US2025444A - Telephone system - Google Patents

Description

D. C. CROWE TELEPHONE SYSTEM Dec. 24, 1935.

Filed Aug. 19, 1933 2 Sheets-Sheet'l J Cram/ Dec. 24, 1935. D. c. CROWE D 14 TELEPHONE SYSTEM Filed Aug. 19, 1933 2 Sheets-Sheet 2 ii? 5H? 7 3 the first mentioned subscriber.

Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application August 19, 1933, Serial No. 685,944 In Sweden August 29, 1932 9 Claims.

The present invention relates to telephone systems. More particularly the invention relates to telephone systems with party lines in which each of the subscribers stations allotted to the party line is provided with a relay which upon being energized brings about the connection of the station to the line. A primary object of the invention is to provide switching means at the subscribers stations and at the exchange adapted to ensure that only the subscriber of the party line first calling can connect his telephone apparatus to the line whereby other subscribers allotted to the line are prevented from overhearing or disturbing a conversation carried on by Another object of the invention is to design the switching means disposed at the subscribers stations for a minimum of energy consumption. The invention is substantially characterized by the provision at each one of the subscribers stations of a relay arranged to connect the station to the line and to be energized by means of discharge current from a condenser disposed at the subscribers station and adapted to be charged to the necessary voltage by means of a current source disposed in the exchange. In systems with central battery feed said current source may, for example, consist of the normal feed battery. In local battery systems having a special current source in the exchange for call marking said latter current source may be used for charging the condensers. The party line used may consist of a double line with or without earth connection at the subscribers stations, or of a single line with earth return. The invention may find application in automatic as well as in manual telephone systems.

The invention will now be more closely described with reference to the accompanying drawings showing a plurality of embodiments of the same. Figure 1 shows a circuit diagram for an automatic exchange to which is connected a party line with three subscribers stations. Figures 2, 4 and 5 show circuit diagrams for subscribers stations. Figure 3 shows a circuit diagram for a party line with two subscribers and equipped with certain arrangements for signalling. Figure 6 shows a circuit diagram for a manual exchange provided with equipment for serving a party line connected thereto.

In the embodiment shown in Figures 1 and 2 the condenser arranged at each subscribers station is adapted to be charged from the exchange with a voltage volts) exceeding the normal feed voltage which is assumed to be 32 volts.

I and 2 designate the two branches of the party line. The condenser 3 at each subscribers station is connected with one pole to the line branch I and with its other pole to the switch hook 4 of the subscribers set. The bell 5 is with 5 one pole connected to the line branch 2 and with its other pole normally connected to the switch hook 4 through a contact 6 of the latter. When the microtelephone is removed from the switch hook the contact 6 is opened and a relay I is 10 simultaneously shunted to the condenser 3 through a contact 8 of the switch. The microtelephone 9, I0 is connected to the line branches 5 and 2 via a normally open contact II controlled by the relay I. A relay I2 is connected 15 between the line branches I and 2 by means of a normally open contact I3 controlled by the relay 1 and by means of a normally closed contact IA of the switch hook. I designates an impulse sender. In the exchange D the line branch I is connected to the negative pole of a 50 volts battery through a contact I5 controlled by the cut-off relay BR, through the line relay LR, and through the resting contact I6 of said relay and a resistance I'I connected to the nega- 25 tive pole of a 50 volts battery. The line branch I is also arranged to be connected through the working contact I8 of the line relay LR to a point of the battery having a voltage of 32 volts. The line branch 2 is connected to the bank of the searcher S and also, through the resting contact I9 of the relay BR,tothe positive pole of the battery. The other switching members in the exchange are arranged in a manner known per se. 35

When the line is free all condensers 3 on the line are charged to a voltage of 50 volts. When a subscriber makes a call the relay "I is shunted to the condenser 3 through the contact 8 of the switch hook. The discharging current of the condenser energizes the relay '2! which operates and closes the contacts II and I3 and actuates the locking member 2I by means of which the armature of the relay is mechanically locked in attracted position. The closing of the contact I I completes a circuit to the exchange over the branch 2 of the line through the contact I9 of the relay BR to the positive pole of the battery, and over the branch i of the line through contact I5, relay LR, contact I6 and resistance I! to the negative pole of the battery (-50 volts). Relay LR operates, opening contact I6 and closing contact I8. As a result the voltage impressed upon the line is reduced from 50 volts to 32 volts. The

relays I disposed at the subscribers stations are dimensioned in such a manner that they operate in response to the discharging current from the condensers 3 when the latter have been charged with the voltage (in the present case volts) impressed upon the line when it is'free but not when they have been charged to the voltage (32 volts) impressed upon the line after one of the subscribers has made a call (on account of the -voltage drop in the line the charging voltage of the condensers will in the latter case'be less than V 32 volts) If thus, after the line has been engaged one of the other subscribers allotted to the line removes his microtelephone the appertaining relay I will not operate and the subscriber in question can consequently not connect himself to the line. Upon operation of the line relay LR, the starting circuit for the searcher S is also closed through contact 29 whereby the party line is hunted up and connected to a free selector in a manner known per se.

