This presentation summarizes different types of hygrometers used to measure humidity. It describes common hygrometers such as metal coil, hair tension, electronic capacitive and resistive, thermal conductive, chilled mirror dew point, gravimetric, and psychrometers. It provides details on how each type works and typical applications. The presentation was delivered to a lecturer and included outlines, definitions of hygrometers, descriptions of various hygrometer types, references, and thanked the audience at the end.

1. Assalamu alaikum
WELCOME TO OUR
PRESENTATION

2. Date of Submission: February 4, 2015
Presented to:
Tamanna Sharmin
Lecturer
Department of Pharmacy
Primeasia University
Presented by:
122-003-032 122-009-032
122-016-032 122-020-032
122-022-032 122-027-032
122-039-032 122-045-032
122-046-032 122-080-032
122-096-032 113-119-032
113-269-032 113-309-032
082-224-032

3. HYGROMETERS

4. Outlines
• What is a hygrometer
• Types of Hygrometers
• Typical applications
• References

5. What is a Hygrometer?
A hygrometer is a sensor that senses the
amount of evaporated water in air by a
mechanical or electronic method.
A hygrometer is an instrument used for
measuring the moisture content in the
atmosphere.
The first practical hygrometer was
invented by polymath Johann Heinrich
Lambert in 1755.

6. TYPES OF HYGROMETERS
Metal/pulp coil
Hair Tension
Electronic
 Capacitive
 Resistive
 Thermal Conductive
 Chilled Mirror Dew point
Gravimetric
Psychrometer

7. Metal/pulp coil sensor
•Composed of metal or paper coil.
•Coil expands/contracts as humidity
changes.
•Amount of expansion is calibrated to
correspond with actual amount of
humidity.
•Used to show humidity on a dial
display.
•Quite inaccurate, differences between
similar coils are 10% to 20%

8. Hair Tension
The hair on a violin bow and the hair
on my head expands and contracts
according to the humidity. The more
humidity that is the air the longer the
hair is. The less the humidity the
tighter and shorter the hair gets.
This transduces the amount of
humidity into a force which can then
be converted into an electronic or
other mechanical signal.

9. Electronic Capacitive Sensors
A capacitor is like a short term battery
where static charge can be built up and
stored between two metal plates.
Depending on the moisture between the
two plates, more or less charge can be
built up between them. This amount of
charge is referred to as the Dielectric
Constant.
For a electronic capacitive hygromotor,
this relation between energy storage and
humidity can be calibrated to an
accuracy of +/- 2% between 5 and 95%
humidity. Electronic Capacitive Sensors
are low-cost, small, and durable. They
perform well in environments where
temperatures fluctuate frequently.

10. Electronic Resistive Sensors
The famous concept where salt water conducts
electricity to turn a light on is utilized in a
electronic resistive sensor. As humidity
decreases, the salt concentration increases
causing the resistivity of the circuit to decrease.
Thus, resistance is directly proportional to
humidity.
Since voltage changes are much smaller when
dealing with small humidity differences, precise
measurement equipment must be used making
these sensors less practical. Temperature
variation also produces varied results during
constant humidity and must be taken into
account when measuring from this sensor.

11. Thermal Conductive Sensors
As air's humidity changes, so
does it's ability to conduct
heat. An electronic device that
produces heat and another
device that precisely measures
heat can be calibrated to produce
results corresponding to actual
humidity.

12. Chilled Mirror Dew point
At a constant pressure, the temperature at
which water vapor turns to liquid is
positively correlated and proportional to
the humidity.
A Chilled Mirror Dew point hygrometer
uses an optoelectronic sensor to detect
whether there is dew on a glass mirror.
Using a feedback control loop, the
temperature of the mirror is raised and
lowered until condensation occurs. This
temperature is calibrated with a
measurement of humidity.
This type of humidity sensor is one of the
most accurate sensors available.

13. Gravimetric Sensors
A gravimetric hygrometer uses gravity
to calculate humidity. By measuring
the weight of a column of air, a
proportion can be determined when
comparing that weight with the weight
of dry air.
Gravimetric hygrometers are
considered the most accurate primary
method to determine the moisture
content of air.
Gravimetric hygrometers are typically
large and cumbersome to use and are
thus typically used to calibrate less
precise hygrometers.

14. Psychrometer
A psychrometer is a device that is made up of
two thermometers that are placed in two
different mediums.
One thermometer is placed in a wet location
and is entitled the "wet-bulb"
thermometer. When above freezing this is the
colder thermometer. When below freezing this
is the warmer.
Another thermometer is placed in a dry
environment in a similar location and is called
the "dry-bulb" thermometer. This termometer is
usually warmer above 0 degrees C and colder
below 0 degrees C.
The readings from each thermometer are
plotted on a "psychrometric chart" and the
corresponding humidity can be found based on
the altitude that the chart corresponds to.

15. Applications of Hygrometer
Meteorology and weather prediction.
Guitar Shops
Hardwood floor services
Various manufacturing processes.

16. References/Inspirations
•"Hygrometer” -
http://en.wikipedia.org/wiki/Hygrometer
•"Psychrometrics” -
http://en.wikipedia.org/wiki/Psychrometrics

17. Have you any questions?

18. THANK YOU