US2093242A - Testing and private wire arrangement for telephone or like systems - Google Patents

Testing and private wire arrangement for telephone or like systems Download PDF

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US2093242A
US2093242A US4071635A US2093242A US 2093242 A US2093242 A US 2093242A US 4071635 A US4071635 A US 4071635A US 2093242 A US2093242 A US 2093242A
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relay
circuit
contact
outlet
test
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Humphries Horace Edgar
Clark Ronald Isaac Herbert
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Siemens Brothers and Co Ltd
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Siemens Brothers and Co Ltd
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q3/00Selecting arrangements

Description

Sept. 14, 1937. H. HUMPHRIES ET 1. 3 2,093,242

- TESTINGAND PRIVATE WIRE ARRANGEMENT FOR TELEPHONES OR LIKE SYSTEMS Filed Sept. 16, 1955 2 Sheets-Sheet l F/az. 7015. W04

Sept. 14, 1937. H. E. HUMPHRIES ET AL 2,093,242

TESTING AND PRIVATE WIRE ARRANGEMENT FOR TELEPHONES OR LIKE SYSTEMS Filed Sept. 16, 1935 2 Sheets-Sheet 2 RON/u /5 HERBERT CLARK %Z Patented Sept. 14, 1937 UNITED STATES some.

PATET OFFECE TESTING AND PRIVATE WIRE ARRANGE- MENT FOR. TELEPHONE R LIKE SYS- TEMS don, England Application September 16, 1935, Serial No. 40,716

. In Great Britain September 24, 193 1 Claims.

The present invention relates to automatic telephone. and like electric selective systems and more particularly has in View improved testing and private wire arrangements which are designed among other things to prevent the occurrence of double connections or to minimize the likelihood of the occurrence of such connections. In systems in which selecting switches are set under the control of common control apparatus, an outlet from a selecting switch may have to be treated as being a busy one either because the outlet circuit is itself in use or because the common control circuit associated with the outlet circuit is in use, and a double connection may occur either because two searching selecting switches test and seize the same outlet circuit or because two searching selecting switches test and seize two diiferent outlet circuits associated with the same common control circuit. The arrangements according to the invention are -mainly intended for use in common control systems but certain of them are of wider application.

The arrangements according to the invention are suitable for use in systems employing high speed switches such as switches of the motordriven latch-controlled type and in systems of the kind in which during the setting up of a connection there is formed what is known as a through test or private wire, as well as in other systems.

The invention has in view improved arrangements both as regards that part of the circuit of a selecting switch which is concerned with testing the outlets of the switch and bringing the switch to rest on a free outlet and as. regards the test or private wire circuits of such outlets. It

. must be understood that the expression circuit of a selecting switch is intended to include within its scope any necessary common control circuit.

The arrangements according to the present invention are such that the operation of a single change-over contact of a selector test relay serves to suspend the searching operation, to busy the outlet concerned, and to cause a change of condition of an auxiliary relay connected in a circuit independent of the test wire circuit.

According to one feature of the invention, test- I ing and private Wire arrangements are such that m the circuit in which a selector-test relay operates to stop the switch on a free outlet is one which passes over two windings of the relayin series I and a test wiper and the test or private wire of the outlet circuit, and are also such that the test relay has a change over contact which on operation opens a circuit shunting a winding of an auxiliary relay and closes a circuit shunting one of the said two windings of the test relay to mark the outlet busy, the removal of the shunt from the Winding of the auxiliary relay causing this winding to be inserted in the circuit of a magnet or relay controlling or effecting the driving of the switch so that the said magnet or relay is released and the operation of the auxiliary relay is initiated. y The outlet circuit may include a coupling relay adapted on operation to couple the individual outlet circuit to a common control circuit, it being arranged that the relay is operated over the test or private wire as a consequence of the seizure of the outlet circuit.

