US1042440A - Electrostatic voltmeter. - Google Patents

Description

31C. HUBBARD.

BLEGTROSTATIG VOLTMETER.

APPLICATION FILED 0012.13, 1911,

.latented Oct. 29, 1912.

.Illu

m1111111@ l@ T1- M1, ,11111111111111111111111|y M1111 f- :i 2 i Lmrmznmmmmmmzr mmm ELEGTROSTATC VOLTMETER.

Specification of Letters Patent.

Patented ct. 29,1912.

Application filed October 13, 1911. Serial No. 654,444.

To all 'whom it may concern:

Be it known that l, JOHN C. HUBBARD, a citizen of the United States.r residing at *Worcester` in the county of Worcester and State of Massachusetts, have invented a new and useful Electrostatic Voltmeter, of which the following is specification.

The principal objects of the invention are to provide a 'voltmetcr or electrometer of very great sensitiveness; to provide means whereby an ordinary form of electroscope can, by very simple and inexpensive additions, be converted into a sensitive electrostatic volt-meter or electrometer: to provide an instrument of the indicated character having a `constant sensibilityfor a given strength of field whereby measures upon large potentials can be made with the same absolute degree of accuracy as upon small potentials; to provide an instrument of this character useful in all nleasureinents coinmonly made either with the gold-leaf electroscope, quadrant clectrometcr, or electrostatic voltmcter, and which can be used for alternating current voltages as well as for direct.

Further objects pear hereinafter.

Reference is to be had to t-he accompanyine' drawings, in whichrligure 1 is a front elevation of a gold leaf electrometer constructed in accordance with this invention; Fig. Q is a plan of the same; and Fig. 3 is a diagrammatic. view showing the electrical connections.

The invention is shown in a simple form in which a stand is provided having levcling screws 11 for supporting the instrument. On this stand is a shaft 12 to which is xed a easing 18 of conductingmaterial. rThis casing is provided with an insulating plug 14 for supporting a mercury terminal 15 with which is connected a gold leaf indicator 16 depending in the casing. At the bottom the casing is provided with anadjustingjr screw 17 which carries an insulating support 18 on which are mounted two conducting terminals 19 insulated from each other by the support 18 and melting an angle with each other. These are so located that under normal conditions the gold leaf 16 depends between the terminals 19 withouttouohing them. A pair of springs 20 engage the terminals 1.9 and are connected through insulating plugs 21 to binding screws 22. it the sides of the casing oppoand advantages will apsite the indicator are windows 23 through which the position of the indicator may be observed as for example through a microscope 24 supported by the shaft 1Q. The shaft. 12 is mounted to turn in bearings on the support 10 and is provided with a hub 25 which is engaged by a split bushing' 26 on an adjusting frame 2'?. A screw 2S is provided for clamping the split bushing to the hub of the shaft so that any motion of the frame will be transmit-ted to the shaft. he frame is provided with an adjustii'lg screw 280 and a spring-pressed plunger 29 both yengaging a. lug 30 cast on the support 10.

The casing' 13 also provided with a disk 33 concentric with the shaft and provided with a scale 31 preferably with a Vernier 39. by which the angularity can be read.

t will be obvious that by loosening the screw 28 the casing can be turned to any de sired point and then by tightening the screw the frame 27 can be adjusted to any desired degree of neness thus adjusting the position of the casing in like degree.

rlhe principle of the instrument `depends on the fact that when the indicator is charged to a given potential the instrument may be tilted or turned so that the force of gravity7 or some other force, constant in magnitude and direction, acting on the indicator will balance the electric force acting on the same in such a way that the indicator will occupy the same position with 4respect to the other parts of the instrument" as it did in the normal position of the instrument before the indicator was charged. T he potential or voltage which has been applied to the indicator is then proportional to the sine of the angle o of tilt.

The device is connected up as usual. The

diagram illustrates the connections The bindingscrews 22 are connected with the opposite poles of a battery B or the like giving the field plates 19 a constant potential difference. rEhe middle of the battery, screw 1'? and casing 13 are earthed The.

terminal 15 is connected with a switch S which can be connected to the earth, to a known potential, as a standard cell Vs, 'for calibration, or to the unknown potential (Vx).