When the subscriber first calling has completed the conversation and replaces his microtelephone the relay I2 is connected to the line branches through contact I4 of the switch hook. The circuit for the relay [2 was prepared in advance upon operation of the relay I through the closing of contact [3. The relay i2 is therefore energized (from the feed battery in the exchange) upon being connected to the line and releases the locking arrangement 2| for the armature of the relay 1, said armature then returning to its position of rest thereby opening the contacts H and I3. Contact I l interrupts the talking circuit and contact I3 interrupts the circuit for the relay I2. The opening of contact ll causes deenergization of the current feed relay SR in the exchange whereby in a manner known per se, the circuit for the cut-off relay BR is interrupted and the connection released.

It is not necessary 'for the application of the invention to impress upon the line when free a voltage (50 volts) exceeding the voltage impressed upon the line when engaged (32 volts) in order thereby to obtain the necessary difference in charging voltage for the condensers 3 when the line is free and engaged respectively as in the embodiment now described; If the relays 1 are sufliciently sensitive the arrangement will operate even if the same voltage is impressed upon the line when free'andwhen engaged. This is due to the fact that the voltage drop occurring in the line upon connection thereto of a subscribers station reduces the charging voltage for the condensers 3 in the other subscribers stations to a value varyingin accordance with the distance from the exchange. Also in the subscribers station nearest to the exchange the charging voltage in question is sufiiciently much lower than the charging voltage when the line is free to prevent the discharging current from the condenser in that subscribers station, from which a. call is made after the line is engaged, to obtain such a value that the relay 1 operates.

The release of the armature of the relay 1 may also be effected mechanically. Figure 1c shows a circuit diagram of such an arrangement. Upon replacing the microtelephone the switch hook 4 actuates the locking arrangement 2| whereby the armature of. the relay I is released.

In the circuit arrangements shown in Figure 2 the signal bell 5 is shunted over the line in series with a separate condenser 23, whereas, when the switch hook is depressed, the condenser 3 is connected in series with a resistance which in Figure 2A is shown as an inductive resistance and in.

current sent out.

Figure 213 as an ohmic resistance. Said circuit arrangements entail certain advantages in signalling. When effecting signalling with periodically transmitted alternating current in the circuit arrangement according to Figure 1 the bat- 5 tery is connected to the line during the intervals between the ringing periods to render possible the charging of the condenser of the called subscriber so that said subscriber will be connected to the line when removing his microtelephone. 10 During the ringing periods the charge of the. condenser 3 will vary in time with the alternating current wherefore the subscriber cannot be sure to be connected to the line if removing his microtelephone during such a period. Inthe circuit 15 arrangement shown in Figure 2 the time constant for the condenser 3 with resistance 25 must have such a value that the charge of the condenser is not appreciably influenced by the .alternating Provided that. the battery is 20 maintained connected to the line during the entire ringing time-thus during the ringing periods as well as during the intervals between the same the condenser of the called subscriber will maintain a' constant charging voltage during the en-Ili tire ringing time and the subscriber may consequently obtain connection at an arbitrary moment i the ringing period.

In the circuit arrangements shown in Figures 4 and 5 the relays are arranged to be selected 30 with respect to the direction of the discharging current from the condenser 3. In the arrangement according to Figure 4 the necessary selectivity is obtained by making the relay polarized and in the arrangement according to Figure 5'by 85 means of a rectifier 21 connected in series with the relay L The arrangement in the exchange is then such that the battery provided for charging the condensers has its poles reversed when the first call is received. The condensers 3 in 40 the other subscribers stations thereby obtain charging potential of opposite sign. Upon a call from another subcriber allotted to the line the discharging current through the relay I of said latter subscriber will thus have the opposite di- 5 rection, said discharging current being unable, on account of the selective arrangement, toenergize the relay in question. Thus the subscriber last calling cannot connect his set to the line.

Figure 6 shows a circuit diagram for a manual 50 exchange to which is connected a party line consisting of a single conductor and earth return, said exchange being provided with an arrangement causing the potential connected to the line to change its sign upon the occurrence of a call. 65 y A battery 23 is connectedwith its positive pole to earth and when the line is free, with its negative pole through a slow acting relay LE1, the resting contact 31 of the relay LE2 and the resting contact 33 of the relay BR to the line. Upon a call the relay LE1 operates and closes its contact 32 whereby a circuit is closed from earth to a slow acting relay LE2 and a battery 29 the negative pole of which is earthed. The relay LE2 operates and interrupts at contact 3! the circuit for the relay LE1 and connects through contact 3i! the positive pole of the battery 29 to the line.