According to another feature of the invention, the test relay in arrangements embodying the feature previously referred to has associated with it a device having a non-linear current-resistance characteristic, it being arranged that this device serves to increase the discrepancy between the current which flows through the two windings of the test relay when a free outlet is tested and the current which flows when an outlet is tested which is marked busy by being connected to va .point between resistance or impedance elements connected in series between battery andearth.

The above and various subordinate features of the invention are exemplified in the several typicalarrangements embodying the invention which will now be described with reference to the accompanying drawings, in which Fig. 1 is a circuit diagram showing the invention as applied to a selecting switch having a single set of wipers; Figs. 2, 3, and 4 show modifications which are alternative to the arrangement shown in Fig. 1; while Fig. 5 shows the invention as applied to a selecting switch having two sets of wipers.

Referring firstly to Fig. 1, this shows parts of the individual and common control circuits of a selecting switch and parts of an outlet circuit and an associated common controlcircuit. The four rectangles into which the figure is divided by dotted lines correspond to the four circuits concerned, a portion of the individual circuit of the selecting switch being shown in the upper left hand rectangle, a portion of the outlet circult being shown in the upper right hand rectangle, and portions of the common control cirwith the selecting switch and with the outlet circuit are for convenience designated CCS and CCO respectively.

The selecting switch is a motor driven latchcontrolled uniselector adapted to search for a free one of a marked group of outlets, the relevant group being marked in response to the receipt of an impulse train in the associated comrnon control circuit CCS. The marking arrangements in the common control circuit are represented schematically by a cross MA, and are such as to connect the upper side of winding (I) of the test relay T to each of those contacts in the bank of marking wiper G which correspond to outlets in the required group. When the latch magnet LM of the uniselector is energized, a latch is withdrawn from a toothed wheel forming part of the driving mechanism of the switch and the circuit of the driving electromo-tor is closed at a contact of the latch magnet, and in consequence the wipers are rotated at a high speed. When the latch magnet is de-energized, the motor circuit is opened and the latching member engages the toothed wheel referred to, bringing the switch substantially instantaneous- 15 to rest. Contact one is an off-normal contact of the selecting switch and contacts ksl, 1:52, and Iss3 are contacts of the coupling relay which servesv to couple the individual circuit of the selecting switch to the common control circuit CCS. Contact e l is a contact of a relay operated after the marking arrangements in the common control circuit have been set to effect a marking. The test wiper of the selecting switch is designated P. The switch has of course wipers and banks other than those shown. lhe test relay T is a high-speed relay and has a highresistance auxiliary relay TA which operates comparatively slowly. Relay T has only one contact tl, but the auxiliary relay TA has as many contacts as may be necessary to fulfil the requirements of the circuits concerned as a Whole.

The outlet circuit and the common control circuit CCO associated therewith are actuly the individual and common control circuits of a further selecting switch, and contact on. is an off-normal contact of this switch. Relay K in the outlet circuit is a coupling relay adapted on operation to couple the individual outlet circuit to the common control circuit CCO,.it being arranged that the relay is operated over the private wire as a consequence of the seizure of the outlet circuit. The inductive winding of the relay is shunted by a noninductive resistance which may be wound on the core of the relay. The incoming private wire of the outlet circuit is normally connected to the battery-connected resistance YA in common control circuit CCO via the test jack contact, contact on, a break contact of relay JB, and contact and. Contact end is an off-normal contact of a digit switch in control circuit CCO. Relay JB in the control circuit has a break contact individual to each outlet circuit in the group associated with the control circuit. Two of the necessary break contacts are formed by the back contacts of change-over contacts ab! and y'b8, while the remainder are formed by simple break contacts such as 7115. The break contact indi vidual to the outlet circuit shown in the figure is formed by back contact y'bl. Contact al is a contact of a line or impulse-receiving relay included in the common control circuit C00, and is operated in a circuit independent of coupling relay contacts consequent on the seizure of an outlet circuit in the group associated with the control circuit. Contact b l slow-releasing holding relay, it being arranged that this relay is operated on the operation of the line relay just mentioned and then remains operated until the line relay 'next remains steadily released. The battery-connected resistance YA is connected in common over contact 0nd and the break contacts of relay JB to all the outlet circuits of the group associated with common control circuit CCO.

