US2680230A

US2680230A - Compensating network

Info

Publication number: US2680230A
Application number: US191006A
Authority: US
Inventors: Jedediah L Garrison; John P Whistler
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1950-10-19
Filing date: 1950-10-19
Publication date: 1954-06-01
Anticipated expiration: 1971-06-01

Description

n 1954 J, 1.. GARRISON ET AL 8 COMPENSATING NETWORK Filed Oct. 19. 1950 n we mu Rm 1 1.1114 MW 6 LP 2 m m J R w m S W 4 o C G E a 1 5 n I 0 W l. c t R/ N 4 1| 1.. 2E 2 P fig 2 WM 9/ m I 2 1 4 m /z\||1 .0 Rs R 1% 4 o H G B A 0 E wmmwmtw \S kzwoiau Qwwbxmoz @MfiW ATTORNEY Patented June 1, 1954 UNITED STATES PATENT OFFICE COMPENSATING NETWORK Jedediah L. Garrison, Madison, N. J., and John P. Whistler, San Marino, Calif., assignors to Bell Telephone Laboratories, Incorporated, New

York

, N. Y., a corporation of New York Application October 19, 1950, Serial No. 191,006

Claims.

tional voltage pulses in a circuit which includes a magnetic-cored inductor.

A more specific object is to obtain a rectangular voltage pulse from a unidirectional voltage pulse impressed upon a magnetic-cored coil.

, When a unidirectional voltage pulse is impressed upon a resistive load which has a magnetic-cored inductor connected in shunt or in series therewith, neither the voltage across the load nor the current therethrough remains constant over the period of the applied pulse. This is due to the fact that the magnetizing currentv taken by the inductor is not constant over this period. This current rises rapidly at first, as the eddy current flux is established throughout the core structure, and then gradually becomes substantially linear. Since the current drawn from the source varies, its terminal voltage also varies, due to the voltage drop caused by its interval impedance. Therefore, both the voltage supplied to, and the current through, the load will vary accordingly. Such a varying voltage and current are, in many cases, undesirable. For example, a rectangular voltage pulse at the load may be required, or a constant current to actuate a current-operated device.

In accordance with the present invention a compensating network is associated with the inductor to make the load current and voltage sub-v stantially constant. In the embodiments shown the network comprises alplu'rality of impedance branches connected. effectively in parallel withthe inductor. Eachbran'ch includes a resistance One or.

and a capacitance connected in series. more of the branches are designed to make the current drawn from the voltage source substantially linear over the period of the voltage pulse, and one or more other branches are designed to make this current substantially constant over this period. When this current is constant, the ohmic drop in the source is constant, the terminal voltage remains constant, and the load volt age and current remain constant throughout each pulse period.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawings, of which:

Fig. *1 is a schematic circuit of one embodiment of a compensating network in accordance with the invention in which the inductor shunts the load;

Fig. 2 shows the compensating network of Fig. 1 applied to a transformer;

Fig. 3 shows current-time characteristics used in a graphical determination of certain factors appearing in the design formulas for the component elements of the network; and

Fig. 4 is a schematic circuit of another embodiment of the invention in which the load and from the source E substantially linear over the the inductor are connected in series.

Taking up the figures in greater detail, Fig. 1 shows a source of unidirectional rectangular pulses of voltage E and internal impedance Rs,

a resistive load of impedance R1. connected to the source, an inductor designated by its inductance L connected in shunt with the load, and a compensating network in accordance with the invention comprising three impedance branches 40, H and I2 all connected in shunt with the inductor L. If more precise compensation is required, the compensating network may include additional shunt branches, as indicated by the broken lines l3. Each of the branches comprises a resistance and a capacitance connected in series. In the branch ill the resistance has a value R1 and the capacitance a value C1, in the branch H these elements are R2 and 02, respectively, and in the branch [2 they are Rn and Ca.

As indicated, inductor L is assumed to have a magnetic core associated therewith and. may,

for example, be a retardation or choke coil, the

winding of a re1ay,.or the mutual inductance between the primary and secondary windings of a The latter case is illustrated by Fig; l'except that the'inductor' L "has been replaced by a transformer M with a primary wind: ing l5, '.a secondary winding l6, and a magnetic core II. The branches Iii, H and i2 may be placed on the primary side of the transformer 14, as shown, or one or more of them may be transferred to the secondary side, if the values of their component elements are changed to take account of the transformation ratio of the transformer.

In its simplest form the compensating network consists of only the two branches i0 and l I. The circuit will, therefore, be as shown in Fig. 1 if the branch 2 is open-circuited or removed. In accordance with the invention, the values of the resistance R1 and the capacitance C1 in the branch iii are shown to make the current drawn period T4 of the unidirectional voltage pulse and the value of R2 and C2 in the branch H are chosen to make this current substantially constant over the period T4. With this current constant, it follows that the voltage drop across the source impedance Rs will be constant, the terminal voltage will be constant and, therefore, the voltage across and the current through the load R-L will also be constant. As a result, a rectangular voltage pulse will be impressed uponthe load RL.

