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Publication numberUS3856204 A
Publication typeGrant
Publication dateDec 24, 1974
Filing dateMar 12, 1973
Priority dateMar 12, 1973
Publication numberUS 3856204 A, US 3856204A, US-A-3856204, US3856204 A, US3856204A
InventorsChand R
Original AssigneeEcology Board Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Gas emitting device
US 3856204 A
Abstract
A device for emitting a gas at a constant rate into a moving fluid medium to produce an accurately known concentration of the gas in the medium. The gas is held in a small cylinder under pressure in equilibrium with its liquid phase or solely in its gaseous phase, and permeates through a silicone material filling an accurately dimensioned passage through one end of the cylinder. Permeation rates may be selected from a wide range by varying the dimensions of the passage, and the device has a relatively low sensitivity to temperature variations.
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Description  (OCR text may contain errors)

United States Patent 11 1 I Chand Dec. 24, 1974 GAS EMITTING DEVICE Primary Examiner-Lloyd L. King 75 I h 1 mentor Ramesh C and Santa Susana Callf Attorney, Agent, or Fzrm-Fulw1der, Patton, Rleber, [73] Assignee: Ecology Board, Inc., Los Angeles, Lee & Utecht Calif. [22] Filed: Mar. 12, 1973 ABSTRACT [21] Appl. No.2 340,300 A device for emitting a gas at a constant rate into a moving fluid medium to produce an accurately known concentration of the gas in the medium. The gas is [52] US. Cl. 239/34 held in a Small cylinder under pressure in equilibrium [51] Int. Cl. A24f 25/00, A611 9/04 with its liquid phase or l l i its gaseous phase, and [58] Fleld of Search 239/34, 58; 206/5 permeates through a silicone material filling an accu I rately dimensioned passage through one end of the [56] References C'ted cylinder. Permeation rates may be selected from a UNITED STATES PATENTS wide range by varying the dimensions of the passage, 3,412,935 1 11/1968 OKeeffe 239/34 and the device has a relatively low Sensitivity to 3,655,129 4/1972 Seiner 239/34 perature variations. 3,679,l33 7/1972 Sekiguchi et a. 239/34 3,788,545 1/1974 Budd et al. 239/34 29 Clams, 5 D'awmg GAS EMITTING DEVICE BACKGROUND OF THE INVENTION This invention relates generally to devices for the emission of a gas at a constant rate, and, more particularly, to such devices used'in the production of calibration samples for gas or liquid analyzers, and in which the gas is emitted through a permeable material into a moving fluid medium.

Previously available devices of this type have employed an elongated tube of a permeable, polymeric plastic material to hold a gas under pressure and partially in the liquid phase. At a constant temperature, the vapor pressure of the substance will be constant and molecules of the substance will permeate through the walls of-the tube at a constant rate, thereafter to be intermixed or dissolved in a constantly moving fluid medium stream surrounding the tube. Tube devices of this type are described in a patent to OKeeffe entitled Gas Dispensing Devices, US. Pat. No. 3,412,935.

Although these permeable tube devices were a significant advance in the field, they suffer from two major disadvantages. Firstly, the rate of permeation of the substance through the tube walls is highly sensitive to temperature variations. An increase in permeation rate resulting from an increase in temperature can be considered as having two components: one due to a vapor pressure increase resulting from the temperature increase, and the other due to an inherent property of the permeable material that results in an increase in permeation rate with temperature, at constant pressure. In

, the prior art tube device, these two components are cumulative, and an adverse temperature characteristic results. Accordingly, the device must be maintained at a constant temperature to a high degree of accuracy if the permeation rate is to be held constant, and this problem is further aggravated if the tube is relatively long. since the constant temperature must be maintained over the entire length of the tube.