After the selecting switch with Wipers P and G has been taken into use and the coupling relay with contacts ksl m2, and 10.93 has been operated to couple the individual circuit of the switch to the common control circuit 008, then as soon as the marking arrangements in this control circuit have been set to effect a marking, contact el is closed and completes an operating circuit for latch magnet LM. The circuit for magnet LM passes over back contact tl, contacts tal and el, and front contact Icsl. The uniselector is consequently advanced in search of a free one of the marked group of outlets. During search, test wiper P and marking wiper G co-operate to the end that when a marked outlet is encountered windings (I) and (II) of high speed test relay T and a dry-plate rectifier RE; are connected in series between the test bank contact and earth, so that the relay operates to a battery connection via resistance YA in the common control circuit CCO'associated with the outlet circuit if a free and marked outlet is reached. The rectifier is of course connected in the sense which allows such operation to occur. When test relay T is thus operated, contact tl opens the short-circuit about the winding of auxiliary relay TA and short circuits rectifier RE and winding (II) of relay T. The resistance YA is of a value which sufiices to prevent the high speed test relays associated with two difierent selectors from holding in parallel on their windings (I). Such holding would of course give rise to a double connection. The insertion of the high resistance winding of the auxiliary relay into the latch magnet circuit causes the latch magnet to release and provides an operating circuit for the auxiliary relay. The short circuiting of rectifier RE and winding (II) of relay T connects the private wire of the outlet to earth through a low impedance (i. e. the low resistance winding (I) of relay T) to mark the outlet busy. This marking would normally be subsequently replaced by a busy marking from another source.

It should be noted that the momentary operation of high speed test relay T for a period insuflicient to bring about the operation of auxiliary relay TA has no lasting effect on'either the uniselector or its common control circuit. The rectifier RE prevents relay T from being operated by a positive or booster battery condition existing for metering purposes on the private wire of a busy outlet when the outlet is tested. The rectifier is also arranged to serve, by virtue of its non-linear current-resistance characteristic as regards currents in the conducting direction, to increase the discrepancy between the current which fiows when a free out let is tested and the current which flows when an outlet is tested which is marked busy by the fact that the relevant test bank contact is connected to a point between resistance or impedance elements connected in series between battery and earth (e. a point between a resistance such as is a contact of a YA and elements comprising a relay such as K and its shunt and the low-resistance winding of c a high-speed test relay such as T). Instead of a rectifier, some other device (e. g. a metal or.

carbon filament lamp) having a non-linear current-resistance characteristic may alternatively be employed to give the last mentioned effect, but in this case of course a dual effect would not be obtained. the device would be placed according to its nature either in series or parallel with the high lays it may be necessary or desirable to provide the low-resistance holding winding of a test relay such as T with more turns than the number indicated by a consideration of the relay circuits in the static condition.

When test relay T is operated as previously described and brings about the operation of relay TA, contact tal disables the back contact of change-over contact fl and contact m2, operates the switching relay H of the individual selector at contact hl on the release of the switching relay H.

When relay H is operated, circuits are closed (over wipers of the selecting switch not shown in the figure) which serve to bring about the operation of the line relay in the common control circuit CCO associated with the seized outlet circuit. The operation of contact al of this line relay closes a circuit for operating relay JB on its winding (I), and shortly after this a holding circuit for relayJB is closed at contact bl. When relay JB operates, it list by opening its break contacts opens what may be termed the testing in circuits of the outlet circuits of the group associated with common control circuit CO0, and

