US3258634A

US3258634A - Non-tubulent plow ion chamber t. a. rich

Info

Publication number: US3258634A
Authority: US
Publication date: 1966-06-28
Anticipated expiration: 1983-06-28

Description

June 28, 1966 T. A. RICH 3,258,634

NON-TUBULENT FLOW ION CHAMBER Filed Aug. 16, 1961 2 Sheets-Sheet l F/gJ.

Inventor.-

Theodore A. Rich,

by W U/w His Attorney June 28, 1966 T. A. RICH 3,258,634

NON-TUBULENT FLOW ION CHAMBER Filed Aug. 16, 1961 2 Sheets-Sheet 2 Inventor": Theodore A. Rich, by

His Attorney- United States Patent 3,258,634 NON-TURBULENT FLOW ION CHAMBER Theodore A. Rich, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Aug. 16, 1961, Ser. No. 131,890 3 Claims. (Cl. 313-431) The present invention relates to a new and improved ion chamber.

More particularly, the invention relates to a new and improved ion chamber construction which renders the ion chamber relatively insensitive to changes in the atmosphere and which assures proper operation of the ion chamber over extended periods of time under widely varying environmental conditions.

An ion chamber is a device which comprises a conductive collecting chamber having a coaxially disposed collector-electrode member which is maintained at a different electric potential from the collecting chamber. Because of this arrangement an electric field exists between the chamber and the collector-electrode member which acts on negative ions, electrons, and other small charged particles having high mobility to cause them to be collected on the collector-electrode member to produce an output electric current indicative of the number of such small charged particles present in the atmosphere. With currently available ion chambers, it is not always possible to obtain a measurable ion current with an ion chamber of reasonable proportions in connection with prevailing flow rates of the gases being sampled. Further, when the device is to be used in an outdoor environment, fluctuations in the wind velocity or direction will cause wide fluctuations in the output readings of known ion chamber constructions. Additionally, many of the known ion chambers deteriorate in an outdoor environment due to breakdown from high moisture content in the air, etc.

It is therefore a primary object of the invention to provide a new and improved ion chamber which is relatively insensitive to changes in the atmosphere in which it is used, and is capable of accurately measuring the number of ions present in the atmosphere over a wide range of flow rates through the chamber.

Another object of the invention is to provide an ion chamber having the above characteristics which has a long operating life and which is not susceptible to breakdown due to high moisture content in the environment in which it is used.

In practicing the invention a new and improved ion chamber is provided which comprises an electrically conductive collecting chamber and a conductive collector member coaxially supported within the collecting chamber for collecting ions thereon from gaseous samples introduced into the chamber and deriving an output eletric current indicative of the number of ions collected. In a preferred embodiment of the invention, the new and improved ion chamber is completed by a horn-shaped nozzle which is secured adjacent the electrically conductive chamber for introducing the gases being sampled into the chamber under streamline flow conditions. In a preferred embodiment of the invention, the collecting chamber is supported within an outer casing and electrically isolated therefrom, and circulating dry air is introduced into the space between the outer casing and the collecting chamber which serves to maintain the insulating supports used in the ion chamber in a dry, highly insulating condition. In another embodiment of the invention, shaped collecting plates are used to define the collecting chamber and are so shaped as to force the air passing through the chamber into a streamline flow condition.

Other objects, features and many of the attendant advantages of this invention will be appreciated more readily as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein like parts in each of the several figures are identified with the same reference numeral, and wherein:

FIGURE 1 is a sectional view of a new and improved ion chamber constructed in accordance with the invention;

FIGURE 2 is a cross-sectional view of an element of the ion chamber taken through plane 22 of FIGURE 1; and

FIGURE 3 is a perspective view of a second embodiment of the invention which employs shaped parallel plates to define the ion collecting chamber.

The ion chamber shown in FIGURE 1 of the drawing comprises essentially a cylindrically shaped casing 11 fabricated from an electrically conductive material such as aluminum, brass, and the like. The casing 11 has an annular flange portion 12 which is secured by means of bolts to an annular fiat mounting plate 13. Secured within the collecting chamber 11 is a long cylindrical rodlike collecting member 14 having a tapered upstream end portion which serves a purpose to be described more fully hereinafter. The collector-electrode member 14 is secured to an insulating post 15 having a teardrop-shaped cross-section shown in FIGURE 2 of the drawing, and which is secured between diametrically opposite sides of the collecting chamber by means of a plurality of screws. The collector-electrode member 14 is disposed in coaxial relationship within an inner cylindrical open ended collecting chamber 16 fabricated from an electrically conductive material such as aluminum, brass, or other similar material. The inner collecting chamber 16 has a plurality of annular insulating supports 17 secured around its exterior surface and to the interior surface of the outer casing 11 so that the inner collecting chamber 16 is securely held in coaxial relationship with respect to the collector-electrode member 14.