The value of R1 depends upon the magnitudes of the source impedance Rs, the load impedance R1,, and a certain normalized current B. The value of C1 is dependent upon these same factors and a time constant T1. The value of R2 depends upon Rs, R1,, B, and the normalized steady state value H of the magnetizing current, and the value of C2 is dependent upon the same factors and a time constant T3. The factors B, T1 and T3 may be determined by the characteristic of the magnetizing current im' drawn by the inductance L from the source E over the pulse period Ti. Explicitly, these element values are given by the following formulas:

1 RSRL R1" RS+RL R R O RS+RL) 2 1. RgR HB RS+RL and R R C RS+RL)' A graphical method of determining the required values of the factors B, T1 and T3 will now be presented with the aid of Fig. 3 in which normalized current in amperes is plotted against the time t in seconds over the period T4 of the pulse. The solid-line curve It gives the normalized magnetizing current i111 drawn by the inductor L. The normalized current 2111 is obtained by dividing the magnetizing current im', indicated in Fig. 1, by the voltage E of the source. The current im may be found with the aid of a cathode-ray oscilloscope or it may be computed, for example, from information presented in a paper by A. G. Ganz entitled Applications of Thin Permalloy Tape in Wide Band Telephone and Pulse Transformers, published in the Transactions Section of Electrical Engineering, vol. 65, April, 1946, pages 177 through 183.

It will be noted that the curve it rises sharply at first and then more gradually until at the point d, corresponding to the time T2, it becomes substantially linear and remains linear for the rest of the pulse period T4. The required value of the normalized current B is obtained by extending the linear portion of the curve [8 to the left, as shown by the broken line i9, until it intersects the current axis.

Next, a perpendicular line 213 is dropped from the point on the curve IE to the time axis and a horizontal line 2i is drawn from the current axis at the point B to intersect the perpendicular 26 at the point f. Then the broken line curve 22 is constructed by lowering the curve 18 at each point by a. distance equal to the difference between the curves i9. and 21. starts at zero and rises smoothly to the point f.

Thus, curve 22 Now, to find the time constant T1, a horizontal line is drawn from a point A on the current axis equal to 0.632 B until it intersects the curve 22 at the point It, and a perpendicular is dropped from this point to the time axis to find T1.

If the values of B and T1 thus found are substituted in Formulas 1 and 2 values of R1 and C1 will be found such that, if only the compensating branch H] is employed, the current drawn from the source E by this branch and the inductor L will be substantially linear over the pulse period T4, as shown by the straight line i9 and the straight portion of the curve i8. As already pointed out, however, this current should not only be linear but should also be constant. The compensating branch H is added for this purpose. The method employed is to build up the linear current already obtained to a constant value equal throughout the pulse period to the steady state value H shown by the horizontal line 26 The required value of the resistance R2 is found from Equation 3. The time constant T3 may be found graphically by drawing a horizontal line 25 from a point G on the current axis, where until it intersects the curve It at the point 1n, and then dropping a perpendicular line 26 from this point to meet the time axis at Ta. The required capacitance C2 may now be found from Equation 4.

If the compensating network employs only the two branches [0 and H with the element values determined as explained above, the current drawn from the source E will be substantially constantover the pulse period T4, as shown by the curve 24, the ohmic drop in the source impedance He will be substantially constant, and the voltage across and current through the load R1. will be nearly enough constant for most applications. However, a further improvement in the constancy of this current and voltage may be made, if required, by adding one or more impedance branches to aid the branch [0 in making the current linear, and one or more branches to aid the branch I I in making the current constant. Each of these additional branches preferably comprises the series combination of a resistance and a capacitance, and the branches are connected in shunt with the inductance L. The branch I2 shown in Fig. 1 is one such added branch. If additional branches are used, the required values of the elements R1, C1, B2 and C2 will, in general, differ from those obtained by the formulas presented herein. The required values of the component resistances and capacitances in the added branches may be found from additional normalized currents and time constants which may be found from the characteristic of the magnetizing current shown in Fig. 3 by a graphical method similar to the one described above.

When the compensating network is used with a transformer, as in the circuit of Fig. 2, the

' required values of the component elements in the branches l0 and I! may be found in the manner already described, except that in this case the magnetizing current characteristic [8 will, of course, apply to the transformer I4 instead of the inductance L.

Another embodiment of the invention is shown in Fig. 4, which is the same circuit as that shown. in Fig. 1 except that. the shunt load R1. is omitted and a series load of impedance R2 is connected between the source E and. the first shunt branch [0. In this case the required values of the elements in the branches l0 and I l to make the current drawn from the source E substantially constant throughout the period T4 of the voltage pulse are given by the following formulas:

and

in which the factors B, H, T1 and T3 are determined in the manner previously described.

In the circuit of Fig. 4 if only the two compensating branches l0 and H are used the current through and voltage across the load RP will be substantially constant over the pulse period T4. The constancy may be further improved, if required, by the addition of one or more branches such as 12, as explained above in connection with Fig. 1.