then by closing front contact y'bl. connects bat tery-connected resistance YA to the lower ends of the windings of the coupling relays of all these outlet circuits. Since the other ends of these windings are connected to the respective incoming private wires over ofi-normal contacts such as on, the effect of the closure of front contact gibl is that coupling relay K in the seized outlet circuit is operated in a circuit which is completed to earth over bank contact and wiper P of the selector which has seized the outlet circuit. When relay K operates, contact 7c earths the private wire and contact 702 bridges contact on. The inductive winding of a coupling relay such as K and the associated non-inductive resistance form a low impedance combination, so

that the application of a busying condition to the private wire incoming to one outletcircuit busies all the other circuits of the group as long as the said private wire is connected through to the common control circuit. Owing to the fact that each coupling relay has only one inductive winding trouble due to transformer action between windings is avoided.

The operation of the switching relay (not shown in the figure) of the seized outlet circuit at a subsequent stage of the setting-up process brings about the continued release of the line relay in common control circuit 000, which in turn brings about the release of the holding re- In such an alternative arrangement,

back contact bl.

'of a slow-releasing holding relay, it being arranged as in the case of the arrangements of ,relays of all these outlet circuits. ,.quent operation of the circuits is similar to that described with reference to Fig. 1.

oiated with the control circuit.

lay and its, contact bl. As soon as contacts al and bl have both fallen back, relay JB releases and at contact gibl releases coupling relay K.

Offrnormial contact 0nd of the digit switch in common control circuit CCO ensures that an outlet circuit'associated with the control circuit can only be seized when the digit switch is at the normal. position. During the setting of the digit switch and of the selector of the outlet circuit, a circuit for the coupling relay K is provided over ffront contact 7'b8. speed test .relay or a winding thereof. We have found that for high speed switches and test re- Typical values for the resistances of winding (I) of relay T,,winding (II) of relay T, the winding of relay TA, the winding of relay K, the noninductive shunt across K, and resistance YA are i 35 ohms, ohms, 2000 ohms, 35 ohms, ohms and 550 ohms respectively.

Referring now to Fig. 2, this shows arrangements alternative to those shown in the two right hand rectangles of Fig'. l. arrangements for an outlet circuit and an assooiated common control circuit CCO, the incoming private wire of the outlet circuit is normally connected through to a battery-connected resistance YA in the control circuit over a test jack, an ofinormal contact on (corresponding to the similarly designated contact in Fig. 1), a rectifier R, and Contacts bl and b2 are contacts Fig. I that this relay is operated consequent on the operation of a line relay in circuit 000 and that the said'line relay is operated in a circuit independent of coupling relay contacts consequent on the seizure of an outlet circuit in the group associated with the control circuit. Relay K is the coupling relay of the outlet circuit and corresponds to the similarly designated relay in Fig. 1. The'break contact formed by back contact bl is connected in the testing-in circuits of all the outlet circuits in the group associated with common control circuit CCO'. Rectifier R is of course connected in the sense which allows current to flow from earth via a test relay testing the condition of. the outlet circuit.

When the outlet circuit is seized and the line and holding relays in the common control circult 000 are operated, the changing over of contact. b-l first opens What may be termed the testing-in circuits of the outlet circuits of the group associated with the common control circuit, and then connects battery-connected resistance YA to the lower ends of the windings of the coupling The subse- The rectifiers such as R in the several outlet circuits of the group serve to prevent earth on the private wire of one circuit from being transmitted to the private wires of the other circuits.

Referring vnow to Fig. 3, this shows further arrangements alternative to those shown in the two right hand rectangles of Fig. 1. The con- ,tacts, relay, rectifier and resistance shown correspond to those bearing the same designations in Fig. ,2. In these further alternative arrangements for an outlet circuit and an associated common control circuit 000, the incoming private wire of. the outlet circuit is normally connected through to the battery-connected resistanc'e YA in the control circuit simply over the test jack, the off-normal contact on, and the rectifier R, the resistance being connected in common to all the outlet circuits in the group asso- As regards the coupling relays such as K of the outlet circuits In these alternative of the group, the lower end of the winding of each relay is connected to the corresponding ends of all the other relays.