The second disadvantage of the prior art tube devices is that they are suited only for the production of very low concentrations of the gaseous substance. In another version of the prior tube devices, the substance permeates through a generally annular permeable element at one end of the tube, but this device produces even lower permeation rates, and concentrations down to l millionth of a part per million. For some applications, such as the calibration of ambient monitors for the detection of pollutants in the atmosphere, only small concentrations are involved. For example, the

concentration of sulfer dioxide in the atmosphere rarely exceeds 1 part per million '(ppm), and the tube devices are well enough suited to produce calibration samples with this order of concentration. For other applications, however, such as the calibration of stack monitors" for the analysis of effluent gases from industrial chimney stacks or from engine exhausts, higher concentrations are often encountered. For example, S0 concentrations are typically in the range 100 to 1,000 ppm, and it is difficult and highly inconvenient to obtain calibration samples in this range with the tube devices of the prior art.

Higher concentrations can, of course, be obtained by decreasing the flow rate of the fluidmedium used as a carrier, but this has practical limitations and too low a flow rate reduces the concentration accuracy of the resulting mixture. A larger tube will also result in higher concentrations, but again there are practical limitations, since a length or diameter increase of several hundred times may be required to obtain the desired range of permeation rates. As a practical matter, higher concentration calibration samples have hitherto been obtainable only by premixing gases in very large cylinders, and this method produces an inherently unreliable sample, especially after some time has elapsed between preparation and use of the sample, as is usually the case.

It is apparent, therefore, that there has been an urgent need for a device for the preparation of calibration samples which retains the advantages of prior devices, but which is less sensitive to temperature variations, and which may be made to produce a wide range of concentrations in the samples. The present invention fulfills this need.

SUMMARY OF INVENTION The present invention resides in a new device for emitting a gaseous substance at a predetermined rate into a moving fluid medium. Briefly, and in general terms, the device includes a sealed vessel for holding the substance to be emitted under pressure, the vessel having a passage filled with a permeable polymeric plastic material through which the substance permeates and is emitted outside the vessel.

The permeable polymeric plastic material used in the device has a much higher permeation rate and much less sensitivity to temperature variations than the material used in prior devices. This allows the use of a novel structure having a relatively low cross-sectional area of permeable material, but a relatively high rate of emis sion of the substance. Furthermore, the substance may be held either in equilibrium with its liquid phase or entirely in its gaseous phase, the latter resulting in an even more favorable temperature characteristic for the device. Also, the rate of emission can be widely and easily varied byemploying different dimensions for the passage, without increasing the overall size of the device except as is required to increase the life of the device between refills.

More specifically, in a presently preferred embodiment of the invention, the vessel takes the form of a hollow metal cylinder, closed at one end except for the passage which is formed therethrough, and adapted at the other end to receive a pressure seal. The polymeric plastic, a silicone material in the presently preferred embodiment, is positioned in the passage and cured to form a permanent bond with the metal, after which the vessel is evacuated and filled with a liquefied gaseous substance. In a variation of this preferred embodiment, the gaseous substance is stored in the cylinder under a pressure not sufficient to liquefy the substance. The substance may be any of a wide variety of fluids, including water, and the passage in the vessel can be dimensioned to provide any emission rate over a wide range,

' to meet the requirements of various applications.

Furthermore, the structure of the present invention allows easy connection with the moving fluid medium by means of a simple T-junction. Thus, the device may be readily adapted for use with any analyzer or may be conveniently housed integrally with an analyzer.

It will be appreciated from the foregoing that the present invention overcomes the major disadvantages of prior art devices, in that sensitivity to temperature variations is considerably lessened and calibration samples having a wide range of concentrations can be easily produced. Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS ture characteristic of the device of FIG. 1 utilizing the gaseous and liquid phases of the substance; and

FIG. 5 is a graph illustrating the temperature characteristic of the device utilizing only the gaseous phase of the substance.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the device of the present invention is used to dispense a gaseous substance at a constant rate, the gas thereafter being mixed with a moving fluid medium to provide a sample containing a known concentration of the gas, which is then typically used to calibrate an analyzer of gases or liquids. The device includes a sealed vessel (FIGS. 1-3) in which the gaseous substance is held under pressure, and a quantity of permeable polymeric plastic material 11 through which the substance permeates and escapes from the vessel.

