US1988989A - Retardation device - Google Patents

Description

' Jan. 22, 1,935. G. VIARD 1,988,989

RETARDATION DEVICE Filed oct. 31. 1951 2 sheets-sheet' 1 Jan. 22, 1935. G. VIARD 1 RETARDATION DEVICE 2 Sheets-Sheet 2 Filed Oct. 31, 1931 Fig. 5

Patented Jan. 22, 1935 UNITED STATEs PATENT oFFlcEf;

" 1,988,989' l n' l n nr;TARDAfrIoN".onvloif:v i Georges Viard, Paris, France, `assigner to'Lignes Telegraphiques-et Telephoniques, Paris, France, `a. corporation of France v,

Applieatinn october 31, 193i, serialv No. 572,370

, In France December 18, 1930 1 Claim.

The present invention relates to retardation devices for use in electrical transmission systems. It is Well-.known that the operation of certain devices in transmission systems is sometimes con- 5 trolledA byk the .communication currents, and in thiscase, it is gnerally'neeessary .to retard the subsequent .transmission of these currents inl order to permit the previous operation of the devicesA controlled.

The retardation devices usually .employed comprise network sections composed of series connected inductance coils vand shunt condensers. lIn order to obtain an appreciable retardation, it is necessary, however, to use a large number of these sections, which becomes lvery expensive.

VThe present invention has for object to overcome the above disadvantage and provide a new type of retardation section which allows of obtaina vmuch greater retardation than with 'the sections hitherto employed.

.A .second lobject of the invention is to provide a retardation vsectionwhereby the retardation of the' current is, for a wide `band of frequencies, independent ojf the frequency of thesaidcurrent.

Oltherlobjeclts and advantages 'of the invention wiIl be apparent 'fromthe description vtaken heref' inerte-r witn'referenee to theaccompanyinsdraw: ings,inwhich:

J.,- 2 .represent diagrammatically sections 'of retardation networks constructed according to the invention.

Fig. 4 represents the type of retardation section customarily employed hitherto.

Figs. 5 and 6 represent retardation curves of the network sections described with reference to Fig. 4 and Fig. 1 respectively.

With reference to Fig. 1, the quadripole section according to the invention is of the diagonal crossconnected type and is composed of series-connected inductances and two condensers connected shunt at the ends. 'I'he inductance f is advantageously formed, in the style of aiPupin coil, by two windingswound round -a core. In Fig. 2, the network section according to' Fig. `1 is (o1. 17a-44) u illustrated in its .equivalent T form. Further, byK a 4suitable arrangement -of the two windings, the condensers'placed in thedia'gonal bran'cliesjnay. be replaced whouy orin part by the uniformly distributed capacity ofthe two windings; such a section is diagrammatically represented in Fig. 3. The end capacities g are not shown this Iiigure. A

The articial linesh-itherto employed are composed of sections, one of which is illustrated in Figi. 4. 'The' pulsatance corresponding rto Vthe c'u't- It is known, on the other hand, that the dura tion t of the propagatiomi. e., the retardation time) per section, is gvenby:

at that is, by takinn iff J The curve in Fig. 5 represents the graph of t as a function of 11. From this curve, it is seen that for a frequency f1 corresponding to m, the retardation time t is given by:

But the duration of the transients of the transmission system, which may be calculated by the formula:

da) @y dan dw a minimum, (where ca -.0) has been increased y the quantity 1, where:

w v1-I1 I! N similar sections are used, the din'ationo! the transients will be increasedby Nr.

This effect may be harmful for it is generally endeavoured, in transmission systems, to limit the duration of the transients as much as possible.

This detrimental effect can only be diminished 5 by choosing for we a higher value, which reduces soV 111. But at the same time, the value of t is reduced. One is then led 4to increase the number N of the sections inorder to retain the same retardation value.

It will be shown in the following that with sections constituted according to the present invenf tion, the variation of the retardation withthe frequency is rendered absolutely negligible for a conor: A

1 a/L(K+ C) KL@2 It is deduced from this Equation (2) that the pulsatance corresponding to the cut-off frequency of the section is:

-1 a-cos 1 sin Naim

, 2 K h i .K uf- VLC as for the section of Fig. 4.. If we put:

K-l-c-g K-C l-i) -or e,

the Equation (2) becomes.;y

The retardation time t is given, from Equations (1) and (2'), by:

In Fig. 6 t is plotted against 1, for several values of g2. It is seen that for e2 approximate to 0.6,

which corresponds to:

the retardation time varies but very slightly with the frequency for a wide frequency band, hence there is but a very slight increase of the duration of the transients. Moreover, the constant value of retardation is considerably increased in 'comparison with the curve 62:1, which corresponds to the value K :0, that is to say therefore, in comparison with the section of ordinary line illustrated in Fig. 4 and having the same cutoff frequency. .For @2:05,V the increase is about 30%. To obtain a pre-determined retardation without increasing the duration of the transients by too large a quantity, a much smaller number of sections will thus be necessary, by employing' the presentvinvention, than would be the c'ase with an artiiicial line constituted from sections such as that of Fig. 4. Y f

On the other hand, the new network sections according to the invention havingv but a single inductance, like ordinary sections, their cost willv not be appreciably higher.

I.claim:- 1 An electric retardation network section consisting essentially of a network of the diagonal GEoaEs VIARD.

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