Measure dew point and relative humidity

Sling Psychrometer

Range 20°F to 120°F
9" Permacolor™ filled thermometers
Temperature accuracy ± 0.2°
Folding swivel handle
Hard plastic protective case
6 replacement wicks

We no longer stock this fine item, but recommend
Captains Nautical Supply as a source.

$149.00   ...item# 1328PJ

The instrument is used by wetting the clean wick with distilled water, then swirling it around for about 30 seconds and then reading the wet bulb and dry bulb temperatures. With these values you can look in tables (included with the device) to learn the dew point of the air and its relative humidity.

By plotting dew point and temperature as a function of time you can often predict when fog will form. Accurate sling psychrometers like these can also be used to calibrate hygrometers that read the relative humidity directly on a dial.

Here is a quick test of 4 units showing the dependability of the thermometers. The wet and dry bulb temperatures should be identical for all units on a given time when sitting side-by-side at rest, out of breezes, and on a uniform temperature base. Also keep in mind looking at the dial, that tenths of a degree must be estimated. These were read using a magnifying glass, being careful to avoid parallax errors, and being careful to not get so close to the thermometer that radiant heat from your own body does not change the reading, which is a real concern, since the result is sensitive to tenths of a degree. Clearly they are all well within the specs given by Taylor. This is a crucial condition, because the accuracy of the humidity and dew point results are a direct computation from the temperature data. (Unit 4 was sold on Day 2.)

For more notes on humidity and dew point measurement see our page on humidity.


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