US2299660A - Automatic telephone system - Google Patents

Description

1942- G. E. STOVNEBRIDGE, JR- 2,299,650

AUTOMAT IG TELEPHONE SYSTEM Filed June 25, 1941 GEN NVENTOR.

I GEORGE E STONEBRIDGE JR.

ATTORNEY Patented Oct. 20, 1942 AUTOMATIC TELEPHONE SYSTEM George E. Stonebridge, In, New York, N. Y., as-

signor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware,

Application June 23, 1941, Serial No. 399,266

6 1 Claims.

- used in such systems.

More in particular the invention may be considered as a direct improvement in the ringing arrangements using grounded interrupted generator, such as shown in the Lomax Patent 1,569,430, issued January 12, 1926. In this Lomax patent the ringing circuit extends from grounded generator, the common interrupter springs, to normally closed back contacts on the ring-cut-off relay of the connector, and through make contacts on the switching relay to the lower, or positive, line wiper. In case this wiper encounters a grounded positive line conductor, or in case any portion of the above described circuit becomes grounded, trouble occurs. That "is, this fault ground may substantially short-circuit the generator thereby causing damage to it, provided a protecting resistance, such as a series lamp, is not provided in the ringing circuit. In addition, when the generator is ringing on a grounded ringing circuit on one connector switch all other connectors using this same generator are deprived of ringing current due to the first connector shunting the ringing supply to ground. This condition exists until the subscriber using this first connector hangs up.

The main object of the invention is to overcome the above-mentioned defects by providing circuits such that the ringing circuit is out Oh when a grounded line is encountered. In the instant case, a marginal relay is provided in the ringing circuit which will not operate on normal maximum ringing current transmitted over the line conductors through the -condenser and ringer at the substation and the upper winding of the connector cut-off relay, but which will operate when the connector rings to ground on a defective line. This marginal relay operates to cause the energization of the connector ring-cut-ofi relay to disconnect the generator whenever the lower, or positive, line wiper encounters a grounded positive line conductor.

The means by which the foregoing object is accomplished will be fully set forth hereinafter,

reference being had to the accompanying drawing which shows sufiicient of the apparatus to enable the invention to be explained and understood.

Referring now to the drawing, it should be stated that only the ringing circuit of the presrelay 33, release relay 34, ring-cut-off relay 31, switching relay 4!), and the common ringing generator Gen. and interrupter Int. are identical to the correspondingly numbered relays and ringing machine RM shown in the connector H in the Lomax Patent 1,569,430. The only addition to this circuit is the marginal relay 4| and its make contacts 42 for operating the ring-cut-ofi relay. The substation A corresponds to the substation A shown in the above-mentioned Lomax patent. PI and F2 represent faults, which for the purpose of explaining the invention, ground either line conductor M2 or 2 of substation A.

Having given a brief'description of the apparatus, the operation of the same will now be described in detail. For this purpose it will be assumed that the connector switch including the ringing circuit of the drawing is seized and operated in the same manner as described in Patent 1,569,430. Upon seizure of this connector the line relay 33 energizes and operates release relay 34 over an obvious circuit. In response to dialling the two digits of the called line, the wipers BI and 83 are operated to the bank contacts 84 and 8B and the switching relay 40 is energized and locked energized in case the called line is idle as described in the Lomax patent. In response to the operation of switching-relay 40 the new ringing circuit is closed. This circuit includes grounded generator and interrupter make contacts 75 of the common ringing machine RM, through the added marginal relay 4|, back contacts 51 of the ring-cut-off relay 31, make contacts 61 of switching relay 40, lower, or positive, line wiper 83, bank contact 88, positive line conductor 212, through the condenser C, ringer R and normally-closed switch-hook contacts of substation A, negative line conductor 2| bank contact 84, negative line wiper 8 I, make contacts 63, back contacts 55 and through the upper winding of ring-cut-ofi relay 31 to the common grounded battery. The ring-cut-ofi relay, as is well known, does not operate in this circuit due to the copper slug on its armature end and its copper sleeve. The new marginal relay is of such value that it also will not operate over the above-traced circuit including the ringer R and the upper winding of ring-cut-ofi relay 31. The copper slug on the heel end of relay 4| is provided to lower the impedance of this relay so as not to effect the ringing current. In response to the operation of the ringer R subscriber A responds by removing his receiver thereby disconnecting the ringer R and conent invention is fully disclosed andthat line 55 denserC and substituting a direct current path through substation A for energizing ring-cut-off relay 31. The marginal relay 4| is also included in this energizing circuit for the ring-cut-oif relay and it is immaterial whether this marginal relay 4| operates or not since its only function is to operate the ring-cut-ofi relay which operated over the called subscribers loop.

The operation of the ring-cut-ofi relay 3'! completes the talking circuit between the calling and called subscribers lines as described in the Lomax patent.

In both the Lomax Patent 1,569,430 and Wicks Patent 1,667,915 the circuits of the ring-cut-off relays are such that these relaysare energized in case the upper, or negative, line Wiper encounters ground. The circuit for energizing the ring-cut-off relay 31 of the said Lomax patent is the same as the drawings shown inthe instant application and may be traced as follows: from the fault ground, such as F2, negative line conductor 2| l, bank contact 84, negative line wiper 8|, contact 63, back contacts 55, and through the upper winding of ring-cut-off relay 3? to battery. The circuit for energizing the ring-cut-oii relay in Wicks Patent 1,667,915 may be traced from the fault ground on the upper or negative, line conductor, connector bank 4%, negative line wiper 45B, armature spring 435 and its front contact of switching relay till, armature spring 425 and its back contact of ring-cut-ofi relay 6%, upper winding of ring-cut-off relay G64, and through the interrupter springs of the ringing machine to battery connected generator. From the foregoing it will be seen that it is customary to operate the ring-cut-ofl relay and disconnect ringing current from the called line whenever a faulty ground is encountered by the upper, or negative, line wiper of the connector switch.

