US2717942A - Voltage divider - Google Patents

Description

Sept. 13, 1955 w J, RE S 2,717,942

VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet l FIG. 2.

W/LL/AM J. ANDREWS BY M @flw P 13, 1955 w. .1. ANDREWS 2,717,942

VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet 2 Eli E 120 E 240 EA: E I20 E 240' s[o PICK- OFF, E A:

/ R'= FILAMENT TO FILAMENT RESISTANCE E 4 PHASE TO PHASE RESISTANCE I E :20 R= APPROXIMATELY E 4240' WHE $E 7Z=TOTAL NUMBER OF FILAMENTS PICK-OFF EA FIG. 4.

INVENTOR. WILL/AM J. ANDREWS BY 6 /7M Sept. 13, 1955 w. J. ANDREWS VOLTAGE DIVIDER 4 Sheets-Sheet 3 Filed June 16, 1952 p MECHANICAL ANGLE uwdtm EDEFOMJM Sept. 13, 1955 2,717,942

W. J. ANDREWS VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet 4 CLO " FIG O I I I I I 4| 0 I l I I I I J 0 00 120 |a0 240 300 360 420 0 60 |ao 240 300 360 420 ELECTRICAL PHASE 0 "I ELECTRICAL PHASE 0 I l I 4 -60 50 40 20 I0 0' [0 20 30 [3, MECHANICAL DEGREES INVENTOR.

WILLIAM J. ANDREWS I I J {5, MECHANICAL DEGREES United States Patent VOLTAGE DIVIDER William J. Andrews, Lancaster, Pa., assignor to the United States of America as represented by the Secretary of the Navy Application June 16, 1952, Serial No. 293,719

Claims. (Cl. 20155) The present invention relates to continuously adjustable voltage dividers, and, more particularly, to voltage dividers developed for use with polyphase alternating current systems, whereby smooth transitions between the instantaneous voltages of the respective conductors may be attained.

Heretofore there has been no satisfactory simple apparatus for accomplishing this result, for ordinarily a usable device for this purpose would require a large number of series-connected resistors of the voltage divider type to give the required continuous variation through the multiple phases over and over again in proper order of succession.

A principal object of this invention, therefore, is to provide a simple and reliable polyphase voltage divider.

Another object is to provide a polyphase voltage divider that can be made very compact without losing its smoothness of voltage control.

To provide a polyphase voltage control whereby various rates of variation may be secured by radially shifting the location of a contact element that slidingly contacts the resistor of the voltage divider, is another main object of this invention.

A still further object of the invention is to provide a polyphase voltage divider having a plurality of independent voltage divider sections, each having an individual contact element that is likewise adjustable independently of any other contact element.

Other objects and many of the attendant advantages of this invention will be appreciated readily as the same becomes understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a face view of the multiple resistor of an adjustable voltage divider, embodying the invention;

Fig. 2 is a cross-section taken along line 22 of Fig. 1;

Fig. 3 illustrates a multi-tap resistance potentiometer equivalent to the arrangement shown in Fig. 1;

Fig. 4illustrates the potentiometer of Fig, 3 connected in a three-wire delta arrangement;

Fig. 5 illustrates a vector diagram for the arrangements shown in Figs. 3 and 4;

Fig. 6 illustrates graphical representations of theoretical phase error angle versus mechanical motion in equivalent electrical degrees of the pick-off for three and four phase excitations;

Fig. 7 illustrates the graphical representation of electrical phase angle versus mechanical angle for a typical segment of section 12 of the potentiometer arrangement shown in Fig. 1;

Fig. 8 shows the graphical representation of theoretical output voltage versus electrical phase angle for an arbitrary selected value of maximum pick-off voltage measured with respect to ground of two (2) volts;

Fig. 9 shows a graphical representation of output voltage versus electrical phase angle for a typical segment of section 12 of the potentiometer arrangement illustrated in Fig. 1;

Fig. 10 illustrates a graphical representation of output voltage versus electrical phase angle for another typical segment of section 12 of the potentiometer arrangement in Fig. 1;

Fig. 11 illustrates a graphical representation of lobe pattern as a function of mechanical motion of section 12 of the potentiometer arrangement of Fig. 1; and

Fig. 12 illustrates a graphical representation of a lobe pattern as a function of mechanical motion for section 16 of the potentiometer arrangement of Fig. l.

The device is designed to be used with a star-connected polyphase power system, having a neutral return conductor. The voltage divider has a characteristic repetition pattern of conducting lines, each interval of which has the same number of lines as the number of phases of the power system. Thus in the present case, designed for use with a three-phase power source, there are three lines in each interval. Consequently the fourth, fifth and sixth lines are electrically connected with the first, second and third line, respectively, and so on, the third line following any given line thus representing the same conductor of the three-phase power supply mains.