When the outlet circuit is seized due to a selector test relay operating in series with the resistance, the earthing of the private wire P causes the coupling relay K to operate, the operating circuit being earth on wire P, test-jack contact, contact on, winding of the relay, the coupling relays and rectifiers of all the other outlet circuits of the group, resistance YA,.battery. The coupling relays of the said other outlet circuits do not operate as the current which flows is shared between. them.

During the release of common control circuit 000 consequent on the operation of the switching relay of the outlet circuit, a break contact (not shown) included in the control circuit and connected in series with resistance YA is momentarily opened to bring about the release of coupling relay K.

Referring now to Fig. 4, this also shows arrangements alternative to those shown in the two right hand rectangles of Fig. 1. Contacts kl, k2, on, and b2, and relay K correspond to the items similarly designated in Fig. 3. The incoming private wire of the outlet circuit is normally connected to battery via the winding of. the coupling relay K in parallel with a metallic filament lamp LO, the test jack contact, offnormal contact on, and a condenser QA in parallel with carbon filament lamp LC and resistance YA. Condenser QA and the circuit in parallel therewith are connected in common to all the outlet circuits in the group associated with common control circuit 000. The resistance of metallic filament lamp LO rises as current commences to flow therethrough while the resistance of carbon filament lamp LC falls with flow of current. The effect of the metallic filament lamp is as it were to bring coupling relay K gradually into circuit when the outlet circuit is seized. The object of condenser QA and lamp LC in the common control circuit is to provide a test-in circuit which prevents two high speed test relays from holding in parallel to the battery connection in the one common control circuit but which assists in the process of increasing the current through the winding of the relevant coupling relay subsequent to the seizure of an outlet circuit.

When the holding relay of the common control circuit CO is released after the circuit has performedits function as regards a seized associated outlet circuit, the falling back of contact 122 connects earth over off-normal contact 0nd of a digit switch in the control circuit to the lower end of. the operated coupling relay and thereby brings about the release of this relay.

Contact hi is a contact of the switching relay of the outlet circuit and when operated changes the connections to lampLO so that the lamp serves as a supervisory lamp.

Referring now to Fig. 5, this shows arrangements corresponding to those shown in the two left hand rectangles of Fig. 1 but providing for testing two outlets simultaneously. As in the arrangement of Fig. 1, the selecting switch is a motor-driven latch-controlled uniselector adapted to search for a free one of a marked group of outlets, the relevant group being marked in response to the receipt of an impulse train in the associated common control circuit CCS. The marking arrangements in the common control circuit include a digit switch with a wiper DSI,

and are such as to connect earth via contact ml to each of those contacts in the bank of marking wiper G which correspond to outlets in the required group. One contact in the bank of wiper G corresponds to two outlets, since the selecting switch has two sets of speaking and test wire wipers and banks. The two test wire wipers are shown in the figure, being designated PP and PS. The circuits are arranged so that outlets occupying corresponding positions in the two sets of banks are tested simultaneously. The methods of testing and control are similar in principle to those described with reference to Fig. 1. Contact ons is an off-normal contact of the selecting switch and contacts ksl5 are contacts of the coupling relay which serves to couple the individual circuit of the selecting switch to the common control circuit CCS. Contact el is a contact of a relay operated after the marking arrangements in the common control circuit have been set to effect a marking. The common control circuit CCS contains a high speed test relay TP corresponding to test wiper PP and a similar high speed test relay TS corresponding to test wiper PS. Each test relay has associated with it a rectifier (REP or RES) which performs the same functions as rectifier BE in Fig. 1. High resistance relay TA serves as an auxiliary relay for both test relays, and corresponds to the similarly designated relay in Fig. 1.

