslin will evaporate faster. The dry bulb indicates the temperature of the air. The wet bulb helps determine the relative humidity.
With air less than 100 per cent relative humidity, the wet bulb will display a lower temperature than the dry bulb and is known as wet-bulb depression. A special chart is used to convert the wet-bulb depression to relative humidity or the relative humidity can be determined by correlating the readings with those on a simple slide rule, which is supplied with each instrument.
Optional: Case Call for more details