In accordance with the present invention, the vessel 10 is formed from a material impervious to the substance contained therein, and the permeable plastic material 11 fills a passage 12, as best shown in FIG. 2, extending from the inside to the outside of the sealed vessel. The structure uses a permeable material such as silicone, which has less sensitivity to temperature variations than materials used in prior devices, and a higher permeation rate/Thus, the device has a more desirable temperature characteristic than existing devices, and the rate of emission of the gaseous substance can be preselected from a wide range of rates by proper selection of the dimensions of the passage 12.

More specifically, the vessel 10 employed in a presently preferred embodiment of the invention is a hollow cylinder of stainless steel or other material impervious to, and practically non-reactive with the substance to be contained therein. As best illustrated in FIG. I, the cylinder 10 has an open upper end 13 threaded internally to receive a pressure seal 18, which is normally not removed except for refilling the cylinder, and a solid lower end 14 of substantial length through which the passage 12 extends along the axis of the cylinder. The terms upper and lower as used herein are descriptive only with respect to the figures, and the device is not limited to operation in a particular orientation.

The cylinder 10 has a reduced diameter, both inside and outside, over a substantially long lower end portion 17 of the cylinder, to facilitate fitting the device to pipes containing the moving fluid into which the gaseous substance is to be emitted. Accordingly, the lower end portion 17 has a threaded nut 19 and an associated sealing ring 21 fitted thereto for engaging a threaded pipe fitting 22.

For relatively low permeation rates, the cylinder 10 is typically 0.5 inch in outside diameter, reducing to 0.25 inch in diameter at its lower end 17 for convenient fitting to quarter-inch diameter gas lines. The passage 12 in this size of cylinder 10 is typically a few hundredths of an inch in diameter and about a quarter-inch long. For higher permeation rates, the cylinder 10 may be 2 or more inches in diameter and 8 or 9 inches long, to provide a reasonably long life between refills, and the passage 12 may be a half-inch or more in diameter. The higher permeation rates may be obtained by increasing the diameter of the passage 12 or decreasing its length, or both.

The permeable material 11 used in the presently preferred embodiment is a silicone polymeric compound chemically classified as dimethyl polysiloxane. Many compounds of this type are commercially available and can be used in the present invention. By way OfICXflI'II- ple, the dimethyl compound PR1939, manufactured by Products Research and Chemical Corp., Los Angeles, California, and dimethyl RTV compound 630, manufactured by General Electric Co., Waterford, New York, have each been found suitable in the presently preferred embodiment.

Before the silicone material .11 is positioned in the passage 12, the entire cylinder 10 is cleaned with a degreasing agent to remove any possible contaminants. Then the silicone material 11, which is typically relatively viscous, is drawn into the passage 12 by applying a partial vacuum to the cylinder 10 at its upper end 13. When the silicone material 11 completely fills the passage and any trapped air bubbles have been removed, the partial vacuum is removed and the silicone material is cured at a temperature of approximately F, preferably for at least 24 hours. During curing, the silicone material 11 hardens and becomes permanently bonded to the walls of the passage 12.

Two variant forms of the preferred embodiment are presently contemplated. In the first, the gaseous substance is introduced into the cylinder 10 in a liquefied state, and is held there under pressure with its liquid and gaseous phases in equilibrium, as was the case in the prior tube devices. In the second form, the substance is held at a lower pressure entirely in its gaseous phase. Although this latter form suffers from a shorter life between refills and a gradual fall in permeation rate as the cylinder 10 is emptied of gas, it can still be designed as a practical device, and, as will be discussed in detail below, it has the advantage of a very favorable temperature characteristic.

