Measuring and testing – Gas analysis – Moisture content or vapor pressure
Reexamination Certificate
1999-02-12
2001-06-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
Moisture content or vapor pressure
C073S029020, C073S029050, C073S335010, C374S016000, C374S017000, C374S018000, C374S019000, C374S020000, C374S028000
Reexamination Certificate
active
06250134
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention refers to an apparatus for determining the dew-point and/or the content of vapor in the air, particularly for the use in radio sondes. The apparatus comprises a dew-point mirror assembly, including a source of light, a reflector, a cooling element thermally coupled to the reflector, a temperature sensor for measuring the temperature of the reflector and a detecting sensor that receives the light emitted by the light source and reflected by the reflector. Included in the apparatus is a space or region that receives temperature sensitive components of the dew-point mirror assembly, whereby means are provided for stabilizing the temperature in this space or region.
In order to determine the content of vapor in the free atmosphere, radio sondes carried by a balloon are used as a matter of routine nowadays. Thereby, frequently the so-called adsorption moisture sensors are used that operate with the help of a hygroscopic plastic film. Reasonable results can be obtained with the aid of those sensors in a temperature range of between +50° C. and −35° C. Below a temperature of −35° C., i.e. above approximately 7000 m height, depending on the weather and the latitude, the measurements are uncertain or not usable anymore because those sensors stop operating. The reason for that limit of possible measurements can be found in the physics of the adsorption measurement method.
For this reason, dew-point mirror assemblies are used more and more nowadays. The measuring method using those dew-point mirror assemblies is simple and well defined. A mirror is subjected to the air to be analyzed and cooled by means of a cooling element until it is misted up, i.e. until a condensate of water or, at lower temperatures, of ice is formed on its surface. Now, the temperature of the mirror is controlled in such a way that the condensate layer remains stable, i.e. the condensate layer does not evaporate and no new condensate is created. In this stable condition, the surface of the mirror has a temperature that corresponds to the vapor saturation temperature. The temperature of the surface of the mirror is measured by means of a thermometer integrated into the surface of the mirror. Based on the dew-point temperature and the simultaneously measured air temperature, the relative humidity of the air can be calculated.
PRIOR ART
In the dew-point mirror assemblies known in the prior art, the reflection characteristics of the mirror is checked by means of an opto-electronic circuitry. For this purpose, the surface of the mirror is illuminated by means of a light source radiating under an angle of 45° towards the mirror. In the known apparatuses, a semiconductor light source in the form of a light emitting diode (LED) is used as the light source. Opposite to the LED, there is provided a photo transistor, mounted under an angle of 45° as well, to measure the light reflected by the mirror. If the surface of the mirror is covered with condensate, a portion of the light is diffused by the water drops or ice crystals in all directions. Thus, less light is reflected to the photo transistor. The electric signal delivered by the photo transistor serves as instantaneous value in a control system that controls the current in the cooling element of the mirror and thereby keeps the reflection characteristics of the mirror in a stable condition.
By means of such dew-point mirror measurement apparatuses, accurate results can be obtained usually in a temperature range of between +50° C. and −40° C. However, at temperatures below −40° C. and particularly at low air humidity, where there is a great difference between air temperature and dew-point temperature, a limit is reached with the dew-point mirror measurement apparatuses hitherto used in radio sondes at which the required measurement accuracy or the operation thereof is no longer ensured.
This can be explained by the fact that the detecting sensor as well as most of the other electronic components are not specified to operate at temperatures below −40° C. In order to fix this problem, apparatuses are known in the art that are provided with a temperature stabilized region or space for receiving the temperature sensitive components. However, not all of the temperature sensitive components can be located in that temperature stabilized region because certain components, particularly the light source and the detecting sensor, are inevitably subjected or have to be inevitably subjected to the ambient air. Thus, the desired measurement accuracy cannot be ensured with these apparatuses as well.
Even if prototypes of dew-point mirror measurement apparatuses are known by means of which satisfying results can be obtained also at temperatures below −40° C., these apparatuses are not appropriate to be used in radio sondes since such dew-point mirror measurement apparatuses are very expensive, have a weight of up to several kilograms and require electrical power of 100 W and more. Due to the heavy weight and the enormous power consumption, they can be used on no account in radio sondes because the load carrying capacity of customary carrier balloons for radio sondes is limited.
OBJECTS OF THE INVENTION
Thus, it is an object of the invention to improve an apparatus for determining the dew-point and/or the content of vapor in the air of the kind referred to herein before in such a way that the apparatus supplies accurate measuring results also at very low temperatures while it is inexpensive, has a low weight and a low power consumption.
It is another object of the present invention to provide a method by means of which the presence of over-saturated air and/or air containing water drops or ice crystals can be recognized.
SUMMARY OF THE INVENTION
To meet these and other objects, the present invention provides, according to a first aspect, an apparatus for determining the dew-point and/or the content of vapor in the air, particularly for the use in radio sondes. The apparatus comprises a dew-point mirror assembly, including a source of light, a reflector, a cooling element thermally coupled to the reflector, a temperature sensor adapted to measure the temperature of the reflector and a detecting sensor that receives the light emitted by the light source and reflected by the reflector. Included in the apparatus is a space or region that receives temperature sensitive components of the dew-point mirror assembly, whereby means are provided for stabilizing the temperature in this space or region.
The detecting sensor is located in the temperature stabilized space or region, and the dew-point mirror assembly further comprises a light wave conductor. Thereby, the detecting sensor is optically coupled to the reflector by means of the light wave conductor.
In order to be in a position to determine the temperature of the mirror more accurately than up to now, the above mentioned temperature sensor can be designed as a thermo element. By the proposed design of the thermo element, parasitic heat flows caused by the temperature sensor can be avoided. Parasitic heat flows caused by the temperature sensor always arise if the mirror is very small and the temperature of the mirror is substantially lower than the ambient temperature. By means of the proposed reflector/thermo element combination, the above explained problems can be avoided to a very high degree and the temperature of the mirror can be determined more accurately.
According to a preferred embodiment, the apparatus comprises a sensor head containing the light source, the reflector, and the input end of the light wave conductor. Thereby, the apparatus is provided with a valve member for varying the flow cross section for the ambient air flowing through the sensor head. The valve member operates in dependence of the barometric pressure and the flow velocity of the ambient air flowing through the sensor head. By the provision of such a valve member, the apparatus can be constructively designed such that the heat transition between the housing of the se
Larkin Daniel S.
Meteolabor AG
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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