Dec. 3, 1946. P. D. zoT‘rU 2,412,191 VOLTMETER Filed' March 31, 1944 ' 4 sheets-sheet 1 f2.7 F@ 2 ' Bydvuïßâwwavê Dec. v3, 1946. I P. D. zoT'rU 2,412,191 voLTMETER Filed March 31, 1944 4 Sheets-Sheet 2 INVENTOR. 55., 3 ß 207-70. Patented bec. 3, _1946 _ UNITED STATES PATENT OFFICE 2,4i2.19l VOLTMETER Paul D. Zottu, Indian Hills, Ky., assigner to The Girdler Corporation, Louisville, Ky., a cor poration oi’ Delaware Application March 3l, wat, Serial No. 528,34@ 6 Claims. (Ci. lili-m95) ¿L This invention relates to measuring instru ments, more particularly to the measurement or" voltages at high frequency, and has for an oh ject the provision oi1 a wide-range voltzneter of a simple, rugged construction and accurate 5 » throughout the Wide range of voltages which it E in the output circuit of the rectifier is calibrated in terms of the line voltage or the voltage to be measured. Hence, if the meter reads 500, the voltage measured will be either 590 or a ñxed multiple thereof depending upon the setting of the spherical conductor. ` is capable ci measuring. For a more detailed explanation of the inven In the development of high-frequency systems tion and for further objects and advantages for application to manufacturing processes there thereof, reference is to be had to the following has been need for a relatively simple means of lo description, taken in conjunction with the ac measuring the voltages developed in the circuits. comparu/ing drawings in which: It has long been recognized that electrical energy Fig. l is a wiring diagram, diagrammatically at high frequency produces diathermy or inillustrating the relation oi the parts and their ternal heating of a wide variety of materials. associated circuits; These materials may vary from poor conductors l5 Fig. 2 is a fractional side elevation of the high to dielectrics or materials generally considered as non-conductors. For such a wide variety of voltage capacitor; Fig. 3 is a sectional View taken on the line 3-3 applications, the voltage and frequency of the of Fig. 5; output circuit are adjusted to best suit a partio- ular application. Fic". d is a sectional view taken on the line 4_4 2li of Fig. 2; ln accordance with the present invention, a FS. 5 is a fractional sectional elevation taken wide range voitineter is provided, which is rel» on the line aïe-5 of Fig. i; ` a'tively accurate over a range of from 500 to Fil?. 6 diagï'amm?lîìicßlìy illustrates a mûdiñed öûjloü volts or more. From the circuit to be form of theinventlon; v tested, a voltage is applied to two series-connect~ 25 Fig. ‘7 is a plan view of an iris disc shown in Fig. ed capacitors, one of which is adjustable between predetermined calibrated positions. For high voltages the adjustable capacitor preferably consfmts ci an enlarged conductor forming one plate of the capacitor' and a fiat conductor forming 30 the other plate oi the capacitor. The flat plate upoorted from a metallic housinsy having an „lng above the :'iat plate. The enlarged or .’ierical conductor is movable aient” a path nora to the fiat plate and to the opening in the 35 using. By increasing the spacing or air gap herr/veen the spherical conductor and the iiat conductor, the voltmeter is set for operation to measure voltages between differing limits. This adjustment forms la multiplier for the voltmeter. . 4o For low voltages, the distance between the' spherical conductor and the ñat conductor is relatively short. while for a voltage near the maximum which is to be measured the distance is substantial. The second capacitor may be i5 large in comparison with the one including the Spherical conductor. inasmuch as the voltage divides across the capacitors inversely >with their capacitance, only t; and Fig. 8 is a plan View oi a second iris disc hav ing a smaller opening. Referring to the drawings, a system embody ing the invention will ‘first be described, followed by a more detailed description oi’ the structural features or the multiplying capacitor. In the system or" Fig. l, the invention is shown as com pricing va high-voltage high-frequency vûltm‘èter‘ for the measurement of the voltage V appearing across the terminals ill and li. This voltage di-vides across two capacitors l2 and lil, connect» ed in series between terminals i@ and il. Both capacitors are adjustable. For a given setting the capacity of the capacitor i3 is usually much larger than that of the capacitor l2. ln conse quence, the voltage across the capacitor i3 is us ually smaller than the voltage across the capaci tor l2 for the reason that the-voltage divides across the capacitors inversely with their ca pacitance. By making the capacitor~ itl very large in comparison with the capacitor li?, the voltages applied to the measuring circuit may not only be of a reasonable order of magnitude, but a fraction of the voltage to be measured appears 50 entirely safe from an equipment and personnel across the larger capacitor.