After the selecting switch with wipers PP, PS, and G has been taken into use and the coupling relay with contacts lest-6 has been operated to couple the individual circuit of the switch to the common control circuit CCS, then as soon as the marking arrangements in this control circuit have been set to effect a marking, contact el is closed and completes an operating circuit for latch magnet LM. The circuit for magnet LM passes over back contacts tpl, tsl, and ms, contact el, and front contact ksl. The uniselector is consequently advanced in search of a free one of the marked group of outlets. When during search a pair of marked outlets is encountered, each high speed test relay and its associated rectifier is connected between the relevant test bank contact and earth. If both outlets happen to be free, one of the relays as usual has preference as regards bringing about the seizure of the corresponding outlet. The relay which has preference is the one designated TP.

When testrelay TP operates, its contact tpl disconnects earth from contact tsl, thereby rendering any coincident operation of relay TS ineffective as regards busying an outlet and removing the short circuit from the winding of relay TA, and applies earth to the junction of windings (I) and (II) of relay TP, thereby busying the outlet concerned. The insertion of the high resistance winding of relay TA into the latch magnet circuit causes the latch magnet to release and the relay to operate. When relay TA operates, the opening of contact ta! disconnects earth from both rectifiers, and the change of condition of contacts m3 and M2 connects in series between battery and earth the winding of relay HC and windings (I) and (II) of relay WC. Relay HC is provided in order to control the operation of the wiper switching relay H in an individual selecting switch circuit, and relay WC is provided to control the operation of the wiper choosing relay WS in an individual selecting switch circuit. Relay HC will not operate in series with the high resistance winding (I) of relay WC. Relay WC operates as soon as the series circuit just referred to is closed, while relay I-IC operates as soon as contact @062 has closed and short circuited winding (I) of relay WC. This arrangement ensures that the wiper choosing operation in the individual circuit is effected before the line wire wipers are connected in circuit. Contact wci operates wiper choosing relay WS, this relay on operation connecting up the set of wipers. of the uniselector which includes test wiper PP. Contact hci operates switching relay H, which performs the same functions as the corresponding relay in Fig. 1.

When during search a pair of marked outlets is encountered and test relay TS operates but test relay TP does not operate owing to the fact that the outlet tested thereby is busy, contact is! disconnects earth from contact ms and applies it to the junction of windings (I) and (II) of relay TS, thereby busying the outlet tested by that relay. The latch magnet releases and auxiliary relay TA operates as in the case just described. When relay TA operates, contact taZ completes an operating circuit for relay I-IC which includes back contact tpl. Relay WC is of course not operated in the case now being considered, since the other set of wipers of the uniselector is involved.

We claim:-

1. In a telephone system, a selector switch, a magnet for causing said switch to advance in search of an idle trunk, a circuit including said magnet and an auxiliary relay in which only the relay is able to energize due to its high resistance, there being, however, a normal short circuit path around said relay to prevent the same from operating and. to enable said magnet to operate, a test relay, a circuit including the test wiper of said switch for energizing said test relay when an idle trunk is found, and contacts on said test 40 relay for opening said short circuit path whereby said auxiliary relay is energized and the said magnet is deenergized to stop the switch.

2. A telephone system as set forth in claim 1 in which the test relay has two windings one of 45 which is short circuited on operation of the relay to make the selected trunk line busy,

3. In a telephone system, a selector switch, trunk lines accessible to said switch and to other switches, circuit arrangements such that the test 50 contacts of idle trunks have a certain potential thereon while the test contacts of busy trunks have a lower potential, a test relay in said switch,

a circuit for said relay including a test wiper adapted to engage said test contacts when the 55 switch is searching, said test relay being adapted to energize when the test contact of an idle trunk is encountered but not when the test contact of a busy trunk is encountered, and a device connected in the circuit of said test relay which acts to increase the discrepancy between the current which flows in the test relay when an idle trunk is tested and the current which flows when a busy trunk is tested.