After the silicone material 11 has been cured in the cylinder passage 12, the cylinder 10 is evacuated and filled with the desired gaseous substance through the open upper end 13. If the substance is normally gaseous at room temperature, and is to be introduced in the liquid state, the cylinder 10 is usually cooled below the boiling point of the substance to minimize loss of liquid when the cylinder is sealed.

FIG. 3 diagrammatically illustrates how the device of the present invention would typically be connected for use. For calibrating an analyzer 22, the cylinder 10 is connected by a T-junction 23 to emit the gaseous substance at a constant rate through the silicone 11 into the fluid medium flowing at a constant rate along a pipe 24 to the analyzer. The fluid medium may be an inert gas, such as nitrogen, in which the emitted substance is mixed, or, in some applications, it may be a liquid in which the emitted substance is dissolved. The fluid medium is drawn from a supply system 25, which typically includes a pump, a pressure regulator and a flow meter, none of which is illustrated.

A constant temperature is preferably maintained by means of some heating element 27 wrapped around the cylinder and supplied with power through a control unit 28 which includes an adjustable thermostat (not illustrated), thus maintaining a constant rate of emission of the substance contained in the cylinder 10.

1 When liquefied gas is used, it has been found that a constant temperature need be maintained only to within approximately 0.5C, whereas a variation of 01C was all that could be tolerated in prior devices with comparable accuracy, In the form of the invention in which the substance is held entirely in its gaseous phase, the temperature tolerance is even greater, and, in somce cases, temperature control may be unnecessary.

This important aspect of the invention, that the operation of the device is much less sensitive to temperature variations than was the case with previously available devices, is well illustrated in FIG. 4, which is a graph showing the variation of permeation rate of sulfur dioxide (S0 in nanograms (grams X 10') per minute (ng/min), plotted on a logarithmic scale, with temperature in degrees centigrade (C). The solid line 29 is typical of previous devices made for this purpose, while the broken line 31 shows the improvement effected by the present invention, in which the S0 is held in liquefied form. For example, the permeation rate for both devices is approximately 315 ng/min at 262C. At 362C, the permeation rate of the old tube device increases to 730 ng/min, while the rate for the new device increasesto only 410 ng/min; i.e., an increase of l32 percent, or approximately 13 percent per degree centigrade, for the old device compared with an increase of 30 percent, or only 3 percent per degree centigrade, for the new device of this invention. In that particular temperature range, then, the new device is approximately only one-fourth as sensitive to temperature changes as the prior device.

The variation of permeation rate with temperature can be considered as having two components: one due to a vapor pressure change resulting from the temperature change, and the other due to an inherent property of the permeable material that results in a change in permeation rate when the temperature is varied at constant pressure. The first component canbe easily determined from vapor pressure tables. For example, for S0 the vapor pressure increases from 33.45 p.s.i. to 66.45 p.s.i. for a temperature change from 10C to 30C, i.e. the vapor pressure increases almost exactly by a factor of two. Thus, the permeation rate will be doubled by an increase of temperature from l0C to 30C because of the vapor pressure increase.

This first component of the permeation rate variation is shown graphically by'the curve 32 in FIG. 4. Note that only the slopes of the lines 29, 31 and 32 are of interest, since the points of intersection with the y axis can be varied by changing the cross-sectional area of the permeable material.

Note also that the second component of the permeation rate variation, the component inherent to the permeable material, is positive for the prior device, resulting in the steeper characteristic curve 29, but is negative for the new device of this invention, resulting in the improved characteristic curve 31. Using the same S0 example, the permeation rate for the prior device increases from ng/min at 10C to 440 ng/min at 30C. Of this 360 ng/min increase, only approximately 80 ng/min results from the vapor pressure increase (a twofold increase), and the remaining 280 ng/min results from the unfavorable temperature characteristic of the permeable material of the prior device. For the device of this invention, over the same temperature range, the permeation rate increases from 200 ng/min to 350 ng/min, and a 200 ng/min increase due to the vapor pressure change is offset by a 50 ng/min decrease due to the different permeable material of the invention.

