US1717400A - Phase-shifting network - Google Patents

Description

June 18, 1929. NYQUIST JUAOB PHASE SHIFTING NETWORK Filed Aug. 25, 1926 I ZZZ/02.6

IN I! EN TOR flW 0 BY I t A TTORNEY S.

same an. is, 1929. 1,117,400

UNITED STATES PATENT OFFICE.

HARRY NYQUIST. OF MILLBUEN, NEW JERSEY, ASSIGNOB. TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION 01 NEW YORK.

PEASE-SHIFTING NETWORK.

Application filed August 25, 1926. Serial No. 131,495.

This invention relates to a network by of this being determined by the characterwhich a source of alternating current voltage istics of the network appearin between the 55 may be obtained, the phasethereof being conin mt and output terminals. T iie network in veniently controlled and varied. The netthlsfi ure comprises twobranches in parallel 5 work comprises a circuit with two input each Eranch being made up of two halves terminals to which an alternating current and each half com rising a reactance element source may be connected, and two output and a resistance e ement. More specifically 60 terminals from which potential difference the one branch is made up of the followin b bta'dtl 1 ft] tt'l e 0 me Xe pw'se 0 en la elements taken in order: An inductance 10 di erence being completely controlla le with- 2 out altering the condition of the source. The R R invention may find application in many a reslstence 5 a Second i ce 5 and an 65 places such as that illustrated in my applica- L tion Serial No. 90,653, filed February 25,1926, Inductance The second branch is similarlvlvsllch one form of my invention is shown 1 made up of the following lments taken The par ose of this invention is to design a in the order of a capacity a resistance 70 networ 0 these general characteristics, and, R 2

at the same time, one which Will provide a resistance :2. and a capacity It will 2 source of alternating electromotive force,

appear later that the mldpoints O, and 0 which, while variable in phase, shall be constant in amplitude of the two branches are at the same potential 75 Still a further purpose of the invention is and therefPre there 13 oblectlon and i to provide such a source which shall be as some i It may be aJdwmtageous to connect simple as possible in its adjustments to obthese filrectly b n h wn. For tain the desired phase shift and as simple in mmphclty of g the reslsmflces e 11 its adjustments as possible for changes in made oftbe q e mm s Varmble so contact wlth a point on the resistances in each 7 frequency. The invention will be better understood from the following description branch are two cflmductms 6 and 7 leading to the output terminals 3.

taken in connection with the accompanying drawings which embody certain examples of In Order to Obtam i"? results deslleda the my invention the invention it lf being inductances and capac ties are made of such 85 value that for the particular frequency given fined by the appended claims.

In the drawing Figure 1 represents one the generator A there shall exist the rea ion form of network for obtaining the desired shift in phase of an alternating current 1 source. Fig. 2 is a modification thereof. p "ifi' Figs. 3 and 4 are still further modifications in which one type of reactance element only where g 20 and 5; represent the inductance 40 is used, Fig. 5 is a vector diagram of E. k

F.s involved in the circuits and Fig. 6 is a and capacity and resistance of the various eleview of a mechanical device for o aining ments shown, and =21ra: frequency. The the desired phase shift. reason for this relatlonship will bebetter un' Referring more articularly to Fig 1, there (iOIStOOd by the fOllOWlDg COIlSldBIfltlOllS. 45 i shown source f lt ti E, M F The current flowing through the capacity A. this source having any desired frequency branch W1 1 be which we may represent by f. This source e is connectedto the input terminals of a net 1 R 1 (2). work which has two output terminals 3, from which, by suitable adjustment, it will be possible to obtain an alternating current voltage Where 6 IS the p tentgl difference across the of the frequenc given by the generator A, network and j= /1 and where the de- 1 5 but of controlla le phase and magnitude, all nominator of this expression represents the which shows that the currents in the two branches are not in phase with each other. If we give the inductances and ca acities such values that the relations 1) ho d, then these two current relations take on the form e e (l 7') R(1 2R 9 and e e (1 7') R 1 j) T (5) from which it appears that z', and a, differ in phase by 90.

The potential difference which exists between the point 0 and a point S between which there exists the resistance 1', will then be O and a point S the resistance 1' and that between the point between which there exists will be The potential difference, then, between the points S and S as measured from output terminals 3 will be the difference between these values, that is,

the magnitude e is given by 0b, which is 90 in phase behind orz. If the contact 7 includes between itself and the point 0 an amount of resistance 1' the potential difference over that resistance will be e, and is indicated as such in Fig. 5. Similarly, for a resistance 1' in op- I posite' branch there will be potential difference e,'. The resultant of these two components, represented by their vector sum, is shown on the diagram as 00 and it will be noted that the magnitude and the phase of his resultant will depend upon the values 1', and 1' It is also evident that if the proper relationship is maintained between these two resistances, that their vector sum will, in magnitude, always be equal to e, and such a relationship on the diagram is indicated by the two compliments e, and 6,. In order that this relations 'p shall be maintained, it will be evident that the following shall hold where u gives the phase angle of the resultant, using the base of 0a as the reference. Under these conditions, it will be observed that while the phase of the resultant E. M. F. may be shifted through the angle 360 or any part thereof, the magnitude remains constant and this feature of a constant magnitude with any desired change in the phase contitutes an important feature of this invention. In order to accom lish this result the contacts S and S shouid be varied together in such manner as to maintain the relationship given above and any suitable mechanism ma be used for this. One means for accomplis ing this is shown in Fig. 6, in which there are two crank-shafts 21 and 22 in parallel with each other and each having two throws insulated from one another and 90 apart. The connecting rods 26 and 27 make contact respectively with and travel over the resistances between the inductances of one branch and between the capacities of the other branch of the network. In view of the circular motion and the 90 phase relationship of the two arms, it is seen that the resistances included at any moment across the output terminals 3 of Fig. 1 are in accordance with the relations of Equation (9).

