US2407910A - Electrical signaling system - Google Patents

Description

Sept; 17, 1946. R, AYL R HAL 2,407,910

ELECTRICAL SIGNALING SYSTEM Filed June 30, 1943 INVENTOR'S REGINALD TAYLOR GEORGE moms BAKER ATTORNEY P atented Sept. 17, 1946 ELECTRICAL SIGNALING SYSTEM Reginald Taylor and George Thomas Baker,

Liverpool, England, assignors, by mesne assignments, to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 30, 1943, Serial No. 492,832 In Great Britain August 20, 1942 11 Claims. 1

The present invention relates to electrical signaling systems such as automatic telephone systems in which trains of impulses are utilised to effect the setting of automatic switches or the like and i particularly concerned with arrangements for overcoming the efiects of distortion in the break-make ratio of impulses comprising interruptions in a normally closed circuit. Such distortion as is Well known is due to the efiect of the inductive and capacitative properties of the line on the responding relay and may become very serious where long lines or a number of impulse repetitions are involved.

The chief object of the invention is to provide a simple and reliable arrangement for correcting for the effects of distortion and enabling the ratio of received impulses to be restored to its original or even a more desirable value.

The invention may be of particular value in connection with systems employing to some extent at least switches having circuit arrangements of the type disclosed in our application S. No. 434,762 filed Mar. 14, 1942. It is shown that such switches need no longer be dependent upon the usual break to make ratio of received impulses, but rather upon the period which elapses between corresponding points in successive impulses so that the only limit is that the actual speed of impulsing must not be so slow that the period between similar points in successive impulses exceeds a predetermined amount. When such period is exceeded, a switching operation is arranged to take place characteristic either of the end of an impulse train or of the release of the connection depending upon the final condition of the control circuit. Such a method of impulsing is sometimes referred to as speed timing. The speed timing impulse responding cir-.

cuit thus provides a means of response to incoming impulses which operates equally well no matter how badly they are degraded due to the reactive nature of the line and its terminations or to the number of stages of impulse repetition involved.

In order that advantage can be taken of such arrangements on existing automatic telephone networks or for interworking from networks emplOying speed timing selectors into ordinary networks of existing types, it is necessary to provide means for remaking received distorted impulses so that they can be passed on in a form acceptable to existing equipment.

One means, particularly applicable to long distance dialling, is disclosed in our application S. No. 446,900 filed June 13, 1942, in which trains of distorted impulses are received on a speed timing impulse responding circuit including an electro-mechanical impulse storage and regenerating device, so that received impulse trains are retransmitted in a form corrected as regards ratio and at the nominal speed for the system concerned.

Such an arrangement does more than is really necessary for satisfactory selector operation, since it is only the impulse ratio which is distorted during transmission, the speed of impulsing being unaffected. The present invention provides an impulse responding circuit which, in accordance with the impulsing speed concerned, will produce a suitable outgoing impulse ratio which will be acceptable to the receiving apparatus involved.

According to one feature of the invention, in an electrical signaling system employing trains of impulses comprising interruptions in a. control circuit, an impulse repeater is provided in which incoming impulses are repeated without storage at the speed at which they arriv but with a ratio of break to make substantially independent of thi speed and of the ratio of the incoming impulses.

According to-another feature of the invention,

in an electrical signaling system employing trains of impulses comprising interruptions in a, control circuit, an impulse repeater is provided in which the length of the first repeated interruption is fixed and the length of subsequent interruptions is adjusted dependent on the speed of the incoming impulses but regardless of their ratio of break to make.

A further feature of the invention is that in an electrical signaling system employing trains of impulses comprising interruptions in a control circuit, an impulse repeater is provided in which incoming impulses are repeated without storage at the speed at which they arrive but with a ratio of break to make which progressively approaches a predetermined value for successive impulses of a train.

The invention will be better understood from the following description of one method of carrying it into efiect, which should be taken in conjunction with the accompanying drawing comprising Figs. 1-3. These all show the invention applied to an outgoing impulse repeating relay set at a tandem automatic telephone exchange, access to the relay set being had over one 01' more ranks of tandem selector switches operated over a junction line from a calling automatic exchange, while the relay set itself connects with an outgoing junction from the tandem exchange to a 3 distant automatic exchange. Fig. 1 shows the complete circuits of the relay set in question,

while Figs. 2 and 3 are fragments only showing alternative circuit connections involving a socalled stabilising condenser QY which functions to reduce the oscillatory nature of the output impulse ratio control exerted by the circuit of Fig. 1.