The upstream end of the collecting chamber 16 terminates just short of the annular mounting plate 13, and is in axial alignment or coextensive with the small diameter end or exit surface of a horn-shaped nozzle 18 secured adjacent to it. The nozzle 18 is rigidly mounted on the upstream end of'the ion chamber by means of a plurality of spacers 19 secured between the outer edge of the annular mounting plate 13 and the outer edge of the horn-shaped nozzle 18. The exact configuration of the horn-shaped nozzle 18 which flares outwardly from its exit surface to its entry surface is not of particular importance provided that it serves to increase smoothly and substantially the axial component of the velocity of the gaseous medium passing through the nozzle and introduced into the ion chamber. This shape is conveniently that of a standard ASME nozzle used for measuring air flow. The nozzle 18 may be fabricated from the same material as the collecting chamber 16 and the collectorelectrode member 14, and may be electrically connected to the end plate 13. However, the end of the nozzle 18 terminating adjacent the collecting chamber 16 is spaced a short distance apart from the end of the chamber so that an air space exists between the ends of the nozzle and the collecting chamber 16 for a purpose to be described more fully hereinafter.

To insure a long operating life for the ion chamber irrespective of the environment in which the chamber is used, means are provided for maintaining the insulating support 15 and the annular insulating rings 17 in a dry, highly insulating condition. This means comprises an input tube 21 which is connected to the space intermediate the outer casing 11 and the collecting chamber 16, and

which is connected to a source of filtered and dry air. In certain applications, this filtered and dry air may actually be air which is passed through the ion chamber with sufficient velocity to be introduced back through a suitable filtering and drying apparatus to the conduit 21, and hence into the space intermediate the outer casing 11 and the collecting chamber 16. In order to insure that the air circulates on all sides of the insulating rings 17, bypass tubes 22 are provided around the insulating rings 17 so that the drying air is circulated through all of the space intermediate the outer casing 11 and the collecting chamber 16. This air also passes through the air space between the ends of the collecting chamber 16 and the small diameter end of the nozzle 18, and through an air space between the downstream end of the collecting chamber 16 and a tapered guide 23 secured to the outer casing 11 adjacent the downstream end of the collecting chamber 16. The drying air in its passage through the ion chamher will therefore bathe the insulating rings 17 and insulating support so as to maintain these insulating supports in a dry, highly insulating condition thereby avoiding leakage of current due to moisture on their surface and the like.

In order to provide an electric potential to the collecting chamber 16, a conductive wire 24 is soldered or otherwise secured to the exterior surface of the collecting chamber 16 and is led out through a suitable insulating conduit 25 to a terminal post 26 secured to the fiange plate 13. By connecting the terminal 26 to a suitable power supply, an electric potential can be applied to the collecting chamber 16. Similarly, in order to obtain an output electric current from the collector-electrode member 14, a terminal post 27 is provided that is connected to the collector-electrode member 14, and to an output conductor 28. The output conductor 28 is secured through an insulating bushing to an output terminal 29 fastening to an outer housing 31 to which the flange plate 13 is secured, and which serves to support the ion chamber in position for use in measuring the ion content in the atmosphere. By connecting an appropriate output indicating instrument and a source of electric potential to the output terminal 2% in the manner shown by J. A. Chalmers on pages 32 of his book entitled Atmospheric Electricity, Oxford University Press, Amen House, London, 1949, an electrical indication can be obtained of the value of the output current supplied through the conductor 28. By such an arrangement a measurement of the number of ions present in the atmosphere being sampled by the ion chamber can be obtained.

In operation, the air entering the horn-shaped nozzle 18 invariably will have some radial velocity components. As this air enters the smaller diameter throat section of the nozzle, the axial velocity component is increased some sixteen times or more over the radial velocities present so that the radial velocities become small in comparison. Hence, the air passing through the nozzle is forced into a streamline flow condition and in this condition is introduced into the ion chamber comprised by the collecting chamber 16 and the collector-electrode member 14. The upstream end of the collector-electrode member 14 is rounded or shaped so as not to interfere or introduce turbulence into the air flowing through the chamber. By introducing the air into the ion chamber in a streamline flow condition, a greatly improved collection efiiciency is achieved. This results from the fact that during the transit time required for an ion introduced in the chamber to move through the length of the ion chamber for a streamline flow condition, the percentage of small charged particles whose radial transit time is such as to cause them to be deposited on the collector-electrode member 14 and thereby produce an output current, is increased. Hence, collection emciency is improved.

