Hygrometers

A presentation on Hygrometer

1. Assalamu alaikum W ELCOME T O O UR P RESENTATION

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