4. A telephone system as set forth in claim 3 in which the device in circuit with the test relay comprises a rectifier.

5. In a telephone system, a plurality of selector switches, a common control circuit, a coupling relay in each switch for associating it withsaid control circuit, and means for energizing the coupling relay in any switch in series with the coupling relays of the other switches in parallel.

6. In a telephone system, a plurality of selector switches, a common control circuit, a coupling relay in each switch for connecting it to said control circuit, incoming test leads for said switches, respectively, which normally extend through to said control circuit and connect to a common source of current, means for connecting the test lead of a seized switch to the other pole of said source, and means in said control circuit responsive to the seizure for inserting the said coupling relays in the respective test leads of said switches, whereby the coupling relay of the seized switch is energized, and each of the other switches is made busy over a circuit including its own coupling relay in series with the coupling relay of the seized switch.

7. In a telephone system, a selector switch, a common control circuit, a coupling relay for temporarily associating said switch with said control circuit, a circuit for said relay closed upon seizure of the switch, and means for delaying the energizing of said relay comprising a device connected in shunt thereof whose resistance rises as current flows in said circuit.

8. A system as set forth in claim '7, in which the shunt connected device comprises a metallic filament lamp.

9. In a telephone system, a selecting switch, a common control circuit, a coupling relay for temporarily associating said switch with said control circuit, a circuit for said relay closed upon seizure of the switch, and means for delaying the energization of the relay comprising a device in series with the relay whose resistance falls as current commences to flow.

10. A system as set forth in claim 9 in which the series connected device is a carbon filament lamp.

HORACE EDGAR HUMIPHRIES. RONALD ISAAC HERBERT CLARK.

US2093242A 1934-09-24 1935-09-16 Testing and private wire arrangement for telephone or like systems Expired - Lifetime US2093242A (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2529471A (en) * 1945-05-04 1950-11-07 Siemens Brothers & Co Ltd Marking arrangement for final selector switches
US2709203A (en) * 1949-12-31 1955-05-24 Hartford Nat Bank & Trust Co Device for use in automatic signalling systems for engaging an apparatus
US2727095A (en) * 1951-04-19 1955-12-13 Mercer Richard Telecommunication systems
US2740840A (en) * 1951-07-26 1956-04-03 Int Standard Electric Corp Outgoing junction circuit
US2748196A (en) * 1953-05-01 1956-05-29 Automatic Elect Lab Telephone system
US2778879A (en) * 1950-07-27 1957-01-22 Hartford Nat Bank & Trust Co Control device for use in automatic signalling system
US3121775A (en) * 1959-12-23 1964-02-18 Bell Telephone Labor Inc Line insulation testing in telephone systems
US4207438A (en) * 1977-10-14 1980-06-10 Societa Italiana Telecomunicazioni Siemens S.P.A. Rotary selector adapted to scan a line multiple in a step-by-step telephone exchange

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2529471A (en) * 1945-05-04 1950-11-07 Siemens Brothers & Co Ltd Marking arrangement for final selector switches
US2709203A (en) * 1949-12-31 1955-05-24 Hartford Nat Bank & Trust Co Device for use in automatic signalling systems for engaging an apparatus
US2778879A (en) * 1950-07-27 1957-01-22 Hartford Nat Bank & Trust Co Control device for use in automatic signalling system
US2727095A (en) * 1951-04-19 1955-12-13 Mercer Richard Telecommunication systems
US2740840A (en) * 1951-07-26 1956-04-03 Int Standard Electric Corp Outgoing junction circuit
US2748196A (en) * 1953-05-01 1956-05-29 Automatic Elect Lab Telephone system
US3121775A (en) * 1959-12-23 1964-02-18 Bell Telephone Labor Inc Line insulation testing in telephone systems
US4207438A (en) * 1977-10-14 1980-06-10 Societa Italiana Telecomunicazioni Siemens S.P.A. Rotary selector adapted to scan a line multiple in a step-by-step telephone exchange

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Publication number Publication date Type
GB439323A (en) 1935-12-04 application

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