US 2462820 A
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Description (OCR text may contain errors)
1949- c. FL WALLACE 2,462,820
STATIC ELIMINATION IN MANOMETERS Filed March 12, 1945 V v INVENTOR. 679491.555 #1440105 4 flW/w. 4%
1i TZjORA/Ey Patented Feb. 22, 1949 UNITED STATES PATENT OFFICE STATIC ELIMINATION IN MANOME'IERS Charles F. Wallace, Westfield, N. J assignor to Wallace & Tier-nan Products, Inc., Bclleville, N. J., a corporation of New Jersey Application March 12, 1945, Serial No. 582,340
My present invention relates to static elimination in manometers and more particularly to manometers such, for example, as a mercury barometer, wherein means are provided for pre- 2 opposite sign, i. c. either negative or positive (respectively). It has been suggested that a theory tending to explain this phenomenon is that the mercury does not wet the tube and hence does Venting the effect p t e h of the e c y 5 not have such contact therewith as can bleed an column of static electricity which causes some inelectrical charge from the inside walls of the accuracies in the readings. tube. However, the present invention is not In working with manometers, particularly merpredicated upon any particular theory; and this cury barometers, it has been found that the presis only suggested by way of possible explanation. ence of static electricity inside the transparent A further and more specific object of the prestube conta a column of liq id, the height of out invention is to provide an inside coatin on which is indicative of a pressure or other condition a manometer tube of the above described characto be measured, causes relatively small, but appreter, which will be in close contact with the lube ciable, errors in the height of the liquid column. and will be per se electrically conducting, while For example, in a mercury barometer, this error being sufficiently transparent or translucent, so as may be in the order of magnitude of .005 inch to permit avisual reading of a height of the liquid of mercury. Where the utmost accuracy is of imcolumn in the tube and so that any static elecportance, it is necessary that means be provided tricity which may accumulate inside a tube by for eliminating this error. The provision of such reason of the liquid ther in being moved up and means is a primary object of the present invendown or for any other reason, may be bled off to tion. a suitable ground so that it will not interfere with The presence of static electricity has been noted the liquid column attaining a level accurately inin the following way. If a small piece of very thin dicative of the magnitude of a condition to be inaluminum foil is cemented on the upper edge only dicated thereby. to the side of a tube and is bent so that its bottom Other and more detailed objects of the present edge is approximately /8 from the tube such as invention will become apparent from the follow a glass tube containing a mercury column and the ing specification and appended claims, whentaken mercury run up or down several times past the in connection with the accompanying drawin s, in place at which the aluminum foil is secured, it will which: be found that when the mercury rises upwardly Figure 1 is a fore-shortened view, partly in past the aluminum foil, the uncemented part of elevation and partly in central vertical section, the latter will remain outwardly away from the showing a portion of a mercury barometer wheretube; and when the mercury is moved down past in the tube is coated interiorly in accordance this foil, it will move toward the tube and stay with the present invention; and close to the glass. When, however, a tube used for Fig. 2 is a detail view in horizontal section on a liquid column to measure pressure is treated as the line 22 of Fig. 1. hereinafter more particularly set forth and in ac- I have chosen to illustrate my invention as apcordance with the present invention, this eifect is plied to a mercury barometer, although I contemnot present. Further, upon comparison between plate that it is equally applicable to any and all an untreated manometer and one constructed or types of manometers and also may be applicable prepared in accordance with the present invento manometers using liquids other than mercury. tion, it is found that the untreated manometer The drawings illustrate a mercury barometer usually shows a higher readin if it has been including a container l, which may be constructused recently, in the order of magnitude of .005 ed in the usual manner to contain a pool of merinch of mercury, than that of the treated manomcury and which may have an opening to the eter. The fact that the mercury itself is elecatmosphere through a top portion 2 thereof or trically conducting apparently does not serve to may be connected in a manner (not shown) to a bleed such static electricity away from the survessel in which there is a gaseous pressure which face of the tube in which it is enclosed, as the it is desired to indicate. There is provided a tube phenomenon has been particularly noticed as 3 in the usual manner, which preferably extends aforesaid in connection with mercury barometers. dOWn n o a p o of mercury de t e n ainer It is assumed, but not herein relied upon that in I, but does not extend completely to the bottom the case of mercury manometers at least, the thereof, this tube preferably being of transparent mercury has a charge of one sign (either positive 5 or translucent material such as glass. The indior negative) while the glass has a charge of the eating liquid, in this case mercury, is shown at 4 up to a height or level indicated at 5 in the tube. Thus, if the level of the mercury in the container l is maintained at a given point in any suitable manner known to the art, the height of the column of mercury 4, that is the level or top surface 5, may be read in connection with an appropriate gauge or scale in any desired and/ or known manner. The construction thus far described may be considered as the standard equipment of the prior art.
As above set forth, I have found that the presence of static electricity which tends'to collect on the inside surface of the tube 3 causes the error in the height of the mercury column, which tends to cause it to read high and by an amount which has been found to be in the order of magnitude of .005 inch.
My present invention provides means for bleeding off this static electricity, so that it will not interfere with or affect the height of the column. For this purpose I preferably provide on the inside surface of the tube 3 a coating of some electrically conductive material, which preferably also is sufficiently transparent or translucent so that the height of the liquid, that is the level 5, may be visually read or otherwise ascertained. While I contemplate that various types of coatings might be adequate for this purpose, including sprayed metal, the type I have found most advantageous for practical use is a thin film deposited from an aqueous colloidal solution of graphite, such as that known commercially as Aquadag. This coating is shown diagrammatically in the accompanying drawings at 6. It will be understood that while the layer ii as shown in the drawings is of substantial thickness, this is for illustrative purposes only and is not to be taken as .an accurate illustration indicative of the actual dimensions of the thickness of the coating which is in practice very thin, so that it will not seriously interfere with the transparency r transluency of the coated tube and thus interfere with a visual reading of the height of the top surface level of the liquid column. Preferably the entire interior surface of the tube is coated, although I contemplate that if only that portion extending for a substantial distance above and below the probable height of the liquid column 5, many, if not all, the desired results of this invention would still be attained. In view of the fact that most liquids used in manometers are per se to some extent electrically conducting, it has been found that there will be a sufiicient contact if the tube is coated for a substantial length below the surface of the liquid 5 to effect a bleeding off and consequent grounding of the static electricity from the layer or coating 6 to the fluid itself.
While I have shown and specifically described herein but one embodiment of the present invention and have pointed out in connection with this description the essential characteristics thereof,
it will be understood that various modifications may be made therein within the above teachings and as will be apparent to those skilled in the art therefrom. I do not wish to be limited, therefore, except by the scope of the appended claims, which are to be construed validly as broadly as the state of the prior art permits.
What I claim is:
1. A manometer, comprising a non-metallic and non-electric conducting tube containing a liquid, the level of the surface of which in said tube is indicative of the magnitude of a condition, and an electrically conducting coating inside said tube and. in contact with said tube and with the liquid therein for bleeding off static electricity on the inside of said tube, so as to prevent any effect of such static electricity upon the level of the surface of the liquid in'said tube.
2. A manometer in accordance with claim 1, wherein said tube is a transparent glass tube, said coating is a substantially transparent layer of graphite, and said liquid is mercury.
CHARLES F. WALLACE.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 127,752 Emery et a1 June 11, 1872 379,305 Brown Mar; 13, 1 888 546,802 Ayrton et al. Sept. 24, 1895 815,814 Green Mar. 20, 1906 2,346,483 Goss Apr. 11, 1944