Before proceeding with the detailed circuit description the principle of operation will be dealt with generally and it may be pointed out that the circuit arrangement entirely ignores the ratio of incoming impulses, and functions on the basis of their speed alone to give a suitable output ratio which will be acceptable to any selector in the system.

It is assumed that the telephone networks employ selector switches of the decimal step-by-step two-motion type employing the well-known, A, B

and C impulse responding relay triad and responsive to impulses at a nominal speed of ten impulses per second and of a nominal break to make ratio of 2-1.

The switches are readily responsive to impulses having a speed range of from 8l2 I. P. S. providing there is no serious ratio distortion, the transmitted break and make periods over this range of speeds being as follows,

Speed Break period Make period energised when impulsing starts have a good margin on the first impulse'and generally tend tofail only on the last of a long train of say 9 or 10 impulses.

On the first release of the relay set impulse responding A relay, a 55 m. 5. break period is deliveredin the output circuit regardless of the length of time the A'relay stays down. After the 55 m. s. period the remainder of the first impulse is then measured, that is to say, until the A relay once again releases at the commencement of the break I period of the second impulse, this period constituting the make period of the first output impulse.

If this output make period is 28 m. s., thus corresponding to the 55 m. s. break which obtains at a speed of 12 I. P. S., the second output break period can also be 55 m. s. with a resultant make period of 28 m. s. and these Values can remain unchanged throughout the train. If the first output make period exceeds 28 m. s. thereby indicating-that the speed is of a. value less than 12 I. P. S., a suitable increase in the second output .break periodwill be made. The second output make period comprising the difference between the complete second impulse time and the second break period will thereupon determine the length for the third break period and so on. Similarly, in the unlikely event of the make period being less than 28 m. s., thereby indicating a speed exceeding 12 I. P. S., the second output break period will be suitably reduced from the 55 m. s. value. The second output make period which will be greater than the first output make period owing to the reduction of the break period will then determine the length of the third output break period and so on. In this manner the output break and make periods are so adjusted as to give an outgoing junction to the distant automatic exchange.

, The various timing functions involved in the operation of the circuit are performed by condenser/resistance timing circuits each of which after a predetermined charging period builds up a suiiicient potential across its condenser to strike a gas discharge tube connected in circuittherewith and so to energise a relay to perform the required controlling function. The tube NTA, preferably a neon tube, and associated condenser QX perform the timing function in connection with the ratio replacement feature of the relay set, while neon tube NTB in association with condenser QW performs the speed timing function so .as to enable the appropriate circuit changes to be made at the end of each train of impulses.

Preferably the neon tubes are arranged to strike at a voltage of the order of .150 volts and this voltage is built up across the condensers which are connected to .the exchange battery of 50 volts by connecting in series therewith a high voltage supply HV, at a potential of 150 volts, via a suitable adjustable resistance. The supply HV is shcwn separately in various parts of the circuit as different batteries (in the same manner as is the ordinary 50 volt exchange battery supply), and its negative pole is connected to earth so that a charging voltage of 200 volts is available from the two batteries inseries.

When the relay set is taken into use, relay A operates and at contacts at brings up relay B which locks over contacts hi and at contactsbZ prepares a circuit for the outgoing pulsing relay PU, at contacts 174 applies guard earth to themcoming P lead, at contacts 125 connects a loop comprising the supervisory relays Dand I across the outgoing negative and positive conductors in order to seize the distant automatic equipment, and at contacts b3 completes a charging circuit for condenser QX v'ia thepotentiometer arrangement comprising adjustable resistances YY and YZ. The values of thes'eresistancesare suchthat condenser QX will be charged to avoltage somewhat lower than the striking voltage of the neon tube NTA, say about volts, and the'circuit is now ready to receive trains of impulses. 0

When relay A releases in response tothe break period of the first impulse received, relay PU rapidly operates, locks over contacts pul and at contacts 1M6 opens the outgoing seizing loop so as'to repeat the break period of the impulse to the distant automatic exchange. At contacts pus it completes a charging circuit for condenser QX Via the variable resistance YX and at contacts pueit operates relay C to prepare forthe charging of the speed timing condenser QW Via variable resistance YW and contacts 02, the charging of this condenser being prevented at present by the connection of the low resistance shunt thereon via contacts pu4 and resistance YA.

Contacts zmZ connect neon tube NTA and relay E.

across condenser QX, while the remaining contacts pal are only required in the modifications shown in Figs. 2 and 3. Relay C in Operating, at contacts cl disconnects the original potentiometer circuit, looks at contacts 03 and at contacts 04 short-circuits the supervisory relays D and I to provide an impedance-free impulse repeatin loop to the distant exchange.

