Humidity contain of
water vapour in air or other gas. Water vapour is the gaseous form of water,
and can be thought of much like any other kind of gas. It is normally transparent
Humidity is the term
for the amount of water that is contained in gaseous environment. With most
cases, measurement of humidity is for an air environment at atmospheric
pressure and ambient or raised temperatures.
Humidity measuring
devices:
Hygrometers:
Devices that indirectly
measure humidity by sensing change in physical or electrical properties in
materials due to their moisture content are called hygrometers.
Materials such as hair,
skin, membranes, and thin strips of wood change their length as they absorb
water. The change in length is directly related to humidity.
Such devices are used
to measure relative humidity from 20 to 90 percent, with accuracies of about +
- 5%. Their operating temperature range is limited to less then 700 C.
HAIR
HYGROMETER
Hair hygrometer is the
simplest and oldest type of hygrometer.
As the relative
humidity increases, hair becomes longer, and as the humidity drops it becomes shorter.
On very humid days, your hair actually becomes longer and this extra length
cause the fizziness that gives us bad hair days.
Human hair lengthens by
3 percent when the humidity changes from 0 to 100 percent, this property of
hair can be used to operate a pointer or recording pen through a system of mechanical
linkage.
The transducer element
consists of strands of hair which are generally arranged parallel to each
other.
This instrument uses
strands of human or horse hair with the oils removed attached to levers that
magnify a small change in hair length.
Advantages
·
Simple in construction.
·
Low cost.
·
Simple In operation.
Disadvantages
·
They are not as accurate as other kinds
of hygrometers such as the SLING PSYCHROMETER.
·
It needs frequent adjustment and
calibration.
·
It also tends to have large errors at
very high and very low relative humidity.
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