As the voltage divider is to be used in apparatus wherein space is extremely limited, it must be made as small as is consistent with adequate performance, and hence the lines must be spaced closely, which in turn requires that the width of each line should be as small as is readily feasible, and that the lines he placed as nearly uniformly as possible. For example, in one type of voltage divider wherein the conductors are carried by a Bakelite disk having a diameter of three inches, the lines do not exceed 0.002" in width and are positioned within a maximum tolerance of 0.0005".

The conducting lines mentioned above are preferably metallic and advantageously may consist of silver. They may be applied to the surface of the Bakelite disk in any suitable way, for example, by printing, of the kind used in printed radio circuits. The lines, however, form merely the underlying network which is covered by a uniform coating of resistance material. This is preferably of a relatively high-resistance type, having a value exceeding 50,000 ohms per square. Such high value is chosen because of the close spacing of the conductive lines, which otherwise would produce undesirably low resistances between consecutive lines.

Referring now to Fig. 1 for a detailed description of the invention, there is shown a circular disk 10 made of insulating material having suitable mechanical characteristics. It has been found, for example, that Bakelite and certain other synthetic resins are satisfactory for the purpose. In section 12 of the disk 10 there are several sets of parallel conducting lines, while sections 14 and 16 have sets of convergent conducting lines.

In section 12, the first conducting line 18 at the left is connected through a heavier conductor 20 to a projection 22 of an innermost bus bar 24 which is shown as circular with projections 22 and 26 extending therefrom to facilitate making connections thereto. Counting to the right and in the clockwise direction in section 12, the fourth conducting line 27 is, likewise, electrically connected to projection 22 through the conductor 28, and so on progressively, with the result that every third line after conducting line 27 of the parallel series is connected to the bus bar 24. An enlargement of bus bar 24, shown at 29, connects through to the other face 30 of the disk 10 to a preferably silver slip ring 31 which will be described presently. The connection is made through a hole 32 filled with silver paste.

The second of the parallel conducting lines of section 12 is designated as 33 and it is connected electrically through a heavier conductor 34 to the outermost bus bar 36 which is, likewise, of general circular shape, and has a tab 37 extending inwardly for connection to a second silver slip ring 38 on the other face of disk 10. This connection to slip ring 38 is made through a silver paste filled post 39. The line 33, like line 18, is also the first member of a series of parallel lines, comprising this line 33 and every third line to the right therefrom so that beginning with line 33 every third line therefrom is connected electrically to the bus bar 36.

Finally, the third conducting line 40 at the left of section 12 is connected by a heavier conductor 42 toa third bus bar 44 which includes a series of projections 46 between the successive conductors of the series 34 that connects to bus bar 36. The projections or lugs 46 are insulated from bus bar 36, but are all individually connected to a third slip ring 48 on face 30 by silver paste filled posts in the form of a pin, such as indicated by 50. As in the other series, starting with line 40 every third line therefrom and counting to the right, is connected to the adjacent lug 46, and these lugs 46, in turn, are all connected to a third silver slip ring 48 on the other face 30 of the disk 10.

It will be seen that section 12 has now been described as comprising a series of parallel conductors, connected in regular order to the three bus bars 24, 36, and 44.

The first conducting line 54 in the converging series of conducting lines in section 14 at the left is connected through a heavier conductor 56 to the outermost bus bar 36. Counting to the right, that is in the counterclockwise direction, in section 14, the fourth conducting line 58, likewise, is electrically connected to bus bar 36 through a heavier conductor of the type indicated by 56, and so on progressively, with the result that every third conducting line to the right from line 58 of the converging series is connected to the bus bar 36.

The second conducting line 60 of the converging series of lines of section 14 is electrically connected through a heavier conductor 62 to bus bar 24. Beginning with line 60, every third line thereafter, moving to the right, is connected through a heavier conductor to bus bar 24.

In section 14, the third conducting line 64 of the series of converging lines, and every third line thereafter, is electrically connected to the third bus bar 44 through lugs or projections 65 and heavy conductors, such as 66.

All three sets of conducting lines, as previously indicated for the conducting series in section 12, are connected to their respective slip rings 38, 31, and 48 on face 30 of the circular disk 10.

The conducting lines 67, 68, and in section 16 are connected in the same manner as the lines 54, 60 and 64, in section 14. Each third line thereafter from lines 67, 68, and 7t) (counting to the right) is connected like in section 14. It is to be pointed out that the number of contacts and lines in section 16 does not necessarily have to be of the same number as the contacts and lines in section 14.