On the operation of relay PU condenser QX will start charging up and it is arranged that it will reach the striking voltage of neon tube NTA in 55 m. s. Tube NTA then strikes and brings up relay E which at contacts el releases relay PU regardless of whether the impulse responding relay A is still normal or not, and completes a locking circuit for itself if relay A is still normal. Relay PU in releasing, at contacts pu3 completes a discharge path for condenser QX via resistance YZ, at contacts Ipufi closes the loop to the distant exchange so as to terminate the break portion of the outgoing impulse and at contacts p114 removes the shunt from across condense QW so as to initiate the charging of this condenser. Relay C, it will be seen, remains looked over contacts er2 and 03 independently of relay PU and further consideration of the operation of the speed timing circuit for controlling relay C and involving tube NTB and condenser QW will be deferred until the operation of the ratio replacement circuit has been completed.

As previously mentioned, relay PU in restoring at contacts pu3 completes a discharge circuit for condenser QX,'while at contacts 1W2 it opens the operating circuit for relay E. The latter relay is maintained operated for so long as relay A remains normal over contacts cl, b2 and al and this arrangement ensures that relay PU hall not re-operate until the next release of relay A.

The voltage to which condenser QX discharges is dependent on the time relay PU is normal, i. e. until the beginning of the break period of the second received impulse at which time relay PU is re-operated, and at contacts p143 reconnects condenser QX up to the charging circuit via resistance YX. If this released period of relay PU, which determines the make period of the first outgoing impulse, is just the correct length to correspond to a 55 m. s. break, i. e. if it is no longer than the 28 m. 5. make period which obtains at 12 LP. S., it is arranged that condenser QX will have discharged to the same value, namely 100 volts, as at the commencement of the first break. Hence the second output break will also be 55 m. s. with a resultant make of 28 m. s. as determined by the difierence between the complete impulse length of 83 m. s. and the output break period of 55 m. s. and these values will remain unchanged throughout the train.

If, therefore, impulses are received at a speed of 12 I. P. S., thenregardless of their ratio they are repeated with a replaced break to make ratio of 2-1 (55 m. s. break, 28 m. s. make) corresponding to the nominal 2-1 ratio at which they were transmitted at the distant sending end, and which is most suitable for the satisfactory operation of the distant automatic exchange selectors.

If the length of time relay PU is released exceeds 28 m. 5., thereby indicating that the length of the complete impulse is greater than 83 m. s. and hence that the impulsing speed is less than 12 I. P. S., condenser QX when discharged via resistance YZ will drop below its original voltage of 100 volts and the time required for charging it up again to the tube striking voltage of 150 volts will therefore be greater so that the break.

period of the nextiimpulse will be lengthened.

In the unlikely event of the released period ofrelay PU being too short to correspond to a 55 satisfactory operation of the selector switches. It should be mentioned that in some circum-.v

stances it may not be essential to maintain in the output the nominal 2-1 break to make ratio at all impulsing speeds as in order to secure the most satisfactory operation of the selector switches it may be desirable to effect slight alterations in the outgoing ratio over the speed range.

Considering now the operation of the speed timing circuit involving condenser QW and tube NTB, this functions by determining whether the actual length'of each impulse is greater or less 1 than a fixed predetermined period which is approximately equal to the length of the longest impulse which can be tolerated, namely, a 143 m. s. impulse which corresponds to the minimum dial speed of 7 I. P. S.

If the predetermined value is exceeded without a further impulse arriving, it is an indication either that the impulse train has finished or that the calling party has hung up prematurely. In the former case the timing circuit on coming into operation and bringing up relay ER releases relay C at contact e72 and re-introduces the supervisory relays .D and I across the outgoing leads at contacts 6T3, while in the latter case since the A relay will be normal, relay B will also be released at contacts erl and will restore the relay set to normal.

If impulses follow one another within the predetermined time period, the next impulse will reset the timing device by discharging condenser QW'and the timing operation will recommence. This re-setting operation is repeated for each impulse of a train until the last impulse of the train has been received when the tube NTB is able to strike and operate relay ER as described above.

In the arrangement described in the previously mentioned specification No. 434,762 the timing circuit is adapted to effect a switching operation after 143 m. s. measured from the beginning of the break period of the first impulse of a train (neglecting the magnet operating time), the arrangements being that it will be reset if a succeeding break is received within thi 143 m. s. period. In the present instance, instead of using one 143 m. s. timing circuit to compare the period extending between, say, the beginning of one break period to the same point in the next, it

the minimum speed of impulsing of 7 I. P. S.