If the axial transit time i is defined as the time required for a small ion to move through the entire length of the collecting chamber 16, and the maximum radial transit time tl is defined as the time required for the same ion to flow across the entire diameter of the collecting chamber 16 (hence, the maximum radial distance to he travelled by an ion to be collected) then by inspection it is believed obvious that for collection z rl (1) The radical transit time ti is given by the expression 72 "'i '2 2MV, in r, 2

where The axial transit time tis given by the expression Q where L is the length of the ion chamber; and

Q is the flow in cubic centimeters per second. Substituting expression (2) and (3) in Equation 1 gives the following expression for 100% collection where M is the critical mobility of the particular chamber for the potential applied and for the geometry used.

With prior art devices, the above relations hold for streamline fiow conditions only. With these conventional size devices, it is necessary to maintain the Reynolds number below 2,000 to assure streamline fiow; however, with the Reynolds number at this low value, the volume of flow Q is far too low to give a reliable current measurement. With the present invention, the nozzle forces the air being monitored into a streamline flow condition for the useful length of the collecting chamber 16 even at Reynolds numbers as high as 50,000. Accordingly, the invention permits the collection of some 25 times as much current as with conventional configurations while still maintaining the desirable current-voltage relationship implied in the above expressions.

In addition to the above, when operating with high flow rates slight variations in the wind velocity and direction of the air being sampled by the ion chamber will not greatly affect collection etliciency of the ion chamber. These characteristics, when coupled with the greatly improved operating life due to the continual bathing of the insulating supports with clean dry air while the ion chamber is in operation, make available to the industry a considerably improved device for measuring small charged particles present in the air.

A second embodiment of the invention is shown in FIGURE 3 of the drawing. The ion chamber shown in FIGURE 3 comprises essentially a plurality of spaced apart collecting elements whose opposing surfaces are properly shaped to bring about streamline flow conditions of the air passing through the ion chamber as collection occurs. For this reason, the ion chamber is comprised of a pair of spaced apart shaped

plates

51 and 52 constructed of electrically conductive material such as aluminum, brass, etc., and which define a collection chamber. The shaped

plates

51 and 52 are held in spaced apart relationship by a plurality of electrically insulating supporting posts 53 which have their outer ends secured to the shaped

plates

51 and 52, respectively, and their inner ends secured to an inner collector member 54.

The collector member 54 is likewise formed of electrically conductive material and is shaped in the form of a hollow airplane wing in that its two exterior surfaces taper divergently outward from the upstream or input end of the ion chamber to the downstream or output end of the ion chamber. This configuration of the collector member 54 in conjunction with the shaped

plates

51 and 52 which are shaped to converge inwardly coming from the upstream or input end of the ion chamber to the downstream or output end causes the cross-section of the air space between the several members to converge slightly. This convergence causes the air passing through the ion chamber to be forced into a streamline flow condition as it passes through the collection chamber and thereby improves collection efiiciency in the same manner as described in connection with the species of the invention shown in FIGURE 1 of the drawing.

In order to supply an electrical potential to the chamber formed by the

outer collector plates

51, 52, a terminal means 55 is connected to the center of the shaped plate 51 and a similar terminal is provided for the shaped plate 52 so that an electric field will exist between these plates and the central collector member 54. This electric field will cause ions and other small charged particles contained in the air passage through the ion chamber to be collected on the collector member 54 and will produce an output ion current which is supplied through an ouput conductor 56 to an output indicating instrument (not shown) that will provide an indication of the number of ions collected on the collector member 54. From the above description it can be appreciated that the species of the invention shown in FIGURE 3 operates in much the same fashion as the species of the invention shown in FIGURE 1 with the exception that the walls of the ion chamber itself are shaped to force the air passing through the chamber into a streamline flow condition as the air is passing through the ion chamber rather than forcing the air into the streamline flow condition prior to its introduction into the chamber.

From the foregoing description, it can be appreciated that the invention provides a new and improved ion chamber which is relatively insensitive to changes in the atmosphere in which it is used, and is capable of accurately measuring the number of ions present in the atmosphere over a wide range of air flow rates through the chamber. Further, because of its design, the ion chamber is capable of operating over long periods without breakdown even in the presence of high moisture content in the environment in which the ion chamber is used.