In accordance with the present invention circuit arrangements are shown for causing the operation of the ring-cut-off relay to disconnect ringing current when the lower, or positive, line wiper of the connector encounters a faulty ground on the positive line conductor of the called line. Therefore, with the circuits as shown in the instant application, the ring-cut-off relay of the connector'is automatically operated to cut off the ringing current in response to either the negative or positive line wiper encountering a faulty grounded line conductor.

It will now be assumed that the connector wipers 8i and 83 have been connected to bank contacts 84 and 88, that the switching relay 40 has completed the ringing circuit, and that the positive line conductor H2 is grounded at El by a faulty ground. Under this condition the following circuit exists: from grounded generator, interrupter make contacts 15 of the common ringing machine RM, through the marginal relay 4|, resting contact and armature spring 57, contacts 6'1, positive line wiper 83, bank contact 88, and positive line conductor 252 to the fault ground at Fl. Marginal relay 4| is energized in this circuit and at contacts 52 completes a circuit through the lower winding of cut-01f relay 31 to cause the latter relay to energize and disconnect the generator from the grounded line conductor at armature spring Relay 3'! at contacts 56 completes a locking circuit for itself from the release trunk ground at armature 5! of release relay 34 so that relay 3? is maintained operated after relay H deenergizes which it does when its energizing circuit is opened at contact 51. During the period that the grounded generator is ringing to ground on the positive line,

a partial short circuit exists through the generator which would be harmful thereto if the same persisted. However, since relay 4| causes the operation of relay 3'! this partial short circuit is of such short duration that no harm is done to the generator. Also, during this short period, the ringing current is shunted to ground thereby depriving all other connectors of ringing current which at the time are in'ringing position, but this period is now of such short duration, due to the operation of the cut-off relay, as to be negligible.

Having described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim is:

1. In a telephone system, a called line having a pair of line conductors, a connector switch having a pair of line wipers, means for connect ing said line wipers with said line conductors, means for transmitting ringing current over said line conductors to signal the called subscriber, a ring-cut-off relay in said connector operated in response to the called subscriber answering for disconnecting said ringing current from the called line, said ring-cut-off relay also operative in case a particular one of said line wipers encounters a grounded line conductor and also operative in case the other line wiper encounters a grounded line conductor for disconnecting ringing current from the called line whereby irrespective of which line conductor is grounded said ring-cut-oif relay is operated to disconnect ringing current.

2. In a telephone system, a called line having a pair of line conductors, a connector switch having a pair of line wipers, means for connecting said line Wipers with said line conductors, means for transmitting ringing current over said line conductors to signal the called subscriber, a ring-cut-oif relay in said connector operative to disconnect said ringing current from the called line, and means for operating said cut-off relay under any one of the following conditions, first, in response to the called subscriber answering, second in case one of said line wipers encounters a grounded line conductor, and third in case the other of said line wipers encounters a grounded line conductor.

3. In a telephone system, a called line having a pair of line conductors, means for connecting with said line conductors and for transmitting ringing current over said line conductors to signal the called line, a ring-cut-oif relay operative to disconnect said ringing current from the called line, and means for operating said ringcut-oif relay under any one of the following conditions: first, in response to the called subscriber answering, second, in case a particular one of said line conductors is grounded, and third, in case the other of said line conductors is grounded.

4. In a telephone system, a called line including a pair of line conductors and a bridged ringer, a battery having one pole thereof grounded, a generator connected to the grounded pole of said battery, means for connecting with said line conductors, a series ringing circuit including the grounded pole of said battery, said generator, the winding of a marginal relay, a particular one of said line conductors, said bridged ringer, the other of said line conductors, the Winding of a ring-cut-off relay, and the opposite pole of battery, means for completing said circuit to signal the called subscriber, said marginal relay being unresponsive to the normal ringing current in said circuit transmitted from said generator through said ringer and the winding of said ring-cut-ofi relay and operative only in case said particular one of said line conductors is grounded, said ring-cutofi relay also being unresponsive to the normal ringing current in said circuit transmitted from said generator through said ringer and operative in response to the called subscriber disconnecting said bridged ringer and substituting a direct current bridge across said conductors and also operative during said ringing period in case said other line conductor is grounded, means operated by said ring-cut-off relay for disconnecting said generator from said line conductors, and means responsive to the operation of said marginal relay for operating said ring-cut-ofi relay to disconnect said generator from the called line.

5. In a telephone signalling system, a called line having a pair of line conductors; a ringing circuit including a grounded generator, a marginal relay, said line conductors, and a ring-cutoif relay; means for completin said circuit to signal the called subscriber over said line conductors, said marginal relay operated in said circuit by said grounded generator only in case a particular one of said line conductors is grounded, and means responsive to the operation of said marginal relay for operating said ring-cut-ofi relay to disconnect said generator from the called line conductors.

' 6. In a telephone signalling system, a called line having a negative line conductor and a positive line conductor; a series ringing circuit including a grounded generator, a marginal relay, said positive line conductor, the called subscriberfs ringer, said negative line conductor, a

'ring-cut-ofi relay and a battery having one pole grounded; means for completing said circuit to operatesaid called subscribers ringer, said marginal relay operative in said circuit by said grounded generator only in case said positive line conductor'is grounded, and means controlled by the operation of said marginal relay for operating said ring-cut-ofi relay to open said circuit thereby disconnecting said generator from said grounded positive line conductor.

GEORGE E. STONEBRIDGE, JR.

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