What is claimed is:

1. In combination, a resistive load of impedance Z adapted for connection to a source of unidirectional voltage pulses of internal impedance Rs, a magnetic-cored inductor connected in shunt with said load, and a compensating network for making the voltage across and the current through said load substantially constant over the pulse period, said network comprising a plurality of impedance branches connected effectively in shunt with said inductor, each of said branches comprising the series combination of a resistance and a capacitance, the resistance R1 and capacitance C1 in one of said branches having values chosen to make the current drawn from said source substantially linear over said period, and the resistance R2 and capacitance C2 in a second of said branches having values chosen to make said last-mentioned current substantially constant over said period, in which R1, 01, R2 and C2 have approximately the following values:

ing the first curve at each point by a distance equal to the diflerence between the extended porto 0.632 B, and reading the time T3 at which said first curve attains a value equal to 2. In combination, a resistive load of impedance Z adapted for connection to a source of unidirectional voltage pulses of internal impedance Rs, a magnetic-cored inductor connected in series with said load, and a compensating network for making the voltage across and the current through said load substantially constant over the pulse period, said network comprising a plurality of impedance branches connected effectively in shunt with said inductor, each of said branches comprising the series combination of a resistance and a capacitance, the resistance R1 and capacitance C1 in one of said branches having values chosen to make the current drawn from said source substantially linear over said period, and the resistance R2 and capacitance C2 in a second of said branches having values chosen to make said last-mentioned current substantially constant over said period, in which R1, C1, R2 and C: have approximately the following values:

where H is the normalized value of the steady state magnetizing current drawn from said source by said inductor, and the factors B, T1 and T2 may be found graphically by plotting a first curve of the normalized magnetizing current in amperes against time over one period of said pulses, extending linearly the linear portion of the curve to the current axis to find the point of interception B, constructing a second curve by lowering the first curve at each point by a distance equal to the difference between the extended portion of the first curve and B, reading the time T1 at which the second curve attains a value equal to 0.632 B, and reading the time T3 at which said first curve attains a value equal to 0.632(H-B) +B.

3. In combination, a resistive load of impedance Z adapted for connection to a source of unidirectional voltage pulses of internal impedance Rs, a magnetic-cored inductor connected in parallel with said load, the series combination of a resistance R1 and a capacitance C1 in a path shunting said inductor for making the current drawn from said source substantially linear over the pulse period, and the series combination of a resistance R2 and a capacitance C2 in a second path shunting said inductor for making said current substantially constant over said pulse period, in which R1, C1, R2 and C2 have approximately the following values:

R 1, m..li? "'H-B R -i-Z and R Z s-lZ R2 where H is the normalized value of the steady state magnetizing current drawn from said source by said inductor, and the factors B, T1 and T2 may be found graphically by plotting a first curve of the normalized magnetizing current in amperes against time over one period of said pulses, extending linearly the linear portion of the curve to the current axis to find the point of interceptime B, constructing a second curve by lowering the first curve at each point by a distance equal to the difference between the extended portion of the first curve and B, reading the time T1 at which the second curve attains a value equal to 0.632 B, and reading the time T3 at which said first curve attains a value equal to 0.632(HB) +B 4. The combination in accordance with claim 3 which includes an additional impedance branch shunting said inductor, said additional branch comprising the series combination of a resistance and a capacitance proportioned to make said Z adapted for connection to a source of unidirectional voltage pulses of internal impedance Rs, a magnetic-cored inductor connected in series with said lead, the series combination of a resistance Rd and a capacitance C1 in a path shunting said inductor for making the current drawn from said source substantially linear over the pulse period, and the series combination of a resistance R2 and a capacitance C2 in a second path shunting said inductor for making said current substantially constant over said pulse period, in which R1, 01, R2 and C; have approximately the following values:

where H is the normalized value of the steady state magnetizing current drawn from said source by said inductor, and the factors B, T1 and T2 may be found graphically by plotting a first curve of the normalized magnetizing current in amperes against time over one period of said pulses, extending linearly the linear portion of the curve to the current axis to find the point of interception B, constructing a second curve by lowering the first curve at each point by a distance equal to the difference between the extended portion of the first curve and B, reading the time T1 at which the second curve attains a value equal to 0.632 B, and reading the time T3 at which said first curve attains a value equal to 8. The combination in accordance with claim 7 which includes an additional impedance branch shunting said inductor, said additional branch comprising the series combination of a resistance and a capacitance proportioned to make said current more nearly constant.

9. The combination in accordance with claim 7 which includes an additional impedance branch shunting said inductor, said additional branch comprising the series combination of a resistance and a capacitance proportioned to make said current more nearly linear.

10. The combination in accordance with claim 9 which includes a second additional impedance branch shunting said inductor, said second additional branch comprising the series combination of a resistance and a capacitance proportioned to make said current more nearly constant.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,801,342 Gannett et a1. Apr. 21, 1931 2,035,457 Blumlein Mar, 31, 1936 2,317,482 Peterson Apr. 27, 1943 2,431,952 Maxwell Dec. 2, 1947 2,470,825 Mathes May 24, 1949 2,480,511 Schade Aug. 30, 1949