It is to be noted further that the lines of section 14, such as 54, 60, and 64, as well as the lines 67, 68, and 70, do not converge at the center 72 of the circular disk 10, but at different off-center points, such as indicated by 74 and 76. As will be presently pointed out, this is done so that a contactor located a greater radial distance from the center 72 of the circular disk 10, will contact a smaller number of lines, such as 54, 60, and 64, than a contactor located at a shorter radial distance from the center 72 of the circular disk 10, for the same angular movement of the contactors.

In each section, namely sections 12, 14, and 16, a suitable resistance material, such as carbon in graphite form, is deposited or printed in uniform thickness on the surfaces 78, 80, and 82 of disk 10 so as to embed all the conducting lines, such as 18, 33, 40, and 27 in section 12, lines 54, 60, and 64 in section 14, and lines 67, 68, and 70 in section 16, and so forth in each section, and

also to offer the necessary resistance between the sets of conducting lines.

There is one major difference between the arrangement of the conducting lines in section 14, and the conducting lines of section 16. In sections 14 and 16, it is to be observed that the angular spacings between conducting lines, such as 54 and 60, or 60 and 64, and so on, in section 14, are greater than the angular spacings between conducting lines, for example, 67 and 68 or 68 and 70, and so on, in section 16. The conducting lines of these sections 14 and 16 have been arranged in this manner so as to give a difference in the proportionality constant (that is a variable gyro compensation factor of angular rate to phase). Thus, with the wider angular spacings in section 14, a smaller phase change is obtained with a fixed angular rate than is obtained for section 16 which contains the closer angular spacings of conducting lines.

Scales 84, 86, and 88, corresponding to various values of a gyro compensation factor, are provided as indicated.

In section 12, the parallel conducting lines have been arranged so that the gyro compensation factor (or proportionality constant) varies as the cosine of the angle measured between a vertical line passing through the center of the section 12 and the center 72 of circular disk 10, and the instantaneous position or location of a contactor or pointer, that is, a line passing through the location of the contactor and the center 72 of circular disk 10.

In the converging sections 14 and 16, the change in phase angle is linear with the change in angle. Thus, for example, in section 14, the phase angle at conducting line 54 would correspond to 0 phase angle, at conducting line 60 to 120 phase angle, at conducting line 64 to 240 phase angle, and at conducting line 58 to 360 or 0 phase angle, and will thus repeat thereafter as previously indicated. Thus between conducting lines 54 and 60, the phase angle changes 120. Half way between these two conducting lines 54 and 60, the phase angle would be 60. By means of this arrangement in sections 14 and 16, the phase that the signal is deviated from the reference signal will, therefore, be directly proportional to the rate of change of angular position.

The multi-tap, phase shifting potentiometer thus described can be utilized for possible use as the free gyro take-off element in the phase follow-up scanning interferometer system. It is one of the properties of such a take-off element that a small angular motion of the gyro will produce a 360 phase shift in output signal. Another property is that the angular rnotion-output phase relationship will be a continuous and essentially linear function over discrete regions of the potentiometer. Another important advantage of the system described so far is that certain non-linear compensation factors can be introduced over a relatively broad region of the potentiometer.

Briefly reviewing the potentiometer described in detail above, it comprises a gridwork of fine silver filaments, such as 18, 33, and 40, and the like applied to a Bakelite disk 10 and overlaid with a thin coating of resistance material, such as graphite. The pick-off for the potentiometer is merely a contact button which slides over the resistance material, and is constrained radially at a point corresponding to the center 72 of disk 10.

The various filaments or conducting lines, such as 18, 33 and 40, are energized by a three phase A. C. source so that, as previously pointed out, adjacent conducting lines carry voltages which differ in phase by 120", that is, in sequence: 0, 120, 240, 0, 120, and 240.

With the resistance material overlay, such as deposited in the areas 78, 80, and 82, on the conducting lines or filaments, this assembly becomes equivalent to a multitap, resistance potentiometer as shown in Fig. 3. It is at once apparent that each set of four (4) filaments or conducting lines 94, 96, 98, and constitutes a delta connected resistance load. Since the conducting lines 94 and 100 are energized by identical phase voltage, it

55 is obvious that these two points coincide electrically and thus close the delta. The equivalent circuit of Fig. 3 is shown in Fig. 4. The value of resistance in each leg 104, 106, or 108 of the delta 102 is the paralleled sum of all filament to filament or conducting line to conducting line resistances representing that particular leg.

The pick-off 109 is used to measure the pick-off phase and voltage with respect to ground 110, thus the A. C. voltage source or transformer secondary which feeds the potentiometer should be connected center grounded Y.

In Fig. 5, there is shown a vector diagram 112 for the potentiometer and pick-01f voltages and their respective phase angles. As mentioned above, the variation of or phase angle is essentially linear with variation of 13 or mechanical angular motion of the pick-off, at least over small areas of the potentiometer.

