instrument

by sakthivel A
(chennai,tamilnadu,india)

Hygrometer & psychrometer construction, working , uses, advantage & disadvantage and clear diagrams.

Barry's Response - Thanks Sakthivel. It's never easy getting really accurate humidity readings. In general, a hygrometer captures humidity data using one of various methods. Some measure changes in: electrical conductivity, shapes of coils made of metal and paper, reflections in refrigerated mirrors and even tension in hair.

The photo shows a psychrometer, an old-school technology which has two thermometers in one compartment. One is kept wet, using a wick or a sock-like cover, and the other stays dry.

The operator holds the handle and spins the larger part, like one of those old-style New Year's party noisemakers. After a minute or so of air passing between the thermometers, they yield different temperature readings and must be read immediately afterwards for the results to be accurate.

We get relative humidity by measuring wet-bulb temperature and dry-bulb temperatures and consulting a psychrometric chart to give us the correct humidity. Some psychrometers have an analog scale on the casing to make this calculation (giving a relative humidity in percent) and others do it electronically.

This object in the photo, called a sling psychrometer, lets the user get readings by attaching it to a handle. Some psychrometers can be swung on a rope to get a quicker result from the air.

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