NTB in a time not less than 88 m. s. so as to provide an overall timing period of 143 m. s. In the case of an impulse train at any impulsing speed above the minimum of '7 I. P. S.,- relay PU will operate to initiate the break period of the next impulse before the lapse of 143 m. s. from its first operation and hence condenser QW will be discharged without the tube striking. At the end of the second output break period as determined by the impulsing speed concerned, relay PU in releasing will initiate the timing of a second 88 m. s. period and so on until the end of the impulse train.

At the end of the train relay PU will fail to re-operate and condenser QW will therefore reach the striking voltage of tube NTB 88 m. s. after the end of the last output break period and tube NTB will flash and will bring up relay ER. Relay ER in operating opens the locking circuit of relay 0, and at contacts er3 connects resistance YBacros the outgoing speaking conductors. On release of relay C the supervisory relays D and I in parallel with resistance YB are introduced across the outgoing speaking conductors, resistance YB serving to obviate any danger of release of the distant battery feeding relay due to the initial high impedance of the supervisory relays. When the voltage on condenser QW falls below the holding voltage of tube NTB, this tube will de-ionise and relay ER will commence to release slowly. On the release of relay ER, resistance YB is disconnected from the outgoing speaking conductors.

Further received impulse trains are dealt with as before described and after the last train has been received the relay set functions in known manner, relay D which is polarised by rectifiers MBA and MR3 serving to extend the called partys supervision signals back to the calling side of the circuit by reversing the connections of relay A tothe speaking conductors.

If the subscriber should hang up during dialling, a break simulating an impulse will be received so that when relay E operates after the condenser QX charging period relay PU will be released and relay E will remain locked to the earthed back contacts al so that relay PU cannot be re-operated. 88 m. s. after the release of relay PU tube NTB will flash to bring up relay ER which as before opens the locking circuit of relayC. In this instance however since the A relay is not now operated, and since the alternative holding circuit for relay B is opened by contacts erl, relay B will now release and will release relay E and initiate release of the connection.

Returning again to the ratio replacement timing circuit, since the 55 m. s. fixed first output break period corresponds to the break period of a 12 I. P. S. break impulse at the nominal 2-1 break/make ratio, and since it is desirable that at a speed of 12 I. P. S. the output impulses shall have this ratio to secure the most satisfactory operation of the selectors, it follows that if the resultant first output make period is 28 m. s. corresponding to an i'mpulsing speed of 12 I. P. S. it is necessary to make condenser QX discharge from 150 volts to say 100 volts in 28 m. s. thus providing a 55 m. second break 'period and so on as described;

If however, the received impulses are at a speed of say I. P; 6., the first output make 8 period will be m. sand condenser'QX will dischargeto a value lower than 100 volts. 7 If the 2-1 break/make output ratio is also to be mailtained'at this speed, the next charging time re- 7 quired by condenser QX to reach the tube NTA striking value must then be 66% m. s. to produce the appropriate second output break period for 10 I. P. S. Under this condition condenser QX will subsequently only have 33 m. s. discharge time during the second output make period. It will then reach a voltage somewhere between the 100 volt Value and the value to which it discharged in the 45 m. first make, and clearly the third charging periodwill not therefore be as great as 66 m. -s. so that the third output break period will lie somewhere between and 66 /3 m. s. and so on.

The correction afforded bythe scheme as shown in Fig. 1 is thus oscillatory in nature and is particularly marked if the maximum correction is placed on the second output impulse as above described by way of example. The introduction of condenser QY into the ratio replacement circuit in the manner shown in Fig. 2 is found to produce a marked stabilisation eilect with the result that the outgoing impulse ratio settles down to the calculated suitable value almost immediately.

Referring now to Fig. 2, it will be. seen that condenser QY is initially charged up to the same 100-volt value as condenser QX. When relay PU operates to connect condenser QX to the charging circuit at contacts pu3, the circuit for condenser QY is disconnected at contacts 10141. When condenser QX is to be discharged after having flashed the tube NTA and having brought up relay E, with the resultant release of relay PU, it initially rapidly shares out its 150 volt striking voltage with the volt charge on condenser QY and both condensers then proceed to dis charge via resistance YZ. On the next operation of relay PU in response to the next release of relay A,the discharge of both condensers is terminated and condenser QX commences to re-charge' When condenser QX is to be discharged, it will initially share out its volt charge with whatever charge has remained on condenser QY after the last discharge and both condensers will then proceed to discharge through resistanceYZ'as before. Similar remarks apply to each succeeding impulse of the train.

The best relative values of condenser QY and QX can be determined by calculation of the condenser charge and discharge times and voltages under simple conditions and such calculation shows the marked improvement which can be effected by the'introduction of the stabilising condenser. 7

An alternative method of stabilising is shown in Fig. 3 where it will be seen that before condenser QX proceeds to discharge via resistance YZ it'shares out its striking voltage of 150 volts with whatever voltage condenser QY has accumulated via variable resistance YV during the chargingtime of condenser QX.