If the substance in the cylinder 10 is entirely in its gaseous phase, the variation of pressure in the cylinder will be nearly directly proportional to the absolute temperature, in accordance with the ideal gas laws. Thus, the permeation rate will also vary in direct proportion to the absolute temperature because of this pressure change, as shown by the curve 33 in FIG. 5. A temperature change from 10C to 30C results in a first component of permeation rate increase of approximately 7 percent, or from 200 ng/min to 214 ng/min in the curve 33 as illustrated.

As was seen in the foregoing discussion relating to the liquefied gas form of the invention, an increase in temperature from 10C to 30C results in a second component of permeation rate change of minus 50 ng/min for the new device. Thus, the combined effect of the two components is, as shown at 34 (FIG. 5), a net decrease of 36 ng/min, i.e., approximately 18 percent change in permeation rate for 20C temperature change, or less than 1 percent per C. With temperature sensitivity this low, temperature control would be totally unnecessary in some situations. Using only the gaseous phase of the substance in the prior devices does not, of course, greatlyimprove the temperature characteristic for those devices, since there is still a large second component of permeation rate increase inherent to the material of the devices.

Although the form of the invention using only the gaseous state of the substance suffers from a shorter life between refills and a gradual decline in permeation rate, the device is still a practical one. Again using S0 as an example, if the cylinder 10 is 8 or 9 inches long and 2 or 3 inches in diameter, it will contain approximately 3 grams of S0 at twice atmospheric pressure. At a permeation rate of 1000 ng/min,this will last for more than 5 years, so that the permeation rate decrease is less than 2 percent per month, an entirely acceptable figure for most applications.

Another important aspect of the invention is that the passage 12 can be easily dimensioned to select any of a wide range of permeation rates. Since the permeation rate is inversely proportional to the length of the passage 12 and directly proportional to the cross-sectional area of the passage, the rate may be varied by changing the length or diameter of the passage. In one form of the presently preferred embodiment, the passage is accurately machined to be 0.016 inch in diameter and 0.25 inch long. By way of example, a l00-fold increase in permeation rate can be achieved by a IO-fold diameter increase, to 0.160 inch, with the length kept constant. No increase in the size of the cylinder 10 would be required unless it was needed to compensate for the shorter life of the device between refills, due to the faster permeation rate.

This availability of higher permeation rates allows the convenient production of accurate calibration samples with concentrations in the hundreds of parts per million, for use in the calibration of industrial stack monitors, for example, where accurate calibration was previously cumbersome and difficult. For example, a high emission rate S tube of the old type would need to be about 50 inches long to generate 100 ppm of S0 at 22C in a carrier gas flowing at 1 liter per minute. Using the present invention, a passage diameter of only approximately 0.5 inch would be needed, and the device need only be 2 inches in diameter and 8 or 9 inches long to attain a life between refills comparable with the old device. Lower concentrations in the order of one part per million are, of course, still obtainable from the device if an appropriately smaller diameter passage is employed.

The substance to be stored in and emitted from the cylinder 10 may be any of a wide range of fluids including, but not limited to, sulfur dioxide, nitrogen dioxide, hydrogen sulfide, ammonia, chlorine, bromine, hydrogen fluoride, propane, propylene, methyl mercaptan, ethyl oxide, n-butane, carbon tetrachloride, formaldehyde, acetaldehyde, and even water. The use of water as the gaseous substance has important application in the accurate calibration of industrial hygrometers, widely used to monitor the environment for certain manufacturing processes. It will be understood that some of the substances named are not suitable for storage entirely in the gaseous phase at ordinary temperatures.

From the foregoing, it will be seen that the invention described herein satisfies a need for accurate, high concentration calibration samples, which were not hitherto conveniently available. Furthermore, the invention is a significant improvement over prior devices of the same type in that sensitivity to temperature variations is greatly decreased, and the device may be more easily connected to a fluid supply line.