Figure 3 shows a circuit diagram for a party line having only two subscriber, the bell of one subscriber being connected between one of the line branches and earth and the bell of the other subscriber between the other branchand earth, and in which selective ringing is arranged The bell 40 of the subscriber A is connected between 7 the branch! and earth Whereas the bell H of the subscriber B is connected between the branch 2 and earth. In other respects the connection of the apparatus corresponds to that shown in Figure 2, except that in Figure 3 the connection of the microtelephone and of the impulse sender to the branch 2 is effected through a contact 42 of the switch hook and through a contact controlled by the relay 7. In addition there is included in the circuit for the relay 1, similarly as in Figure 5, a rectifier 2?. In the exchange (the right hand part of the figure) are arranged two repeating coils 44 and 65 the primary windings of which are fed with ringing current. One pole of the secondary winding of the repeating coil 44 and 45 respectively is connected with the positive and negative pole respectively of a battery. During the signalling period the line branches I and 2 are connected with contact springs 46 and 41 of which contact spring 46 may be connected alternatively to the negative pole of the battery and one pole of the secondary winding of the repeating coil 25 respectively. The contact spring 41 may be connected alternatively to the positive pole of the battery and to the secondary winding of the repeating coil 44 respectively. When ringing up the subscriber 33 having its bell connected to the branch 2 ringing current is sent through the repeating coil M. The springs then occupy the positions shown in Figure 3, the branch I being connected through contacts 43 to the negative pole of the battery and branch 2 through contact 49 and the repeating coil 44 to the positive pole of the battery, the ringing current passing only through the bell i! of the subscriber B. The battery is evidently connected to the line and the condensers 3 are in charged condition even during the ringing period wherefore the called subscriber can connect himself to the line also during this period. When ringing up the subscriber A having his bell 30 connected to the branch I ringing current is sent through the repeating coil 45. The contact springs 46 and t? respectively are then shifted in such a manner that the branch I is connected to the negative pole of the battery through the contact 52 and the repeating coil and the branch 2 connected to the negative pole through the contact 53. The ringing current produced in the transformer 45 then passes only through the bell of the subscriber A.

I claim:

1. In a telephone system an exchange, a current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a condenser at each subscriber station, the said relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, and an armature on the said relay provided with means to lock the relay in attracted position.

2. In a telephone system an exchange, a current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a condenser at each subscriber station, the said relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, an armature on the said relay provided with means to lock the relay in attracted position, a further relay at each of the subscriber stations, an energizing circuit for the condenser at each subscriber station, the said 10 relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, an armature on the said relay provided with means to lock the relay in attracted 1 5 position, a switch hook at each subscribers station and means to enable the said switch hook to cooperate with the said armature so as to release the armature upon the microtelephone being replaced on the switch hook. 20

4. In a telephone system an exchange, a current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a condenser at each subscriber station, the said 25 relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, another relay at the exchange adapted to operate in response to a call 30 first coming in, and means controlled by the last mentioned relay to bring about a lowering of the voltage impressed upon the line when the line is free.

5. In a telephone system an exchange, a cur- 35 rent source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a polarized relay and a condenser at each subscriber station, the said relay being connected 40 into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, another relay at the exchange adapted to operate in response to a call first coming in, and means controlled by the last mentioned relay to reverse the poles of the charging battery.

6. In a telephone system an exchange, a current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a condenser at each subscriber station, the said relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, a rectifier connected in series with the said relay, another relay at the exchange adapted to operate in response to a call first coming in, and means controlled by the last mentioned relay to reverse the poles of the charging battery.

7. In a telephone system an exchange, a current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and 6 a condenser at each subscriber station, the said relay being connected into circuit so as to be energized by means of discharging current from the condenser charged by means of the current source at the exchange, a switch hook, at resistance connected in series with the condenser when the said switch hook is depressed, the said resistance being so dimensioned that the charge of the condenser is not essentially influenced by signalling alternating current sent out on the line.

'8. In a telephone system, an exchange; a direct current'source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a condenser at each subscriber station, the

' said relay having for purpose to connect the said station to the said line and being connected into circuit so as to be energized by means of discharging current from the condenser said condenser being connected into circuit so as to be normally charged by means of the said source at the exchange and ready for being discharged through the corresponding relay immediately upon the calling of the subscriber.

9. In a telephone system, an exchange, a direct current source disposed at the exchange and a party line extending therefrom, a number of subscriber stations connected to the said line, a relay and a feed current blocking condenser at each subscriber station, the said relay having for purpose to connect the said station to the said line and being connected into circuit so as to be energized by means of discharging current from the condenser said condenser being connected into circuit so as to be normally charged by means of the said source at the exchange and ready for being discharged through the corresponding relay immediately upon the calling of the subscriber.

DOUGLAS CORMACK CROWE.

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