Having described two embodiments of a new and improved ion chamber constructed in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in the light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A new and improved ion chamber comprising an inner cylindrically shaped electrically conductive collecting chamber having upstream and downstream ends,

a cylindrically shaped collector member coaxially arranged within and electrically insulated from said inner chamber, a plurality of insulating supports secured to the outer surfaces of said inner chamber, an outer casing secured to said insulating supports and electrically insu lated from both said collecting chamber and said collecting member and enclosing said inner cylindrically shaped collecting chamber, first terminal means electrically connected to the collecting chamber, second terminal means electrically connected to the collecting member, a hornshaped nozzle means flaring outwardly from its exit surface to its entry surface secured to said outer casing and held in longitudinal alignment with the upstream end of said inner chamber and having said exit surface adjacent to and coextensive with said upstream end under streamline flow conditions.

2. The combination set forth in claim 1 further characterized by a space to allow for circulating dry air between said outer casing and said inner chamber for maintaining said insulating supports in a dry, highly insulating condition.

3. A new and improved ion chamber comprising an inner cylindrically shaped electrically conductive collecting chamber having upstream and downstream ends, a cylindrically-shaped collector member coaxially arranged within and electrically insulated from said collecting chamber, a plurality of annularly shaped insulating members secured around said cylindrically shaped collecting chamber, an outer cylindrically shaped casing secured to said annularly-shaped insulating members and enclosing said inner collecting chamber, and providing space for circulating dry air between said outer casing and said inner chamber for drying said insulating members and maintaining them in a highly insulating condition, first terminal means electrically connected to the collecting chamber, second terminal means electrically connected to the collector member, and a horn-shaped nozzle means flaring outwardly from its exit surface to its entry surface secured to said outer casing and held in longitudinal alignment with the upstream end of said inner chamber and having said exit surface adjacent to and coextensive with said upstream end, said nozzle means being shaped to introduce the gaseous samples being monitored into said chamber under streamline flow conditions.

References Cited by the Examiner UNITED STATES PATENTS 2,504,772 4/1950 White 32433 2,898,549 8/1959 Miller 32430 2,913,893 11/1959 Mathews et al 32430 X 2,916,409 12/1959 Bucek 315-111 X 3,154,682 10/1964 Hartz et a1. 250-44 3,176,222 3/1965 Atkisson 3246 1 FOREIGN PATENTS 398,722 9/1933 Great Britain.

WALTER L. CARLSON, Primary Examiner.

FREDERICK M. STRADER, Examiner.

R. V. ROLINEC, C. F. ROBERTS,

Assistant Examiners.

Claims

3. A NEW AND IMPROVED ION CHAMBER COMPRISING AN INNER CYLINDRICALLY SHAPED ELECTRICALLY CONDUCTIVE COLLECTING CHAMBER HAVING UPSTREAM AND DOWNSTREAM ENDS, A CYLINDRICALLY-SHAPED COLLECTOR MEMBER COAXIALLY ARRANGED WITHIN AND ELECTRICALLY INSULATED FROM SAID COLLECTING CHAMBER, A PLURALITY OF ANNULARLY SHAPED INSULATING MEMBERS SECURED AROUND SAID CYLINDRICALLY SHAPED COLLECTING CHAMBER, AN OUTER CYLINDRICALLY SHAPED CASING SECURED TO SAID ANNULARLY-SHAPED INSULATING MEMBERS AND ENCLOSING SAID INNER COLLECTING CHAMBER, AND PROVIDING SPACE FOR CIRCULATING DRY AIR BETWEEN SAID OUTER CASING AND SAID INNER CHAMBER FOR DRYING SAID INSULATING MEMBERS AND MAINTAINING THEM IN A HIGHLY INSULATING CONDITION, FIRST TERMINAL MEANS ELECTRICALLY CONNECTED TO THE COLLECTING CHAMBER, SECOND TERMINAL MEANS ELECTRICALLY CONNECTED TO THE COLLECTOR MEMBER, AND A HORN-SHAPED NOZZLE MEANS FLARING OUTWARDLY FROM ITS EXIT SURFACE TO ITS ENTRY SURFACE SECURED TO SAID OUTER CASING AND HELD IN LONGITUDINAL ALIGNMENT WITH THE UPSTREAM END OF SAID INNER CHAMBER AND HAVING SAID EXIT SURFACE ADJACENT TO AND COEXTENSIVE WITH SAID UPATREAM END, SAID NOZZLE MEANS BEING SHAPED TO INTRODUCE THE GASEOUS SAMPLES BEING MONITORED INTO SAID CHAMBER UNDER STREAMLINE FLOW CONDITIONS.