ln order to use the instrument in measuring potentials it is first necessary to calibrate it. The case and '-'idieator are put to earth while the field plates 19 are put at a constant dierence of potential as described. rli`he microscope or reading device of the indicator is so adjusted that the indicator stands at a delinitely measured place in the field; for instance, when the microscope is used, the image of the indicator is seen to coincide with a cross hair or marl; at the focus of the eyespiecc oit the said microscope. The earth connection with the indicator is now broken, and the indicator is connected with one pole of a. standard cell of potential VS, the other pole being to earth. Then Using thi-s value ot 7c it is then possible to measure arly unknown potential by connecting it in place ot the standard cell. The unknown potential may also be measured by direct comparison. Let VS be the 'known potential, VX the unknown, o5 the angular reading for the known potential, and ex the angular reading for the unknown potential, then The theory may be stated in eral Way follows: Let the suspended or supported in an electric field produced between the plates i9 charged Mto a deinite difference of potential. Suppose now that the indicator be uncharged or put to some definite potential which, for convert ience, We shall call Zero, and let the position of the indicator with reference to the plates 19, or `with reference to any bodies which produce the field he measured. Call this the zero position of the indicator. Now let the indicator be charged to the potential which is to be measured. The indicator will. be deiicctcd or turned by the electric field acting upon the charge on the indicator. l

vmore gen indicator be ,lhe framework or case which carries thc system of field bodies and the support of the indicator is now turned or-rotated in such a direction that the indicator is drawn by some torce, constant in direction and magnitude, such as the force of gravity, back into its original position with reterence'to the field und the system which produces it.. The iudicator is now in equilibrium under the action of two forces, (a) the deliecting torce ci the electric field, and (o) the restoring force, (gravity). Let ythe angle through which the instrument has been turned be o. Then We have Vrie sin. o,

where Vis thc potential to bc measured, c., that applied to thc indicator, t is a constant ol thc instrument which depends upon the strength of the field and upou the deus-ity aud structure ot the iiulicator, and is the angle through which the instrument has been turned in order to restore the indicator to its initial position. For, consider meente any portion of the indicator, rThe torce G, which has been called the restoring torce is constant in magnitude and direction and exerts the moment CLGIGQ sin. e,

when n the perpendicilar distance from the lintx ot acticn ot the torce G to the point ot' support the indicator, and r is the distance trom the point considered to the axis of support.

- Let the 'torce li be thc componentof the electric force acting; at the same point perpendicular to the radius to the point from the airis of support. This force is, by elec- -triral theory, prffportional to the potentiai applied to the indicator, th` is FIKV, since by tue manipulation of the instrument above described, the indicator is in a field ot constant strength and tix-ed direction with respect to the indicator. The momentot this force is KW7. These two moments are equal and opposite, or,

lfrGr sin. cpr-'0. Since this is truc 'tor any portion ot the lndicator 1l is truc tor all. portions and we have, therefore,

i" r: KG/l) sin. cpv-:viii e,

as stated.

Although l have illustrated and described the invention as applied to a gold lealc cicrtroscopc, it is to bc understood that this is donc tor illustrative purposes and do not wish to limit myself thereto, but

What l do claim isl. in an electrostaticvoltmetelg the combination ot an indicator adapted to be charged and to be moved, a pair ot terminals adapted to be connected with constant source ot .electricity to keep them at a con staut potential dilterence forinlluencing the indicator to move it, a casing for supporting the terminals and indicator, and means whereby said casing can bo moved to bring thc indicator when charged bui-l; to the position it assumed when not charged.

2. ln a device ol the character described, the combination with. a, movable casinghot` a' support thereon, an indicator on the support adapted to be charged and to be moved thereby, a pair ot teri'ninals carried by the casing on opposite sides ot the indicator for connection with the opposite poles ot a constant source ot electricity to keep them at a constant potential difference, and means whereby the casing can bc moved for the purpose oi" restoring the indicator to its u1u-.harmed position by the aid of an independent torce while the indicator and terminals are charged.

3. ln a device ci" the character described, the combination oit a casing having a support thereon, a freely inovabie indicator carried by said support, e pair of terminals insulated from each other and mounted on seid casing in position to influence the indicater when charged to cause the indicator to move, and ineens whereby said casing can be rotated on en exis for he purpose of bringing he indicator back to its uncharged position by the aid of gravity when charged.

4. n e device of the character described, he Combination Wit-h :i support, of a shaft supported hereon and capable of being turned by henri, a. casino fixed to the shaft, an indicator in the casing, ineens for eiectricaily inh'iencing the inciiooi'or, en adjush able frame connected Wih said support mounted et one end of seid shaft, and means for fixing seid freine *no the shaft, whereoy the shaft can he jenrned by -the adjustment of the frames 5. in e device of the character described, Jthe coinhinaion with e support, of a shaft Re@ to the shaft, an indicoor in the casing, means for eiectrioaiiy lninencing the indirotatobiy supporeri thereon, a easing cater, an adjustable frame connected Wihf said suppori and mounted at one end of seid my hond, in die presence of JWo subseri..fing` witnesses.

Ul-1N C. HUBBARD,

-iVitnesses ALBERT E. F Y, C. Formeel 1i//essonE having e

Images