> The fractional volt~ standpoint. ‘ age which appears across the larger capacitor is The voltage appearing across the capacitor i3 applied to a rectiîying device which produces an is applied by conductors it and it to a rectify output current proportional to the applied highù ing` device, preferably a diode lf3. The reßtiñêd frequency voltage. A current meter connected 55 output from the diode is applied to a suitable in« aaiaiai 3 to the measurement òf the output voltage of a dicating device, such, for example, as a milliam high frequency> oscillator or generator. During meter I1, having a scale preferably calibrated in the starting up of such an oscillator, the load is> volts. By means of the network comprising the to be gradually applied. Suitable adjustments series-connected resistors I8, I9, 20 and 2|, and of the circuit constants must be made to produce the capacitor 22,- a substantially constant load is maximum output . voltage. The problem is to provided for the radiofrequency voltage which determine whether a given change in capacitance appears across the capacitor I3. The milliam or lnductance is in the right direction to increase meter I1 is connected in series with the resistor the output voltage. Small changes in the circuit 2| which is variable or adjustable in order to provide an initial setting for the voltmeter which il) constants frequently produce small changes inthe output voltage. These may not be of suiii will read full-scale value for some convenient voltage across or between conductors I4 and I5. By means of a normally open sensitivity switch cient magnitude to produce positive deflectiony ofv the meterv I1. However, by temporarily closing the sensitivity switch 25 to exclude the resistors 25, the resistors I9, 20 and 2| may be removed I9, 20 and 2|, the sensitivity of the meter is -ma or bypassed from the circuit of the milliammeter terially increased. For each incremental change I1. While the removal of these resistors greatly of voltage, the ldeflection of the meter is mate increases the reading and sensitivity of the meter rially greater than with the sensitivity switch in I1 the load across the capacitor I3 remains sub its normally open position. Hence, whenever the stantially constant. This result is accomplished voltage is low,_the sensitivity switch 25 may be by the circuit including resistor I 8 and the ca 20 operated to by-pass the foregoing resistors and pacitor 22 whose reactance is relatively low as the resultant greater deflections will then indi compared with the impedance offered by the cate and clearly show the direction of the change resistors I9, 20 and 2| to the radiofrequency cur in the output voltage. ~ rent. Hence, the inclusion or exclusion of the resistors I9-2I from the circuit does not mate 25 In terms of operation, the operator can then ` . ascertain with certainty the effect of changing rially change the load across the capacitor I3. 'I‘he diode I6 is provided with a filament trans- ' the tuning, the- circuit constants or other variables of the high frequency oscillator as it is brought former 21 whose primaryv is >connected to a suit up to full load operation. It may be observed able source of alternating current supply 29. The midpoint ofthe secondary winding is connected 30 again that operation of the sensitivity switch 25A does not materially change the load across the by conductor 30 to the indirectly heated cathode capacitor I3 since that load is largely established ~ of the diode I6. 'I'he direct.,.-current circuit .for by the resistor I8 and the series capacitor 22»,k the meter I1, previously referred to, may be traced whose reactance is relatively low as compared from the indirectly heated cathode by way of with the impedance offered by the resistors conductor I4, the meter I1, conductor 32, variable I 9-2I. ' resistor 2|, the resistors I9g'fand 20 connected in Coming now to the structural features charac parallel with each other, the resistor I8 and by terlzing the invention, the capacitor I2 comprises ` conductor I5 to the anode of the diode I6. the conductor or electrode 35 supported by a The initial calibration of the voltmeter-is rela tively simple. With the spherical conductor 35 40 metallic stem 36 which is held in any desired position by means of a split-ring clamping de comprising the upper high voltage plate or elec vice 31 provided with a clamping screw 38. The trode of capacitor I2 in a position of approxi mately maximum spacing from a iiat conductor 40 forming the other plate or electrode of the capacitor I2, the maximum voltage for which the meter is designed is applied. Thus, for a live inch _spacing between the electrodes 35 and 40, a voltage of 50,000 volts may be appliedbe tween terminals I0 and II. 'I'he frequency may be of any value within wide limits, for example, stem 36 as shown in Fig. 5 may be made of tubing with the lower end plugged, and threaded for threaded engagement with the electrode 35. As shown, the electrode 35 is spherical in shape and though this is the preferred construction, the invention is not limited thereto since other shapes , may be used. For the higher voltages the elec trode 35 should be provided with smooth or rounded edges to prevent corona discharge. from some thousands of cycles per second to a The cooperating capacitor electrode or plate hundred million cycles or more per second. With t0 is shown in Fig. 3 to be circular although it the aforesaid voltage of 50,000 (peak) volts lat a can be of any desired configuration. Preferably frequency of say one million cycles per second, the capacitor I3 is adjusted until the pointer of 55 it is supported, Figs. 2 and 5, below the upper wall dla. of a metallic housing 4I by means of an in meter I1' is deflected to its maximum or full-scale position. This may be accomplished by an R. F. « ' sulating supporting bar M. voltage of the order of 100 volts across the capaci tor I3. The capacitor I3 and the resistor 2| are now locked in vtheir adjusted positions. For all other voltage'ranges, the capacitor I2 is adjusted by moving spherical conductor 35 to predetermined positions. Thus it is in effect a multiplier and fixes the range of voltages