Theoretically, this is not strictly possible with three phase excitation. From the vector diagram in Fig. 5, it can be shown that It is of interest to examine the quantity fl, which is called the phase error, e, since its value will indicate any deviation from the desired linearity. The phase error is thus:

V35, -1 H E 6 tan 2400 5 q This function repeats every 120 in [3. Fig. 6 shows graphical representations 114 and 116 of e versus p3, as given in Equation 2 above for three (3) phase and four (4) phase excitations. It will be noted that an error in electrical phase up to 111 will exist for certain values of ,8. (As an average value for the potentiometer, an error of 11 in electrical phase corresponds to about A; in mechanical angle ,8).

The curve 120 in Fig. 7, showing 5 versus ,8, was plotted from experimental data taken from a typical segment of the potentiometer. The deviation from linearity which is apparent from the curve 120 is in good agreement, at least within the limits of accuracy inherent in the measuring technique employed, with the theoretical deviation which could be expected.

From the same vector diagram 112 of Fig. 5, it is possible to show that the amplitude of the pick-off voltage with respect to ground 110 is given by the relation max E *2 sin 150 (3) a function which repeats every 120 in b. Curve 124 of E vs. is shown plotted in Fig. 8 for an arbitrarily selected value of Emax. Actual pick-off voltage as a function of phase shift for two typical segments of the potentiometer is shown by curves 126 and 128 of Figs. 9 and 10.

It is well to point out that four phase excitation reduces the theoretical maximum phase errors by a factor of nearly three and also reduces the magnitude of the voltage amplitude fluctuations. The theoretical phase error that might be expected with four phase excitation is shown by curve 116 of Fig. 6 for comparison with three phase excitation.

As mentioned previously, it is desirable to introduce certain compensation factors into the 5, [3 relationship.

Referring now to section 12, Fig. 1, the potentiometer was so designed that This relation describes the interferometer lobe pattern in space, where )t is the radiation wave length and d the antenna horn spacing. By varying the pick-off radius, it is possible to change the A/ d ratio through certain limits. Fig. 11, showing a curve 132 of 6 versus iqfi/ 360, was plotted from experimental data and agrees closely with Equation 4.

Sections 14 and 16 of the potentiometer were designed to produce a nearly linear {3 relationship, and still provide for Md alteration through a variable pick-off radius arm. Experimental results plotted for section 16, Fig. 12, show a curve 138 such that the relation is linear out to the region 5::30. Almost similar results could be expected from section 14 of the potentiometer as previously described.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A continuously adjustable polyphase voltage divider resistor, comprising, a base having at least two faces, a plurality of sets of conductive elements located on the first of said two faces, the conductive elements of respective sets being arranged in regular recurrent sequence with respect to each other, each set including elements connected electrically to each other, resistance material distributed over the first face of said disk and in contact with said conductive elements, a plurality of slip rings corresponding in number to said plurality of sets of conductive elements, said slip rings being located on the second face of said two faces, means for connecting each set of conductive elements to a separate slip ring, and contact means bearing on said resistance material, said contact means being arranged to be shifted toward and away from the center of said base.

2. A continuously adjustable polyphase voltage divider resistor, comprising a base having at least two faces, a plurality of sets of conductive elements located on the first of said two faces, the conductive elements of respective sets being arranged in regular recurrent sequence with respect to each other, said conductive elements in each set being substantially parallel and evenly spaced, each set including elements connected electrically to each other, resistance material distributed over said first face of said disk and in contact with said conductive elements, a plurality of slip rings corresponding in number to said plurality of sets of conductive elements, said slip rings being located on the second face of said two faces, and means for connecting each set of conductive elements to a separate slip ring.

3. A continuously adjustable polyphase voltage divider resistor, comprising, a base having at least two faces, a plurality of sets of conductive elements located on the first of said two faces, the conductive elements of respective sets being arranged in regular recurrent sequence with respect to each other, with the conductive elements in each set being angularly arranged and substantially evenly spaced with respect to each other so as to converge to a common center, each set having elements connected electrically to each other, resistance material distributed over said second face of said two faces of said disk in contact with said conductive elements, a plurality of slip rings corresponding in number to said plurality of sets of conductive elements, said slip rings being located on the second face of said two faces, means for connecting each set of conductive elements to a separate slip ring, and contact means bearing on said resistance material, said contact means being arranged to B= isin- Eq. 4

be shifted toward and away from the center of said base.

4. An arrangement as set forth in claim 3, wherein the conductive elements of each set converge to a center other than the center of said base.

5. An arrangement as set forth in claim 3, wherein said contacts can be moved in a curved path in addition to being shifted toward or away from the center of the base of said resistor.

References Cited in the file of this patent UNITED STATES PATENTS Garman Jan. 21, 1941 Faus July 8, 1941 FOREIGN PATENTS France Mar. 30, 1943 France May 7, 1942

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