Although one embodiment of the invention has been described in detail for purposes of illustration, it will be appreciated that various modifications may be made without departing from the spirit and scope of the invention.

I claim:

1. A device for emitting a gaseous substance at a predetermined rate, comprising:

a sealed vessel for holding said substance under pressure, said vessel being impermeable to said substance and having an exit for emission of said substance; and

a quantity of permeable polymeric silicone material positioned in said exit, said material having a permeability which decreases with increasing temperature and constant pressure in said vessel, whereby said substance permeates through said material and is emitted from said vessel at the predetermined rate, and said device has a characteristically low overall sensitivity to temperature variations.

2. A device as set forth in claim 1, wherein said quantity of permeable polymeric silicone material is a dimethyl polysiloxane.

3. A device as set forth in claim 1, wherein said substance is held by said sealed vessel partially in the liquid phase.

5. A device for emitting a substance at a predeter- 5 mined rate, comprising:

a sealed vessel for holding said substance under pressure, said vessel being impermeable to said substance and having an exit passage for emission of said substance; and

a quantity of permeable polymeric plastic material completely blocking said passage, said material having a permeability which decreases with increasing temperature and constant pressure in said vessel, whereby said substance permeates through said material blocking said passage and is emitted from said vessel at the predetermined rate, and said device has a characteristically low overall sensitivity to temperature variations.

6. A device as set forth in claim 5, wherein said permeable polymeric plastic is a silicone polymer.

7. A device as set forth in claim 6, wherein said silicone polymer is a dimethyl polysiloxane.

8. A device as set forth in claim 6, wherein said substance is held by said sealed vessel partially in the liquid phase.

9. A device as set forth in claim 5, wherein said permeable polymeric plastic is a silicone polymer and said substance is held by said sealed vessel partially in the liquid phase, said device further including temperature control means to maintain said vessel and said substance at a substantially constant temperature.

10. A device as set forth in claim 9, further including removable vessel sealing means.

11. A device as set forth in claim 5, wherein said substance is selected from the group consisting of sulfur dioxide, nitrogen dioxide, hydrogen sulfide, ammonia, chlorine, bromine, hydrogen fluoride, propane, propylene, methyl mercaptan, ethyl oxide, n-butane, carbon tetrachloride, formaldehyde, acetaldehyde, and water.

a quantity of a permeable silicone polymeric material completely filling said passage and bonded to the walls thereof, said material having a permeability which decreases with increasing temperature and constant pressure in said vessel;

connection means for connecting said device to the moving fluid stream, whereby said substance permeates through said silicone material at the predetermined rate and is emitted into the moving fluid stream through said connection means, and said device has a characteristically low overall sensitivity to temperature variations.

13. A device as set forth in claim 12, further including sealing means removably attached to said vessel to allow filling and refilling thereof with said substance.

14. A device as set forth in claim 13, wherein:

said vessel is a hollow cylinder; and

said passage is a tube through one end of said cylinder.

15. A device as set forth in claim 14, wherein said connection means includes a T-shaped pipe fitting connecting said cylinder to a line enclosing the fluid stream.

16. A device as set forth in claim 12, wherein said substance is selected from the group consisting of sulfur dioxide, nitrogen dioxide, hydrogen sulfide,'ammonia, chlorine, bromine, hydrogen fluoride, propane, propylene, methyl mercaptan, ethyl oxide, n-butane, carbon tetrachloride, formaldehyde, acetaldehyde, and water.

17. A device as set forth in claim 12, wherein said substance is held by said sealed vessel partially in the liquid phase in equilibrium with the gaseous phase.

18. A device as set forth in claim 12, wherein said substance is held by said sealed vessel solely in the gaseous phase.

19. A device as set forth in claim 12, further including temperature control means for maintaining said sealed vessel and said substance at a substantially constant temperature, and thereby maintaining a constant rate of emission of said substance.

20. A device as set forth in claim 19, further including sealing means removably attached to said vessel to allow filling and refilling thereof with said substance.

