Humidity measurement

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Humidity is the amount of water content present in the atmosphere. You have felt sticky when you touch your skin when you visit the beach or open ocean.

This is due to the presence of water vapor in the air. Relative Humidity is the most common measuring method, it is the ratio of the amount of water vapor present in the air to the maximum amount it can be accumulated.

The instrument used for measuring humidity is a hygrometer.

Before knowing the measuring methods, lets us understand some terms, the dew point is the temperature at which air is saturated with water and condensation begins.

Dew point indirectly influences the humidity; with an increase in dew point temperature increases the moisture content.

The simplest hygrometer, a sling psychrometer – consists of two thermometers mounted together with a handle attached to a chain.

One thermometer is ordinary.

The other has a cloth wick over its bulb and is called a wet-bulb thermometer. The ordinary one (dry) thermometer measures air temperature.

The other wet one, since it consists of wet cloth at the tip, as the water molecules from the tip evaporate by taking heat, this lowers the reading in the thermometer.

This way the relative humidity is measured. At 100% relative humidity no water will evaporate from the wet-bulb and the readings on both thermometers will be the same.

There are types of hygrometers like dewpoint meters, electrolysis hygrometer, hair hygrometer, etc.

Hair hygrometer is an old method for measuring humidity by observing changes in natural and synthetic materials. The human hair hygrometer utilizes a bundle of hairs, held under tension on an instrument that can hold.

Expansion and contraction of the bundle due to changes in humidity and temperature is observed using the gauge-dial mechanism.

Back to: Instrumentation and Control

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