It is apparent that if the frequency of the generator A is changed, corresponding changes must be made in the inductances and in the capacities or in the resistances in order to restore or maintain the conditions of relations (1). For this reason, it will be desirable to make these variable or to make the resistances variable, and this is indicated in Fig. 1 by the arrows passing through the elements.

Various modifications may be made in the network in order to obtain somewhat different results. In Fig. 2, for example, the number of resistance elements of each branch have been increased and so located that only half of the resistance of each branch occurs adjacent to the bridge 0 O The mathematical analysis in this case is similar to that for Fig. 1, and differs only in that the maximum voltage at the output terminals is onehalf as great.

In some cases, it may be desirable to reduce the number of types of elements included in the network. This is particularly true if the frequency of the generator A is to be changed in which case the adjustment which must be made may be brought about by changes in the 'inductances or in the capacities. In general,

able inductances, and F 3 shows a circuit.

in which the inductances ve been dispensed with. As shown in that figure, the inductances of Fig. 2 have been removed, and the resistances in that branch which are adjacent to the bridging point 0 are shunted by condensers of capacity 20. In this case, it may be shown that the current flowing through these resistances adjacent 0 1s given by and the current through the branch which has not been altered is 121 1 1 y'pOR (11) If, now, the condition is set that similar to that of Fig. 1 and described by means of Fig. 5 again exists. And if the same relationship regarding the values of r,

and r, be maintained, then the output voltage will remain constant in amplitude without regard to the total change in phase.

In some cases, it may be desirable to use condenser units of the same type or size in the two parallel branches. Such an arrangement is shown in Fig. 4, the capacities 20 being replaced by capacities 20 of the same size as in the parallel branch. In order to maintain the proper relationships, it is necessary in this case to also alter the value of the resistances in the branch in which the condensers have been changed, these resistances now taking on the value In this case,

the current through the resistance r, is four times as great as that in r. but if the ad ustments are so controlled that sin b r cos b then the output voltage will be of constant magnitude and the same as that for Fig. 3.

It may be mentioned that each of the circuits can be shown in a slightly different form in which they take on the appearance of the conventional Vheatstone bridge network. Also it may be pointed out here that the ini put impedance of the network of Fig. 1 and of Fig. 2 is R, in both cases being pure resistances. On the other hand, the input impedances of Figs. 3 and 4 can be shown to be equal, respectively, to

R R 3 -1) r- 2)- VVhat is claimed is:

1. A source of single phase alternating E. M. F. and a. network associated therewith adapted to serve as a source of E. M.VF. of variable phase, said network comprising two parallel branches across the terminals of said source, each possessing lumped reactance and resistance, and means for keeping the delivered E. M. F. of constant amplitude.

2. In a variable phase shift network, two branches in parallel, each possessing capaci tance and resistance, each branch as seen from its midpoint being made up of two identical portions with the elements arranged in the same order, movable terminals attached to the resistances of said branches and adapted to deliver E. M. F. of variable phase and constant amplitude.

3. A variable phase shift network comprising two branches in parallel, each possessing reactance and resistance, each branch as seen from its midpoint being made up of two identical portions with the elements arranged in the same order, terminals making movable contact with the resistances and means to so relate the movements of the contacts as to deliver E. M. F. of variable phase and constant amplitude.

4. In a variable phase shift network, two branches in parallel, each possessing capacities and resistances, each branch as seen from its midpoint being made up of two identical portions with the elements arranged in the same order, and with resistance elements adjacent the midpoints, terminals making movable contact with the rcsistances, and means to so relate the movements of the contacts as to deliver E. M. F. of variable phase and constant amplitude.

5. A variable phase shift network for delivering E. M. F. of variable phase, comprising two branches in parallel adapted to be supplied from an AC source, the one branch comprising four equal resistance elements in series and a condenser bridged across each of the two inner resistance elements, the second comprising four resistance elements in series each equal to the resistance elements of the first branch and further comprising a condenser between each pair of outer resistance elements, and variable contact leads from points on the inner resistance elements.

6. A variable phase shift network for delivering E. M. F. of variable phase, comprising two branches in parallel adapted to be supplied from an AC source, the one branch comprising four equal resistance elements in series and a condenser bridged across each of the two inner resistance elements, the second com rising four resistance elements in series cac 1 equal to the resistance elements of the first branch and further comprising a series condenser adjacent each outer resistance element, and variable contact leads from points on the inner resistance elements, the impedance of each of the shunting condensers in the first branch being one-half that of each of the resistance elements, and the impedance of each of the condensers in the second branch being twice that of each resistance element, the contact leads hein, so related in their movement as to yield E. M. F. of constant amplitude.

7. In a variable hase shift network, two branches in paralle each possessing capacitance and resistance, each branch as seen from its midpoint being made up of two identical portions with the elements arranged in the same order, movable terminals attached to the resistances of said branches, and means for so moving the terminals with respect to each other that the potential difference across said terminals shall be of constant amplitude and variable phase.-

In testimony whereof, I have signed my name to this specification this 24th day of August, 1926.

HARRY NYQUIST.

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