Measuring and testing – Gas analysis – Moisture content or vapor pressure
Reexamination Certificate
1999-08-31
2001-07-10
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Moisture content or vapor pressure
C073S031010, C324S076140, C324S640000
Reexamination Certificate
active
06257049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to humidity sensors. More particularly, it relates to an apparatus and technique providing a more accurate, reliable and cost effective humidity sensor than is conventionally available.
2. Background of Related Art
Long term ambient humidity measurement is difficult to achieve with any high degree of accuracy or reliability.
Previous humidity sensors typically use mechanisms including delicate moving parts and materials having variable properties. One example of such a humidity sensor includes the use of a bundle of hair (e.g., blond human hair). Another is a coil enveloped in hydroscopic paper which expands/contracts with humidity. Such humidity sensors typically exhibit low measurement accuracy, particularly at the extremes of 0-20% and 80-100% humidity.
Humidity sensors having higher accuracy exist, but typically at the cost of higher maintenance and short accuracy lifetimes in the field. For instance, a humidity sensor using a chilled mirror is known wherein the mirror is chilled to the dew point which, along with the temperature, provides a fairly accurate humidity measurement. However, such higher accuracy humidity sensors , including lithium chloride and wet/dry bulb automated, are typically expensive to manufacture and require rigid and frequent maintenance (e.g., to clean the mirror).
Perhaps the more popular type of humidity sensor are solid state humidity sensors. While solid state humidity sensors are reasonably priced and accurate, they have been known to fail or degrade fairly quickly (e.g., after about 1 year or so), and thus tend to be both inaccurate and somewhat unreliable after a period of time.
Accordingly, there is a need for a humidity sensor which is accurate not only at a nominal humidity level but also at the extreme measurement levels, which is reliable, and which requires minimal if any maintenance.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a humidity sensor comprises a microwave transmitter and a microwave detector. A passage structure is between the microwave transmitter and the microwave detector. The passage structure includes at least one hole to allow ambient air to flow thereacross. A humidity value is calculated based on an absorption of microwave energy output by the microwave transmitter as measured by the detector.
A method of determining the humidity of ambient air in accordance with another aspect of the present invention comprises transmitting a known amount of microwave energy across the ambient air. An amount of absorption of microwave energy by water vapor contained in the ambient air is detected, and the amount of absorbed microwave energy is correlated to a particular value of humidity.
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Bollman William H.
Lucent Technologies - Inc.
Wiggins David J.
Williams Hezron
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