21. A device as set forth in claim 20, wherein:

said vessel is a hollow cylinder; and

said passage is a tube through one end of said cylinder.

22. For use with apparatus for the analysis of fluid mixtures, a device for generating a calibration mixture with a predetermined concentration of a substance, said device comprising: 1

a vessel for holding said substance under pressure,

said vessel being impermeable to said substance and having a passage through which said substance is emitted into a moving stream of an inert fluid medium;

a body of a permeable silicone polymeric material completely filling said passage and bonded to the walls thereof to limit emission of said substance to a constant rate for a constant temperature, said material having a permeability which decreases with increasing temperature and constant pressure. in said vessel, thereby providing for said device a characteristically low overall sensitivity to temperature variations.

23. A device as set forth in claim 22, wherein:

said vessel is a hollow cylinder; and

said passage is located at one end of said cylinder.

24. A device as set forth in claim 23, wherein said connection means includes a T-shaped pipe fitting connecting said cylinder to a pipe enclosing the moving stream of fluid.

25. A device as set forth in claim 22, wherein said substance is selected from the group consisting of sulfur dioxide, nitrogen dioxide, hydrogen sulfide, ammonia, chlorine, bromine, hydrogen fluoride, propane, propylene, methyl mercaptan, ethyl oxide, n-butane, carbon tetrachloride, formaldehyde, acetaldehyde, and water.

26. A device as set forth in claim 22, wherein said substance is held by said sealed vessel partially in the liquid state in equilibrium with the gaseous phase.

27. A device as set forth in claim 22, wherein said substance is held by said sealed vessel solely in the gaseous phase.

28. A device as set forth in claim 22, further including temperature control means for maintaining said sealed vessel and said gaseous substance at a constant temperature.

29. A device as set forth in claim 1, wherein said substance is held by said sealed vessel entirely in the gaseous phase.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4106698 *Dec 29, 1976Aug 15, 1978Yorker Research CorporationPersonal automatic vaporizer
US4399942 *Nov 9, 1981Aug 23, 1983Gc IndustriesGas emitting device
US4849174 *Aug 14, 1987Jul 18, 1989American Air LiquideGas generating device
US4998431 *Sep 27, 1989Mar 12, 1991Vaisala OxField usable calibrator for humidity meters
US5156334 *Aug 15, 1990Oct 20, 1992Kimbell Charles LGas permeation system
US5294378 *Feb 16, 1993Mar 15, 1994S.A.E.S. Getters SpaCalibrating apparatus for isothermally introducing moisture into a stream of dry gas at a very slow rate
US8720794Oct 18, 2011May 13, 2014Real Sensors, Inc.Gas permeation devices
US20110240019 *Jan 31, 2011Oct 6, 2011Geno LlcNitric Oxide Delivery System
US20110259325 *Apr 26, 2011Oct 27, 2011Geno LlcDelivery of ultra pure nitric oxide (NO)
WO2007065570A1 *Nov 25, 2006Jun 14, 2007Areva Np GmbhMethod and device for calibrating a humidity sensor
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Classifications
U.S. Classification239/34
International ClassificationG01N1/28, G05D11/035, G05D11/00
Cooperative ClassificationG01N1/28, G05D11/035
European ClassificationG01N1/28, G05D11/035
Legal Events
DateCodeEventDescription
Apr 20, 1981AS02Assignment of assignor's interest
Owner name: AMBAC INDUSTRIES, INC., ONE OLD COUNTRY RD., CARLE
Effective date: 19810406
Owner name: ECOLOGY BOARD, INC.
Apr 20, 1981ASAssignment
Owner name: AMBAC INDUSTRIES, INC., ONE OLD COUNTRY RD., CARLE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ECOLOGY BOARD, INC.;REEL/FRAME:003848/0892
Effective date: 19810406
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ECOLOGY BOARD, INC.;REEL/FRAME:003848/0892