Hygrometer Sensor Technology
MENG 572 - SENSOR TECHNOLOGYDESCRIPTION, CHARACTERISTICS, AND RECENT ADVANCES OF HYGROMETER TECHNOLOGY
TECHNICAL REPORT
OCTOBER 20, 2011
DESCRIPTION
A Hygrometer is an instrument used for measuring the moisture content in the environmental air, or humidity. There are multiple types of hygrometers; modern day ones used in electronic devices use either temperature of condensation or changes in electrical capacitance/resistance to measure humidity changes. The following humidity sensors are currently available:
CAPACITIVE
In capacitive humidity sensors, the effect of humidity on the dielectric constant of a polymer or metal oxide material is measured. Capacitive sensors are subject to contamination, drift and aging effects, but are suitable for many applications.
RESISTIVE
In resistive humidity sensors, the change in electrical resistance of a material due to humidity is measured. Resistive sensors are less sensitive than capacitive sensors because they also tend to depend both on humidity and temperature thus the sensor must be combined with a temperature sensor.
THERMAL CONDUCTIVITY
In thermal conductivity humidity sensors, the change in thermal conductivity of air due to humidity is measured. These sensors measure absolute humidity rather than relative humidity.
CHILLED-MIRROR DEW-POINT
Chilled-mirror dew-point hygrometers are currently the most precise humidity sensors that are readily available. An optoelectronic mechanism is used to detect condensation on a chilled mirror surface which is controlled by electronic feedback to maintain equilibrium between evaporation and condensation. This process allows a close measurement of the dew-point temperature, thus determining the humidity.
CHARACTERISTICS
The following characteristics must be considered when working with hygrometers:
- Accuracy
- Complexity and Reliability
- Condensation Recovery
- Contaminant Resistance
- Cost of Operation
- Cost of Production
- Interchangeability
- Operation Environment
- Size and packaging
- Stability
RECENT ADVANCES
Recent Advances have allowed for development of very accurate hygrometers using a variety of methods, such as using optical fibers and alpha rays (Shigeaki Matsumoto) or by measuring the speed of sound and the temperature in air (Pekka Hiismaki). Humidity sensors have been used in medical devices such as humidifiers for years (S E Tilling), but recently they have been used in other biomedical applications, which require fast and accurate measurements, by using a silicon integrated detector (G. Tarapata). Computers have vastly aided the development of these sensors, by developing new methods of super-cooled water recognition in dew point hygrometry that involve computer aided morphology-based image processing (Z. Wawrzyniak).