for the meter I1. If the meter is calibrated in volts from 0 to 500, then for the highest range the multiply ing factor may be 100. By decreasing the spacing between the capacitor electrodes 35 and 40 by predetermined increments, other multiplying fac tors in steps of III, from 1 to 100, may be provided. Once calibrated, the voltmeter as a whole con tinues effective as a satisfactorily accurate measuring device. _ The importance of the sensitivity feature will be apparent by assuming the voltmeter is applied This bar is carried between adjusting nuts at the ends of threaded screws t5- and «36 which extend downwardly through the upper wall or cover plate Bla of housing 5I. The iiat circular electrode 40 is fas tened to the bar 44 by means of a threaded screw d1 and'cooperating nut. The plate d0 is counter sunk so that the head of screw ä'lis flush with the upper surface thereof. ` Just above the electrode 40 the central portion of the housing @la is cut away to provide opening 43, shown as circular and of somewhat less di ameter than that of the electrode 40. This open ing is closed by means of an insulating closure member 68, held in place by means of additional nuts on the screws 45 and 46. , The movable electrode 35 is supported from the upper plate «ila of housing «il by means of three insulators 50, 5I and 52, which may oe of aclarar , - 7 trode with respect' to said first electrode thereby to change the voltage range of the device. 2. The combination, with a high-voltage meas uring device in which a rectiñed current varies in accordance with the voltage »to be measured, of a metal plate having an opening extending through the mid-portion thereof, a capacitor in Y ent positions with respect to each other to change the capacity between them and the range of volt-A age to be measured, and shielding means, inter posed between said two electrodes having an opening therein for the passage therethrough of a part only of the electrostatic field which would otherwise extend between said two electrodes. 5. The combination, with a high-voltage high cluding at least a first electrode and a second 4 frequency measuring device of the type in which electrode, electrical insulating means for support ing said i-lrst'electrode in spaced relation with 10 a rectified current varies in accordance with the voltage to be measured, of a series-circuit includ said opening and concentrically thereof, a plu ing two capacitors one of which is relatively large rality of insulating supports secured to said plate with respect to the other, said -smaller capacitor and extending outwardly therefrom, means in being characterized by the provision of two elec cluding a clamping device carried by the outer trodes one of which is movable relative tothe ends of said insulating members, said second elec other. means including one of said electrodes for trode including a supporting stem adapted to be applying to said series-circuit the voltage to be held by said clamping device, whereby' said last measured, means for holding one `of said elec named electrode may be supported in different predetermined positions with respect to said first electrode. ' _ 3. In a high-voltage high-frequency measuring device in which a vrectified current varies in ac cordance with the voltage to be measured, the combination of a pair of series-connected capac itors across which the voltage divides inversely with respect to their capacities, a circuitcon trodes in diñerent predetermined positions with 20 respect to the other to predetermine the capacity therebetween and thereby iix the voltage range of the measuring device, and adjusting shielding ’ means interposed between said electrodes for pre determining the proportion of the electric ñeld which may then exist between said electrodes further to change the voltage range of the meas uring device. 6. The combination, with a high-voltage meas including a rectifying device for producing said uring device in which a rectiñed current varies in rectified current, a network connected in parallel with said larger capacitor for producing a sub 30 accordance with the voltage to be measured, of a metal plate having an opening extending through stantially constant load across said larger ca the mid-portion thereof, a capacitor including at pacitor, said network including a resistor and a least a first electrode and a second electrode, elec third capacitor connected in series with veach trical insulating means for supporting said first other and in shunt across said large capacitor, electrode in spaced relation with said opening, a said network also including at least one additional nected vacross the larger of said capacities and resistor, and means for increasing the magnitude of said rectified current Without asubstantially changing the load across said larger capacitor comprising a switch for removing said last-named plurality of insulating supports secured to said plate and extending outwardly therefrom, means including a .clamping device carried by the outer ends of said insulating members, said second elec current varies in accordance with the voltage to be measured, of a. high-voltage capacitor which comprises electrodes relatively movable to diiîer predetermined positions with respect to said first 40 trode including a supporting stern adapted to be resistor from said circuit. held by said clamping device, whereby said last 4. The combination, with a high-voltage high named electrode may be supported in different frequency measuring device in which a rectified electrode. PAUL D. ZOTTU.