Gas and liquid contact apparatus – With external supply or removal of heat – Processes
Reexamination Certificate
1999-09-24
2001-10-09
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
With external supply or removal of heat
Processes
C261S135000, C261S142000, C073S001060
Reexamination Certificate
active
06299147
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for generating a defined relative humidity in a gas, and in particular for generating a defined relative humidity in air used in calibrating humidity sensors.
DESCRIPTION OF RELATED ART
As humidity sensors become used in more applications, such as in air conditioning technology, the need arises for devices which can be used to calibrate those sensors. Devices suited for this purpose are also known as “humidity generators”. These devices supply a gas having a defined relative humidity value (RH) to a measuring chamber, in which can be placed the humidity sensors to be calibrated, or at least key components of those sensors.
One method for adjusting the relative humidity in a chamber is by using salt solutions, in accordance with DIN 50008. Another method uses so-called two-pressure/two-temperature humidity generators, that have also become widely used. In the latter method, air that is saturated with water vapor is produced in a saturator chamber at a temperature T
1
and a pressure p1, and is subsequently expanded to a pressure p2 at a temperature T
2
in a measuring chamber. The relative humidity in the measuring chamber can be determined by measuring the average pressures p1, p2 and temperatures T
1
, T
2
. Alternatively, by varying these parameters, the desired relative humidity RH can be obtained in the measuring chamber. Humidity generators of this type are described in the publication “Humidity Sensing, Measurements and Calibration Standards”, P. H. Huang, Sensors, February 1990, pages 12-21.
The problem with humidity generators constructed in this manner is the relatively substantial investment needed to obtain the equipment, and in particular the components needed to perform temperature control, temperature measurements, and temperature stabilization.
A less expensive variation of this kind of humidity generator is a so-called two-pressure generator. In the two-pressure generator, appropriate measures are used to maintain equivalent temperatures in the saturator chamber and in the measuring chamber. The desired relative humidity RH is adjusted by merely varying the pressure ratio between the saturator chamber and the measuring chamber. The relative humidity is a function of the ratio of p1 and p2, given by the formula RH=f(p2/p1). All the quantities entering into this equation are measured or are given, so a desired RH can be obtained. Humidity generators of this kind are described, for example, in JP 09-257283. The theory of operation of these devices, thus, is that the desired relative humidity RH is adjusted by varying the pressure ratio of p1and p2.
However, there are several drawbacks associated with the known two-pressure humidity generator of this type. For example, vapor in the air that is fully saturated to RH=100% can condense out in the area between the saturator chamber and the valve unit, causing air that is no longer fully saturated to pass into the measuring chamber. This situation causes errors in the RH that is actually found in the measuring chamber.
Accordingly, there is a need for an improved device for providing gas having a defined relative humidity that obviates some of the drawbacks of currently known devices.
SUMMARY OF THE INVENTION
The present invention is directed to a device for generating a defined relative humidity in a gas that substantially obviates one or more of the problems due to limitations and disadvantages of the related art, and that is suitable for testing complete or disassembled humidity sensors. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Other advantages of the invention will be realized and obtained by the apparatus and method particularly pointed out in the written description and claims hereof, as well as the appended drawings.
One aspect of the present invention is thus a compact device having a simplest possible design for generating a defined relative humidity in a gas. The device also avoids the problems mentioned above of current humidity generators.
This objective is achieved by a device for producing a gas having a defined relative humidity, which includes a saturator chamber holding the gas at a pressure P1, a measuring chamber holding the gas at a pressure P2 connected to the saturator chamber via at least one connecting line. The relative humidity of the gas is adjusted by varying pressures P1 and P2. A valve unit is disposed in the connecting lines, and a heating device is in thermal contact with the valve unit and with a portion of the connecting lines between the saturator chamber and the valve unit.
In another embodiment, the invention is a method for generating a defined relative humidity in a gas, that includes introducing the gas at a first pressure in a saturator chamber, increasing the relative humidity of the gas to 100% in the saturator chamber, flowing the gas to a measuring chamber via a connecting line and a valve unit, and controlling a pressure regulator of the valve unit to obtain a second pressure in the measuring chamber lower than the first pressure. The method also includes controlling the ratio of the first pressure to the second pressure to obtain the defined relative humidity in the measuring chamber, and heating the valve unit and a portion of the connecting line.
The humidity generator according to the present invention ensure an extremely compact, simply designed device. In addition, the generator according to the present invention avoids the problem of vapor condensing in the area of the connecting conduit or valve unit upstream of the measuring chamber.
The construction of the generator according to the invention ensure a constant stream of gas into the measuring chamber, over the entire range of relative humidity values that can be produced by the device. The stream of gas into the measuring chamber does not fluctuate in response to varying relative humidity values. This feature is advantageous, because it improves the overall accuracy of the calibration system.
According to the invention, a device is created which makes it possible to produce a gas with desired relative humidity values RH simply by varying the pressure ratio between the two chambers. In particular, the amount of equipment required is considerably reduced as compared to known humidity generators, so that the resulting system can be easily assembled and transported.
One advantageous specific embodiment according to the present invention includes a two-pressure relative humidity generator. However, it is also possible to implement the scheme according to the present invention by using a two-pressure/two-temperature humidity generator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 3659604 (1972-05-01), Melville et al.
patent: 3987133 (1976-10-01), Andra
patent: 4177667 (1979-12-01), Rolf et al.
patent: 4220460 (1980-09-01), Partus
patent: 4711294 (1987-12-01), Jacobs et al.
patent: 5457983 (1995-10-01), Sauvageau et al.
patent: 5502659 (1996-03-01), Braster et al.
patent: 6010118 (2000-01-01), Milewicz
patent: 9-257284 (1997-09-01), None
patent: 9-257283 (1997-09-01), None
P.H. Huang, Humidity Sensing, Measurements And Calibration Standards, Sensors, Feb. 1990, pp. 12-21.
Fischer & Porter: Differenzdruckregler 53 R 2110.
Bushey C. Scott
E&E Elektronik GES m.b.H.
Kenyon & Kenyon
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