It' should be pointed out that the .'ratio' replacement circuit is completely independent of incoming junction resistance values so that it is unnecessary for the circuit to be associated with any particular junction line. Moreover, since it entirely ignores the ratio of the incoming impulses it will function to give the desired output as long as any impulses are received, no matter how badly they are degraded, provided relay .A

relay PU and opens it sufficiently long to release relay E.

What we claim as new and desire to secure by Letters Patent is:

1. In a signaling system, a repeater responsive to received make and break impulses over an incoming circuit for repeating the same over an outgoing circuit, a relay in the repeater operated by the first interruption of the incoming circuit, a second relay responsive to the operation of the first relay to open the outgoing circuit, a condenser, a gas discharge tube, means for charging the condenser to the striking voltage of the tube, and means responsive to the striking of the tube to terminate the operation of the second relay and thereby close the outgoing circuit.

2. In a signaling system, an impulse repeater controlled over an incoming circuit by break and make impulses to repeat similar impulses in an outgoing circuit, a relay in said repeater responsive to a break in the incoming circuit, a second relay operated by the first relay to control the outgoing circuit, a condenser, a gas discharge tube, said condenser connected in a charging circuit by the operation of said second relay and continuing to charge until it reaches the striking voltage of said tube, and means operated when the tube strikes for causing restoration of the second relay.

3. A system as claimed in claim 2 in which said second relay closes a discharge circuit for said condenser for a time dependent on the next interruption of said incoming circuit, the amount of discharge controlling the time of operation of said second relay upon its next energization.

4. In an impulse repeater, a line relay responsive to received impulses consisting of breaks and makes of an incoming circuit, an outgoing circuit, a relay controlled by the line relay for opening the outgoing circuit when the line relay is deenergized, a condenser having a preliminary charge and connected for an additional charge by said second relay to time the break of the outgoing circuit, means for discharging said condenser to different points responsive to subsequent received impulses to thereby determine the time of break of the outgoing circuit upon the next operation of said second relay.

5. A system as claimed in claim 2 including a second condenser and a gas discharge tube for timing the released time of said second relay, and means for terminating impulsing conditions if said second relay is released for more than a predetermined time.

6. In an impulse repeater, a line relay responsive to received break and make impulses, a second relay controlled by each deenergization of the line relay to repeat a break impulse,-a condenser and a gas discharge tube for timing the break of each repeated impulse in accordance with the time between received break impulses, and a second condenser and a second gas discharge tube for preventing further operations in case the time between received break impulses exceeds a predetermined time.

7. In a signaling system, an impulse repeater having an input circuit over which impulsesof varying speed and break to make ratio are received, relay means in said repeater responsive to said received impulses for repeating corresponding impulses over an output circuit without storage and at the same speed as received, and timing means comprising an aperiodic circuit and a gaseous discharge tube associated with said relay means for causing the break to make ratio of the repeated impulses to have a desired value which is substantially independent of the speed or ratio of the received impulses.

8. In a signaling system, an impulse repeater having an input circuit over which impulses of varying speed and break to make ratio are received, relay means in said repeater responsive to said received impulses for repeating corresponding impulses over an output circuit without storage and at the same speed as received, and timing means associated with said relay means for causing the first repeated break impulse to have a fixed length and for varying the length of subsequently repeated break impulses in accordance with the speed of the received impulses.

9. In a signaling system, an impulse repeater, a circuit over which impulses of varying speed and break to make ratio are at times received, relay means in said repeater responsive to said received impulses for repeating corresponding impulses over a further circuit without storage and at the same speed as received, a first timing means associated with said relay means for causing the break to make ratio of the repeated impulses to have a desired value which is substantially independent of the speed or ratio of the received impulses, and a second timing means associated with said relay means for terminating impulsing conditions a predetermined time interval after the last impulse of a series.

10. A signaling system as claimed in claim 9 in which each of said timing means comprises an aperiodic circuit and a gaseous discharge tube.

11. In a signaling system, a first circuit over which impulses are at times transmitted, a gas discharge tube, means associated with said first circuit for initiating an impulse over a further circuit and for initiating the flow of an aperiodic current in a circuit connected to said tube in response to the receipt of an impulse over said first circuit, said aperiodic current causing the tube to fire a predetermined time interval thereafter, and said means being operated when said tube fires to terminate the impulse over said further circuit.

REGINALD TAYLOR. GEORGE THOMAS BAKER.

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